Rainer Sharna R, Cameron Elissa Z, Edwards Amy M, Bennett Nigel C, Thomas Hannah G, Swanepoel Daniël
School of Biological Sciences, University of Tasmania, Hobart 7000, Australia.
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0028, South Africa.
J Mammal. 2023 Apr 21;104(5):993-1002. doi: 10.1093/jmammal/gyad021. eCollection 2023 Oct.
Sperm competition results from postcopulatory continuation of male-male competition for paternity. The level of sperm competition is predicted to be highest in species with greater polyandry and weakest in monogamous pairs. Sperm competition levels can be indexed using traits that reflect male investment in fertilization, particularly relative testes mass (RTM). However, the relationship between RTM and levels of sperm competition may also be influenced by precopulatory competition selecting for higher levels of testosterone, also produced by the testes. To test the relationship between RTM and both pre- and postcopulatory male-male competition we compared two bathyergid mole-rat species, the promiscuous and the monogamous eusocial . The promiscuous species had not only larger RTM, but also a greater proportion of spermatogenic tissue, maximizing germ cell production as well. Conversely, the eusocial species had smaller testes, but a higher proportion of interstitial tissue (which contains the androgenic Leydig cells) and higher levels of testosterone. Consequently, testicular traits as well as testes mass may be under selection, but these are not normally measured. More research is required on relative investment in different testicular traits in relation to both pre- and postcopulatory selection pressures.
精子竞争源于交配后雄性之间为争夺父权而持续的竞争。预计在多配偶制程度较高的物种中精子竞争水平最高，而在一夫一妻制配偶中则最弱。精子竞争水平可以通过反映雄性在受精方面投入的特征来衡量，特别是相对睾丸质量（RTM）。然而，RTM与精子竞争水平之间的关系也可能受到交配前竞争的影响，这种竞争会促使睾丸产生更高水平的睾酮。为了测试RTM与交配前和交配后雄性之间竞争的关系，我们比较了两种囊鼠科鼹形鼠，即滥交的 和一夫一妻制的群居 。滥交的物种不仅RTM更大，而且生精组织的比例也更高，从而使生殖细胞产量最大化。相反，群居物种的睾丸较小，但间质组织（其中含有产生雄激素的莱迪希细胞）的比例较高，睾酮水平也较高。因此，睾丸特征以及睾丸质量可能都受到选择，但这些通常并未被测量。需要更多关于不同睾丸特征相对于交配前和交配后选择压力的相对投入的研究。
