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Pollen diversity on male Hylonycteris underwoodi (Glossophaginae) Julia Hoeh Department of Zoology, University of Wisconsin ABSTRACT Nectivorous bats play important roles in pollination syst ems in the tropics, by transferring pollen carried on their bodies between the plants that they visit for nectar. The purpos e of this study was to evaluate diversity indices of pollen loads found on individuals of Hylonycteris underwoodi (Glossophaginae). It was conducted in the Selvatura Adventure Park in Montev erde, Costa Rica during the rainy season, and related pollen load diversity to aspect ratio, wing tip index, and mass of individuals (N = 30 males). The pollen load on individuals had low richness (2.20 0.81), diversity (0.09 0.16), and evenness (0.09 0.15) due to the large abundance of Markea sp. pollen grains. Markea sp. was present on every individual, suggesting a specialization by H. underwoodi Neither the variation of the overall pollen load nor the variation in the abundance of Markea sp. pollen grains could be explained by aspect ratio, wing tip index, or mass of the individuals. RESUMEN Los murcielagos nectarivoros juegan un papel importante en los sistemas de polinizacin en los trpicos, transfiriendo polen continuamente en sus cuerpos entre las plantas que visitan. El propsito de este estudio fue el de evaluar la diversidad de carga de polen encontrada en los individuos de Hylonycteris underwoodi (Glossophaginae). Fue realizado en Se lvatura, Monteverde, Costa Rica, dur ante la estacin lluviosa. Se relaciono la diversidad con la carga de polen, la proporcin del aspecto, el ndice de punta del ala, y a la masa de individuos (N = 30 machos). La carga del polen en individuos tuvo una riqueza (2,2 0 0,81), diversidad (0,09 0,16) y uniformidad (0,09 0,15) baja debido a la gran abundancia de Markea. Markea fue encontrada en todos los individuo s, sugiriendo una especializacin de H. underwoodi Ni la variacin de la carga general de polen ni la variacin en la ab undancia de sp de Markea podr an ser explicados por la proporcin de aspecto, ni por el ndice de punta del ala, ni por la masa de los individuos INTRODUCTION Hylonycteris underwoodi (Glossophaginae), a common Ne otropical bat (Arita 1993) found in Monteverde, Costa Rica, visits many flower species each night. They feed on nectar (LaVal and Rodriguez-H 2002) and in the process disperse pollen. In many populations, nectar is the ma in source of energy for H. underwoodi year round in Costa Rica (Tschapka 2003). Species diversity of bats increases toward the equator, as well as, in lower elevations due to the increased variety of food resources (LaVal and Rodriguez-H 2002). This is possibly in part because flowers specialized for bat pollination are restricted primarily to the tropics (LaVal and Rodri guez-H 2002). Though this pollination system is important to the diversity of the tropics, the bats within this nectar-feeding guild are understudied. Tschapka (2003) preformed a study analyzing niche partitioning of nectar resources between four Glossophaginae species. He examined how bat species differ in 1
the number and kinds of flowers they visit, and how that correlates to the variation in size and wing morphology between these four species. However, little is known about the variation within each of these spec ies. As a generalist nectivore, H. underwoodi has been found to carry an assortment of pollen t ypes in varying abundance. However, specialization may occur for cer tain seasons, times of the night, or foraging bouts. My study examines individual H. underwoodi and how they differ in the number and kinds of plant species they visit. Variation in body mass was shown as one of the factors that influence nectar partitioning between species of Glossophagin ae (Tschapka 2002). Mass variation within H. underwoodi is expected to correspond to flower choice based on nectar quality or quantity. Larger individuals may have hi gher absolute energy requirements and may seek more nectar productive plants. Larger ba ts, in this study assumed to be older, may have learned the location and species of the mo st nectar productive plants and specialized on those nectar