Pre- and postcopulatory competition affect testes mass and organization differently in two monophyletic mole-rat species, Georychus capensis and Fukomys damarensis.

This article examines how relative testes mass (RTM) and testicular tissue composition reflect differing levels of sperm competition and precopulatory male–male competition in two African mole-rat species with contrasting mating systems: the promiscuous Cape mole-rat (Georychus capensis) and the monogamous eusocial Damaraland mole-rat (Fukomys damarensis). The promiscuous species exhibited significantly larger RTM and a higher proportion of spermatogenic tissue, consistent with intense postcopulatory sperm competition, whereas the eusocial species had smaller testes but a greater proportion of interstitial tissue associated with higher testosterone levels, likely linked to precopulatory competition and social dominance. These findings support RTM as a useful indicator of sperm competition but highlight that testicular tissue organization and androgen production also influence reproductive strategies, suggesting that RTM alone may not fully capture the complexity of male reproductive investment. The study underscores the importance of considering both pre- and postcopulatory selection pressures when interpreting testes morphology in relation to mating systems.