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Aspects of biology of Megalobulimus paranaguensis (Gastropoda, Acavoidea) in the coastal plain of the Brazilian southeast

Aspectos da biologia de Megalobulimus paranaguensis (Gastropoda, Acavoidea) na planície costeira do sudeste brasileiro

ABSTRACT

We studied the reproductive biology of Megalobulimus paranaguensis (Pilsbry & Ihering, 1900), a large and long-lived land gastropod from the Atlantic Rainforest of Brazil. The study was conducted at an urban park in the city of Santos, state of São Paulo. For 4 years, we counted the egg postures and annual eclosion rate of 32 captive snails and looked for associations between egg posture and the climatical variables of the period. The annual mean posture of 8.7 eggs per snail obtained in our results is a small number, but typical of Brazilian macromollusks. The annual eclosion rate was 31%. The beginning of the annual activity period of snails occurred in the middle of March, and lasted 33.97±3.02 weeks. The dormancy period started in the beginning of November, and lasted 18.39±3.11 weeks. There were two egg posture peaks, a minor peak between March and May, and a major peak between August and November, with greater values in September. Megalobulimus paranaguensis has a well-defined seasonal reproductive pattern influenced by environmental temperature and temperature range. Furthermore, in this snail, reproduction is negatively influenced by temperature increasing and temperature range.

KEYWORDS
Aruá-do-mato; egg posture; land snail; Atlantic Rainforest; reproduction

RESUMO

Nós estudamos a biologia reprodutiva de Megalobulimus paranaguensis (Pilsbry & Ihering, 1900), um grande e longevo gastrópode terrestre da Floresta Atlântica na costa sudeste do Brasil, em um parque urbano na cidade de Santos, Estado de São Paulo, ao longo de quatro anos, pelo número de posturas e taxa de eclosão anual de 32 caracóis cativos. Relacionamos estes dados com variáveis climáticas do mesmo período. Obtivemos uma média anual de posturas de 8.7 ovos por caracol, um número baixo, típico da fauna de macromoluscos terrestres brasileiros. A taxa de eclosão anual foi de 31%. O início do período anual de atividade ocorreu em meados de março e dura 33.97±3.02 semanas; e o início da dormência ocorreu no começo de novembro; com duração de 18.39±3.11 semanas. Existem dois picos de postura, um menor entre março a maio e um pico maior antes da estivação, entre os meses de agosto a novembro, com maiores valores em setembro. Megalobulimus paranaguensis possui um padrão sazonal reprodutivo bem marcante influenciado pela temperatura do ambiente e amplitude de temperatura. A reprodução é influenciada negativamente pelo aumento da temperatura e da amplitude de temperatura.

PALAVRAS-CHAVE
Aruá-do-mato; posturas de ovos; caracol terrestre,; Mata Atlântica; reprodução

