Clinal variation in body size and sexual dimorphism in an Indian fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae)

Abstract

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 1200 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.

Mating system of a Neotropical roost-making bat: the white-throated, round-eared bat, Lophostoma silvicolum (Chiroptera: Phyllostomidae)

“…Few other bats, one of them the paleotropical Cynopterus sphinx (Balasingh et al 1995;Storz and Kunz 1999), seem to invest a comparable effort into roost-making. Males of this species are also larger than females in the part of their range where the species is more polygynous (Storz et al 2001a). …”

“…Actual roostmaking has not been observed in this species, but it is most likely done by males. It is unknown if roost-making in this species is less costly or other selective forces have caused larger size of females, as in populations of C. sphinx (Storz et al 2001a). But we suggest that sexual dimorphism is a strong indicator for high male investment in L. silvicolum, regardless of whether it is a sexually selected trait or an indicator of a male's higher ability to invest in roost-making and/or harem maintenance.…”

Testing for Genetic Evidence of Population Expansion and Contraction: An Empirical Analysis of Microsatellite Dna Variation Using a Hierarchical Bayesian Model

“…Cynopterus sphinx is generally restricted to low elevations and does not live in primary wet-evergreen forest (Bates and Harrison 1997;Storz and Kunz 1999;Storz et al 2001a). In this same region, available evidence suggests that C. brachyotis is almost exclusively restricted to tropical wet-evergreen and semievergreen forests of the Western Ghats, a mountain range that parallels the western coast of peninsular India (Bates and Harrison 1997;Pradhan and Kulkarni 1997;Balasingh et al 1999).…”

Study on the population structure of the paradoxical frog, Pseudis bolbodactyla (Amphibia: Anura: Hylidae), using natural markings for individual identification

“…Several factors can be responsible for geographic variations in morphology (KUPFER 2007), including predation (SCHNEIDER et al 2000), climatic changes, or other environmental parameters (CASTELLANO et al 2000) such as sexual selection, sexual dimorphism (STORZ et al 2001), genetic drift, founder effect (DEMETRIUS 2000), and distance from the Equator (BLACKBURN et al 1999). However, the causes and maintenance of these variations are complex and are not always understood (AVISE 2000).…”