Sakaluk Scott K, Eggert Anne-Katrin
Ecology Group, Department of Biological Sciences, Illinois State University, Normal, Illinois, 61790-4120.
Institut für Zoologie der Albert-Ludwigs-Universität, Albertstr. 21a, D-79104, Freiburg, Federal Republic of Germany.
Evolution. 1996 Apr;50(2):694-703. doi: 10.1111/j.1558-5646.1996.tb03879.x.
Manipulation of ejaculates is believed to be an important avenue of female choice throughout the animal kingdom, but evidence of its importance to sexual selection remains scarce. In crickets, such manipulation is manifest in the premature removal of the externally attached spermatophore, which may afford females an important means of postcopulatory mate choice. We tested the hypothesis that premature spermatophore removal contributes significantly to intraspecific variation in sperm precedence by (1) experimentally manipulating spermatophore attachment durations of competing male Gryllodes sigillatus and (2) employing protein electrophoresis to determine the paternity of doubly mated females. The relative spermatophore attachment durations of competing males had a significant influence on male paternity, but the pattern of sperm precedence deviated significantly from the predictions of an ideal lottery. Instead, paternity data and morphological evidence accorded best with a model of partial sperm displacement derived here. Our model is similar to a displacement model of Parker et al. in that sperm of the second male mixes instantaneously with that of the first throughout the displacement process, but the novel feature of our model is that the number of sperm displaced is only a fraction of the number of sperm transferred by the second male. Regardless of the underlying mechanism, female G. sigillatus can clearly alter the paternity of their offspring through their spermatophore-removal behavior, and employ such cryptic choice in favoring larger males and those providing larger courtship food gifts. We discuss how female control of sperm transfer and intraspecific variation in sperm precedence may be important precursors to the evolution of gift giving in insects.
在整个动物界，人们认为对射精产物的操控是雌性进行选择的一个重要途径，但关于其对性选择重要性的证据仍然稀少。在蟋蟀中，这种操控表现为过早移除体外附着的精包，这可能为雌性提供了一种交配后选择配偶的重要方式。我们通过以下方式检验了精包过早移除对精子优先度种内变异有显著贡献这一假设：（1）通过实验操控竞争雄性西格姬蟋精包的附着时长；（2）采用蛋白质电泳来确定双重交配雌性的父系身份。竞争雄性精包的相对附着时长对雄性父系身份有显著影响，但精子优先模式与理想随机抽样的预测有显著偏差。相反，父系身份数据和形态学证据与在此推导的部分精子置换模型最为相符。我们的模型与帕克等人的置换模型相似之处在于，在整个置换过程中，第二个雄性的精子会立即与第一个雄性的精子混合，但我们模型的新颖之处在于，被置换的精子数量只是第二个雄性转移精子数量的一部分。无论潜在机制如何，雌性西格姬蟋显然可以通过其移除精包的行为改变后代的父系身份，并利用这种隐秘选择来青睐体型较大的雄性以及那些提供较大求偶食物礼物的雄性。我们讨论了雌性对精子转移的控制以及精子优先度的种内变异如何可能是昆虫中礼物赠送行为进化的重要先决条件。
