Abstract
Piper species are important components of the understory in tropical and subtropical forests, and some species are of economic and medicinal importance. This genus has been studied in different areas of science. However, some questions remain unanswered after the new circumscription as proposed by phylogenetic studies. Here, I review different aspects related to the reproductive biology of Piper species (phenology, sexual expression, floral biology, pollination and mating systems), comparing the results between Neotropical (representing most of the studies carried out so far) and Paleotropical regions. Seventy-five species were analyzed. Some patterns can be observed, mainly in Neotropical species, such as the predominance of annual flowering and fruiting, dichogamy (generally incomplete protogyny) with gradual and sequential exposure of stigmas, asynchronous pollen release, and pollination by insects. Some aspects have been poorly studied, such as variations in sexual expression, the efficiency of different pollinators, and the chemical composition of floral volatiles associated with their role in pollination. In addition, I discuss remaining gaps and further studies that are required, mainly on Paleotropical Piper species, to obtain basic information on the reproductive biology of these plants. From this, comparisons with Neotropical species can be made, allowing the verification of patterns in this genus.
Key words
floral biology; mating system; phenology; pollination; sexual expression
Resumo
Espécies de Piper são importantes componentes do sub-bosque em florestas tropicais e subtropicais, e algumas espécies são de importância econômica e medicinal. Esse gênero tem sido estudado em diferentes áreas da ciência. No entanto, algumas questões permanecem sem resposta após a nova circunscrição proposta pelos estudos filogenéticos. Aqui, reviso diferentes aspectos relacionados à biologia reprodutiva das espécies de Piper (fenologia, expressão sexual, biologia floral, sistemas de polinização e reprodutivo), comparando os resultados entre as regiões neotropical (representando a maioria dos estudos realizados até agora) e paleotropical. 75 espécies foram analisadas. Alguns padrões podem ser observados, principalmente em espécies neotropicais, como a predominância de floração e frutificação anual, dicogamia (geralmente protoginia incompleta) com exposição gradual e sequencial dos estigmas, liberação assíncrona de pólen e polinização por insetos. Alguns aspectos têm sido pouco estudados, como as variações na expressão sexual, a eficiência dos diferentes polinizadores e a composição química dos voláteis florais associados ao seu papel na polinização. Além disso, discuto as lacunas remanescentes e são necessários mais estudos, principalmente sobre as espécies de Piper paleotropicais, para obter informações básicas sobre a biologia reprodutiva dessas plantas. A partir disso, comparações com espécies neotropicais podem ser feitas, permitindo a verificação de padrões nesse gênero.
Palavras-chave
biologia floral; sistema reprodutivo; fenologia; polinização; expressão sexual
Introduction
Piper has a predominantly Pantropical distribution, although it occurs in some subtropical regions (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.). It has over 2,100 species and is the second-largest genus of angiosperms (Simmonds et al. 2021Simmonds SE, Smith JF, Davidson C & Buerki S (2021) Phylogenetics and comparative plastome genomics of two of the largest genera of angiosperms, Piper and Peperomia (Piperaceae). Molecular Phylogenetics and Evolution 163: 107229.), with the highest diversity of species occurring in tropical America (700 species) and South Asia (300 species) (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.). Species of this genus grow as shrubs, herbs, climbers, or treelets, and are important components of the understory in tropical forests (Hartshorn & Hammel 1994Hartshorn GS & Hammel BE (1994) Vegetation types and floristic patterns. In: McDade LA, Bawa KS, Hespenheide HA & Hartshorn GS (eds.) La Selva: ecology and natural history of a neotropical rain forest. The University of Chicago Press, Chicago. Pp 73-89.; Greig 2004Greig N (2004) Introduction. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 1-4.). Some species are of economic importance, such as Piper nigrum L. (black pepper), which is used worldwide as a condiment (Greig 2004Greig N (2004) Introduction. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 1-4.), and P. betle L. (betel vine) and P. methysticum G. Forst. (kava kava) which are used medicinally (Di Stasi et al. 2002Di Stasi LC, Hiruma-Lima CA, Mariot A, Portilho WG & Reis MS (2002) Piperales medicinais. In: Di Stasi LC & Hiruma-Lima CA (eds.) Plantas medicinais na Amazônia e na Mata Atlântica. Ed. Unesp, São Paulo. Pp. 120-138.; Dyer et al. 2004Dyer L, Richards J & Dodson C (2004) Isolations, synthesis, and evolutionary ecology of Piper amides. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 117-139.). Studies on the genus Piper have been conducted in several areas of science. In 2004, the book “Piper: a model genus for studies of phytochemistry, ecology, and evolution” was published, which addresses different ecological and evolutionary aspects, such as mutualistic interactions with ants (Letourneau 2004Letourneau DK (2004) Mutualism, antiherbivore, and trophic cascades: Piper ant-plants as a mesocosm for experimentation. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 5-32.) and bats (Fleming 2004Fleming TH (2004) Dispersal ecology of Neotropical Piper shrubs and treelets. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 58-77.), in addition to aspects of pollination biology (Figueiredo & Sazima 2004Figueiredo RA & Sazima M (2004) Pollination ecology and resource partitioning in neotropical Pipers. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 33-57.). Despite the existing knowledge of this genus, some questions remain to be answered, especially after phylogenetic studies have redefined the circumscription of the genus (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.; Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.).
The systematics of Piperaceae has changed over time since Kunth’s work in 1839, changing the number of genera within this family, in addition to the use of infrageneric groups or sections in some taxonomic treatises (see a summary of the taxonomic history of Piper by Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.; Sen & Rengaian 2022Sen S & Rengaian G (2022) A review on the ecology, evolution and conservation of Piper (Piperaceae) in India: future directions and opportunities. The Botanical Review 88: 333-358.). After phylogenetic studies using sequences from the ITS region and chloroplast intron psbJ-petA (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.; Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.), the circumscription of Piper was altered to incorporate further genera. Three major clades are recognized, corresponding to the geographic distribution of the species. Neotropical species are divided into eight subclades, most of which are currently considered subgenera: Macrostachys, Radula, Peltobryon, Pothomorphe, Enckea, Ottonia, Schilleria, and the P. cinereum/P. sanctum complex, all of which are hermaphroditic (bisexual flowers) and are considered a basal group (Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.; Sen & Rengaian 2022Sen S & Rengaian G (2022) A review on the ecology, evolution and conservation of Piper (Piperaceae) in India: future directions and opportunities. The Botanical Review 88: 333-358.). By contrast, Paleotropical species are categorized into two geographic clades, i.e., tropical Asia (Piper s.s.) and the South Pacific (Macropiper), which produce unisexual flowers and are predominantly dioecious. Recent studies have evaluated the phylogeny of Asian pipers and found 17 infrageneric groups that constitute a sister group to the South Pacific group (Asmarayani 2018Asmarayani R (2018) Phylogenetic relationships in Malesian-Pacific Piper (Piperaceae) and their implications for systematics. Taxon 67: 693-724.; Sen et al. 2019Sen S, Dayanandan S, Davis T, Ganesan R, Jagadish MR, Mathew PJ & Ravikanth G. (2019) Origin and evolution of the genus Piper in Peninsular India. Molecular Phylogenetics and Evolution 138: 102-113.).
Here, I review the different aspects of reproductive biology of Piper, especially those related to pollination. I compare Neotropical with Paleotropical species and discuss knowledge gaps and potential topics for future studies.
Reproductive phenology
Phenological studies of Piper species have been conducted mainly in the Neotropical region. Here, I address reproductive phenophases of 67 species (Tab. S1, available on supplementary material <https://doi.org/10.6084/m9.figshare.22626970.v1>). However, there are studies that have examined leaf production in Neotropical (Marquis 1988Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.; Angulo-Sandoval & Aide 2000Angulo-Sandoval P & Aide TM (2000) Leaf phenology and leaf damage of saplings in the Luquillo Experimental Forest, Puerto Rico. Biotropica 32: 415-422.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.) and Paleotropical (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247., 2018) species of this genus, as well as vegetative propagation (Gartner 1989Gartner BL (1989) Breakage and regrowth of Piper species in rain forest understory. Biotropica 21: 303-307.; Greig 1993Greig N (1993) Regeneration mode in neotropical Piper: habitat and species comparisons. Ecology 74: 2125-2135.; Lasso et al. 2009Lasso E, Engelbrecht BMJ & Dalling JW (2009) When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs. Oecologia 161: 43-56., 2012Lasso E, Dalling JW & Bermingham E (2012) Tropical understory Piper shrubs maintain high levels of genotypic diversity despite frequent asexual recruitment. Biotropica 44: 35-43.; Souza et al. 2009Souza LA, Moscheta IS, Mourão KSM, Albiero ALM, Iwazaki MC, Oliveira JHG & Rosa SM (2009) Vegetative propagation in Piperaceae species. Brazilian Archives of Biology and Technology 52: 1357-1361.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.). Valentin-Silva & Vieira (2015)Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589. addressed issues that link vegetative propagation and its contribution to the reproductive phenophases of two Piper species.
