Department of Biology, Dalhousie University, Life Science Center, 1355 Oxford Street, Halifax, NS B3H 4R2, Canada.
Department of Biological Sciences, Mount Holyoke College, Amherst, Massachusetts.
Evolution. 2018 Feb;72(2):261-273. doi: 10.1111/evo.13395. Epub 2017 Dec 6.
Male genital diversification is likely the result of sexual selection. Female genital diversification may also result from sexual selection, although it is less well studied and understood. Female genitalia are complex among whales, dolphins, and porpoises, especially compared to other vertebrates. The evolutionary factors affecting the diversity of vaginal complexity could include ontogeny, allometry, phylogeny, sexual selection, and natural selection. We quantified shape variation in female genitalia using 2D geometric morphometric analysis, and validated the application of this method to study soft tissues. We explored patterns of variation in the shape of the cervix and vagina of 24 cetacean species (n = 61 specimens), and found that genital shape varies primarily in the relative vaginal length and overall aspect ratio of the reproductive tract. Extensive genital shape variation was partly explained by ontogenetic changes and evolutionary allometry among sexually mature cetaceans, whereas phylogenetic signal, relative testis size, and neonate size were not significantly associated with genital shape. Female genital shape is diverse and evolves rapidly even among closely related species, consistent with predictions of sexual selection models and with findings in invertebrate and vertebrate taxa. Future research exploring genital shape variation in 3D will offer new insights into evolutionary mechanisms because internal vaginal structures are variable and can form complex spirals.
男性生殖器多样化可能是性选择的结果。女性生殖器多样化也可能是性选择的结果，尽管这方面的研究和理解还比较少。在鲸鱼、海豚和鼠海豚中，雌性生殖器非常复杂，与其他脊椎动物相比尤其如此。影响阴道复杂性多样性的进化因素可能包括个体发生、比例关系、系统发育、性选择和自然选择。我们使用二维几何形态测量分析来量化女性生殖器的形状变化，并验证了该方法在研究软组织方面的应用。我们探讨了 24 种鲸目动物（n = 61 个标本）的宫颈和阴道形状变化模式，发现生殖器形状主要在阴道相对长度和生殖道整体纵横比上发生变化。生殖器的广泛形状变化部分可以通过性成熟鲸目动物的个体发生变化和进化比例关系来解释，而系统发育信号、相对睾丸大小和新生儿大小与生殖器形状没有显著关联。女性生殖器形状多种多样，在亲缘关系密切的物种中也迅速进化，这与性选择模型的预测一致，也与无脊椎动物和脊椎动物分类群的发现一致。未来对 3D 生殖器形状变化的研究将提供对进化机制的新见解，因为内部阴道结构是可变的，可以形成复杂的螺旋。
