Università di Torino, Department of Life Sciences and Systems Biology, University of Turin, via Accademia Albertina 13, 10123 Torino, Italy.
Integr Comp Biol. 2013 Oct;53(4):689-700. doi: 10.1093/icb/ict043. Epub 2013 May 9.
Related species share genetic and developmental backgrounds. Therefore, separate-sex species that share recent common ancestors with hermaphroditic species may have hidden genetic variation for sex determination that causes some level of lability of expression of gender. Worms of the polychaete species Ophryotrocha labronica have separate, dimorphic sexes and their ancestor was hermaphroditic. Ophryotrocha labronica has a worldwide distribution and populations may differ in the degree of gender specialization. We analyzed the extent to which O. labronica had fixed or labile expression of gender. We found that there were up to four different sexual phenotypes, namely, pure males, males with oocytes, pure females, and females with sperm; the relative frequency of these sexual phenotypes varied in three geographically-distant populations. These sexual morphs had either male or female morphology. However, populations differed in the extent to which worms were sexually dimorphic. In the less dioecious-like population (in which pure males and females were virtually absent, all worms had both oocytes and sperm and sexual dimorphism was relatively weak), males with oocytes had slightly plastic female allocation that depended on mating opportunities-a clearly hermaphroditic trait. Males with oocytes and females with sperm were not functional hermaphrodites. They only used one type of gametes to reproduce and in this respect they probably differed from many cases of inconstancy of gender described in the literature. We consider these populations as novel examples of intermediate states between androdioecy and dioecy. This study contributes to our understanding of breeding systems as continuous gradients rather than as distinct clear-cut alternatives.
相关物种具有遗传和发育背景的相关性。因此，与雌雄同体物种具有最近共同祖先的雌雄异体物种可能具有隐藏的性别决定遗传变异，导致性别表达的某种程度的不稳定性。多毛类物种 Ophryotrocha labronica 的雌雄异体，形态不同，其祖先为雌雄同体。Ophryotrocha labronica 分布广泛，种群在性别专业化程度上可能存在差异。我们分析了 O. labronica 性别表达的固定或不稳定程度。我们发现，存在多达四种不同的性别表型，即纯雄性、带有卵母细胞的雄性、纯雌性和带有精子的雌性；这些性表型的相对频率在三个地理上遥远的种群中有所不同。这些性形态具有雄性或雌性形态。然而，种群在性二态性的程度上存在差异。在不太像雌雄同体的种群中（几乎没有纯雄性和雌性，所有的蠕虫都既有卵母细胞又有精子，性二态性相对较弱），带有卵母细胞的雄性具有略微可塑的雌性分配，这取决于交配机会——这是一种明显的雌雄同体特征。带有卵母细胞的雄性和带有精子的雌性不是功能性雌雄同体。它们仅使用一种类型的配子繁殖，在这方面，它们可能与文献中描述的许多性别不稳定性情况不同。我们认为这些种群是雌雄同体和雌雄异体之间中间状态的新例子。这项研究有助于我们理解繁殖系统是连续的渐变，而不是明显的明确替代方案。
