Males and Females Gain Differentially from Sociality in a Promiscuous Fruit Bat Cynopterus sphinx

Abstract

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 Cynopterus sphinx. 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.

Social structure of the harem-forming promiscuous fruit bat,Cynopterus sphinx, is the harem truly important?

“…We genotyped all the individuals at eight microsatellite loci following Garg et al [ 22 , 26 ] and for each locus calculated summary statistics like the number of alleles, observed and expected heterozygosities and polymorphic information content in cervus v. 3.0.7 [ 28 , 29 ]. We used coancestry v. 1.0.1.7 software [ 30 ] to estimate relatedness between individuals.…”

“…Harems are labile and are maintained throughout the year despite the presence of well-defined mating periods [ 5 ]. Available scientific literature suggests that the harems do not play a role in the social organization or the genetic mating system of C. sphinx [ 21 , 22 , 26 ]. While short-term data suggest a resource defence polygyny [ 24 ], temporal data spanning more than six seasons strongly reveal a promiscuous mating system in C. sphinx [ 22 ].…”

“…However, long-term genetic data and limited monthly census revealed that harem size could not predict the reproductive success of males and the variance in male reproductive success in C. sphinx [ 22 ]. Males which were loyal to a colony had a higher reproductive success compared with males which were not a stable part of the colony [ 26 ], suggesting that the colony, rather than the harem, is the mating unit in C. sphinx . In the present study, we build on these previous efforts by using long-term behavioural observations (weekly census) to more comprehensively assess the social system of C. sphinx .…”

The modulating role of group stability on fitness effects of group size is different in females and males of a communally rearing rodent

“…the social and promiscuous fruit bat Cynopterus sphinx attain direct reproductive benefits, while females obtain both direct and possibly indirect kin benefits (Garg et al 2015). Among rodents, the number of males in the group contributes the most to variation in Alpine marmot (Marmota marmota) male direct fitness, whereas the number of females contributed the most to variation in female direct fitness, implying social benefits are driven by the number of same-sex subordinates present in the group (Lardy et al 2015).…”

“…Fitness effects of group living can be sex specific (e.g. Garg et al 2015;Lardy et al 2015). Reproductive success of males typically depends on mating opportunities, which generally increase in groups with a relatively large and stable number of adult females (e.g., Breuer et al 2010;L'Italien et al 2012).…”