Evolutionary biology of enantiomorphy and mirror-image populations in tree snails.

我们已经成功地记录了一种交配行为，这可能解释了树蜗牛种类中的对形性是如何发生的。目前认为，对映异型不能在面对面交配的模式下实现手间交配，在这种模式下，两个伴侣同时进行互惠交配。通过野外观察和实验室的实验观察，我们惊奇地发现手性二态种之一的非洲角足鼠（Amphidromus atricallosus）就是以这种方式交配的。视频分析证实了它们面对面的双向交配。根据我们对基于照片和视频图像的视觉信息的分析，很明显，具有左右颠倒生殖器的对映异体可以进行阴茎的反向插入，这在物理上是几乎不可能的。因此，目前的研究结果暴露了一个新的问题；它们是如何同时实现对映异构体之间的相互交配的。我们没有发现它们表现出典型的面对面交配行为的独特性。相反，视觉记录表明，它们可能有生殖器和插入行为，使它们能够克服身体上的限制，相互交配。分子系统发育分析结果表明，手性二态群属单系。在这个群体的祖先最初从一个右旋的物种分化出来的时候，对形性已经进化为在整个两栖属的辐射中保持的祖先状态。这种手性分化模式表明，群体内部的对形性可以通过进化获得特定的特征来维持。

We have succeeded in film recording a mating behavior that may explain how the enantiomorphy within species of tree snails Amphidromus. It is currently believed that the enantiomorphs could not achieve inter-chiral mating in the mode of face-to-face mating in which the two partners perform reciprocal matings simultaneously. Surprisingly we have discovered that one of chirally dimorphic species Amphidromus atricallosus copulates in this mode by means of field observations and experimental observations in the laboratory. The video-film analysis has confirmed their two-way copulation in the face-to-face position.According to our analysis of visual information based on photographs and video images, it is clear that the enantiomorphs with left-right reversed genitalia can perform reciprocal insertion of penes which are supposed to be physically hardly possible. Therefore, the current results have exposed a new question ; how do they achieve the reciprocal copulation between the enantiomorphs simultaneously. We have not detected any uniqueness in their behavior that exhibit a typical face-to-face mating. Instead, the visual record suggests that they may have genitalia and insertion behavior that allows them to copulate each other by overcoming the physical constraint.The results of molecular phylogenetic analysis have demonstrated that the chirally dimorphic group of species is monophyletic. At the initial divergence of the ancestor of the group from a dextral species, the enantiomorphy has evolved as the ancestral state maintained throughout the radiation of the genus Amphidromus. This pattern of chiral divergence suggests that the enantiomorphy within populations could be maintained by evolutionary acquisition of a particular character.