The baculum is an enigmatic bone within the mammalian glans penis, and the driving forces behind its often bizarre shape have captivated evolutionary biologists for over a century. Hypotheses for the function of the baculum include aiding in intromission, stimulating females and assisting with prolonged mating. Previous attempts to test these hypotheses have focused on the gross size of the baculum and have failed to reach a consensus. We conducted three-dimensional imaging and apply a new method to quantify three-dimensional shape complexity in the carnivoran baculum. We show that socially monogamous species are evolving towards complex-shaped bacula, whereas group-living species are evolving towards simple bacula. Overall three-dimensional baculum shape complexity is not related to relative testes mass, but tip complexity is higher in induced ovulators and species engaging in prolonged copulation. Our study provides evidence of postcopulatory sexual selection pressures driving three-dimensional shape complexity in the carnivore baculum.

中文翻译：

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交配后的性选择和食肉动物杆状体形状复杂性的演变

阴茎骨是哺乳动物龟头内的一块神秘骨头，一个多世纪以来，其怪异形状背后的驱动力一直吸引着进化生物学家。生殖器功能的假设包括帮助插入、刺激雌性和帮助延长交配时间。以前测试这些假设的尝试集中在杆的总大小上，但未能达成共识。我们进行了 3D 成像并应用了一种新方法来量化食肉动物 baculum 的 3D 形状复杂性。我们表明，社会一夫一妻制的物种正在向复杂形状的 bacula 进化，而群居物种正在向简单的 bacula 进化。整体三维杆状结构复杂度与相对睾丸质量无关，但在诱导排卵和参与长时间交配的物种中，尖端的复杂性更高。我们的研究提供了交配后性选择压力驱动食肉动物杆状体三维形状复杂性的证据。