Identifying the evolutionary drivers of sexual signal complexity is a key challenge in the study of animal communication. Among mammals, male bovids and cervids often perform elaborate gestural displays during courtship, consisting of ritualized movements of various parts of the body but the causes underlying interspecific variation in complexity of such displays remain poorly understood. Here we apply the comparative method to investigate which factors may have either promoted or constrained gestural repertoire size. We found that sexual selection was a strong predictor of gestural display complexity in male bovids and cervids. Repertoire size was positively correlated with breeding group size, an indicator of the intensity of sexual selection on males. Moreover, repertoires were larger in species adopting non-territorial and lek breeding mating systems than in species adopting resource-defence territoriality, a finding that can be explained by more emphasis on direct benefits than indirect benefits in resource-defence systems, where male mating success may also be less skewed due to difficulty in monopolising mates. The results also indicate that gestural repertoire size was positively correlated with the number of closely-related species occurring in sympatry. This is consistent with display complexity being selected to facilitate species recognition during courtship and thereby avoid interspecific hybridization. At the same time, repertoire size was negatively associated with male body mass, possibly due to the energetic and mechanical constraints imposed on movements in very large species. By contrast, we found no evidence that the habitat drives selection for complex gestural courtship displays.

中文翻译：

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性选择和物种识别促进有蹄类动物复杂的雄性求爱表现

识别性信号复杂性的进化驱动因素是动物交流研究中的一个关键挑战。在哺乳动物中，雄性牛科动物和鹿科动物在求偶期间经常进行复杂的手势展示，包括身体各部位的仪式化动作，但这种展示复杂性的种间差异的原因仍然知之甚少。在这里，我们应用比较方法来研究哪些因素可能促进或限制手势库的大小。我们发现，性选择是雄性牛科动物和鹿科动物手势展示复杂性的有力预测因素。库的大小与繁殖群体的大小呈正相关，繁殖群体的大小是雄性性选择强度的指标。此外，采用非领地和列克繁殖交配系统的物种比采用资源防御领地性的物种的保留范围更大，这一发现可以通过在资源防御系统中更强调直接利益而不是间接利益来解释，在资源防御系统中，雄性交配成功由于难以垄断配偶，也可能不那么扭曲。结果还表明，手势库的大小与同域中出现的密切相关物种的数量呈正相关。这与选择展示复杂性以促进求偶期间的物种识别并从而避免种间杂交是一致的。与此同时，技能大小与雄性体重呈负相关，这可能是由于大型物种的运动受到能量和机械限制。相比之下，我们没有发现任何证据表明栖息地会驱动复杂手势求爱展示的选择。