Reproductive phenology studies require adult individuals already capable of producing inflorescences. Fleming (1985)Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700. suggested as an inclusion criterion the sampling of individuals with a height of ≥ 1 m. However, this criterion is not suitable for all Piper species (see Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.). The latter authors proposed the mandatory presence of reproductive structures (inflorescences with flower buds, flowers, or fruits; Fig. 1a) in individuals or inflorescence scars on branches (Fig. 1b), which indicates previous reproductive episodes. Thus, sampling of juvenile individuals can be avoided, which would bias the results.
a-b. Criteria for sampling adult Piper individuals - a. presence of reproductive structures; note spikes with floral buds (light green color; black arrow), flowers at anthesis (cream color; white arrow), and fruits (green color; arrowhead); b. presence of inflorescence scar on the branch (circle).
The number of sampled individuals varies among phenological studies on Piper species. However, to facilitate the comparison of results between studies, some standardizations must be applied. When possible, at least 15 adult individuals of each species should be sampled in biweekly observations, which has been suggested as suitable for phenological studies (Morellato et al. 2010aMorellato LPC, Camargo MGG, d’Eça-Neves FF, Luize BG, Mantavoni A & Hudson IL (2010a) The influence of sampling method, sample size, and frequency of observations on plant phenological patterns and interpretation in tropical forest trees. In: Hudson IL & Keatley MR (eds.) Phenological research: methods for environmental and climate change analysis. Springer, Dordrecht. Pp. 99-121.). Monthly observation is not appropriate, as some phenophases may not be recorded in some species (see Mariot et al. 2003Mariot A, Mantovani A & Reis MS (2003) Uso e conservação de Piper cernuum Vell. (Piperaceae) na Mata Atlântica: I. Fenologia reprodutiva e dispersão de sementes. Revista Brasileira de Plantas Medicinais 5: 1-10.).
Standardization of the analyses is also important. Phenological data can be analyzed using activity and intensity indices (Morellato et al. 2010aMorellato LPC, Camargo MGG, d’Eça-Neves FF, Luize BG, Mantavoni A & Hudson IL (2010a) The influence of sampling method, sample size, and frequency of observations on plant phenological patterns and interpretation in tropical forest trees. In: Hudson IL & Keatley MR (eds.) Phenological research: methods for environmental and climate change analysis. Springer, Dordrecht. Pp. 99-121.), which allow evaluation of the period of occurrence of phenophases and their duration, in addition to other phenological parameters. The frequency and duration of phenophases can be classified according to Newstrom et al. (1994)Newstrom LE, Frankie GW & Bake HG (1994) A new classification for plant phenology based on flowering patterns in lowland tropical rain forest trees at La Selva, Costa Rica. Biotropica 26: 141-159.. Phenophases can be described using circular statistics (Morellato et al. 2010bMorellato LPC, Alberti LF & Hudson IL (2010b) Applications of circular statistics in plant phenology: a case studies approach. In: Hudson IL & Keatley MR (eds.) Phenological research: methods for environmental and climate change analysis. Springer, Dordrecht. Pp. 339-359.) and their seasonality can be assessed using the Rayleigh test (Zar 2010Zar JH (2010) Biostatistical analysis. Prentice-Hall, Upper Saddle River. 944p.). To test the potential effects of abiotic factors (e.g., mean temperature, precipitation, and day length) on phenology, generalized linear models can be used for analyses (Crawley 2007Crawley MJ (2007) The R book. John Wiley & Sons, Chichester. 942p.).
Floral buds
Inflorescence production has been examined in a few studies, both on Neotropical (Marquis 1988Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.; Mariot et al. 2003Mariot A, Mantovani A & Reis MS (2003) Uso e conservação de Piper cernuum Vell. (Piperaceae) na Mata Atlântica: I. Fenologia reprodutiva e dispersão de sementes. Revista Brasileira de Plantas Medicinais 5: 1-10.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.; Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.) and Paleotropical (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247., 2018) species. Some Neotropical Piper species show latent flower buds (Marquis 1988Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.; Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.), i.e., inflorescences are produced throughout the year, whereas anthesis of the flowers is restricted to a short period of the year, typically at the beginning of the rainy season. In addition, these species flower before those that do not have latent flower buds, and the duration of flowering is shorter, representing a possible escape mechanism from water stress (Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.). It is also possible that this temporal separation of the flowering period of these two species groups may reduce the competition for common pollinators. Due to the presence of latent flower buds, the separation of flowering into two phenophases (floral buds and flowers at anthesis) is important to consider avoiding errors in the calculation of phenological parameters (duration, concentration, start, and peak dates), in addition to not overestimating the period of availability of floral resources (pollen) to floral visitors.
Only two Paleotropical Piper species have been studied regarding phenology: P. mullesua Buch.-Ham. ex D.Don (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247.) and P. sylvaticum Roxb. (Devi et al. 2018Devi WD, Gajurel PR & Rethy P (2018) Phenological behavior of Piper sylvaticum Roxb. (Piperaceae), a medicinally useful species occurring in Eastern Himalayan region. International Journal of Plant Reproductive Biology 10: 84-89.), both of which are dioecious. The respective authors recorded spike production throughout the year in both male and female P. mullesua and male P. sylvaticum plants. These results indicated that these species may have latent flower buds. However, this topic needs to be further explored in these and other Paleotropical Piper species, by observing whether they occur in both types of individuals (male and female) of dioecious species, as well as in inflorescences of monoecious species.
As some species with latent flower buds occur in different habitats (seasonal and aseasonal forests), it would be interesting to evaluate populations in these habitats to verify whether the production of latent inflorescences is an intrinsic characteristic of these species or a response to the environment. As an alternative option, greenhouse experiments could be conducted to evaluate the influence of water stress on the production of inflorescences and, consequently, on flowering (flowers at anthesis). According to Wright (1991)Wright SJ (1991) Seasonal drought and the phenology of understory shrubs in a tropical moist forest. Ecology 72: 1643-1657., water stress can delay inflorescence production in Piper species; however, this study did not assess whether this effect also occurred in species with latent flower buds.
Flowers at anthesis
Flowering (flowers at anthesis) commonly occurs once per year (annual pattern sensuNewstrom et al. 1994Newstrom LE, Frankie GW & Bake HG (1994) A new classification for plant phenology based on flowering patterns in lowland tropical rain forest trees at La Selva, Costa Rica. Biotropica 26: 141-159.), as observed in Neotropical Piper species studied at different locations (Opler et al. 1980Opler PA, Frankie GW & Baker HG (1980) Comparative phenological studies of treelet and shrub species in tropical wet and dry forests in the lowlands of Costa Rica. Journal of Ecology 68: 167-188.; Fleming 1985Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700.; Figueiredo & Sazima 2004Figueiredo RA & Sazima M (2004) Pollination ecology and resource partitioning in neotropical Pipers. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 33-57.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.; Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.). When assessed at the community level, this phenophase typically occurs throughout the year (continuous pattern sensu Newtrom et al. 1994), as observed by Figueiredo & Sazima (2000)Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460. and Valentin-Silva et al. (2018a)Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684. in Brazil and by Thies & Kalko (2004)Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376. in Panama. This continuous pattern in the community is due to the different phenological patterns observed at the species level, such as annual, subannual, and continuous flowering (sensuNewstrom et al. 1994Newstrom LE, Frankie GW & Bake HG (1994) A new classification for plant phenology based on flowering patterns in lowland tropical rain forest trees at La Selva, Costa Rica. Biotropica 26: 141-159.).
In Paleotropical species, an annual flowering pattern has also been observed at the species level (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247., 2018). However, the flowering peak can be simultaneous between male and female plants (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247.) or sequential, with male plants flowering at a higher intensity before female plants (Devi et al. 2018Devi WD, Gajurel PR & Rethy P (2018) Phenological behavior of Piper sylvaticum Roxb. (Piperaceae), a medicinally useful species occurring in Eastern Himalayan region. International Journal of Plant Reproductive Biology 10: 84-89.).
