Reproductive biology and pollination of Aechmea distichantha Lem . ( Bromeliaceae )

(Reproductive biology and pollination of Aechmea distichantha Lem. (Bromeliaceae)). Reproductive biology, including phenology, fl ower biology, pollination, and the reproductive system in the bromeliad Aechmea distichantha were studied in an Araucaria forest in the state of Paraná. Phenology and reproduction in terricolous plants were followed in October 2006 and May October of 2007. Flowering peaked from June to September and fruiting was from June to October. Flower anthesis lasted one day. Flowers were pollinated the most by the hummingbird Stephanoxis lalandi and the most common butterfl y visitor was Lychnuchoides ozias ozias. Nectar concentration declined during anthesis, while nectar volume was constant. Aechmea distichantha is self-compatible with 30-45% fruit formation in self-pollination tests. Sunlight infl uences reproduction: when controlling for bromeliad and infl orescence size, plants in sunlight produced more seeds per fruit than plants in the shade. Reproduction was also associated with infl orescence size when controlling for bromeliad size. Th at is, larger infl orescences in similar sized plants produced more fl owers and more seeds per fruit.

Reproduction may also be infl uenced by the environment in which the plant is found and in which resource availability may vary (Lechowicz & Bell 1991).Environmental variation may also infl uence fi tness by aff ecting the number and abundance of pollinating species (Herrera 1995).In the Bromeliaceae, environmental variation can infl uence reproductive success within and among populations (Paggi et al. 2007).For example, light regime can infl uence individual size and consequently their reproductive success (Lenzi et al. 2006).Small scale variation, such as fl ower numbers and density, can infl uence visitation by pollinators and hence infl uence reproductive success (Grindeland et al. 2005;Makino et al. 2007).
Here we examine reproductive biology of the bromeliad Aechmea distichantha Lem.Th is bromeliad is common in the Atlantic Rain Forest and is considered a generalist or pioneer epiphyte (Borgo & Silva 2003).Specifi cally, we examine phenology, fl oral biology and the reproductive system to examine how variation in the local environment may infl uence reproductive success, in southern Brazil.