rich flowers. Smaller or younger individuals may either have lower absolute energy needs, or may not have th e experience to specialize on more productive flowers. Bat size should therefore corres pond to the diversity or abundance of pollen based on nectar productivity of the flower. Diversity and abundance of pollen is also influenced by the foraging strategy of the bat. As outlined by Findley et al (1972) aspect ratio and wi ng tip index are related to foraging choices between bat species. Asp ect ratio and wing tip index are defined as: Aspect Ratio Index = Length of forearm (mm) + Length of 3rd finger (mm) Length of 5th finger (mm) Wing Tip Index = Length of 3rd finger (mm) / Length of forearm (mm) A low aspect ratio has been found in forest dwelling bats, while high aspect ratio is found in migrants and open air feeders. Wi ng tip corresponds to hovering ability of interspecific bats. Both indices correlate with foraging strategies and differences in bat energetic requirements. Intr aspecific wing variation of H. underwoodi has not been evaluated to determine if the differences are great enough to correlate with foraging behaviors. If the intraspecifc differences do influence foraging strategies then amount and variety of pollen found on the individuals should correspond to varying aspect ratio and wing tip indices. I analyzed richness, diversity, and ev enness of pollen samples from individual H. underwoodi males to investigate proposed ideas of intraspecific niche partitioning and nectar specialization. I was interested in se eing if the range of th ese indices could be explained by the morphological characteristics of mass, aspect ratio and wing tip index. MATERIALS AND METHODS The study was conducted at Selvatura Adventur e Park in Monteverde, Costa Rica, from October 21 to November 16, 2007. Bats were captured using a mist net positioned near the nectar feeders in the hummi ngbird garden of Selvatura. Mist nets were tended from 1800 till 1900 hr when capture was not impeded by weather. Thirty male individuals of H. underwoodi were collected, and they were individually placed in cloth bags. The mass of the individual was determ ined with a Pesola 50g scale. Scotch tape was used to remove pollen from the forehead, the snout, th e venter, the back, a nd the uropatangium. 2
Pollen samples were affixed to a microsc ope slide, labeled an d later counted and identified in the lab. Following the removal of the pollen, the length of the forearm, third, and fifth digit were measured with calip ers. Length measurements were used to calculate, for each individual, the Aspect Ratio Index and the Wi ng Tip Index as described in the previous section. Once the length and weight measur ements were taken and the pollen samples were collected the individual was released. In the lab, pollen from each indivi dual and body section was counted and identified using a compound microscope to genus or morphospecies based on descriptions by Roubik and Moreno (1991) and Jost (2004). The pollen richness, diversity and evenness per individual were estimated using the Sh annon-Weiner Index. Pollen indices were analyzed using regressions for each of the morphological measurements, as well as the aspect ratio index and wing tip index. The location of pollen on the body was compared using a Chi-squared Test of Independence. RESULTS A range of sizes was found for male H. underwoodi for all of the morphological measurements gathered (Table 1). The grea test variability in a single parameter was found in the third digit length. TABLE 1. Averages with standard deviations and ranges for morphological measurements and pollen data from Hylonycteris underwoodi (N = 30) in Selvatura Adventure Park, Monteverde Average (S.D.) Range Mass of Body (g) 8.00 ( 0.59) 6.5-9.5 Forearm Length (mm) 34.00 ( 2.05) 30-40 3rd Digit Length (mm) 70.47 ( 2.83) 68-80 5th Digit Length (mm) 45.93 ( 2.13) 42-50 Aspect Ratio 2.28 ( 0.13) 2.06-2.64 Wing Tip Index 2.08 ( 0.11) 1.89-2.29 Total Pollen Load (N) 421.80 ( 337.93) 4-1476 Pollen richness (S) 2.20 ( 0.81) 1.0-4.0 Pollen diversity (H') 0.09 ( 0.16) 0.00-0.82 Pollen evenness (E) 0.09 ( 0.15) 0.00-0.75 Intraspecific variation was found for polle n load, richness, di versity and evenness (Figure 1). Pollen was identified from eight di fferent plant species in varying abundance. The diversity values and evenness for indivi dual bats is low (Figure 1) due to the overwhelming abundance of one species ( Markea sp.) of pollen. Markea sp. was present on all individuals sampled, yet the range in abundance of pollen found on individuals extends from four grains to over 1,000. The frequency of bats with greater amounts of pollen grains was also more evenly distributed for Markea sp. than other common pollen samples, such as Vriesea sp. and Mucuna sp. (Figure 2a). 3