Phenological patterns of species may differ between habitats. For example, Thies & Kalko (2004)Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376. observed that Piper species occurring in forest gaps tended to have longer flowering periods than species that occurred within the forest; in addition, the peak flowering period differed between habitats. Abiotic factors, such as climate, can also influence phenological patterns. Valentin-Silva et al. (2018a)Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684. showed that day length was positively correlated with the number of species flowering, as the flowering peak occurred during the rainy season when days are longer. This environmental variable is considered a trigger for flowering and is one of the most accurate predictors of this phenophase (Stevenson et al. 2008Stevenson PR, Castellanos MC, Cortés AI & Link A (2008) Flowering patterns in a seasonal tropical lowland forest in western Amazonia. Biotropica 40: 559-567.). This result corroborates the climatic hypothesis, which predicts that phenological activity is related to the seasonality of limiting environmental variables such as water and light availability (van Schaik et al. 1993van Schaik CP, Terborgh JW & Wright SJ (1993) The phenology of tropical forests: adaptive significance and consequences for primary consumers. Annual Review of Ecology and Systematics 24: 353-377.; Fenner 1998Fenner M (1998) The phenology of growth and reproduction in plants. Perspectives in Plant Ecology, Evolution and Systematics 1: 78-91.).
Biotic factors such as pollinators can also influence phenological patterns. Fleming (1985)Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700. observed a temporal partition among five Piper species observed in Costa Rica, which can be interpreted as a mechanism to avoid or reduce competition for common pollinators and increase pollination effectiveness (competition hypothesis; van Schaik et al. 1993van Schaik CP, Terborgh JW & Wright SJ (1993) The phenology of tropical forests: adaptive significance and consequences for primary consumers. Annual Review of Ecology and Systematics 24: 353-377.; Fenner 1998Fenner M (1998) The phenology of growth and reproduction in plants. Perspectives in Plant Ecology, Evolution and Systematics 1: 78-91.). By contrast, Valentin-Silva et al. (2018a)Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684. examined 17 species of Piper co-occurring in Brazil and found an overlap in the flowering period between species groups (e.g., five of the eight species with latent flower buds flowered simultaneously at the beginning of the rainy season). As these species produce flowers with similar morphology, simultaneous flowering may attract more pollinators, thereby increasing pollination rates (facilitation hypothesis; van Schaik et al. 1993van Schaik CP, Terborgh JW & Wright SJ (1993) The phenology of tropical forests: adaptive significance and consequences for primary consumers. Annual Review of Ecology and Systematics 24: 353-377.; Fenner 1998Fenner M (1998) The phenology of growth and reproduction in plants. Perspectives in Plant Ecology, Evolution and Systematics 1: 78-91.). Both competition and facilitation may be important in different areas, depending on pollinator availability. As these hypotheses are difficult to test in natural settings, the role of biotic vectors as modulators of plant phenology can be evaluated using the null model analysis (see Staggemeier et al. 2010Staggemeier VG, Diniz-Filho JAF & Morellato LPC (2010) The shared influence of phylogeny and ecology on the reproductive patterns of Myrteae (Myrtaceae). Journal of Ecology 98: 1409-1421.).
The phylogenetic hypothesis predicting that closely related species tend to exhibit more similar phenological patterns than more distantly related species (Kochmer & Handel 1986Kochmer JP & Handel SN (1986) Constraints and competition in the evolution of flowering phenology. Ecological Monographs 56: 303-325.) was tested on Piper species. However, Valentin-Silva et al. (2018a)Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684. found no association between phylogenetic relatedness and phenological patterns of the examined species; regardless, these authors suggested that the predominance of annual flowering frequency may be related to phylogenetic factors. Improving the phylogenetic resolution of species-rich clades, together with more phenological information, may thus provide new perspectives on how evolutionary history has affected the phenology of Piper species.
Fruiting
As with flowering, fruiting commonly follows an annual pattern at the species level (Opler et al. 1980Opler PA, Frankie GW & Baker HG (1980) Comparative phenological studies of treelet and shrub species in tropical wet and dry forests in the lowlands of Costa Rica. Journal of Ecology 68: 167-188.; Fleming 1985Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700.; Marinho-Filho 1991Marinho-Filho JS (1991) The coexistence of two frugivorous bat species and the phenology of their food plants in Brazil. Journal of Tropical Ecology 7: 59-67.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.; Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.; Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.) and shows continuous pattern at the community level (Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.; Valentin-Silva et al. 2018aValentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.) in the Neotropics. In the Paleotropics, two Piper species showed a continuous pattern of fruiting (Devi et al. 2016aDevi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247., 2018). Most of these studies did not separate data on immature and mature fruits due to the difficulty of recording ripe fruits in biweekly or even weekly observations (e.g., Valentin-Silva & Vieira 2015Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.), as these fruits remain on the plant for one or two days (Marquis 1988Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.). Therefore, the fruiting period is long, which may be related to the low availability of ripe fruits per plant and night (Fleming 1981Fleming TH (1981) Fecundity, fruiting pattern, and seed dispersal in Piper amalago (Piperaceae), a bat-dispersed tropical shrub. Oecologia 51: 42-46.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.). Fleming (1981)Fleming TH (1981) Fecundity, fruiting pattern, and seed dispersal in Piper amalago (Piperaceae), a bat-dispersed tropical shrub. Oecologia 51: 42-46. observed that in P. amalago L., a few ripe fruits (1--3) were available per night over a period of 3-4 weeks. These analyses of ripe fruit availability and removal rate by dispersers were based on daily observations at night, as Neotropical Piper species are generally dispersed by frugivorous bats (Fleming 2004Fleming TH (2004) Dispersal ecology of Neotropical Piper shrubs and treelets. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 58-77.; Thies & Kalko 2004Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.), mainly Carollia perspicillata (Linnaeus 1758) (Marinho-Filho 1991Marinho-Filho JS (1991) The coexistence of two frugivorous bat species and the phenology of their food plants in Brazil. Journal of Tropical Ecology 7: 59-67.; Lima & Reis 2004Lima IP & Reis NR (2004) The availability of Piperaceae and the search for this resource by Carollia perspicillata (Linnaeus) (Chiroptera, Phyllostomidae, Carolliinae) in the Parque Municipal Arthur Thomas, Londrina, Paraná, Brazil. Revista Brasileira de Zoologia 21: 371-377.). Further information on the dispersal ecology of Neotropical Piper species was compiled by Fleming (2004)Fleming TH (2004) Dispersal ecology of Neotropical Piper shrubs and treelets. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 58-77.; however, the dispersal mechanisms of Paleotropical Piper species are still poorly understood.
Phenological patterns of fruiting can also differ between species, depending on the habitat in which they occur. Thies & Kalko (2004)Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376. observed fruiting in Piper species growing in a forest throughout the year, but with a staggered pattern among species. This pattern can be interpreted as a response to the limitation of dispersers, which helps reduce interspecific competition for dispersers in addition to reducing competition for germination sites. The authors also confirmed that Piper species occurring in forest gaps showed fruiting throughout the year, with each species showing more than one peak of fruit production and longer fruiting periods. The overlap of these long fruiting periods is associated with a broad spectrum of dispersers (bats, birds, and probably ants) and with the need for specific conditions for seedling establishment (gap formation).
Some of the hypotheses on factors influencing phenological patterns were also tested with respect to fruiting. Valentin-Silva et al. (2018a)Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684. showed that the number of species with fruits was positively correlated with mean temperature and day length of the months prior to the occurrence of the phenophase, and there was no phylogenetic structuring. Fruit production was constant throughout the year (continuous fruiting pattern), which is associated with the maintenance of frugivorous disperser populations (Snow 1965Snow DW (1965) A possible selective factor in the evolution of fruiting seasons in tropical forest. Oikos 15: 274-281.). These results indicate the importance of dispersers as modulators of the fruiting phenology of Piper species, as suggested by Thies & Kalko (2004)Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376..
Sexual expression
The sexual expression of Piper species is variable and tends to be related to the geographic distribution of the clades. Twenty-two species were analyzed (Tab. S1, available on supplementary material <https://doi.org/10.6084/m9.figshare.22626970.v1>;). Neotropical species are considered to exclusively produce bisexual flowers (Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.). However, functionally male flowers (staminate) have been observed in natural populations of four species, i.e., P. arboreum Aubl., P. caldense C.DC., P. cernuum Vell., and P. chimonanthifolium Kunth (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.; Valentin-Silva et al. 2018bValentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.). Staminate flowers of these species showed cryptic unisexuality (flowers morphologically bisexual but functionally unisexual sensuMayer & Charlesworth 1991Mayer SS & Charlesworth D (1991) Cryptic dioecy in flowering plants. Trends in Ecology and Evolution 6: 320-325.).
