Animal Evolutionary Ecology, Department for Biology, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany.
Front Zool. 2011 Nov 11;8:30. doi: 10.1186/1742-9994-8-30.
Sex allocation theory predicts that in small mating groups simultaneous hermaphroditism is the optimal form of gender expression. Under these conditions, male allocation is predicted to be very low and overall per-capita reproductive output maximal. This is particularly true for individuals that live in pairs, but monogamy is highly susceptible to cheating by both partners. However, certain conditions favour social monogamy in hermaphrodites. This study addresses the influence of group size on group stability and moulting cycles in singles, pairs, triplets and quartets of the socially monogamous shrimp Lysmata amboinensis, a protandric simultaneous hermaphrodite.
The effect of group size was very strong: Exactly one individual in each triplet and exactly two individuals in each quartet were killed in aggressive interactions, resulting in group sizes of two individuals. All killed individuals had just moulted. No mortality occurred in single and pair treatments. The number of moults in the surviving shrimp increased significantly after changing from triplets and quartets to pairs.
Social monogamy in L. amboinensis is reinforced by aggressive expulsion of supernumerous individuals. We suggest that the high risk of mortality in triplets and quartets results in suppression of moulting in groups larger than two individuals and that the feeding ecology of L. amboinensis favours social monogamy.
性别分配理论预测，在小的交配群体中，同时雌雄同体是最佳的性别表达形式。在这些条件下，雄性分配被预测为非常低，而总个体生殖产出最大。对于生活在对中的个体来说尤其如此，但一夫一妻制极易受到双方的欺骗。然而，某些条件有利于雌雄同体的社会一夫一妻制。本研究探讨了群体大小对单身、成对、三对和四对社会一夫一妻制虾 Lysmata amboinensis 群体稳定性和蜕皮周期的影响，Lysmata amboinensis 是一种先雄后雌的同时雌雄同体。
群体大小的影响非常强烈：在三对中的每一对和四对中的每一对中，恰好有一个个体在攻击性相互作用中被杀死，导致群体大小为两个个体。所有被杀的个体刚刚蜕皮。在单人和双人处理中没有死亡发生。在从三对和四对变为两对后，幸存虾的蜕皮次数显著增加。
L.amboinensis 的社会一夫一妻制通过对多余个体的攻击性驱逐得到加强。我们认为，三对和四对个体的高死亡率导致了大于两个个体的群体中蜕皮的抑制，并且 L.amboinensis 的摄食生态学有利于社会一夫一妻制。