0 2 4 6 8 10 12 14 0.1-1.0 1.1-2.0 2.1-3.0 3.1-4.0Pollen species richness (S)Frequency of bats a. 0 2 4 6 8 10 12 14 16 18 < 0.010.01-0.100.11-0.200.21-0.300.31-0.40> 0.41Pollen species diversity (H')Frequency of batsb. 0 2 4 6 8 10 12 14 16 18 < 0.010.01-0.100.11-0.200.21-0.300.31-0.40> 0.41Pollen species evenness (E)Frequency of batsc. FIGURE 1. Frequency of Hylonycteris underwoodi individuals (N = 30) carrying loads of pollen of different species richness (a), di versity (b), and evenness (c) at Selvatura Adventure Park in Monteverde. 4
0 1 2 3 4 5 6 7 8 9 <101101-200201-300301-400401-500501-600601-700701-800>800 Number of Markea grains (N)Frequency of batsa. 0 2 4 6 8 10 12 14 16 18 20 < 1.01.0-1.92.0-2.93.0-3.94.0-4.95.0-5.9>5.9Number of Vriesea grains (N) Frequency of batsb. 0 2 4 6 8 10 12 14 16 18 20 < 1.0 1.0-1.9 2.0-2.9 > 2.9Numbers of Mucuna grains (N)Frequency of batsc. FIGURE 2. Frequency of Hylonycteris underwoodi individuals (N = 30) carrying different intervals of three types of pollen, Markea sp. (a), Vriesea sp. (b), and Mucuna sp. (c) at Selvatura Advent ure Park in Monteverde. Pollen grains were found mostly in the uroptangium for Markea sp. (Figure 3) and other pollen types (Figure 4). No clear tr ends were found between the amount of pollen per bat and the mass of the bat (p = 0.80, n = 30, F = 0.07), the aspect ratio (p = 0.10, n = 30, F = 2.96), or wing tip index (p = 1.18, n = 30, F = 1.94), though the trend is best fit 5
for aspect ratio (Figure 5). Also, no trend was found for mass (p = 0.88, n = 30, F = 0.024), aspect ratio (p = 0.11, n = 30, F = 2.75), or wing tip index (p = 0.17, n = 30, F = 1.99) when compared with Markea sp. pollen loads (Figure 6). 0 1000 2000 3000 4000 5000 6000 7000 8000 Head BackUropatangiumVenterBody regionNumber of Markea grains FIGURE 3. Placement of pollen grains of Markea sp. on Hylonycteris underwoodi males collected at Selvatura Adventure Park in Monteverde. 0 5 10 15 20 25 30 35 HeadBackUropatangiumVenterBody regionNumber of pollen grains Mucuna Vriesea Burmeistera Morphospecies A Morphspecies B Morphospecies C Morphospecies D FIGURE 4. Placement of pollen grains of Mucuna sp., Vriesea sp., Burmeistera, and Morphospecies A-D on Hylonycteris underwoodi males collected at Selvatura Adventure Park, Monteverde. 6
0 200 400 600 800 1000 1200 1400 1600 6789Mass of Bat (g)Number of Pollen Grains1 0 0 200 400 600 800 1000 1200 1400 1600 2.002.202.402.602.80Aspect RatioNumber of Pollen Grains 0 200 400 600 800 1000 1200 1400 1600 1.851.952.052.152.252.35Wing Tip IndexNumber of Pollen Grains FIGURE 5. Regression analyses of the number of pollen grains with respect to mass (R2 0.0023, y = 27.8x + 199.4), aspect ratio (R2 0.0958, y = -825.86x + 2303.4), and wing tip index (R2 0.0647, y = 747.39x 1131) of Hylonycteris underwoodi collected at Selvatura Adventure Park, Monteverde. 7
0 200 400 600 800 1000 1200 1400 1600 66.577.588.599.51Mass of Bat (g)Markea Pollen Grainsa.0 0 200 400 600 800 1000 1200 1400 1600 2.002.102.202.302.402.502.602.70Aspect RatioMarkea Pollen Grainsb. 0 200 400 600 800 1000 1200 1400 1600 1.851.952.052.152.252.35Wing Tip IndexMarkea Pollen Grainsc. FIGURE 6. Regression analyses of the number of Markea sp. pollen grains with respect to mass (a.R2 = 0.0009, y = 16.8x + 278.8), aspe ct ratio (b.R2 = 0.0895, y = -798.09x + 2231.5), and wing tip index (c.R2 = 0.0663, y = 756.44x 1158.4) from Hylonycteris underwoodi males collected at Selvatura Adventure Park, Monteverde. 8