Variations in the distribution of flowers on inflorescences were also reported by Valentin-Silva et al. (2018b)Valentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.. In P. arboreum, P. caldense, and P. cernuum, spikes with bisexual flowers and spikes with staminate flowers were observed. In addition to these types of inflorescences, P. chimonanthifolium showed spikes with bisexual and staminate flowers (mixed spikes), a characteristic described for the first time in a Neotropical Piper species. In all four species, the male spikes and the portion of mixed spikes with staminate flowers senesced after pollen release. Moreover, the distribution of inflorescence types varied between individuals of these four species, which directly influences their sexual expression (Valentin-Silva et al. 2018bValentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.). Piper cernuum was considered andromonoecious, whereas the populations of P. arboreum and P. chimonanthifolium appeared to be in transition to this type of sexual expression, as they are andromonoecious and hermaphrodite individuals. Piper caldense is probably androdioecious because individuals have hermaphrodite and male functions. Androdioecy is rare in angiosperms (Pannell 2002Pannell JR (2002) The evolution and maintenance of androdioecy. Annual Review of Ecology and Systematics 33: 397-425.), and studies on other populations of this species may help answer this question.
A further interesting characteristic of P. arboreum, P. caldense, P. cernuum, and P. chimonanthifolium is variation in pistil length and in the size of spikes with bisexual and staminate flowers, indicating sexual dimorphism, as observed by Valentin-Silva et al. (2018b)Valentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.. The authors suggested that inflorescence length may be a diagnostic characteristic to identify the types of individuals in Neotropical Piper species that show sexual expression different from hermaphroditism. Because of the small size of flowers, analysis of floral morphology related to the functionality of flowers during anthesis is essential to determine the sexual expression of Neotropical Piper species. It is likely that studies of this type in other populations in the Neotropics will reveal further species with functionally unisexual flowers.
In the Paleotropics, Piper species with unisexual flowers and dioecy are predominant (Wanke et al. 2007Wanke S, Jaramillo MA, Borsch T, Samain MS, Quandt D & Neinhuis C (2007) Evolution of Piperales - matK gene and trnK intron sequence data reveal lineage specific resolution contrast. Molecular Phylogenetics and Evolution 42: 477-297.; Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.). In the Asian tropics, there are some species with bisexual flowers, such as Piper longum L. (Kanimozhi & Sujatha 2015Kanimozhi K & Sujatha VS (2015) Reproductive biology of Piper longum L. Journal of Tropical Agriculture, 53: 206-212.), and in the South Pacific, some species are monoecious (Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.). Despite this, Ollerton (1996)Ollerton J (1996) Interactions between gall midges (Diptera: Cecidomyiidae) and inflorescences of Piper novae-hollandiae (Piperaceae) in Australia. The Entomologist 115: 181-184. noted in P. novae-hollandiae, an Australian species usually described as monoecious, individuals that only had spikes with staminate flowers. Female inflorescences tend to be shorter than those of males in some Paleotropical Piper species (Kanimozhi & Sujatha 2015Kanimozhi K & Sujatha VS (2015) Reproductive biology of Piper longum L. Journal of Tropical Agriculture, 53: 206-212.; Devi et al. 2016bDevi WD, Gajurel PR & Rethy P (2016b) Bisexuality in dioecious male plant: an unusual phenomenon of sex expression in Piper species. International Journal of Plant Reproductive Biology 8: 82-86.), indicating sexual dimorphism, similar to Neotropical species that have bisexual and staminate flowers.
Mixed inflorescences were observed in three dioecious species. Piper pedicellatum C.DC. has some inflorescences with bisexual and pistillate flowers in addition to female inflorescences (Lei & Liang 1998Lei LG & Liang HX (1998) Floral development of dioecious species and trends of floral evolution in Piper sensu lato. Botanical Journal of the Linnean Society 127: 225-237.). Piper sylvaticum has some inflorescences with bisexual and staminate flowers in addition to male inflorescences (Devi et al. 2016bDevi WD, Gajurel PR & Rethy P (2016b) Bisexuality in dioecious male plant: an unusual phenomenon of sex expression in Piper species. International Journal of Plant Reproductive Biology 8: 82-86.). In Piper mullesua, a few pistillate flowers have been observed along with staminate flowers in addition to male inflorescences (Devi et al. 2016bDevi WD, Gajurel PR & Rethy P (2016b) Bisexuality in dioecious male plant: an unusual phenomenon of sex expression in Piper species. International Journal of Plant Reproductive Biology 8: 82-86.). However, these studies did not examine potential differences in length between these types of inflorescences. It would thus be interesting to analyze these variations in other populations, preferably under natural settings (Devi et al. 2016bDevi WD, Gajurel PR & Rethy P (2016b) Bisexuality in dioecious male plant: an unusual phenomenon of sex expression in Piper species. International Journal of Plant Reproductive Biology 8: 82-86. studied cultivated individuals), or even in herbarium material (see Valentin-Silva et al. 2018bValentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.) to confirm such changes in the sexual expression in these species, considering that sexual expression can vary in time and space (Sakai & Weller 1999Sakai AK & Weller SG (1999) Gender and sexual dimorphism in flowering plants: a review of terminology, biogeographic patterns, ecological correlates, and phylogenetic approaches. In: Geber MA, Dawson TE & Delph LF (eds.) Gender and sexual dimorphism in flowering plants. Springer-Verlag, Berlin. Pp. 1-31.).
Floral biology
The minute flowers of Piper appear, at first glance, morphologically similar; both bisexual and unisexual flowers are perianthless and are protected by a bract, with 1-10 stamens and 3-4 carpels (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.). However, there are variations regarding flower (relative size of filament and anther, orientation of the anther opening, presence or absence of pedicel) and inflorescence (packaging of flowers, position, length, presentation, color, and arrangement) (Jaramillo & Manos 2001Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.). Studies involving aspects of floral biology were carried out with 29 species.
In bisexual flowers, floral events (pollen release and stigmatic exposure) are usually separated by time, characterizing dichogamy. Most Piper species show complete or incomplete protogyny (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Valentin-Silva et al. 2015Valentin-Silva A, Coelho VPM, Ventrella MC & Vieira MF (2015) Timing of pollen release and stigma receptivity period of Piper vicosanum (Piperaceae): new insights into sexual reproduction of the genus. American Journal of Botany 102: 626-633., 2018c; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.), however, there are reports of incomplete protandry (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Kikuchi et al. 2007Kikuchi DW, Lasso E, Dalling JW & Nur N(2007) Pollinators and pollen dispersal of Piper dilatatum (Piperaceae) on Barro Colorado Island, Panama. Journal of Tropical Ecology 23: 603-606.) and adichogamy (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.). Apart from adichogamy, these reproductive mechanisms favor xenogamy. Despite this, autogamy or geitonogamy may occur in self-compatible species when an overlap between the pistillate and staminate phases of the flower occurs (Lloyd & Schoen 1992Lloyd DG & Schoen DJ (1992) Selfand cross-fertilization in plants. I. Functional dimensions. International Journal of Plant Sciences 153: 358-369.).
As most Piper species are protogynous, anthesis begins with the exposure of stigmas, which occurs sequentially and gradually and in a basipetal direction (Valentin-Silva et al. 2015Valentin-Silva A, Coelho VPM, Ventrella MC & Vieira MF (2015) Timing of pollen release and stigma receptivity period of Piper vicosanum (Piperaceae): new insights into sexual reproduction of the genus. American Journal of Botany 102: 626-633., 2018c; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.). This mode of stigmatic papillae exposure is related to both incomplete protogyny and stigma longevity (4-16 days; Valentin-Silva et al. 2018cValentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295.), which increases the likelihood for stigmas to receive sufficient pollen grains (Cruden 2000Cruden RW (2000) Pollen grains: why so many? Plant Systematics and Evolution 222: 143-165.). Valentin-Silva et al. (2018c)Valentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295. observed this trait in Neotropical Piper species with three and four stigmas, indicating that the mode of stigmatic papillae exposure was independent of the number of carpels in the flower.