Megalobulimus Miller, 1878, which includes species popularly known as "aruá-do-mato", is a group of giant Neotropical land snails that belong to the subfamily Megalobuliminae (Strophocheilidae) (Bouchet & Rocroi, 2005Bouchet, P. & Rocroi, J. P. 2005. Classification and Nomenclature of Gastropod Families. Malacologia 47:1-397.). The genus has great diversity, with 83 described species, 63 of which occur in Brazil (Simone, 2006Simone, L. R. L. 2006. Land and freshwater molluscs of Brazil. São Paulo, EGB, Fapesp. 390p., 2012Simone, L. R. L. 2012. Taxonomical study on a sample of pulmonates from Santa Maria da Vitória, Bahia, Brazil, with description of a new genus and four new species (Mollusca: Orthalicidae and Megalobulimidae). Papéis Avulsos de Zoologia 52:431-439.; Borda & Ramirez, 2013Borda, V. & Ramirez, R. 2013. Re-characterization of the Red-lip Megalobulimus (Gastropoda: Strophocheilidae) from Peru with description of a new species. Zoologia 30:675-691. DOI: 10.1590/S1984-46702013005000008.
https://doi.org/10.1590/S1984-4670201300...
; Fontenelle et al., 2014Fontenelle, J. H.; Cavallari, D. C. & Simone, L. R. L. 2014. A new species of Megalobulimus (Gastropoda, Strophocheilidae) from Brazilian shell mounds. Strombus 21:30-37.). Like other land snails, the species of Megalobulimus are nocturnal (Bequaert, 1948Bequaert, J. C. 1948. Monograph of the family Strophocheilidae, a Neotropical family of terrestrial mollusks. Bulletin of Museum of Comparative Zoology of Harvard 100:1-210.). During the day, or during dormancy periods, individuals bury themselves in the soil or leaf litter (Bequaert, 1948Bequaert, J. C. 1948. Monograph of the family Strophocheilidae, a Neotropical family of terrestrial mollusks. Bulletin of Museum of Comparative Zoology of Harvard 100:1-210.). They are iteroparous hermaphrodite snails with annual periodicity and great longevity, can live up to 35 years (Pinto-de-Oliveira et al., 1984Pinto-de-Oliveira, M.; Rezende, G. J. R. & Castro, G. A. 1984. Megalobulimus (Phaiopharus) granulosus Rang, 1831 (Gastropoda, Pulmonata, Stylommatophora, Strophocheilidae). Comunicações Malacológicas 15:1-18.; Horn et al., 2005Horn, A. C. M.; Achaval, M. & Zancan, D. M. 2005. The annual reproductive cycle of the snail Megalobulimus abbreviatus (Bequaert, 1948) (Gastropoda, Pulmonata). Brazilian Journal of Biology 65:459-467.; Fontenelle & Miranda, 2012Fontenelle, J. H. & Miranda, M. S. 2012. The use of outer lip in age estimation of Megalobulimus paranaguensis (Gastropoda, Pulmonata). Strombus 19:15-22.), and generally occur in low densities and irregular distribution (Simone, 1999Simone, L. R. L. 1999. Gastropoda terrestres. In: Brandão, C. R. F. & Cancello, E. M. eds. Biodiversidade do estado de São Paulo: Uma síntese do conhecimento ao final do século XX. Vol.5. Invertebrados terrestres. São Paulo, FAPESP, p. 3-8.; Eston et al., 2006Eston, M. R.; Menezes, G. V.; Antunes, A. Z.; Santos, A. S. R. & Santos, A. M. R. 2006. Espécie invasora em unidade de conservação: Achatina fulica (Bowdich, 1822) no Parque Estadual Carlos Botelho Sete Barras, SP, Brasil. Revista do Instituto Florestal 18:173-179.; Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
). Like other Brazilian pulmonates, they have low reproductive potential, spawning 2-5 eggs per batch (Sobreira & Molina, 2002Sobreira, H. B. & Molina, F. B. 2002. Observações preliminares sobre a biologia reprodutiva de Megalobulimus gummatus (Mollusca, Megalobulimidae) em laboratório. Arquivos do Instituto Biológico 69:139-141.).

