Males of Caenorhabditis elegans provide a crucial practical tool in the laboratory, but, as the rarer and more finicky sex, have not enjoyed the same depth of research attention as hermaphrodites. Males, however, have attracted the attention of evolutionary biologists who are exploiting the C. elegans system to test longstanding hypotheses about sexual selection, sexual conflict, transitions in reproductive mode, and genome evolution, as well as to make new discoveries about Caenorhabditis organismal biology. Here, we review the evolutionary concepts and data informed by study of males of C. elegans and other Caenorhabditis. We give special attention to the important role of sperm cells as a mediator of inter-male competition and male-female conflict that has led to drastic trait divergence across species, despite exceptional phenotypic conservation in many other morphological features. We discuss the evolutionary forces important in the origins of reproductive mode transitions from males being common (gonochorism: females and males) to rare (androdioecy: hermaphrodites and males) and the factors that modulate male frequency in extant androdioecious populations, including the potential influence of selective interference, host-pathogen coevolution, and mutation accumulation. Further, we summarize the consequences of males being common vs rare for adaptation and for trait divergence, trait degradation, and trait dimorphism between the sexes, as well as for molecular evolution of the genome, at both micro-evolutionary and macro-evolutionary timescales. We conclude that C. elegans male biology remains underexploited and that future studies leveraging its extensive experimental resources are poised to discover novel biology and to inform profound questions about animal function and evolution.

中文翻译：

---

秀丽隐杆线虫的雄性、异型杂交和性选择。

雄性秀丽隐杆线虫为实验室提供了重要的实用工具，但作为一种更稀有、更挑剔的性别，它们并没有像雌雄同体那样受到同样深度的研究关注。然而，雄性引起了进化生物学家的注意，他们正在利用秀丽隐杆线虫系统来测试有关性​​选择、性冲突、生殖模式转变和基因组进化的长期假设，并做出关于秀丽隐杆线虫有机生物学的新发现。在这里，我们回顾了对雄性秀丽隐杆线虫和其他秀丽隐杆线虫的研究所提供的进化概念和数据。我们特别关注精子细胞作为雄性间竞争和雌性冲突调解者的重要作用，这导致了物种间性状的巨大差异，尽管在许多其他形态特征上具有特殊的表型保守性。我们讨论了在生殖模式从常见的雄性（雌雄异体：雌性和雄性）到罕见的（雌雄同体：雌雄同体和雄性）转变的起源中重要的进化力量，以及调节现存雌雄同体种群中雄性频率的因素，包括选择性干扰、宿主-病原体共同进化和突变积累。此外，我们总结了雄性常见与稀有对适应、性别之间性状差异、性状退化和性状二态性以及基因组分子进化在微观进化和宏观进化时间尺度上的影响。我们的结论是，秀丽隐杆线虫的雄性生物学仍未得到充分开发，未来的研究将利用其广泛的实验资源来发现新的生物学，并为有关动物功能和进化的深刻问题提供信息。