Materials and methods
Aechmea distichantha was studied at the Gruta de Bacaetava Municipal Park (GBMP) (25º13'54"S, 49º12'26"W).Created in May 2000, the park comprises an area of 17.4 ha, in Colombo, in the southern Brazilian state of Paraná.Th e climate is subtropical, with an annual average temperature of 16º C and 1450 mm average rainfall, in an Araucaria forest (Prefeitura Municipal de Colombo 1999).
We studied terricolous plants of Aechmea distichantha.Plants were visited weekly during two phases.Th e fi rst, in October 2006 was to observe fl ower visitors.Th e second, May -October 2007, included observations of fl ower visitors and the experimental study.Twenty plants that were available on the ground were studied weekly through the fl owering period to record fl owering phenology, morphology and biology.Th e number of fl owers in each infl orescence was counted and the duration of time over which the fl ower was open was registered.Th e plants occurred in two diff erent light environmental settings: open areas (considered here as a sunny environment) or in forest understory (considered here as a shade environment).
To compare productivity in diff erent light environmental settings and with diff erent pollinators, we must fi rst con-trol for local variation among plants.First, plant size may confound comparisons of seed set if larger plants produce more.Similarly, larger plants may have larger fl owers and so on.Th us, we estimated plant size by measuring each plant.Th e radius (r) of the plant was estimated by measuring the length of the external-most leaf of the rosette from the base to the tip.Plant height (h) was the length of the most internal leaf near the fl oral scape.Plant size was estimated using those two measurements as radius and height in the formula for the volume of a cylinder (4/3 πr 3 h).Similarly, radius and height of the infl orescence were measured and used to calculate volume as an estimate of infl orescence size.
We tested whether light regime infl uenced reproductive success, as other studies have shown that pollination success is greater under lighter conditions.Since larger plants produce larger infl orescences and larger infl orescences produce more fl owers, we must fi rst control for plant size.Using regression analysis, we estimated the relationship between bromeliad size and infl orescence size (Zar 1999).
From that regression, we used the residuals to examine how infl orescence size infl uences productivity, as if we were comparing infl orescence size among similarly-sized bromeliads.Similarly, we also examined whether fruit production was due to the number of fl owers, controlling for infl orescence size.Th at is, if all infl orescence were the same size, do those with more fl owers produce more fruits?While this may seem obvious, it may not be the case if fruit abortion is common.Th e number of fl owers and fruits were counted in 20 individual plants.Seeds were counted from fi ve fruits per plant.We tested whether light regime (plant in full sun exposure or plant in forest understory) infl uenced reproductive success as the number of fruits and seeds produced per plant, controlling for number of fl owers per infl orescence by a covariance analysis.
Plants were observed in the fi eld to attempt to discover which animals were pollinators.Flowers were observed with binoculars during bouts of approximately 4h in the morning.Some fl ower visitors were photographed.Visits and time duration were noted.Hummingbirds were identifi ed from fi eld guides while invertebrates were collected and identifi ed by specialists.We avoided observing visitors more than once at the same plant (Kaehler et al. 2005).
Nectar was collected, with capillary tubes from fl owers that were previously covered by small bags to prevent removal by animals, from 12 plants every hour on the hour from 07:00 -17:00h.Th erefore, nectar samples are the cumulative production during the time interval while they were sacked.We registered date, time, temperature, relative humidity, and nectar volume at each collection.Samples were then frozen for later analysis.Volume was measured with a Hamilton 50 μl microsyringe and sugar concentration was measured with an Atago portable refractometer.Nectar production was tested for partial correlations with temperature, humidity and time of day (Zar 1999).
When reproductive success was calculated aft er controlling for plant size, we fi rst found that larger infl orescences produced a larger number of fl owers (ln number of fl owers = 5.0 + 0.65 x residual infl orescence volume, r 2 = 0.28, F = 8.42, df = 1,18, p< 0.05).However, neither the size of the infl orescence nor the number of fl owers per infl orescence was infl uenced by light regime (aft er controlling for the size of the bromeliad, t < 1.0, df = 18, p> 0.10).However, the number of fruit produced per plant was much greater in the sun than in the shade, aft er controlling for number of fl owers per infl orescence (t = 3.66, df = 18, p< 0.05, Fig. 1A) and the number of seeds produced per fruit was greater in the sun than shade (t = 2.83, df = 18, p< 0.05, Fig. 1B).Th erefore, controlling for plant and infl orescence size, we found that more seeds are produced per fruit in the sun.
Hummingbirds and butterfl ies both may cause geitonogamy because they visit more than one fl ower infl orescence -1 .Butterfl ies forage slowly, spending up to 1 min fl ower -1 , while hummingbirds usually visit a fl ower for less than 10s.Flowers in the open areas were visited more oft en (both, butterfl ies and hummingbirds) than plants in the understory condition.Nectar content on average was 11.6 μl (95% CI = 10.6 -12.7) and remained constant throughout anthesis (r = 0.20 for correlation with hour of the day, df = 40, p> 0.05), indicating that production occurs only at the beginning of anthesis.Temperature and time were correlated (r = 0.60, df = 42, p< 0.001) while humidity was independent of both temperature and time (r = -0.12,and r = 0.05 respectively, df = 42, p> 0.05), therefore temperature and humidity were tested for a correlation with nectar production and concentration.Nectar volume was independent of both, temperature or humidity (r = -0.30and 0.16, respectively, df = 40, p> 0.05).Nectar concentration, however, was greatest during anthesis early in the morning aft er which it gradually decreased (r = -0.58,df = 40, P < 0.001).Concentration was correlated with temperature (r = 0.40, df = 40, P = 0.0105), but not with humidity (r = 0.17, df = 40, p> 0.05).