One third of the known species of Megalobulimus in Brazil occur in the coastal plain and mountain ranges parallel to the coast, between the South and Southeast (Bequaert, 1948Bequaert, J. C. 1948. Monograph of the family Strophocheilidae, a Neotropical family of terrestrial mollusks. Bulletin of Museum of Comparative Zoology of Harvard 100:1-210.), in the Atlantic Rainforest. This biome is one of the richest in the world in terms of numbers of species, but unfortunately it has been gradually destroyed (Mansur & Leme, 1996Mansur, M. C. D. & Leme, J. L. M. 1996. The endangered giant Megalobulimus from the Atlantic forest of Brasil. Tentacle 6:14-15.; Myers et al., 2000Myers, N.; Mittermeier, R. A.; Mittermeier, C. G.; Fonseca, G. A. B. & Kent, J. 2000. Biodiversity hotspots for conservation priorities. Nature 403:853-858.). The populations of many species of Megalobulimus from this area, for instance M. fragilior (Ihering, 1901), M. parafragilior Leme & Indrusiak, 1990, M. grandis (Martens, 1885), M. lopesi Leme, 1989, M. proclivis (Martens, 1888) and M. paranaguensis (Pilsbry & Ihering, 1900), have been reduced, and some may be threatened (Leme, 1989Leme, J. L. M. 1989. Megalobulimus lopesi sp. n., uma nova espécie de Pulmonata terrestre da mata atlântica brasileira (Mollusca, Gastropoda, Megalobulimidae). Memórias do Instituto Oswaldo Cruz 84:313-318.; Leme & Indrusiak, 1990Leme, J. L. M. & Indrusiak, L. F. 1990. Megalobulimus parafragilior, sp. n., uma nova espécie de Pulmonata terrestre da Serra do Mar (Gastropoda, Megalobulimidae). Papéis Avulsos de Zoologia 37:97-105.; Mansur & Leme, 1996Mansur, M. C. D. & Leme, J. L. M. 1996. The endangered giant Megalobulimus from the Atlantic forest of Brasil. Tentacle 6:14-15.; Fischer & Colley, 2005Fischer, M. L. & Colley, E. 2005. Espécie invasora em reservas naturais: caracterização da população de Achatina fulica Bowdich, 1822 (Mollusca - Achatinidae) na ilha Rasa, Guaraqueçaba, Paraná, Brasil. Biota Neotropica 5:127-144.; Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
). Officially, the Brazilian authorities only list one species of Megalobulimus in their list of threatened species, M. cardosoi (Morretes, 1952), which is endemic to the state of Alagoas, and is critically endangered (Santos et al., 2015Santos, S. B.; ,Miyahira, I. C.; Salgado, N. C.; Heydrich, I.; Pena, M. S.; Colley, E.; Fernandez, M. A.; Thiengo, S. C.; Gomes, S. R.; Silva, M. J. M.; Gonçalves, I. C.B.; Lacerda, L. E. M.; Tallarico, L. F. & Martins, D. S. 2015.Observations on the review of the list of endangered non-marine molluscs of Brazil. Tentacle 23:26-28.).

Megalobulimusparanaguensis (Pilsbry & Ihering, 1900) was described from the city of Paranaguá (state of Paraná), and is distributed in the coastal plain of the Atlantic Rainforest, between Guaratuba, state of Paraná, and Itanhaém, state of São Paulo (Morretes, 1954Morretes, F. L. 1954. Sôbre Megalobulimus paranaguensis Pilsbry & Ihering. Arquivos do Museu Paranaense 10:343-344.). There have been records also between the Island of São Vicente, state of São Paulo (Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
) and the northern coast of the state of Santa Catarina (Agudo-Padron, 2014Agudo-Padron, A. I. 2014. Inventario sistemático de los moluscos continentales ocurrentes en el Estado de Santa Catarina, Brasil. Bioma 2:6-23.), coinciding with a geomorphology characterized by large coastal plains between Serra do Mar, and long beaches interspersed by estuaries (Muehe, 1998Muehe, D. 1998. O litoral brasileiro e sua compartimentação. In: Cunha, S. B. & Guerra, A. J. T. eds. Geomorfologia do Brasil. São Paulo, Bertrand, p. 273-349.). After the introduction of the alien snail Achatina fulica Bowdich, 1822 many individuals of M. paranaguensis have been accidentally killed in control campaigns (Colley & Fischer, 2009Colley, E. & Fischer, M. L. 2009. Avaliação dos problemas enfrentados no manejo do caramujo gigante africano Achatina fulica (Gastropoda, Pulmonata) no Brasil. Zoologia 26:674-683. ).

