Placentotrophy is a particular type of maternal provisioning to developing embryos, in which mothers actively provide nutrients via complex placental structures. Placentotrophy implies less pre-fertilization investment, resulting in a shift from pre- to post-copulatory sexual selection. This change can potentially result in a conflict between females and males. This phenomenon has been demonstrated at the interspecific level in viviparous fishes of the family Poeciliidae, in which males of species that lack placentotrophy have evolved traits related to pre-copulatory sexual selection such as coloration, ornaments, and courtship behavior. Placentotrophic species, on the other hand, have evolved traits associated with post-copulatory sexual selection such as long intromittent organs (gonopodium) and increased sexual coercion behavior. Here we test, for the first time at the intraspecific level, whether there is a similar relationship between a higher degree of female placentotrophy and the evolution of male reproductive traits (larger testes and longer gonopodia) in three species of the genus Poeciliopsis (P. gracilis, P. infans, and P. prolifica). We observed a tendency towards longer gonopodia in males of P. gracilis as well as the largest testes of P. prolifica males in the populations with the highest degrees of placentotrophy. However, the statistical support for these findings was relatively weak. Therefore, we failed to support the hypothesis of a selective effect of female placentotrophy on male gonads and genitalia. We discuss other evolutionary forces that may have driven the observed intraspecific variation in male reproductive traits of Poeciliopsis fishes.

胎盘营养是母体为发育中的胚胎提供营养的一种特殊类型，其中母体通过复杂的胎盘结构主动提供营养。胎盘营养意味着受精前的投入较少，导致性选择从交配前转向交配后。这种变化可能会导致女性和男性之间的冲突。这种现象已在 Poeciliidae 科胎生鱼类的种间水平上得到证实，其中缺乏胎盘营养的物种的雄性已经进化出与交配前性选择相关的特征，例如颜色、装饰和求偶行为。另一方面，胎盘营养物种进化出了与交配后性选择相关的特征，例如长的内伸器官（性足）和增加的性胁迫行为。在这里，我们首次在种内水平上测试了Poeciliopsis属的三个物种（P. gracilis、P. infans和P. prolifica）。我们观察到胎盘营养程度最高的种群中，雄性P. gracilis的生殖足有更长的趋势，而P. prolifica雄性的睾丸也有最大。然而，这些发现的统计支持相对较弱。因此，我们未能支持女性胎盘营养对男性性腺和生殖器选择性作用的假设。我们讨论了可能驱动所观察到的拟青鱼雄性生殖性状种内变异的其他进化力量。