Within population variation in testis size in the mole-shrew (Anourosorex squamipes) (Mammalia: Soricidae)

Abstract

Sperm competition is recognized as a key event occurring during postcopulatory sexual selection. The evolutionarily stable strategy (ESS) predicts that males in poor condition should invest more heavily in sperm compared with males in good condition. We explored the effects of body condition and season on testes mass in the mole-shrew (Anourosorex squamipes). We used the “scaled mass index” as body condition to analyze the effects of season, body condition and body length on testis size. The results showed that testes mass was greatest in summer. Head body-length also significantly affected testis size in the four seasons. In addition, males in good conditions had relatively heavier testes than those in poor conditions in spring, summer and autumn, but not in winter, suggesting that the finding contradicts the prediction of the evolutionarily stable strategy.