Abstract. Variance in reproductive success is a primary determinant of genetically effective population size (N e ), and thus has important implications for the role of genetic drift in the evolutionary dynamics of animal taxa characterized by polygynous mating systems. Here we report the results of a study designed to test the hypothesis that polygynous mating results in significantly reduced N e in an age-structured population. This hypothesis was tested in a natural population of a harem-forming fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The influence of the mating system on the ratio of variance N e to adult census number (N) was assessed using a mathematical model designed for age-structured populations that incorporated demographic and genetic data. Male mating success was assessed by means of direct and indirect paternity analysis using 10-locus microsatellite genotypes of adults and progeny from two consecutive breeding periods (n ϭ 431 individually marked bats). Combined results from both analyses were used to infer the effective number of male parents in each breeding period. The relative proportion of successfully reproducing males and the size distribution of paternal sibships comprising each offspring cohort revealed an extremely high within-season variance in male mating success (up to 9.2 times higher than Poisson expectation). The resultant estimate of N e /N for the C. sphinx study population was 0.42. As a result of polygynous mating, the predicted rate of drift (1/2N e per generation) was 17.6% higher than expected from a Poisson distribution of male mating success. However, the estimated N e /N was well within the 0.25-0.75 range expected for age-structured populations under normal demographic conditions. The life-history schedule of C. sphinx is characterized by a disproportionately short sexual maturation period scaled to adult life span. Consequently, the influence of polygynous mating on N e /N is mitigated by the extensive overlap of generations. In C. sphinx, turnover of breeding males between seasons ensures a broader sampling of the adult male gamete pool than expected from the variance in mating success within a single breeding period.
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.
Abstract. Population subdivision into behaviorally cohesive kin groups influences rates of inbreeding and genetic drift and has important implications for the evolution of social behavior. Here we report the results of a study designed to test the hypothesis that harem social structure promotes inbreeding and genetic subdivision in a population with overlapping generations. Genetic consequences of harem social structure were investigated in a natural population of a highly polygynous fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The partitioning of genetic variance within and among breeding groups was assessed using 10-locus microsatellite genotypes for 431 individually marked bats. Genetic analysis of the C. sphinx study population was integrated with field data on demography and social structure to determine the specific ways in which mating, dispersal, and new social group formation influenced population genetic structure. Microsatellite data revealed striking contrasts in genetic structure between consecutive offspring cohorts and between generations. Relative to the 1998 (dry-season) offspring cohort, the 1997 (wet-season) cohort was characterized by a more extensive degree of within-group heterozygote excess (F IS ϭϪ0.164 vs.Ϫ0.050), a greater degree of among-group subdivision (F ST ϭ 0.123 vs. 0.008), and higher average within-group relatedness (r ϭ 0.251 vs. 0.017). Differences in genetic structure between the two offspring cohorts were attributable to seasonal differences in the number and proportional representation of male parents. Relative to adult age-classes, offspring cohorts were characterized by more extensive departures from allelic and genotypic equilibria and a greater degree of genetic subdivision. Generational differences in F-statistics indicated that genetic structuring of offspring cohorts was randomized by natal dispersal prior to recruitment into the breeding population. Low relatedness among harem females (r ϭ 0.002-0.005) was primarily attributable to high rates of natal dispersal and low rates of juvenile survivorship. Kin selection is therefore an unlikely explanation for the formation and maintenance of behaviorally cohesive breeding groups in this highly social mammal.
Cynopterus sphinx is an ubiquitous frugivorous bat widely distributed in India and South-east Asia. The species roosts individually or in groups of two to several individuals in the overhanging, cryptic and protective spaces on trees and under man-made structures such as roofs and ceilings.The species forages upon fruits, flowers and leaves of a number of wild and a few orchard species of trees in varying proportions. The seasonal variation in its diet is related to both food preference and availability which are determined by annual cycles of flowering and fruiting in the study area.C. sphinx generally plucks the fruits and carries them away from the original tree to feeding perches where it chews the soft parts, swallows the juice and drops seeds and chewed fibres, thus dispersing seeds. Damage caused to orchard fruits by this species is incidental and often marginal, particularly where there are large numbers of wild food species available. In addition C. sphinx plays some role in the pollination of certain plant species.Resume. -Cynopterus sphinx est une chauve-souris frugivore ubiquiste largement repandue en Inde et dans le sud-est asiatique. Ces chauves-souris vivent suspendues, solitaires ou en groupes de deux ou plus, soit dans des arbres ou elles peuvent se cacher et etre protegees, soit sous des toits ou des plafonds.L'espece recherche les fruits, fleurs et feuilles d'arbres sauvages et de certains arbres fruitiers, en proportion variable. Son regime alimentaire varie au cours des saisons en fonction de ses preferences et de la disponibilite des aliments qui est elle-meme determinee par les cycles annuels de floraison et de fructification dans la region.Ceitc chauve-souris arrache generalement les fruits qu'elle transports ensuite a l'ecart de son arbre pour en manger les parties molles ; eile avale le jus et laisse tomber les graines qui se dispersem ainsi, et les fibres mächees. Les dommages causes aux arbres fruitiers par cette espece sont peu importants, surtout quand il y a beaucoup d'especes sauvages ä proximite. C. sphinx joue aussi un certain role dans la pollinisation de certaines plantes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.