Discussion
Most plants in GBMP fl owered in winter when rainfall was low, in contrast to reported fl owering from January to April in Southeastern Brazil (Buzato et al. 2000).Plants with fl owers pollinated by birds tend to fl ower during the wet season, with some species fl owering throughout the year (Arizmendi & Ornelas 1990;Sazima et al. 1995;Araújo et al. 2004).Th e extended fl owering season of Aechmea distichantha favors visits by hummingbirds and butterfl ies.A consequence of this prolonged availability may keep pollinators in the area and thereby infl uence their availability to other species in the local plant community (Machado & Semir 2006).In this study, 68% of fl ower visits were due to hummingbirds, which emphasizes their importance as pollinators (Benzing 2000, Siqueira & Machado 2001;Lenzi et al. 2006).Th e use of bromeliads by both hummingbirds and butterfl ies is common and the butterfl ies seem to favor the genus Tillandsia (Varassin & Sazima 2000).
Aechmea distichantha is facultatively selfi ng, sensu (Lima & Vieira 2006), and may benefi t from "reproductive assurance, " since they may reproduce successfully even in the absence of pollinators (up to 30%, Zhang & Li 2007).Despite that self-compatibility is common in bromeliads (Martinelli 1997;Siqueira Filho & Machado 2001;Lenzi et al. 2006), the importance of selfi ng has not been previously examined in the genus Platyaechmea.Fruit formation in the apomixy treatments indicates that asexual reproduction can occur.Low levels of apomixy were found in the genus Pitcairnia, with few and small seeds being produced as a consequence (Wendt et al. 2001).Th us, apomixy in that species plays a small role in reproduction, as with A. distichantha.Greater reproductive success in natural conditions (80%) as compared to the experimental treatments was also found in Aechmea beeriana (98%, Nara & Webber 2002), Canistrum aurantiacum (89%, Siqueira Filho & Machado 2001) and in Vriesea longiscapa (86%, Martinelli 1997).Greater success in control fl owers may be due to lower rates of abortion than in manipulated fl owers.It is more likely that the greater reproductive success in control fl owers was due to the pollinator carrying pollen from a wide variety of source plants as observed by Kawai & Kudo (2008), with greater genetic variability that may result in greater reproductive success.Such long distance gene fl ow may be due to pollinating species that travel large distances (Barbará et al. 2009).
Light environment directly infl uenced reproductive success in Aechmea distichantha: infl orescences in the sun had 180% more fruit and 120% more seeds than those in the shade.Th is may be due to resource allocation in response to photosynthetic constrains as evidenced by Cervantes et al. (2005).Th e larger production of fruits and seeds may be also aff ected by pollinator behavior since bromeliads in sunny places were visited more oft en.Pollinator foraging may be infl uenced by the environmental light (Kilkenny & Galloway, 2008) and pollen limitation due to reduced pollinator visits may cause the variation in reproduction among bromeliad populations (Paggi et al. 2007).Since hummingbirds are very sensitive to environmental changes in resource supply (Cotton 2007) and avoid unrewarding patches (Sandlin 2000), they may have visited the bromeliads in sunny patches more oft en due to greater fl ower availability.
Th e volume of nectar produced in the morning remained constant throughout the day (when not removed by pollinators), similar to that found in Aechmea lindenii (Lenzi et al., 2006), which suggests that Aechmea distichantha only produces at the beginning of anthesis.On the other hand, concentration was greatest early, at the beginning of anthesis, and gradually declined.Th is suggests that the fl ower reabsorbs the solutes, as has been observed in other hummingbirds pollinated species (Freitas & Sazima 2001;Varassin et al. 2001) including Bromeliaceae (Canela & Sazima 2003).While concentration was independent of volume in A. distichantha, in A. pectinata both varied during anthesis (Canela & Sazima 2003).In both cases, nectar quality (from the pollinator perspective) is greatest in the morning, which appears to be a common trend in the Bromeliaceae (Machado & Semir 2006).
Th e greater rate of hummingbird visits in the morning is likely to be due to the greater quality of the nectar at that time (Canela & Sazima 2003;Machado & Semir 2006).On the other hand, butterfl y visits were always associated with good climatic conditions (higher temperatures, no rain, pers.obs.).
Aechmea distichantha, while self-compatible, has greater reproductive success in natural conditions, perhaps due to pollinator effi ciency and consequently greater outcrossing.Th e greater success in the sun also suggests that it is due to pollinator effi ciency, as trap-lining hummingbirds are more likely to fi nd the more visible fl owers.Additionally, greater success in the sun may be the result of the combined benefi t of greater resource allocation that also infl uences pollinator visitation.

Figure 1 .
Figure 1.Average (+95% confi dence interval for the mean) number of fruits (A) and seeds (B) produced in sunny (left ) and shady conditions (right) in Aechmea distichantha.