Genetic Patterns of Paternity and Testes Size in Mammals

Carl D Soulsbury

doi:10.1371/journal.pone.0009581

Abstract

BackgroundTestes size is used as a proxy of male intrasexual competition, with larger testes indicative of greater competition. It has been shown that in some taxa, social mating systems reflect variance in testes size, but results are not consistent, and instead it has been suggested that genetic patterns of mating may reflect testes size. However, there are different measures of genetic patterns of mating. Multiple paternity rates are the most widely used measure but are limited to species that produce multi-offspring litters, so, at least for group living species, other measures such as loss of paternity to males outside the social group (extra group paternity) or the proportion of offspring sired by the dominant male (alpha paternity) might be appropriate. This study examines the relationship between testes size and three genetic patterns of mating: multiple paternity, extragroup paternity and alpha paternity.Methodology/Principal FindingsUsing data from mammals, phylogenetically corrected general linear models demonstrate that both multiple paternity and alpha paternity, but not extra group paternity, relate to testes size. Testes size is greater in species with high multiple paternity rates, whereas the converse is found for alpha paternity. Additionally, length of mating season, ovulation mode and litter size significantly influenced testes size in one model.Conclusions/SignificanceThese results demonstrate that patterns of mating (multiple paternity and alpha paternity rates) determined by genetic analysis can provide reliable indicators of male postcopulatory intrasexual competition (testes size), and that other variables (length of mating season, ovulation mode, litter size) may also be important.

Highlights

Polyandry, i.e. multiple-mating by females, is known to be widespread across the animal kingdom [1,2]
Conclusions/Significance: These results demonstrate that patterns of mating determined by genetic analysis can provide reliable indicators of male postcopulatory intrasexual competition, and that other variables may be important
Relative Testes Size and Multiple Paternity Multiple paternity was frequent in mammals (x– = 36% litters), but lower than rates found in reptiles (x– =,50% clutches: [7]), possibly because more reptiles mate promiscuously (80%: [25])

Summary

Introduction

I.e. multiple-mating by females, is known to be widespread across the animal kingdom [1,2]. Genetic evidence indicating that offspring within litters or clutches can be sired by different males has been found in invertebrates, fish, amphibians, reptiles, birds and mammals [2,3,4,5,6,7]. A consequence of female multiple-mating is that ejaculates from different males may overlap in the female’s reproductive tract and compete to fertilize her ova (sperm competition; [8]). Increasing the number of sperm inseminated may increase the competitive advantage of one male over another. Ejaculates are costly to produce [9], and male investment in the number of sperm should reflect speciesspecific and locality-specific variance in the degree or likelihood of sperm competition [9,10]. This study examines the relationship between testes size and three genetic patterns of mating: multiple paternity, extragroup paternity and alpha paternity

Methods

Results

Conclusion