Pollen release, in turn, is asynchronous and sequential, as it occurs in one stamen at a time, typically between 10:00 am and 2:00 pm, showing clump formation on the anther (Valentin-Silva et al. 2015Valentin-Silva A, Coelho VPM, Ventrella MC & Vieira MF (2015) Timing of pollen release and stigma receptivity period of Piper vicosanum (Piperaceae): new insights into sexual reproduction of the genus. American Journal of Botany 102: 626-633., 2018c; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.). This pattern differs from that of androecium development, which is asynchronous and occurs in a specific sequence. The lateral pairs of stamens develop simultaneously, and the median pair develops sequentially, with the median-anterior stamen being formed before the median-posterior stamen (Tucker 1982Tucker SC (1982) Inflorescence and flower development in the Piperaceae III. Floral ontogeny of Piper. American Journal of Botany 69: 1389-1401.). During anthesis, pairs of lateral stamens release pollen at different times on the same day or on subsequent days; the median pair of stamens releases pollen sequentially on subsequent days (Valentin-Silva et al. 2015Valentin-Silva A, Coelho VPM, Ventrella MC & Vieira MF (2015) Timing of pollen release and stigma receptivity period of Piper vicosanum (Piperaceae): new insights into sexual reproduction of the genus. American Journal of Botany 102: 626-633., 2018c). This trait was observed in Neotropical Piper species with two, three, four, and six stamens. Therefore, it does not depend on the number of stamens in the flower, although in flowers with more stamens, the period of pollen supply tends to be longer, increasing the likelihood of cross-pollination (Valentin-Silva et al. 2018cValentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295.). Asynchronous and sequential pollen release has also been recorded in the staminate flowers of Neotropical species (Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.; Valentin-Silva et al. 2018cValentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295.).
Based on the similarities between bisexual and unisexual flowers regarding morphology, floral development (Tucker 1982Tucker SC (1982) Inflorescence and flower development in the Piperaceae III. Floral ontogeny of Piper. American Journal of Botany 69: 1389-1401.; Lei & Liang 1998Lei LG & Liang HX (1998) Floral development of dioecious species and trends of floral evolution in Piper sensu lato. Botanical Journal of the Linnean Society 127: 225-237.; Jaramillo et al. 2008Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA. Systematic Botany 33: 647-660.), and sequence of pollen release (Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.; Valentin-Silva et al. 2018cValentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295.), in addition to the long-lived stigmas in P. nigrum (Menon 1949Menon KK (1949) The survey of pollu and root diseases of pepper. Indian Journal of Agricultural Science 19: 89-136.; Martin & Gregory 1962Martin FW & Gregory LE (1962) Mode of pollination and factors affecting fruit set in Piper nigrum L. in Puerto Rico. Crop Science 2: 295-299.), a genus-wide pattern in the dynamics of floral events may exist. However, further studies on Paleotropical Piper species are needed to test this hypothesis. Studies on the floral biology of Paleotropical species generally examined the timing of pollen release and viability, in addition to stigmatic receptivity (Kanimozhi & Sujatha 2015Kanimozhi K & Sujatha VS (2015) Reproductive biology of Piper longum L. Journal of Tropical Agriculture, 53: 206-212.; Chen et al. 2018Chen YS, Dayod M & Tawan CS (2018) Anther dehiscence, pollen viability and stigma receptivity study on cultivars of black pepper (Piper nigrum L.). Pertanika Journal of Tropical Agricultural Science 41: 801-814.), but do not explain how this dynamic occurs. However, Chen et al. (2018)Chen YS, Dayod M & Tawan CS (2018) Anther dehiscence, pollen viability and stigma receptivity study on cultivars of black pepper (Piper nigrum L.). Pertanika Journal of Tropical Agricultural Science 41: 801-814. studied the stigmatic receptivity of ten cultivars of P. nigrum at three anthesis stages using Peroxtesmo KO (Machery-Nagel, Düren, Germany). From the images of this study, it is possible to observe that the stigmatic papillae become receptive sequentially, gradually, and in a basipetal direction, which reinforces the suggested similarity with Neotropical species.
Piper flowers have only pollen as a resource and generally have a sweet or citrusy odor, as reported for 13 Neotropical species (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.) and two Australian species (Ollerton 1996Ollerton J (1996) Interactions between gall midges (Diptera: Cecidomyiidae) and inflorescences of Piper novae-hollandiae (Piperaceae) in Australia. The Entomologist 115: 181-184.). These odors may be related to the attraction of pollinators, which is one of the key functions of volatile organic compounds (Farré-Armengol et al. 2013Farré-Armengol G, Filella I, Llusia J & Peñuelas J (2013) Floral volatile organic compounds: between attraction and deterrence of visitors under global change. Perspectives in Plant Ecology, Evolution and Systematics 15: 56-67.). However, studies to elucidate the chemical composition of these odors and their role in attracting pollinators are scarce. Machado et al. (2021)Machado DB, Ramos YJ, Queiroz GA, Defaveri ACA, Gobatto AA & Moreira DL (2021) Study of volatile chemical constituents and insect-plant interaction in Piper mollicomum Kunth (Piperaceae) from Tijuca Forest, Rio de Janeiro - RJ, Brazil. Revista Virtual de Química 13: 1216-1225. observed that linalool compounds were predominant in the flowers of P. mollicomum Kunth, and their emission was correlated with a higher frequency of bee visits.
Pollination and mating systems
Thirty-six Piper species had floral visitors and pollinators evaluated (Tab. S1, available on supplementary material <https://doi.org/10.6084/m9.figshare.22626970.v1>;). Neotropical Piper species are entomophilous and are pollinated by different species of bees, flies, and beetles (Tab. 1). Therefore, they are generalists in terms of ecology (number of pollinator species sensuOllerton et al. 2007Ollerton J, Killick A, Lamborn E, Watts S & Whiston M (2007) Multiple meanings and modes: on the many ways to be a generalist flower. Taxon 56: 717-728.) and functionality (taxonomic diversity of pollinators sensuOllerton et al. 2007Ollerton J, Killick A, Lamborn E, Watts S & Whiston M (2007) Multiple meanings and modes: on the many ways to be a generalist flower. Taxon 56: 717-728.). Other floral visitors have also been recorded, such as butterflies, wasps, hemipterans, and spiders (Fleming 1985Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700.; Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460., 2004Figueiredo RA & Sazima M (2004) Pollination ecology and resource partitioning in neotropical Pipers. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 33-57.; Figueiredo 2003Figueiredo RA (2003) Coleta de pólen, interações agonísticas e horários de atividade dos visitantes florais (Insecta: Diptera, Hymenoptera) de pimenteiras silvestres (Piperaceae). Revista de Etologia 5: 3-13.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). However, they were not considered pollinators because of their low abundance, their behavior and frequency of visits, and/or the absence of pollen adhering to the body.
Neotropical Piper flowers are typically visited during the day, with a peak in the late morning, mainly between 10:00 am and 11:00 am (Kikuchi et al. 2007Kikuchi DW, Lasso E, Dalling JW & Nur N(2007) Pollinators and pollen dispersal of Piper dilatatum (Piperaceae) on Barro Colorado Island, Panama. Journal of Tropical Ecology 23: 603-606.; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). However, there may be some variations in the peak visiting periods between Piper species (Thomazini & Thomazini 2002Thomazini MJ & Thomazini APBW (2002) Diversidade de abelhas (Hymenoptera: Apoidea) em inflorescências de Piper hispidinervum (C.DC.). Neotropical Entomology 31: 27-34.; Figueiredo 2003Figueiredo RA (2003) Coleta de pólen, interações agonísticas e horários de atividade dos visitantes florais (Insecta: Diptera, Hymenoptera) de pimenteiras silvestres (Piperaceae). Revista de Etologia 5: 3-13.). Visitations by these insects can be seasonal, as their proportions of visits vary throughout the year (Fleming 1985Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700.; Thomazini & Thomazini 2002Thomazini MJ & Thomazini APBW (2002) Diversidade de abelhas (Hymenoptera: Apoidea) em inflorescências de Piper hispidinervum (C.DC.). Neotropical Entomology 31: 27-34.; Wisniewski et al. 2019Wisniewski C, Bornstein AJ & Wood DL (2019) Eating out or dining in: insect-plant interactions among species of Piper in the Rio Abajo Forest Preserve, Puerto Rico. Selbyana, 33: 1-15.). Insects generally exhibit similar visiting behavior, crawling along a part or over the full length of the inflorescence, and they commonly visit more than one inflorescence per plant (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Kikuchi et al. 2007Kikuchi DW, Lasso E, Dalling JW & Nur N(2007) Pollinators and pollen dispersal of Piper dilatatum (Piperaceae) on Barro Colorado Island, Panama. Journal of Tropical Ecology 23: 603-606.; Wisniewski et al. 2019Wisniewski C, Bornstein AJ & Wood DL (2019) Eating out or dining in: insect-plant interactions among species of Piper in the Rio Abajo Forest Preserve, Puerto Rico. Selbyana, 33: 1-15.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). However, the duration of visits varies between insects. Bees and flies tend to show shorter visitation times than beetles, which can remain on the inflorescences for up to an hour, sometimes with little movement (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Figueiredo 2003Figueiredo RA (2003) Coleta de pólen, interações agonísticas e horários de atividade dos visitantes florais (Insecta: Diptera, Hymenoptera) de pimenteiras silvestres (Piperaceae). Revista de Etologia 5: 3-13.; Wisniewski et al. 2019Wisniewski C, Bornstein AJ & Wood DL (2019) Eating out or dining in: insect-plant interactions among species of Piper in the Rio Abajo Forest Preserve, Puerto Rico. Selbyana, 33: 1-15.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.).
