Data from: Sperm competition games: a general model for pre-copulatory male-male competition

Reproductive males face a trade-off between expenditure on pre-copulatory male-male competition – increasing the number of females that they secure as mates – and sperm competition – increasing their fertilisation success with those females. Previous sperm allocation models have focused on scramble competition in which males compete by searching for mates and the number of matings rises linearly with pre-copulatory expenditure. However, recent studies have emphasised contest competition involving pre-copulatory expenditure on armaments, where winning contests may be highly dependent on marginal increases in relative armament level. Here we develop a general model of sperm allocation that allows us to examine the effect of all forms of pre-copulatory competition on sperm allocation patterns. The model predicts that sperm allocation decreases if either the ‘mate-competition loading’, a, or the number of males competing for each mating, M, increases. Other predictions remain unchanged from previous models: (i) expenditure per ejaculate should increase and then decrease, and (ii) total post-copulatory expenditure should increase, as the level of sperm competition increases. A negative correlation between a and M is biologically plausible, and may buffer deviations from the previous models. There is some support for our predictions from comparative analyses across dung beetle species and frog populations.繁殖期雄性个体面临着双重资源权衡：一方面需投入资源开展交配前雄雄竞争，以提升成功获得配偶的雌性数量；另一方面需投入资源应对精子竞争，以提升对已获得配偶的雌性的受精成功率。既往的精子分配（sperm allocation）模型多聚焦于掠夺式竞争场景：雄性通过搜寻配偶展开竞争，交配次数随交配前资源投入呈线性增长。然而近期研究则重点关注涉及交配前武器投入的争斗式竞争，此类竞争中雄性的获胜与否，高度依赖于相对武器水平的边际增量。本研究构建了通用的精子分配模型，借此可检验各类交配前竞争形式对精子分配模式的影响。该模型预测：若“配偶竞争负荷（mate-competition loading）”参数a，或是每桩交配所涉及的雄性数量M增加，则精子分配量会下降。其余预测与既往模型保持一致：其一，单次射精的资源投入应先升后降；其二，随着精子竞争水平提升，总交配后资源投入应随之增加。参数a与M之间的负相关关系在生物学上具有合理性，且可缓冲模型预测与既往研究的偏差。针对蜣螂物种与蛙类种群的比较分析，为本研究的预测提供了一定实证支持。