Data and script for: Weapons evolve faster than sperm in bovids and cervids

In polyandrous species, males face reproductive competition both before and after mating. Sexual selection thus shapes the evolution of both pre- and postcopulatory traits, creating competing demands on resource allocation to different reproductive episodes. Traits subject to strong selection exhibit accelerated rates of phenotypic divergence, and examining evolutionary rates may inform us about the relative importance and potential fitness consequences of investing in traits under either pre- or postcopulatory sexual selection. Here, we used a comparative approach to assess evolutionary rates of key competitive traits in two artiodactyl families, bovids (family Bovidae) and cervids (family Cervidae), where male-male competition can occur before and after mating. We quantified and compared evolutionary rates of male weaponry, body size/mass, testes mass, and sperm morphometrics. We found that weapons evolve faster than sperm dimensions. In contrast, testes and body mass evolve at similar rates. These results suggest strong, but differential, selection on both pre- and postcopulatory traits in bovids and cervids. Furthermore, we documented distinct evolutionary rates among different sperm components, with sperm head and midpiece evolving faster than the flagellum. Finally, we demonstrate that, despite considerable differences in weapon development between bovids and cervids, the overall evolutionary patterns between these families were broadly consistent.

Methods
Length and mass data for a range of sexual and somatic traits of ungulates were compiled from the literature. Male sexual weapon length (n = 135; i.e. antlers in cervids and horns in bovids), sperm head, midpiece and total flagellum length (all n = 53), and male muzzle width (n = 88) were represented by linear measurements. Traits measured using mass values included combined testes mass (n = 71) and male body mass (n = 135).

在一妻多夫制（polyandrous）物种中，雄性在交配前后均面临生殖竞争。因此，性选择同时塑造了交配前与交配后性状的演化，使得不同生殖事件间的资源分配存在权衡。受强烈选择的性状会表现出更快的表型分化速率，而通过探究演化速率，我们可以了解在交配前或交配后性选择下，投资于不同性状的相对重要性及其潜在的适合度后果。

本研究采用比较研究方法，对两个偶蹄目科——牛科（Bovidae）与鹿科（Cervidae）——中关键竞争性状的演化速率进行评估，这两个类群的雄性间竞争均可发生于交配前后。我们量化并比较了雄性武器、体尺寸/体质量、睾丸质量以及精子形态计量学相关性状的演化速率。研究发现，雄性武器的演化速率快于精子形态指标。与之相反，睾丸质量与体质量的演化速率相近。上述结果表明，牛科与鹿科的交配前、后性状均受到了强烈但存在差异的选择。此外，我们还发现不同精子组分的演化速率存在显著差异：精子头部与中段的演化速率快于鞭毛。最后，尽管牛科与鹿科在武器发育上存在显著差异，但二者的整体演化模式大体一致。

研究方法
本研究从已发表文献中汇编了有蹄类动物一系列性性状与躯体性状的长度和质量数据。其中，雄性性武器长度（样本量n=135，即鹿科的鹿角与牛科的角）、精子头部、中段及总鞭毛长度（三者样本量均为n=53）以及雄性吻宽（n=88）均通过线性测量获取。采用质量值测量的性状包括双侧睾丸总质量（n=71）与雄性体质量（n=135）。