Henry P-Y, Bousset L, Sourrouille P, Jarne P
Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, 1919 route de Mende, F-34293 Montpellier cedex 5, France.
Heredity (Edinb). 2005 Dec;95(6):428-36. doi: 10.1038/sj.hdy.6800731.
Although reproductive assurance (RA) might play a central role in the evolution of the selfing rate, this hypothesis has never been seriously investigated in an hermaphroditic animal. We studied the mating system of the freshwater snail Physa acuta in which the availability of mating partners might be highly variable, because this species is an efficient colonizer occupying unstable habitats. A total of 11 populations differing in ecological disturbance regime (water level, openness) and snail densities were monitored over 2 years. The outcrossing rate was estimated in ca 10 families per population using microsatellite markers and the progeny-array approach. Components of fecundity and survival were recorded for each progeny. Predominant outcrossing (t(m)=0.94) was detected, with a few individuals (4%) purely selfing. The outcrossing rate did not explain among-family variation in fitness components. None of the predictions formulated under the RA hypothesis were verified: (i) selfing was related neither to disturbed habitats, nor to temporal density fluctuations, (ii) it was positively related to population density, (iii) it co-occurred with multiple paternity, and (iv) it did not induce delayed reproduction. Explanations for these negative results are discussed in light of other arguments supporting the RA hypothesis in P. acuta, as well as alternative theories explaining the occurrence of partial selfing, as either a genetically fixed or plastic trait.
尽管生殖保障（RA）可能在自交率的进化中发挥核心作用，但这一假说从未在雌雄同体动物中得到认真研究。我们研究了淡水蜗牛尖膀胱螺（Physa acuta）的交配系统，在这种蜗牛中，交配伙伴的可获得性可能高度可变，因为该物种是一种高效的殖民者，占据着不稳定的栖息地。在两年时间里，我们监测了11个在生态干扰状况（水位、开阔度）和蜗牛密度方面存在差异的种群。使用微卫星标记和子代阵列方法，估计了每个种群约10个家系的异交率。记录了每个子代的繁殖力和存活率组成部分。检测到主要为异交（t(m)=0.94），少数个体（4%）为纯自交。异交率并不能解释家系间适合度组成部分的差异。在RA假说下提出的预测均未得到验证：（i）自交既与受干扰的栖息地无关，也与时间密度波动无关，（ii）它与种群密度呈正相关，（iii）它与多重父权同时出现，（iv）它不会导致繁殖延迟。我们根据支持尖膀胱螺RA假说的其他论据，以及解释部分自交发生的替代理论，即作为一种遗传固定或可塑性性状，对这些负面结果的解释进行了讨论。