The visiting behavior of such insects (bees, flies, and beetles) can affect the rates of autogamy and geitonogamy (Lloyd & Schoen 1992Lloyd DG & Schoen DJ (1992) Selfand cross-fertilization in plants. I. Functional dimensions. International Journal of Plant Sciences 153: 358-369.) in self-compatible Piper species. In the Neotropics, both self-compatible (13 species; Marquis 1988Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.; Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Kikuchi et al. 2007Kikuchi DW, Lasso E, Dalling JW & Nur N(2007) Pollinators and pollen dispersal of Piper dilatatum (Piperaceae) on Barro Colorado Island, Panama. Journal of Tropical Ecology 23: 603-606.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.) and self-incompatible species (16 species; Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Vargas-Rojas & Vieira 2017Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.) have been reported. Figueiredo & Sazima (2000)Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460. and Valentin-Silva et al. (2021)Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635. studied seven common species, three of which showed divergent incompatibility systems between the examined populations. Considering that interand intraspecific variation in outcrossing rates is common (Barrett 2003Barrett SCH (2003) Mating strategies in flowering plants: the outcrossing-selfing paradigm and beyond. Philosophical Transactions of the Royal Society B 358: 991-1004.), progeny analyses are required to confirm whether self-compatible Piper species are exclusively autogamous or whether they can benefit from the presence of pollinators.
Despite pollination by different insects, no studies have examined whether pollinators differ in terms of effectiveness in pollinating Piper species. Such studies could be performed on self-incompatible Piper species because of the difficulty in emasculating the flowers and isolating the effect of self-fertilization. Thus, it is possible to assess whether pollinators differ in terms of their contribution to the sexual reproduction of these plants.
In addition to biotic pollinators, wind pollination has been reported in conjunction with insects (ambophily; Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.). The occurrence of anemophily in Piper species is still controversial. Culley et al. (2002)Culley TM, Weller SG & Sakai AK (2002) The evolution of wind pollination in angiosperms. Trends in Ecology and Evolution 17: 361-369. reviewed the origin of anemophily in angiosperms. Even considering that anemophilous species do not consistently possess all characteristics associated with this pollination syndrome, Piperaceae did not appear to be wind-pollinated. Some studies have ruled out this pollination mechanism due to the formation of pollen clumps on the anther, possibly indicating the presence of pollenkitt (Semple 1974Semple KS (1974) Pollination in Piperaceae. Annals of the Missouri Botanical Garden 61: 868-871.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). According to these studies, such pollen clumps can remain on the anther from one day to the next, even after rainfall or wind. By contrast, Figueiredo & Sazima (2000)Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460. observed powdery pollen in Neotropical Piper species. Despite this divergence, other characteristics indicate better suitability of Piper flowers for entomophily: abundant insect visitation in most species and stigmas closely surrounded by stamens (Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). An experiment to simulate the removal of pollen from anthers by the wind showed that when pollen is transported by wind, the distance traveled (up to 30 cm) is insufficient for cross-pollination to occur (Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.). A respective study on Piper species producing powdery pollen may elucidate the importance of wind as a pollen vector in the sexual reproduction of these plants.
Valentin-Silva et al. (2021)Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635. evaluated the role of pollinators in the diversification of floral traits of Neotropical Piper species, and no correlation between the flower morphological characteristics and their pollinators was found, indicating phenotypic generalization. The authors suggest that dispersers which tend to be more specialized than pollinators of Piper may have influenced the diversification of the genus; however, further research is required.
The pollination biology of Paleotropical Piper species has been poorly studied (see Sen & Rengaian 2022Sen S & Rengaian G (2022) A review on the ecology, evolution and conservation of Piper (Piperaceae) in India: future directions and opportunities. The Botanical Review 88: 333-358.), even though these species have predominantly unisexual flowers and probably depend on pollen vectors. The few existing studies were carried out mainly with P. nigrum, species originating in India that is widely cultivated throughout the humid tropics (Greig 2004Greig N (2004) Introduction. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 1-4.). Spring tails (Collembola) were observed to visit the flowers in populations of four varieties of P. nigrum cultivated in Puerto Rico (Martin & Gregory 1962Martin FW & Gregory LE (1962) Mode of pollination and factors affecting fruit set in Piper nigrum L. in Puerto Rico. Crop Science 2: 295-299.). However, as these insects are wingless, they likely contribute little to pollen flow between plants. Some authors proposed that water and wind may be important pollen vectors for sexual reproduction of black pepper (Menon 1949Menon KK (1949) The survey of pollu and root diseases of pepper. Indian Journal of Agricultural Science 19: 89-136.; Gentry 1955aGentry HS (1955a) Introducing black pepper into America. Economic Botany 9: 256-268.,b), however, there is no experimental evidence (see Martin & Gregory 1962Martin FW & Gregory LE (1962) Mode of pollination and factors affecting fruit set in Piper nigrum L. in Puerto Rico. Crop Science 2: 295-299.; Sasikumar et al. 1992Sasikumar B, George JK & Ravindran PN (1992) Breeding behaviour of black pepper. Indian Journal of Genetics and Plant Breeding 52: 17-21.). This species, which comprises several varieties that can be hermaphroditic, dioecious, or monoecious (Menon 1949Menon KK (1949) The survey of pollu and root diseases of pepper. Indian Journal of Agricultural Science 19: 89-136.), is self-pollinating or even apomictic (Gentry 1955bGentry HS (1955b) Apomixis in black pepper and jojoba? Journal of Heredity 46: 8.; Sasikumar et al. 1992Sasikumar B, George JK & Ravindran PN (1992) Breeding behaviour of black pepper. Indian Journal of Genetics and Plant Breeding 52: 17-21.; but see Pooja et al. 2022Pooja S, Sreekala GS & Vijaykumar BN (2022) Breeding system of fruit set in black pepper (Piper nigrum L.). The Pharma Innovation Journal 11: 1755-1759.), both characteristics can be adaptations to cultivation (Martin & Gregory 1962Martin FW & Gregory LE (1962) Mode of pollination and factors affecting fruit set in Piper nigrum L. in Puerto Rico. Crop Science 2: 295-299.). However, the occurrence of apomixis needs to be confirmed through an embryological study, which could also be performed on Neotropical Piper species with a high fruiting rate and low visitation frequency, such as P. umbellatum L. (Figueiredo & Sazima 2000Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.; Valentin-Silva et al. 2021Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.).
In addition to studies on P. nigrum, there are only two other studies on the aspects of pollination with Paleotropical Piper species. Ollerton (1996)Ollerton J (1996) Interactions between gall midges (Diptera: Cecidomyiidae) and inflorescences of Piper novae-hollandiae (Piperaceae) in Australia. The Entomologist 115: 181-184. observed that in Australia, flies (gall midges; Diptera: Cecidomyiidae) visit and lay eggs on male inflorescences of P. novae-hollandiae Miq., which produces sweet-smelling flowers. However, as no female inflorescences were observed, whether these flies contribute to pollen flow between plants is not yet known. An interesting floral visitor was observed by Okuyama (2014)Okuyama Y (2014) Repeated visitation by a sesarmid crab to male inflorescences of Piper sp. Bulletin of the National Museum of Nature and Science, Series B 40: 119-123. in the Philippines, a crab species was found on male inflorescences of an unidentified Piper species. Although the author recorded the presence of anthers attached to the body of this crustacean, the absence of visits to female inflorescences and the record of this crab in only one individual of Piper indicates that this animal probably contributes little to pollen flow between plants.
Conclusion
The reproductive biology of Piper has advanced in recent years, mostly in Neotropical species. Some patterns can be observed, such as the predominance of annual flowering and fruiting, dichogamy (generally incomplete protogyny) with gradual and sequential exposure of stigmas, asynchronous pollen release, and pollination by insects. However, these aspects have not been extensively studied in the Paleotropical Piper species, and further studies are required to obtain basic information on the reproductive biology of these plants. From this, comparisons with Neotropical species can be made, allowing the verification of patterns in this genus. It will also be possible to apply these results to evolutionary studies, for example, regarding floral diversification.
