Data from: No evidence for a trade-off between sperm length and male premating weaponry

Male ornaments and armaments that mediate success in mate acquisition and ejaculate traits influencing competitive fertilization success are under intense sexual selection. However, relative investment in these pre- and postcopulatory traits depends on the relative importance of either selection episode and on the energetic costs and fitness gains of investing in these traits. Theoretical and empirical work has improved our understanding of how precopulatory sexual traits and investments in sperm production covary in this context. It has recently also been suggested that male weapon size may trade off with sperm length as another postcopulatory sexual trait, but the theoretical framework for this suggestion remains unclear. We evaluated the relationship between precopulatory armaments and sperm length, previously reported in ungulates, in five taxa as well as meta-analytically. Within and between taxa, we found no evidence for a negative or positive relationship between sperm length and male traits that are important in male-male contest competition. It is important to consider pre- and postcopulatory sexual selection together to understand fitness, and to study investments in different reproductive traits jointly rather than separately. A trade-off between pre- and postcopulatory sexual traits may not manifest itself in sperm length but rather in sperm number or function. Particularly in large-bodied taxa such as ungulates, sperm number is more variable interspecifically and likely to be under more intense selection than sperm length. We discuss our and the previous results in this context.

介导配偶获取成功的雄性装饰与武器，以及影响竞争性受精成功率的射精相关性状，均处于强烈的性选择压力之下。然而，针对这些交配前性选择（precopulatory sexual selection）与交配后性选择（postcopulatory sexual selection）相关性状的相对投资，取决于两类选择事件的相对重要性，以及投资这些性状所需的能量成本与适合度收益。此前的理论与实证研究，已增进了我们对该研究背景下交配前性性状与精子生产投资的协同变化规律的认知。近期另有研究提出，雄性武器大小可能与作为另一项交配后性性状的精子长度存在权衡（trade-off）关系，但支撑该假说的理论框架仍未明确。我们针对此前在有蹄类（ungulates）中报道的交配前武器与精子长度的关联，在五个类群中开展了验证，并结合元分析（meta-analysis）手段进行了综合分析。在类群内部与类群之间，我们均未发现精子长度与雄性间竞争中发挥关键作用的雄性性状之间存在正负相关关系。若要理解雄性适合度，需同时考量交配前与交配后性选择，且应联合研究不同生殖性状的投资模式，而非单独分析。交配前与交配后性性状间的权衡关系，可能不会体现在精子长度上，而是反映在精子数量或功能层面。尤其在有蹄类这类体型较大的类群中，精子数量的种间变异度更高，且相较于精子长度，其可能承受更强的选择压力。我们将结合该研究背景，对本次及既往相关研究结果展开讨论。