Data from: Postcopulatory sexual selection influences baculum evolution in primates and carnivores

The extreme morphological variability of the baculum across mammals is thought to be the result of sexual selection, particularly, high levels of postcopulatory selection. However, the evolutionary trajectory of the mammalian baculum is little studied and evidence for the adaptive function of the baculum has so far been elusive. Here we use Markov chain Monte Carlo methods implemented in a Bayesian phylogenetic framework to reconstruct baculum evolution across the mammalian class and investigate the rate of baculum length evolution within the primate order. We then test the effects of testes mass (postcopulatory sexual selection), polygamy, seasonal breeding and intromission duration on the baculum in primates and carnivores. The ancestral mammal did not have a baculum, but both ancestral primates and carnivores did. No relationship was found between testes mass and baculum length in either primates or carnivores. Intromission duration correlated with baculum presence over the course of primate evolution, and prolonged intromission predicts significantly longer bacula in extant primates and carnivores. Both polygamous and seasonal breeding systems predict significantly longer bacula in primates. These results suggest the baculum plays an important role in facilitating reproductive strategies in populations with high levels of postcopulatory sexual selection.学界普遍认为，哺乳动物阴茎骨（baculum）的极端形态多样性是性选择（尤其是高强度交配后性选择）作用的结果。然而，目前针对哺乳动物阴茎骨的演化轨迹研究尚少，关于其适应性功能的证据至今仍较为匮乏。本研究采用贝叶斯系统发育框架下的马尔可夫链蒙特卡洛（Markov chain Monte Carlo）方法，重构了整个哺乳纲的阴茎骨演化历程，并探究了灵长目内阴茎骨长度的演化速率。随后，我们检验了睾丸质量（代表交配后性选择强度）、多配偶制、季节性繁殖以及插入时长对灵长类与食肉目动物阴茎骨的影响。 研究结果显示：哺乳动物的祖先并不具备阴茎骨，但灵长类与食肉目的共同祖先均已拥有该结构；无论是灵长类还是食肉目动物，其睾丸质量与阴茎骨长度均未呈现显著相关性。在灵长类的演化历程中，插入时长与阴茎骨的存在与否存在显著关联；而在现生灵长类与食肉目动物中，较长的插入时长可显著预测更长的阴茎骨长度。此外，多配偶制与季节性繁殖两种繁殖策略，均可显著预测灵长类拥有更长的阴茎骨。 上述结果表明，阴茎骨在应对高强度交配后性选择的种群繁殖策略中，发挥着重要的促进作用。