Recently, aspects of the ecology and distribution of some species of Megalobulimus were studied in more detail (Beltramino, 2013Beltramino, A. A. 2013. Distribution of Megalobulimus sanctipauli (Ihering and Pilsbry, 1900) (Gastropoda: Megalobulimidae) in South America. CheckList 9:469-471., 2014Beltramino, A. A. 2014. Distribución histórica y área de distribución potencial del megamolusco terrestre Megalobulimus lorentzianus (Doering, 1876) (Gastropoda: Pulmonata) en américa del sur. Boletín de la Asociación Argentina de Malacología 4:10-13.; Beltramino et al., 2015Beltramino, A. A.; Vogler, R. E.; Gutiérrez-Gregoric, D. E. & Rumi, A. 2015. Impact of climate change on the distribution of a giant land snail from South America: predicting future trends for setting conservation priorities on native malacofauna. Climatic Change 131:621-633. Doi: 10.1007/s10584-015-1405-3.
https://doi.org/10.1007/s10584-015-1405-...
; Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
; Miranda & Fontenelle, 2015Miranda, M. S. & Fontenelle, J. H. 2015. Population dynamics of Megalobulimus paranaguensis in the Brazilian southeast coast. Zoologia 32:463-468. Doi: 10.1590/S1984-46702015000600005.
https://doi.org/10.1590/S1984-4670201500...
; Miranda & Pecora, 2016Miranda, M. S. & Pecora, I. L. 2016. Conservation implications of behavioural interactions between the giant african snail and a Brazilian native species. Ethology, Ecology & Evolution 29:1-9. Doi: 10.1080/03949370.2015.1125951.
https://doi.org/10.1080/03949370.2015.11...
), providing important information about their biology and conservation. On the other hand, data about the reproductive biology of Megalobulimus species are still scarce, and restricted to the studies of Pinto-de-Oliveira et al. (1984Pinto-de-Oliveira, M.; Rezende, G. J. R. & Castro, G. A. 1984. Megalobulimus (Phaiopharus) granulosus Rang, 1831 (Gastropoda, Pulmonata, Stylommatophora, Strophocheilidae). Comunicações Malacológicas 15:1-18.), on Megalobulimus bronni (Pfeiffer, 1847), Sobreira & Molina (2002Sobreira, H. B. & Molina, F. B. 2002. Observações preliminares sobre a biologia reprodutiva de Megalobulimus gummatus (Mollusca, Megalobulimidae) em laboratório. Arquivos do Instituto Biológico 69:139-141.), on Megalobulimus aff. gummatus (Hidalgo, 1870) and Horn et al. (2005Horn, A. C. M.; Achaval, M. & Zancan, D. M. 2005. The annual reproductive cycle of the snail Megalobulimus abbreviatus (Bequaert, 1948) (Gastropoda, Pulmonata). Brazilian Journal of Biology 65:459-467.), on Megalobulimus abbreviatus (Bequaert, 1948Bequaert, J. C. 1948. Monograph of the family Strophocheilidae, a Neotropical family of terrestrial mollusks. Bulletin of Museum of Comparative Zoology of Harvard 100:1-210.). Information obtained by these studies have increased our knowledge of their ecology and can be used to develop conservation and management plans for Megalobulimus spp. The objective of this study was to analyze the activity and oviposition of captive M. paranaguensis at Parque Zoobotânico Orquidário Municipal, and to evaluate which environmental variables affect this pattern.

MATERIAL AND METHODS

This study took place at "Parque Zoobotânico Orquidário Municipal de Santos" (PZOMS), a small 22,000 m2 park located in the municipality of Santos (UTM: 23K E 362672.57, 7348904.53 N). PZOMS presents flat topography, arboreal phytophysiognomy with understory formation and litter accumulation. Its area is fragmented, and has malls, animal enclosures, a 4,300 m2 lake and rainwater drainage channels.

Between January 2007 to December 2010, 32 individuals of M. paranaguensis were captured at the PZOMS, kept captive in boxes and placed in the shade, in understory areas at the park. The boxes were 50 x 80 x 80 cm and had a 0.5 inch screen. Four snails were maintained in each box, which was lined with substrate containing 15 cm of soil + sand and 10 cm of leaf litter. Food was provided ad libitum and it was similar to what is consumed by the free population of the PZOMS, consisting of Malvaviscus, Spathiphyllum, Piper and "jurubeba" (Solanum paniculatum). The leaf litter level was completed weekly, litter was changed monthly and the number of postures (eggs/individual) was counted once a month and divided by the number os specimens in each box. Each egg ovoposed were measured (n=255) in length and width. For the years of 2009 and 2010, the annual eclosion rate were obtained. Voucher specimens of the population studied are deposited in the mollusk collection of the Museu de Zoologia da Universidade de São Paulo (lot MZSP 54629). In addition, the beginning and length of activity and dormancy periods of each snail were monitored. The following environmental variables were obtained for the duration of the experiment, from the website http://www.ciiagro.sp.gov.br/ciiagroonline/#Monitoramento (maintained by EMBRAPA - Agronomic Institute of Campinas) for the municipality of Santos, SP: mean temperature, potential evapotranspiration, number of rainy days, precipitation and temperature range. The temperature range values were obtained by subtracting the mean minimum temperature from the mean maximum temperature from January 2007 to December 2010. A stepwise regression, using AICc as the variable selection criterion between environmental variables and number of postures, was used to evaluate which variables influenced the number of postures. In the results, we only show the environmental variables that have affected the number of postures.

