Wyber Blake W, Tomkins Joseph L, Simmons Leigh W
Centre for Evolutionary Biology, School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Perth 6009, Australia.
Behav Ecol. 2024 Nov 20;36(1):arae095. doi: 10.1093/beheco/arae095. eCollection 2025 Jan-Feb.
Sperm competition is known to favor the evolution of male traits that confer an advantage in gaining fertilizations when females mate multiply. Ejaculate production can be costly and the strategic allocation of sperm in relation to the sperm competition environment is a taxonomically widespread phenomenon. However, variation among males in their ability to adjust ejaculate allocation has rarely been explored. Here, we manipulated the phenotypic condition of male seed beetles, , via larval diet quality and measured ejaculate allocation across varying levels of sperm competition manipulated using olfactory cues. Furthermore, we asked how strategic ejaculation was impacted by previous ejaculation. We found no variation in ejaculate allocation in response to experimentally manipulated cues to sperm competition. Ejaculate allocation was reduced by a male's previous mating history but was unaffected by the larval diets on which males were reared. We suggest that either male seed beetles are unable to adjust ejaculate size to the immediate competitive environment, or that sperm displacement strategies employed by males favor maximal investment at all mating events, especially when unmated females are infrequently encountered. As our study is one of few to examine condition dependence in strategic ejaculation, emphasis should be placed on future studies investigating this possibility across a wider range of taxa and animal mating systems.
已知精子竞争有利于雄性性状的进化，这些性状在雌性多次交配时能在获得受精方面赋予优势。射精的产生可能代价高昂，并且根据精子竞争环境对精子进行策略性分配是一种在分类学上广泛存在的现象。然而，雄性在调整射精分配能力上的差异却很少被探究。在此，我们通过幼虫饮食质量来操纵雄性种子甲虫的表型状况，并测量在使用嗅觉线索操纵的不同精子竞争水平下的射精分配情况。此外，我们还研究了先前射精如何影响策略性射精。我们发现，对于实验操纵的精子竞争线索，射精分配没有变化。雄性先前的交配经历会使射精分配减少，但不受雄性所食用的幼虫饮食的影响。我们认为，要么雄性种子甲虫无法根据当前的竞争环境调整射精量，要么雄性采用的精子置换策略有利于在所有交配事件中进行最大投资，尤其是在很少遇到未交配雌性的情况下。由于我们的研究是少数几个研究策略性射精中条件依赖性的研究之一，未来应着重开展跨更广泛分类群和动物交配系统来探究这种可能性的研究。
