脉红螺交配后的性选择机制

Mechanism of postcopulatory sexual selection in Rapana venosa

交配后性选择是雌性混交动物中的一种普遍现象,其选择机制较为复杂,是性选择研究领域中的重点和难点问题。脉红螺是我国重要的大型经济贝类之一,繁殖形式为多雌多雄混交模式。为了研究该模式繁殖机制,本研究利用6个微卫星标记及行为学观察对脉红螺3个家系进行父权分析。结果表明,3个家系均存在多父性现象,证实脉红螺繁殖属于真正遗传意义上的雌性混交模式。3个家系中父权比例与父本的6个形态学参数及交配持续时间不存在关联性,但均表现出最先与母本交配的父本其后代比例最高,而最后交配的父本其后代比例最低,表明脉红螺交配后性选择存在最先雄性精子优先受精现象,这一现象符合"topping off"假说,即最先交配的雄性排放了大量精子占据了受精囊的主要空间,导致其子代的比例最高;而最后交配的雄性由于受精囊空间的限制,其精子占据空间最少。本研究为海洋无脊椎动物的交配后性选择机制研究提供重要参考资料。

Postcopulatory sexual selection is a common phenomenon in polyandry species. The mechanism of postcopulatory sexual selection is complicated, and it is the key and difficult topics in sexual selection. Rapana venosa is one of the most important commercial molluscs in China, whose females mate with multiple males. In this study, paternity analysis was performed in three families of R. venosa using microsatellite markers and behavior observation. Multiple paternity was observed in all the three families, suggesting that R. venosa was genetic polyandry. There was no correlation between six morphological parameters of males and paternity ratios, and no correlation between the mating duration and paternity ratios. The results showed that the first mating male had most progeny and the last mating male had least progeny. R. venosa exhibited first-male sperm precedence. This pattern of sperm precedence was consistent with the hypothesis of ＂topping off＇, in which a female accepts a large amount of sperm from her first mate, and, if additional space remains in her spermathecae, she then seeks additional mates until she has no need for further sperm. This study provides important information for the studies on mechanism of postcopulatory sexual selection in marine invertebrates.