The spatial and temporal distribution of females influence the evolution of testes size in Australian rodents

Male-male competition after mating (sperm competition) favours adapations in male traits, such as elevated sperm numbers facilitated by larger testes. Ultimately, patterns of female distribution will affect the strength of s perm competition by dictating the extent to which males are able to prevent female remitting. Despite this, our understanding of how the spatial and temporal distributions of mating opportunities have shaped the evolutionary course of sperm competition is limited. Here, we use phylogenetic comparative methods to explore interspecific variation in testes size in relation to patterns of female distribution in Australian rodents. We find that as mating season length (temporal distribution of females) increases, testes size decreases, which is consistent with the idea that it is difficult for males to prevent females from remating when overlap among oestrous females is temporally concentrated. Additionally, we find that social species spatially clustered) have smaller testes than non-social species (spatially dispersed). This result suggests that males may be effective in monopolizing reproduction within social groups, which leads to reduced levels of sperm competition relative to non-social species where free-ranging females cannot be controlled. Overall, our results show that patterns of female distriution, in both space and time, can influence the strength of post-mating sexual selection among species.

Automated summary

This study explores the relationship between testes size and patterns of female distribution in Australian rodents, finding that longer mating seasons are associated with smaller testes size and social species have smaller testes. These findings suggest that patterns of female distribution can influence post-mating sexual selection among species.