Texas A&M University- Corpus Christi, Department of Life Sciences, 6300 Ocean Dr., Corpus Christi, Texas, 78412, USA.
Mount Holyoke College, Department of Biological Sciences, 50 College Street, South Hadley, Massachusetts, 01075, USA.
Sci Rep. 2020 Feb 24;10(1):3257. doi: 10.1038/s41598-020-60287-w.
Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Phocoena phocoena). Males attempt copulation by approaching a female exclusively on her left side. To understand if this unusual lateralized behavior may have coevolved with genital morphology, we quantified the shape of female and male harbor porpoise reproductive tracts using 2D geometric morphometrics and 3D models of the vaginal lumen and inflated distal penis. We found that the vaginas varied individually in shape and that the vaginas demonstrated both significant directional and fluctuating asymmetry. This asymmetry resulted from complex 3D spirals and vaginal folds with deep recesses, which may curtail the depth or direction of penile penetration and/or semen movement. The asymmetric shapes of the vaginal lumen and penis tip were both left-canted with similar angular bends that mirrored one another and correspond with the left lateral mating approach. We suggest that the reproductive anatomy of both sexes and their lateral mating behavior coevolved.
不对称的生殖器和偏侧化的交配行为发生在多个分类群中，但一个性别中的不对称形态是否与另一个性别的偏侧化交配行为相关或共同进化，在很大程度上仍未得到探索。虽然偏侧化的交配行为在分类上广泛存在，但在哺乳动物中，仅在港湾海豚（Phocoena phocoena）中有所了解。雄性通过仅从左侧接近雌性来尝试交配。为了了解这种不寻常的偏侧化行为是否与生殖器形态共同进化，我们使用 2D 几何形态测量学和阴道腔以及膨胀的远端阴茎的 3D 模型来量化雌性和雄性港湾海豚的生殖道形状。我们发现，阴道的形状在个体之间存在差异，并且阴道表现出明显的方向性和波动不对称性。这种不对称性源于复杂的 3D 螺旋和阴道褶皱，具有深凹处，这可能限制阴茎的插入深度或方向和/或精液的运动。阴道腔和阴茎尖端的不对称形状都是向左倾斜的，具有相似的角度弯曲，彼此镜像，与左侧偏侧交配方法相对应。我们认为，两性的生殖解剖结构及其偏侧化交配行为共同进化。