DISCUSSION Pollen load variation was present between Hylonycteris underwoodi individuals. The amount of pollen grains ranged from four to over 1000 found on a single individual. This variation in pollen load was not found to corr elate with body mass, aspect ratio, or wing tip (Figure 5), though it showed the closest tre nd with aspect ratio. This shows that the wing morphology and body mass are not the main cause for variation in pollen load. Other intraspecific variations such as differing olfactor y ability, vari able feeding morphology adaptations (e.g. t ongue length), or timing of foraging bouts may play a greater role in the amount of pollen on an i ndividual. Variations could also be caused by differences in roost location relative to bat pollinated plants, length of foraging time before capture, or daily varia tion in abiotic conditions. Biot ic factors could also affect pollen load on individuals. Th e amount of time the individua l spent at the flower could be related to the amount of polle n carried away by the bat. The frequency of visits to a particular plant species is a lik ely cause for load variation. La stly, the timing of the visit, a bat could arrive at a flower after it ha s been visited by another individual which removed most of the pollen. These other cau ses need to be examined further to understand why such variation of pollen load occurs between individuals of H. underwoodi The diversity and evenness of pollen grains were also variable among individuals. Eight different pollen grains were identified, showing that the individuals had at least eight potential nectar sources. While both H and E had low averages (Avg. = 0.09 Table 1), their ranges still show variation. Again this variation was not found to correlate with mass, aspect ratio, or wing tip within H. underwoodi individuals. The composition of pollen grains present in this study differs from that found on H. underwoodi in a study performed at the same location in the spring of 2004 (Millard), suggesting there may be seasonal causes for the variation in pollen diversity. Perhaps plan ts that are highly productive in the spring are less productive in th e fall. Since the bats were captured early in the evening the composition of pollen may reflect variation in flower timing. The diversity and evenness values were greatly affected by the abundance of one pollen species (Markea sp.). When Markea sp. was highly abundant H and E were very low, and conversely when Markea sp. was present in low abundanc e, H and E were higher. The influence of Markea sp. pollen on diversity and evenness indices leads to further consideration of why th ere is such variability in Markea sp. pollen abundance. Markea sp. pollen was present on every individu al (N = 30) in the study with a wide range of pollen grains found (range = 4 to 1467 grains) per individual. When separated from other pollen data, Markea sp. did not show a correlation to body mass, aspect ratio, or wing tip. Markea sp. pollen abundance may be better explained by temporal or seasonal variation in flower production. A study by Millard (2004), in the dry season found H. underwoodi to carry the greatest abundance of Mucuna sp. with a lower comparable abundance of Markea sp. This suggests that Markea sp. may provide an important nectar resource during the wet season, but be out produced by other bat pollinated flowers during the dry season. Some Markea species have been shown to open close to dusk (1800 hr) and be most productive early in the evening (Voss et al. 1980). Bats may specialize on certain pl ant species at different times of the night based on when 9
10 the flower is most produc tive. The abundance of Markea sp. pollen may therefore be due to the early evening capture times in the study. Body mass and wing morphology variations were not found to correspond with total pollen abundance, Markea sp. pollen abundance, pol len diversity, nor pollen evenness. Perhaps the energetic differences for small and large individuals may not be great enough to cause intras pecific foraging responses. A second possible explanation could be seasonality, Markea sp. may be the most available nectar resource in the wet season of Costa Rica, and regardless of size H. underwoodi must get energy from nectar of Markea sp. Specialization between H. underwoodi and Markea sp. was