RESULTS AND DISCUSSION

We observed the beginning of the annual activity period in the mid-March, lasting 33.97±3.02 weeks; and the beginning of dormancy in the beginning of November, lasting 18.39±3.11 weeks in captive individuals. The annual mean egg posture was 8.7 eggs per snail. There were two egg posture peaks, a minor peak between March to May, and a major peak between August and November, with greater values in September (Fig. 1). The annual eclosion were 31% for both years analysed. The eggs are white, calcareous, elliptical, and are 26.3 ± 1.82 mm length per 20.1 ± 1.16 mm width (Fig. 2). They are partially buried in litter. At birth, newly-born individual sometimes eat the eggs from which they have hatched.

Fig. 1
Mean number of postures of Megalobulimus paranaguensis (Pilsbry & Ihering, 1900) in Parque Zoobotânico Orquidário Municipal de Santos (PZOMS).

Fig. 2
Egg posture of Megalobulimus paranaguensis (Pilsbry & Ihering, 1900) in leaf litter (1b). Scale = 30 mm.

Mean temperature values were greater during summer months (from November to February) and lowest in winter months (from May to August), and these fluctuations were well marked during the year (Fig. 3). The temperature range presented greater values in February, June and July, and minor values in May, September and October (Fig. 4). The stepwise regression mainted the variables mean temperature and temperature range in the model. The stepwise regression revealed that mean temperature and temperature range are negatively correlated with both variables (mean temperature: t = 1.93, p = 0.05, b = - 0.10; temperature range: t = 2.41, p - 0.01, b = - 0.30).

Fig. 3
Seasonal variation of mean temperature per month in municipality of Santos during period sampled.

Fig. 4
Seasonal variation of temperature range per month in municipality of Santos during period sampled.

Megalobulimus paranaguensis has a well-marked seasonal reproductive pattern, influenced by temperature and temperature range. The number of postures decrease with increasing temperatures. Gomot (1990Gomot, A. 1990. Photoperiod and temperature interaction in the determination of reproduction of the edible snail, Helix pomatia. Journal of Reproduction and Fertility 90:581-585.) showed that an increase in temperature, related with photoperiod variations, reduces the number of weeks in the reproductive cycle of Helix pomatia Linnaeus, 1758. The abundance and activity of M. paranaguensis are influenced by humidity and evapotranspiration in the environment (Miranda & Fontenelle, 2015Miranda, M. S. & Fontenelle, J. H. 2015. Population dynamics of Megalobulimus paranaguensis in the Brazilian southeast coast. Zoologia 32:463-468. Doi: 10.1590/S1984-46702015000600005.
https://doi.org/10.1590/S1984-4670201500...
; Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
), which indicate that an increase in the temperature and temperature range result in decreased activity of individuals and, consequently, a decrease in egg production.

Generally, gastropods react to changes in environmental conditions, but also have a circadian cycle and seasonal behavior synchronized by an endogenous biological clock, which anticipate variations in temperature, water and light throughout the year (Lazaridou-Dimitriadou & Saunders, 1986Lazaridou-Dimitriadou, M. & Saunders, D. S. 1986. The influence of humity, photoperiod and temperature on the dormancy and activity of Helix lucorum L. (Gastropoda, Pulmonata). Journal of Molluscan Studies 52:180-189.; Iglesias et al., 1996Iglesias, J; Santos, M. & Castillejo, J. 1996. Annual activity cycles of the land snail Helix aspersa Muller in natural populations of north-western Spain. Journal of Molluscan Studies 62:495-505.). Their characteristic dormancy during the summer months, called aestivation, happens when it is hot or dry (Boss, 1974Boss, K. J. 1974. Oblomovism in the Mollusca. Transactions of American Microscopical Society 93:460-481.). The main function of this dormancy, which is very common among land and freshwater mollusks, is to limit water loss by evaporation (Cáceres, 1997Cáceres, C. E. 1997. Dormancy in Invertebrates. Invertebrate Biology 116:371-383.). In M. paranaguensis, aestivation occurs in response to an increase in evapotranspiration (Miranda & Fontenelle, 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
) and decrease in humidity (Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
) between November and March, which increases water loss to the environment.

