Frías-Alvarez Patricia, Zúñiga-Vega J Jaime
Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, Mexico City, Distrito Federal, Mexico.
Oecologia. 2016 Jul;181(3):645-58. doi: 10.1007/s00442-015-3477-1. Epub 2015 Oct 28.
Superfetation is an unusual reproductive strategy that consists of the presence of multiple broods at different developmental stages within a single female. One hypothesis that was proposed to explain its adaptive significance suggests that, in fishes, superfetation is a response to selective pressures that promote a thin and streamlined body shape, such as high-velocity water systems. Superfetation may allow for reduction in ovary size and hence improve streamlining because superfetating females carry few large, full-term embryos at any given time. We tested this morphological constraint hypothesis using reproductive and morphological data from several populations of two viviparous fishes of the family Poeciliidae (Poeciliopsis gracilis and Poeciliopsis infans). We found no evidence to support the morphological constraint hypothesis. In both species the degree of superfetation varied as a function of a complex interaction between source population and female size, and this interpopulation variation was not associated with the velocity of the water current. Contrary to what we expected, females of P. gracilis with more streamlined bodies were observed in rivers where water velocity is slow or moderate. In P. infans the velocity of the water current did not predict variation in body shape. Our results are noteworthy because a previous study which focused on a congeneric species (Poeciliopsis turrubarensis) demonstrated strong support for this hypothesis. However, based on our evidence we conclude that the association among increased superfetation, streamlined morphologies, and fast-flowing environments is not a general rule and that the adaptive value of superfetation may differ among species.
异期复孕是一种不寻常的生殖策略，指在单个雌性体内存在处于不同发育阶段的多个胚胎。为解释其适应性意义而提出的一种假说认为，在鱼类中，异期复孕是对促进身体形态瘦长且流线型的选择压力的一种反应，比如高速水流系统。异期复孕可能会使卵巢尺寸减小，从而改善身体的流线型，因为进行异期复孕的雌性在任何特定时间携带的大的足月胚胎数量较少。我们利用来自胎鳉科两种胎生鱼类（细纹食蚊鱼和婴食蚊鱼）多个种群的生殖和形态学数据，对这一形态限制假说进行了检验。我们没有找到支持形态限制假说的证据。在这两个物种中，异期复孕的程度随来源种群和雌性大小之间复杂的相互作用而变化，并且这种种群间的变化与水流速度无关。与我们的预期相反，在水流速度缓慢或适中的河流中观察到了身体更具流线型的细纹食蚊鱼雌性。在婴食蚊鱼中，水流速度并不能预测身体形态的变化。我们的结果值得关注，因为之前一项针对同属物种（图鲁巴食蚊鱼）的研究有力地支持了这一假说。然而，基于我们的证据，我们得出结论，异期复孕增加、形态流线型化和快速流动环境之间的关联并非普遍规律，而且异期复孕的适应性价值可能因物种而异。
