Lorenzi M C, Sella G, Schleicherová D, Ramella L
Department of Animal and Human Biology, University of Turin, Turin, Italy.
J Evol Biol. 2005 Sep;18(5):1341-7. doi: 10.1111/j.1420-9101.2005.00916.x.
Sex allocation theory predicts that simultaneous hermaphrodites shift sex allocation facultatively in response to variation in local group size. This study was performed to evaluate the relative investment in each sex function by the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema and to test whether allocation to each sex depends on the number of reproductive competitors. Four experimental groups were set up (in a 2 x 2 factorial design) with small or large group size and with small or large enclosures to control for potential confounding effects of density. We measured the proportion of female and male investment in focal individuals. Results revealed that individuals regulated their reproductive output so that when reproductive competitors were present, the number of female gametes was strongly reduced and the male function increased. In contrast, under monogamy, individuals in small groups produced lower numbers of sperm but had a higher egg output than worms in large groups. Density did not affect sex allocation in our experiment. Our findings provide qualitative support for Local Mate Competition theory, but also show that the pattern of sex allocation specific to this species is more complex than expected by current theory.
性分配理论预测，同步雌雄同体生物会根据当地群体规模的变化，适应性地改变其性分配。本研究旨在评估同步雌雄同体的多毛类蠕虫Ophryotrocha diadema在每个性别功能上的相对投资，并测试每个性别的分配是否取决于生殖竞争者的数量。设置了四个实验组（采用2×2析因设计），分别为群体规模小或大，以及饲养空间小或大，以控制密度可能产生的混杂效应。我们测量了焦点个体在雌性和雄性方面的投资比例。结果显示，个体调节了它们的生殖输出，因此当有生殖竞争者存在时，雌配子数量会大幅减少，而雄性功能增强。相反，在一夫一妻制下，小群体中的个体产生的精子数量较少，但与大群体中的蠕虫相比，其卵子产量更高。在我们的实验中，密度并未影响性分配。我们的研究结果为局部配偶竞争理论提供了定性支持，但同时也表明，该物种特有的性分配模式比当前理论预期的更为复杂。
