Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, Stockholm 10691, Sweden.
Philos Trans R Soc Lond B Biol Sci. 2020 Dec 7;375(1813):20200074. doi: 10.1098/rstb.2020.0074. Epub 2020 Oct 19.
Sperm competition is a powerful selective force that has shaped sexual traits throughout animal evolution. Yet, how fertilization mode (i.e. external versus internal fertilization) influences the scope and potential for sperm competition to act on ejaculates remains unclear. Here, I examine how fertilization mode shapes ejaculatory responses to sperm competition in fishes, a diverse group that constitute the majority of vertebrate biological diversity. Fishes are an ideal group for this examination because they exhibit a wide range of reproductive behaviours and an unparalleled number of transitions in fertilization mode compared to any other vertebrate group. Drawing on data from cartilaginous and bony fishes, I first show that rates of multiple paternity are higher in internally than externally fertilizing fishes, contrary to the prevailing expectation. I then summarize how sperm competition acts on sperm number and quality in internally and externally fertilizing fishes, highlighting where theoretical predictions differ between these groups. Differences in how ejaculates respond to sperm competition between fertilization modes are most apparent when considering sperm size and swimming performance. Clarifying how fertilization mode influences evolutionary responses in ejaculates will inform our understanding of ejaculate evolution across the animal tree of life. This article is part of the theme issue 'Fifty years of sperm competition'.
精子竞争是一种强大的选择力量，它塑造了动物进化过程中的性特征。然而，受精模式（即外部受精与内部受精）如何影响精子竞争对精液的作用范围和潜力尚不清楚。在这里，我研究了受精模式如何影响鱼类的射精反应对精子竞争，鱼类是一个多样化的群体，构成了大多数脊椎动物的生物多样性。鱼类是进行这种检查的理想群体，因为与任何其他脊椎动物群体相比，它们表现出广泛的生殖行为和无与伦比的受精模式转变数量。利用软骨鱼和硬骨鱼的数据，我首先表明，与普遍的预期相反，内部受精的鱼类的多父系率高于外部受精的鱼类。然后，我总结了精子竞争如何作用于内部和外部受精的鱼类的精子数量和质量，强调了这些群体之间的理论预测有何不同。当考虑精子大小和游泳性能时，受精模式对精子竞争的反应如何不同，这一点最为明显。阐明受精模式如何影响精液的进化反应将有助于我们了解整个动物生命之树上的精液进化。本文是主题为“精子竞争 50 年”的特刊的一部分。
