Clinal variation in body size and sexual dimorphism in an Indian fruit bat, \u3ci\u3eCynopterus sphinx \u3c/i\u3e (Chiroptera: Pteropodidae)

Geographic variation in body size and sexual dimorphism of the short-nosed fruit bat (Cynopterus sphinx ) was investigated in peninsular India. Bats were sampled at 12 localities along a 1,200 km latitudinal transect that paralleled the eastern flanks of the Western Ghats. The geographic pattern of variation in external morphology of C. sphinx conforms to the predictions of Bergmann’s Rule, as indicated by a steep, monotonic cline of increasing body size from south to north. This study represents one of the first conclusively documented examples of Bergmann’s Rule in a tropical mammal and confirms that latitudinal clines in body size are not exclusively restricted to temperate zone homeotherms. Body size was indexed by a multivariate axis derived from principal components analysis of linear measurements that summarize body and wing dimensions. Additionally, length of forearm was used as a univariate index of structural size to examine geographic variation in a more inclusive sample of bats across the latitudinal transect. Multivariate and univariate size metrics were strongly and positively correlated with body mass, and exhibited highly concordant patterns of clinal variation. Stepwise multiple regression on climatological variables revealed that increasing size of male and female C. sphinx was associated with decreasing minimum temperature, increasing relative humidity, and increasing seasonality. Although patterns of geographic size variation were highly concordant between the sexes, C. sphinx also exhibited a latitudinal cline in the magnitude and direction of sexual size dimorphism. The size differential reversed direction across the latitudinal gradient, as males averaged larger in the north, and females averaged larger in the south. The degree of female-biased size dimorphism across the transect was negatively correlated with body size of both sexes. Canonical discriminant analysis revealed that male- and female-biased size dimorphism were based on contrasting sets of external characters. Available data on geographic variation in the degree of polygyny in C. sphinx suggests that sexual selection on male size may play a role in determining the geographic pattern of sexual size dimorphism

Mist net Capture and Field Observations on the Short nosed Fruit Bat (Chiroptera: Pteropodidae) Cynopterus Sphinx (Vahl.)

Volume: 98Start Page: 373End Page: 37

Males and Females Gain Differentially from Sociality in a Promiscuous Fruit Bat <i>Cynopterus sphinx</i>

<div><p>Sociality emerges when the benefits of group living outweigh its costs. While both males and females are capable of strong social ties, the evolutionary drivers for sociality and the benefits accrued maybe different for each sex. In this study, we investigate the differential reproductive success benefits of group membership that males and females might obtain in the promiscuous fruit bat <i>Cynopterus sphinx</i>. Individuals of this species live in flexible social groups called colonies. These colonies are labile and there is high turnover of individuals. However, colony males sire more offspring within the colony suggesting that being part of a colony may result in reproductive benefits for males. This also raises the possibility that long-term loyalty towards the colony may confer additional advantage in terms of higher reproductive success. We used ten seasons of genetic parentage data to estimate reproductive success and relatedness of individuals in the colony. We used recapture data to identify long and short-term residents in the colony as well as to obtain rates of recapture for males and females. Our results reveal that males have a significantly higher chance of becoming long-term residents (than females), and these long-term resident males gain twice the reproductive success compared to short-term resident males. We also observed that long-term resident females are related to each other and also achieve higher reproductive success than short-term resident females. In contrast, long-term resident males do not differ from short-term resident males in their levels of relatedness. Our results re-iterate the benefits of sociality even in species that are promiscuous and socially labile and possible benefits of maintaining a colony.</p></div

Modified boxplots depicting the simulated and observed relatedness of recaptured a) adults, b) females, c) males and d) males-females.

<p>The box depicts the 25^th and 75^th quartiles, the solid line is the median and the whiskers are the 2.5% and 97.5% percentiles.</p

Correlation between recapture rate and over all reproductive success for a) females and b) males.

<p>Correlation between recapture rate and over all reproductive success for a) females and b) males.</p

Total number of adult long-term and short-term residents at the colony.

<p>Total number of adult long-term and short-term residents at the colony.</p

Bootstrap test to investigate the relatedness of recaptured individuals to the colony.

<p>Bootstrap test to investigate the relatedness of recaptured individuals to the colony.</p

Distribution of reproductive success of long-term and short-term resident a) females and b) males.

<p>Distribution of reproductive success of long-term and short-term resident a) females and b) males.</p