From existing knowledge, it is possible to point out some gaps that deserve attention. Phenological data can be associated with germination ecology to assess their influence on reproductive success, especially for seasonal vegetation. Phenological responses can also be studied in the context of climate change. For example, the production of flower buds (latent and non-latent) in a scenario of lower precipitation and the consequences for subsequent phenophases and population dynamics. Another interesting point to be evaluated is the frequency of occurrence of cryptic unisexuality in morphologically bisexual flowers, considering that hermaphroditism is a typical characteristic of the Neotropical clade, and the selective pressures that can culminate in changes in the sexual expression of these plants. Regarding floral biology, nothing is known about the dynamics of floral odor release or the plant tissues that produce it. Chemical ecology studies can assess when the release of volatile organic compounds occurs, considering the predominance of dichogamy in Neotropical species and unisexual flowers in Paleotropical species. Moreover, fractions of these floral odors can be used in bioassays that evaluate their role in attracting different pollinators in a generalist pollination system such as Piper. Genetic analyses in self-compatible Piper species can contribute to studies on the evolution of mixed mating systems. Due to the organization of inflorescences and the visiting behavior of pollinators, the occurrence of this type of mating system may not be related to the unpredictability of pollinators, as commonly reported in the literature.
Piperaceae is a mega-diverse (approximately 3,500 species) and early diverging lineage of angiosperms. Besides Piper, there are four other genera in the family (Manekia, Peperomia, Verhuellia, and Zippelia) that have been little studied in relation to their reproductive biology. Information on these plants can be useful for understanding the diversification of angiosperms. Thus, the study of different aspects of the reproductive biology of Piper remains a promising field of research.
Acknowledgments
I thank the National Council for Scientific and Technological Development (CNPq) for the scientific initiation and Master’s scholarships and the Coordination for the Improvement of Higher Education Personnel (CAPES) for the doctoral and postdoctoral scholarships facilitating different works using Piper as a study model.
-
See supplementary material at <https://doi.org/10.6084/m9.figshare.22626970.v1>
References
- Angulo-Sandoval P & Aide TM (2000) Leaf phenology and leaf damage of saplings in the Luquillo Experimental Forest, Puerto Rico. Biotropica 32: 415-422.
- Asmarayani R (2018) Phylogenetic relationships in Malesian-Pacific Piper (Piperaceae) and their implications for systematics. Taxon 67: 693-724.
- Barrett SCH (2003) Mating strategies in flowering plants: the outcrossing-selfing paradigm and beyond. Philosophical Transactions of the Royal Society B 358: 991-1004.
- Chen YS, Dayod M & Tawan CS (2018) Anther dehiscence, pollen viability and stigma receptivity study on cultivars of black pepper (Piper nigrum L.). Pertanika Journal of Tropical Agricultural Science 41: 801-814.
- Crawley MJ (2007) The R book. John Wiley & Sons, Chichester. 942p.
- Cruden RW (2000) Pollen grains: why so many? Plant Systematics and Evolution 222: 143-165.
- Culley TM, Weller SG & Sakai AK (2002) The evolution of wind pollination in angiosperms. Trends in Ecology and Evolution 17: 361-369.
- Devi WD, Gajurel PR & Rethy P (2016a) Phenology of Piper mullesua Buchanan-Hamilton ex D. Don (Piperaceae) - a medicinally important dioecious plant. Pleione 10: 239-247.
- Devi WD, Gajurel PR & Rethy P (2016b) Bisexuality in dioecious male plant: an unusual phenomenon of sex expression in Piper species. International Journal of Plant Reproductive Biology 8: 82-86.
- Devi WD, Gajurel PR & Rethy P (2018) Phenological behavior of Piper sylvaticum Roxb. (Piperaceae), a medicinally useful species occurring in Eastern Himalayan region. International Journal of Plant Reproductive Biology 10: 84-89.
- Di Stasi LC, Hiruma-Lima CA, Mariot A, Portilho WG & Reis MS (2002) Piperales medicinais. In: Di Stasi LC & Hiruma-Lima CA (eds.) Plantas medicinais na Amazônia e na Mata Atlântica. Ed. Unesp, São Paulo. Pp. 120-138.
- Dyer L, Richards J & Dodson C (2004) Isolations, synthesis, and evolutionary ecology of Piper amides. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 117-139.
- Farré-Armengol G, Filella I, Llusia J & Peñuelas J (2013) Floral volatile organic compounds: between attraction and deterrence of visitors under global change. Perspectives in Plant Ecology, Evolution and Systematics 15: 56-67.
- Fenner M (1998) The phenology of growth and reproduction in plants. Perspectives in Plant Ecology, Evolution and Systematics 1: 78-91.
- Figueiredo RA (2003) Coleta de pólen, interações agonísticas e horários de atividade dos visitantes florais (Insecta: Diptera, Hymenoptera) de pimenteiras silvestres (Piperaceae). Revista de Etologia 5: 3-13.
- Figueiredo RA & Sazima M (2000) Pollination biology of Piperaceae species in southeastern Brazil. Annals of Botany 85: 455-460.
- Figueiredo RA & Sazima M (2004) Pollination ecology and resource partitioning in neotropical Pipers In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 33-57.
- Fleming TH (1981) Fecundity, fruiting pattern, and seed dispersal in Piper amalago (Piperaceae), a bat-dispersed tropical shrub. Oecologia 51: 42-46.
- Fleming TH (1985) Coexistence of five sympatric Piper (Piperaceae) species in a tropical dry forest. Ecology 66: 688-700.
- Fleming TH (2004) Dispersal ecology of Neotropical Piper shrubs and treelets. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 58-77.
- Gartner BL (1989) Breakage and regrowth of Piper species in rain forest understory. Biotropica 21: 303-307.
- Gentry HS (1955a) Introducing black pepper into America. Economic Botany 9: 256-268.
- Gentry HS (1955b) Apomixis in black pepper and jojoba? Journal of Heredity 46: 8.
- Greig N (1993) Regeneration mode in neotropical Piper: habitat and species comparisons. Ecology 74: 2125-2135.
- Greig N (2004) Introduction. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 1-4.
- Hartshorn GS & Hammel BE (1994) Vegetation types and floristic patterns. In: McDade LA, Bawa KS, Hespenheide HA & Hartshorn GS (eds.) La Selva: ecology and natural history of a neotropical rain forest. The University of Chicago Press, Chicago. Pp 73-89.
- Jaramillo MA & Manos PS (2001) Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae). American Journal of Botany 88: 706-716.
- Jaramillo MA, Callejas R, Davidson C, Smith JF, Stevens AC & Tepe EJ (2008) A phylogeny of the tropical genus Piper using ITS and the chloroplast intron psbJ-petA Systematic Botany 33: 647-660.
- Kanimozhi K & Sujatha VS (2015) Reproductive biology of Piper longum L. Journal of Tropical Agriculture, 53: 206-212.
- Kikuchi DW, Lasso E, Dalling JW & Nur N(2007) Pollinators and pollen dispersal of Piper dilatatum (Piperaceae) on Barro Colorado Island, Panama. Journal of Tropical Ecology 23: 603-606.
- Kochmer JP & Handel SN (1986) Constraints and competition in the evolution of flowering phenology. Ecological Monographs 56: 303-325.
- Lasso E, Engelbrecht BMJ & Dalling JW (2009) When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs. Oecologia 161: 43-56.
- Lasso E, Dalling JW & Bermingham E (2012) Tropical understory Piper shrubs maintain high levels of genotypic diversity despite frequent asexual recruitment. Biotropica 44: 35-43.
- Lei LG & Liang HX (1998) Floral development of dioecious species and trends of floral evolution in Piper sensu lato Botanical Journal of the Linnean Society 127: 225-237.
- Letourneau DK (2004) Mutualism, antiherbivore, and trophic cascades: Piper ant-plants as a mesocosm for experimentation. In: Dyer LA & Palmer ADN (eds.) Piper: a model genus for studies of phytochemistry, ecology, and evolution. Kluwer Academic/Plenum Publishers, New York. Pp. 5-32.
- Lima IP & Reis NR (2004) The availability of Piperaceae and the search for this resource by Carollia perspicillata (Linnaeus) (Chiroptera, Phyllostomidae, Carolliinae) in the Parque Municipal Arthur Thomas, Londrina, Paraná, Brazil. Revista Brasileira de Zoologia 21: 371-377.
- Lloyd DG & Schoen DJ (1992) Selfand cross-fertilization in plants. I. Functional dimensions. International Journal of Plant Sciences 153: 358-369.