observed in this study preformed in the wet season. Markea sp. may provide the main energy resource for this bat during the wet season, and without it the pollination system that involves many plants during the dry season may collapse. Future studies looking at the impact of forest fragmentation on the growth of Markea sp. and how this affects the apparent food choose of H. underwoodi may be especially beneficial in an area, like the tropics, where forested areas are continuously disappearing. ACKNOWLEDGEMENTS Thank you Karen Masters for helping me turn my crumbled down project into something Im pleased to submit. Thanks to Richard LaVal for his guidance and stories throughout this project, as well as during the field trip. Thank you to Arturo, Kim, Pablo, Taegan, Jaime and Jordan for all of the help collecting bats and providing entertainment during the hours of mist netting and analysis. Thanks to Amy for the revisions and suggestions, we can certainly be in a chiropterophyllic relationship, as long as you specialize. Thank you to the staff at Selvatura Advent ure Park and the Monteverde Research Station. Thanks to my fellow CIEE participants, especially my roommates, for making Costa Rica feel like home. Finally, thank you to Rafa for the transportation and conversations. LITERATURE CITED Arita, H.T. 1993. Rarity in Neotropical bats: correlations with phylogeny, diet, and body mass. Ecological Applications. 3(3): 506-517. Findley, J.S., E. H. Studier, and D.E. Wilson. 1972. Morphologic properties of bat wings. Journal of Mammalogy. 53(3): 429-444. Jost, M. 2004. The Pollen library. C.I.E.E. Spring 2004 Tropical Ecology and Conservation. LaVal, R. K. and B. Rodriguez-H. 2002. Mu rcielagos de Costa Ri ca: Bats. Instituto National de Biodiversidad, Santo Domingo de Heredia, Cost Rica. Millard, E. 2004. Foraging strategies a nd body partitioning of glossophagine bats. C.I.E.E. Spring 2004 Tropical Ecology and Conservation: 1-11. Roubik, D.W. and J.E. Moreno. 1991. Pollen and Spores of Barro Colorado Island. Monographs in Systematic Botany, v.36. Missouri Botanical Garden. Tschapka, M. 2003. Energy density patterns of nectar resources permit coexistence within a guild of Neotropical flower-vis iting bats. Journal of Zoology. 263: 7-21. Voss, R., M. Turner, R. Inouye, M. Fish er, and R. Cort. 1980. Floral biology of Markea neurantha Hemsley (Solanaceae), a bat-pollinated epiphyte. American Midland Naturalist 103 (2): 262-268.
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Diversidad de polen en los machos Hylonycteris underwoodi (Glossophaginae)
Pollen diversity on male Hylonycteris underwoodi (Glossophaginae)
Nectivorous bats play important roles in pollination systems in the tropics, by transferring pollen carried on their bodies between the plants that they visit for nectar. The purpose of this study was to evaluate diversity indices of pollen loads found on individuals of Hylonycteris underwoodi (Glossophaginae). It was conducted in the Selvatura Adventure Park in Monteverde, Costa Rica during the rainy season, and related pollen load diversity to aspect ratio, wing tip index, and mass of individuals (N = 30 males). The pollen load on individuals had low richness (2.20 0.81), diversity (0.09 0.16), and evenness (0.09 0.15) due to the large abundance of Markea sp. pollen grains. Markea sp. was present on every individual, suggesting a specialization by H. underwoodi. Neither the variation of the overall pollen load nor the variation in the abundance of Markea sp. pollen grains could be explained by aspect ratio, wing tip index, or mass of the individuals.
Los murcilagos nectarvoros juegan un papel importante en los sistemas de polinizacin en las zonas tropicales, transfiriendo el polen llevado en sus cuerpos entre las plantas de nctar que visitan. El propsito de este estudio fue evaluar los ndices de diversidad de cargas de polen que se encuentran en los individuos de Hylonycteris underwoodi (Glossophaginae). Este estudio se llev a cabo en Selvatura, Monteverde, Costa Rica durante la estacin lluviosa.
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Tropical Ecology 2007
Ecologa Tropical 2007
Cargas de pollen
t Monteverde Institute : Tropical Ecology