Department of Biological Science, Florida State University Tallahassee, Florida ; Department of Animal Biology, University of Illinois Urbana-Champaign Champaign, Illinois.
Ecol Evol. 2012 Dec;2(12):2935-42. doi: 10.1002/ece3.402. Epub 2012 Oct 22.
Comparative studies documenting a relationship between male gonadal investment and the degree of sperm competition (SC) have usually considered the association between these traits to be driven by qualitative differences in the mating system, such as whether spawning occurs in pairs or groups. However, ecological and demographic differences between conspecific populations may also generate variation in the importance of SC that can drive the evolution of male gonadal investment. In this study, we examined whether variation in population density, which is predicted to influence the level of SC in many animals, is correlated with male gonadal investment among populations of the least killifish, Heterandria formosa, a species with internal fertilization in which multiple mating is common. We complemented this field study by testing whether males respond plastically to experimentally increased levels of SC by increasing investment in testis. This experiment involved two treatments. In the first, we eliminated the potential for sperm competition (NSC) by housing a single male with a single female. In the second, we created a high risk of SC by housing five males with two females. In the field survey, we found significant differences among populations in density and relative testis mass. However, there was no evidence for a correlation between population density and relative testis mass. In our lab experiment, males did not adjust their gonadal investment in response to experiencing different levels of SC for 4 weeks. Our combined results indicate that gonadal investment in male H. formosa is not related to variation in population density.
比较研究记录了雄性性腺投资与精子竞争（SC）程度之间的关系，这些研究通常认为这些特征之间的关联是由交配系统的定性差异驱动的，例如产卵是发生在对还是群体中。然而，同种群体之间的生态和人口差异也可能产生 SC 重要性的变化，从而推动雄性性腺投资的进化。在这项研究中，我们研究了种群密度的变化是否与种群密度有关，种群密度预计会影响许多动物的 SC 水平，这与 least killifish Heterandria formosa 的雄性性腺投资有关，这是一种具有内部受精的物种，其中多次交配很常见。我们通过测试雄性是否通过增加睾丸投资来对 SC 水平的增加做出可塑性反应，补充了这项现场研究。该实验涉及两种处理。在第一种处理中，我们通过将一只雄性与一只雌性饲养在一起来消除精子竞争的可能性（NSC）。在第二种处理中，我们通过将五只雄性与两只雌性饲养在一起来创造高 SC 风险。在现场调查中，我们发现种群密度和相对睾丸质量存在显著差异。然而，没有证据表明种群密度与相对睾丸质量之间存在相关性。在我们的实验室实验中，雄性在 4 周内没有根据经历不同水平的 SC 来调整其性腺投资。我们的综合结果表明，雄性 H. formosa 的性腺投资与种群密度的变化无关。