The number of postures of M. paranaguensis confirms the observation of Miranda & Fontenelle (2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
) that this species is iteroparous. Their study was based on mark-recapture estimates, and spawning peaks in their data coincided with the activity and recruitment peaks obtained by Miranda et al. (2015)Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
and Miranda & Fontenelle (2015)Miranda, M. S. & Fontenelle, J. H. 2015. Population dynamics of Megalobulimus paranaguensis in the Brazilian southeast coast. Zoologia 32:463-468. Doi: 10.1590/S1984-46702015000600005.
https://doi.org/10.1590/S1984-4670201500...
for the same species. The iteroparous pattern also occurs in M. abbreviatus (Horn et al., 2005Horn, A. C. M.; Achaval, M. & Zancan, D. M. 2005. The annual reproductive cycle of the snail Megalobulimus abbreviatus (Bequaert, 1948) (Gastropoda, Pulmonata). Brazilian Journal of Biology 65:459-467.), which indicates that this must be a pattern in the genus. Moreover, the presence of aestivation and a period with no reproductive activity is a characteristic of M. paranaguensis that differs from M. abbreviatus, and it is more similar to the patterns of temperate zone species (Bailey, 1981Bailey, S. E. R. 1981. Circannual and circadian rhythms in the snail Helix aspersa Müller and the photoperiodic controlof annual activity and reproduction. Journal of Comparative Physiology 142:89-94.).

Megalobulimus paranaguensis has low egg production, a pattern that is common in other Brazilian land snails. Jurberg et al. (1988Jurberg, P.; Barros, H. M.; Gomes, L. A. L. & Coelho, A. C. S. 1988. Superfamília Bulimuloidea do Brasil. Bulimulidae: Thaumastus (Thaumastus) taunaisii (Férussac, 1822), com dados biológicos e aspectos comportamentais (Mollusca, Gastropoda, Pulmonata). Boletim do Museu Nacional (Zoologia ) 358:1-47.) reported between 10 to 12 eggs per batch in Thaumasthus taunaisii (Ferrusac, 1822). Within Megalobulimus, 1.44 eggs per batch were recorded for Megalobulimus aff. ovatus (Müller, 1774), 2.87 eggs per batch for Megalobulimus sp. and 3.71 eggs per batch for M. gummatus (Sobreira & Molina, 2002Sobreira, H. B. & Molina, F. B. 2002. Observações preliminares sobre a biologia reprodutiva de Megalobulimus gummatus (Mollusca, Megalobulimidae) em laboratório. Arquivos do Instituto Biológico 69:139-141.; Rios et al., 2004Rios, F. R.; Jacinavicius, F. C. & Molina, F. B. 2004. Taxa de eclosão em ovos de Megalobulimus aff. ovatus (Gastropoda, Pulmonata, Megalobulimidae) incubados em laboratório. Arquivos do Instituto Biológico 71:388-390.). The first behavior performed by newly-born individuals is to eat the egg case. This behavior is important because the shell of young individuals is rather fragile (Jurberg et al., 1988Jurberg, P.; Barros, H. M.; Gomes, L. A. L. & Coelho, A. C. S. 1988. Superfamília Bulimuloidea do Brasil. Bulimulidae: Thaumastus (Thaumastus) taunaisii (Férussac, 1822), com dados biológicos e aspectos comportamentais (Mollusca, Gastropoda, Pulmonata). Boletim do Museu Nacional (Zoologia ) 358:1-47.), and calcium is a limiting element for mollusk survivor, being absorbed by the diet and by animal foot sole (Fournier & Chétail, 1984Fournier, J. & Chétail, M. 1984. Calcium dynamics in land gastropods. American Zoologist 24:857-870.).

