Data from: The consequences of sexual selection in well-adapted and maladapted populations of bean beetles

Whether sexual selection generally promotes or impedes population persistence remains an open question. Intralocus sexual conflict (IaSC) can render sexual selection in males detrimental to the population by increasing the frequency of alleles with positive effects on male reproductive success but negative effects on female fecundity. Recent modelling based on fitness landscape theory, however, indicates that the relative impact of IaSC may be reduced in maladapted populations and that sexual selection therefore might promote adaptation when it is most needed. Here, we test this prediction using bean beetles that had undergone 80 generations of experimental evolution on two alternative host plants. We isolated and assessed the effect of maladaptation on sex-specific strengths of selection and IaSC by cross-rearing the two experimental evolution regimes on the alternative hosts and estimating within-population genetic (co)variance for fitness in males and females. Two key predictions were upheld: males generally experienced stronger selection compared to females and maladaptation increased selection in females. However, maladaptation consistently decreased male-bias in the strength of selection and IaSC was not reduced in maladapted populations. These findings imply that sexual selection can be disrupted in stressful environmental conditions, thus reducing one of the potential benefits of sexual reproduction in maladapted populations.

性选择总体上是促进还是阻碍种群存续，仍是一个悬而未决的科学问题。位点内性别冲突（Intralocus sexual conflict, IaSC）可通过提升对雄性繁殖成功率具有正向效应、却对雌性繁殖力产生负向效应的等位基因频率，使雄性间的性选择对种群产生危害。然而，近期基于适应度景观理论的模型研究表明，在未适应环境的种群中，位点内性别冲突的相对影响可能会减弱，因此性选择或许能在种群最需要的时候促进适应性演化。本研究以在两种不同宿主植物上经历了80代实验进化的豆象为实验对象，对这一预测进行验证。我们通过将两种实验进化种群交叉饲养于对应的替代宿主上，并估算雌雄个体适合度的种群内遗传（共）方差，以此分离并评估未适应环境状态对性别特异性选择强度以及位点内性别冲突的影响。两项核心预测得到了验证：相较于雌性，雄性通常面临更强的选择压力；且未适应环境状态会增强雌性所受的选择强度。但研究发现，未适应环境状态始终会降低选择强度的雄性偏向性，且未适应种群中的位点内性别冲突并未减弱。这些研究结果表明，性选择在胁迫性环境条件下可能会受到干扰，从而降低未适应环境种群中性繁殖的潜在益处之一。