- Machado DB, Ramos YJ, Queiroz GA, Defaveri ACA, Gobatto AA & Moreira DL (2021) Study of volatile chemical constituents and insect-plant interaction in Piper mollicomum Kunth (Piperaceae) from Tijuca Forest, Rio de Janeiro - RJ, Brazil. Revista Virtual de Química 13: 1216-1225.
- Marinho-Filho JS (1991) The coexistence of two frugivorous bat species and the phenology of their food plants in Brazil. Journal of Tropical Ecology 7: 59-67.
- Mariot A, Mantovani A & Reis MS (2003) Uso e conservação de Piper cernuum Vell. (Piperaceae) na Mata Atlântica: I. Fenologia reprodutiva e dispersão de sementes. Revista Brasileira de Plantas Medicinais 5: 1-10.
- Marquis RJ (1988) Phenological variation in the neotropical understory shrub Piper arieianum: causes and consequences. Ecology 69: 1552-1565.
- Martin FW & Gregory LE (1962) Mode of pollination and factors affecting fruit set in Piper nigrum L. in Puerto Rico. Crop Science 2: 295-299.
- Mayer SS & Charlesworth D (1991) Cryptic dioecy in flowering plants. Trends in Ecology and Evolution 6: 320-325.
- Menon KK (1949) The survey of pollu and root diseases of pepper. Indian Journal of Agricultural Science 19: 89-136.
- Morellato LPC, Camargo MGG, d’Eça-Neves FF, Luize BG, Mantavoni A & Hudson IL (2010a) The influence of sampling method, sample size, and frequency of observations on plant phenological patterns and interpretation in tropical forest trees. In: Hudson IL & Keatley MR (eds.) Phenological research: methods for environmental and climate change analysis. Springer, Dordrecht. Pp. 99-121.
- Morellato LPC, Alberti LF & Hudson IL (2010b) Applications of circular statistics in plant phenology: a case studies approach. In: Hudson IL & Keatley MR (eds.) Phenological research: methods for environmental and climate change analysis. Springer, Dordrecht. Pp. 339-359.
- Newstrom LE, Frankie GW & Bake HG (1994) A new classification for plant phenology based on flowering patterns in lowland tropical rain forest trees at La Selva, Costa Rica. Biotropica 26: 141-159.
- Okuyama Y (2014) Repeated visitation by a sesarmid crab to male inflorescences of Piper sp. Bulletin of the National Museum of Nature and Science, Series B 40: 119-123.
- Ollerton J (1996) Interactions between gall midges (Diptera: Cecidomyiidae) and inflorescences of Piper novae-hollandiae (Piperaceae) in Australia. The Entomologist 115: 181-184.
- Ollerton J, Killick A, Lamborn E, Watts S & Whiston M (2007) Multiple meanings and modes: on the many ways to be a generalist flower. Taxon 56: 717-728.
- Opler PA, Frankie GW & Baker HG (1980) Comparative phenological studies of treelet and shrub species in tropical wet and dry forests in the lowlands of Costa Rica. Journal of Ecology 68: 167-188.
- Pannell JR (2002) The evolution and maintenance of androdioecy. Annual Review of Ecology and Systematics 33: 397-425.
- Pooja S, Sreekala GS & Vijaykumar BN (2022) Breeding system of fruit set in black pepper (Piper nigrum L.). The Pharma Innovation Journal 11: 1755-1759.
- Sakai AK & Weller SG (1999) Gender and sexual dimorphism in flowering plants: a review of terminology, biogeographic patterns, ecological correlates, and phylogenetic approaches. In: Geber MA, Dawson TE & Delph LF (eds.) Gender and sexual dimorphism in flowering plants. Springer-Verlag, Berlin. Pp. 1-31.
- Sasikumar B, George JK & Ravindran PN (1992) Breeding behaviour of black pepper. Indian Journal of Genetics and Plant Breeding 52: 17-21.
- Semple KS (1974) Pollination in Piperaceae. Annals of the Missouri Botanical Garden 61: 868-871.
- Sen S, Dayanandan S, Davis T, Ganesan R, Jagadish MR, Mathew PJ & Ravikanth G. (2019) Origin and evolution of the genus Piper in Peninsular India. Molecular Phylogenetics and Evolution 138: 102-113.
- Sen S & Rengaian G (2022) A review on the ecology, evolution and conservation of Piper (Piperaceae) in India: future directions and opportunities. The Botanical Review 88: 333-358.
- Simmonds SE, Smith JF, Davidson C & Buerki S (2021) Phylogenetics and comparative plastome genomics of two of the largest genera of angiosperms, Piper and Peperomia (Piperaceae). Molecular Phylogenetics and Evolution 163: 107229.
- Snow DW (1965) A possible selective factor in the evolution of fruiting seasons in tropical forest. Oikos 15: 274-281.
- Souza LA, Moscheta IS, Mourão KSM, Albiero ALM, Iwazaki MC, Oliveira JHG & Rosa SM (2009) Vegetative propagation in Piperaceae species. Brazilian Archives of Biology and Technology 52: 1357-1361.
- Staggemeier VG, Diniz-Filho JAF & Morellato LPC (2010) The shared influence of phylogeny and ecology on the reproductive patterns of Myrteae (Myrtaceae). Journal of Ecology 98: 1409-1421.
- Stevenson PR, Castellanos MC, Cortés AI & Link A (2008) Flowering patterns in a seasonal tropical lowland forest in western Amazonia. Biotropica 40: 559-567.
- Thies W & Kalko EKV (2004) Phenology of neotropical pepper plants (Piperaceae) and their association with their main dispersers, two short-tailed fruit bats, Carollia perspicillata and C. castanea (Phyllostomidae). Oikos 104: 362-376.
- Thomazini MJ & Thomazini APBW (2002) Diversidade de abelhas (Hymenoptera: Apoidea) em inflorescências de Piper hispidinervum (C.DC.). Neotropical Entomology 31: 27-34.
- Tucker SC (1982) Inflorescence and flower development in the Piperaceae III. Floral ontogeny of Piper American Journal of Botany 69: 1389-1401.
- Valentin-Silva A & Vieira MF (2015) Phenology of two co-occurring Piper (Piperaceae) species in Brazil. Australian Journal of Botany 63: 581-589.
- Valentin-Silva A, Coelho VPM, Ventrella MC & Vieira MF (2015) Timing of pollen release and stigma receptivity period of Piper vicosanum (Piperaceae): new insights into sexual reproduction of the genus. American Journal of Botany 102: 626-633.
- Valentin-Silva A, Staggemeier VG, Batalha MA & Guimarães E (2018a) What factors can influence the reproductive phenology of Neotropical Piper species (Piperaceae) in a semi-deciduous seasonal forest? Botany 96: 675-684.
- Valentin-Silva A, Batalha MA & Guimarães E (2018b) Neotropical Piper species: are they all hermaphroditic? Flora 244-245: 8-14.
- Valentin-Silva A, Batalha MA & Guimarães E (2018c) Dynamics of pollen release and stigmatic exposure in Neotropical Piper species: a possible pattern for the genus. International Journal of Plant Sciences 179: 287-295.
- Valentin-Silva A, Batalha MA & Guimarães E (2021) Disentangling the ecological basis of floral trait variation in Neotropical Piper species. Botanical Journal of the Linnean Society 195: 622-635.
- van Schaik CP, Terborgh JW & Wright SJ (1993) The phenology of tropical forests: adaptive significance and consequences for primary consumers. Annual Review of Ecology and Systematics 24: 353-377.
- Vargas-Rojas DL & Vieira MF (2017) Sex expression, breeding system and pollinators of Piper caldense (Piperaceae) in the Brazilian Atlantic Forest. Acta Biológica Colombiana 22: 370-378.
- Wanke S, Jaramillo MA, Borsch T, Samain MS, Quandt D & Neinhuis C (2007) Evolution of Piperales - matK gene and trnK intron sequence data reveal lineage specific resolution contrast. Molecular Phylogenetics and Evolution 42: 477-297.
- Wisniewski C, Bornstein AJ & Wood DL (2019) Eating out or dining in: insect-plant interactions among species of Piper in the Rio Abajo Forest Preserve, Puerto Rico. Selbyana, 33: 1-15.
- Wright SJ (1991) Seasonal drought and the phenology of understory shrubs in a tropical moist forest. Ecology 72: 1643-1657.
- Zar JH (2010) Biostatistical analysis. Prentice-Hall, Upper Saddle River. 944p.
Publication Dates
-
Publication in this collection
29 May 2023 -
Date of issue
2023
History
-
Received
19 Sept 2022 -
Accepted
21 Dec 2022