The eclosion rate found in our study was low, when compared with another species in literature for another species of genus. Sobreira & Molina (2002Sobreira, H. B. & Molina, F. B. 2002. Observações preliminares sobre a biologia reprodutiva de Megalobulimus gummatus (Mollusca, Megalobulimidae) em laboratório. Arquivos do Instituto Biológico 69:139-141.) found 52.4% eclosion rate for Megalobulimus gummatus (Hidalgo, 1870). Rios et al. (2004Rios, F. R.; Jacinavicius, F. C. & Molina, F. B. 2004. Taxa de eclosão em ovos de Megalobulimus aff. ovatus (Gastropoda, Pulmonata, Megalobulimidae) incubados em laboratório. Arquivos do Instituto Biológico 71:388-390.) found for Megalobulimus aff. ovatus (Muller, 1774) and eclosion rate of 57.9% for specimens introduced at t the Zoological Park of São Paulo, and for F1 generation it was found 34.5% eclosion rate of egg obtained by cross fertilization and 28.6% of the eggs obtained by self-fertilization.

Egg posture peaks in M. paranaguensis occur in the same period as the activity pattern recorded by Miranda & Fontenelle (2015Miranda, M. S. & Fontenelle, J. H. 2015. Population dynamics of Megalobulimus paranaguensis in the Brazilian southeast coast. Zoologia 32:463-468. Doi: 10.1590/S1984-46702015000600005.
https://doi.org/10.1590/S1984-4670201500...
) in natural conditions and same period, but in a reverse way: when there is a major activity peak, egg laying slows down. This pattern indicates a major reproductive activity period, when energy is allocated for reproduction, decreasing the activity of individuals. An interesting characteristic of the egg posture cycle of M. paranaguensis in the study area is that the major peaks occur right before the aestivation period, which occurs between November and March (Miranda et al., 2015Miranda, M. S.; Fontenelle, J. H. & Pecora, I. L. 2015. Population structure of a native and an alien species of snail in an urban fragment of Atlantic Rainforest. Journal of Natural History 49:19-35. Doi: 10.1080/00222933.2014.930756.
https://doi.org/10.1080/00222933.2014.93...
; Miranda & Fontenelle, 2015Miranda, M. S. & Fontenelle, J. H. 2015. Population dynamics of Megalobulimus paranaguensis in the Brazilian southeast coast. Zoologia 32:463-468. Doi: 10.1590/S1984-46702015000600005.
https://doi.org/10.1590/S1984-4670201500...
). In Megalobulimus bronni (Pfeiffer, 1847) from Juiz de Fora (state of Minas Gerais), three egg posture peaks were recorded, a major peak between December and February, followed by a second pre-aestivation peak between April and May, and a post-aestivation peak in September. This differs from the pattern of M. paranaguensis due to environmental differences between both areas. The major peaks in the end of the year can be explained by the major photoperiod in summer months, which increases egg production in pulmonates (Gomot-de-Vaufleury, 2001Gomot-de-Vaufleury, A. 2001. Regulation of growth and reproduction. In: Barker, G. M. ed. The biology of terrestrial molluscs. Wallingford, CABI Publishing, p. 331-355.). Moreover, the young individuals that are born in this period generally aestivate and die because they do not have sufficient energy reserves. In general, in newer cohorts there are high mortality rates (Heller, 2001Heller, J. 2001. Life History Strategies. In: Barker, G. M. ed. The biology of terrestrial molluscs . New York, CABI Publishing, p. 413-446.), which can be more than 94% in M. mogianensis Simone & Leme, 1998 (Romero, 2004Romero, S. M. B. 2004. Growth of Megalobulimus mogianensis (Gastropoda: Megalobulimidae) raised in laboratory from hatching to adulthood. American Malacological Bulletin 18:79-85.). The occurrence of this egg laying pattern can be an important factor in the mortality rate of wildlife populations.

In this paper, we concluded that M. paranaguensis has a well marked seasonal pattern of activity and oviposition. This pattern also directly influendes the surviovorship and activity and juveniles, and can generate a high mortality in younger conhorts.

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Publication Dates

  • Publication in this collection
    2017

History

  • Received
    17 May 2016
  • Accepted
    14 Oct 2016
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