Condition dependence of a multicomponent sexual display trait in Drosophila serrata

Theory predicts that costly sexual displays should evolve condition dependence if the marginal fitness gain from trait exaggeration is greater for high- than for low-condition individuals and that the strength of condition dependence should increase with the strength of directional selection. While there is substantial support for the first prediction, evidence for the latter is much weaker. We undertook a quantitative test of this prediction for a multivariate sexual display consisting of a suite of contact pheromones termed “cuticular hydrocarbons” (CHCs) in Drosophila serrata. We performed a dietary manipulation of condition (i.e., the pool of metabolic resources available for allocation to fitness-enhancing traits) within a half-sibling breeding design, thereby also providing insight into the genetic basis of condition dependence. As predicted, the linear combination of CHCs under the strongest sexual selection from female mate preferences was unusually condition dependent relative to other CHC combinations within the population (P = .049). A significant positive correlation also existed between the strengths of condition dependence and sexual selection among different CHC blends (r = 0.482, P < .001). Finally, sires varied in their response to the dietary manipulation, demonstrating significant genetic variance in condition dependence. Our results are consistent with the evolution of heightened condition dependence of sexual displays in response to persistent sexual selection.

理论预测，若高条件状态个体从性状夸大中获得的边际适合度收益高于低条件状态个体，则代价高昂的性展示应演化出条件依赖性（condition dependence）；且条件依赖性的强度会随定向选择强度的提升而增强。尽管学界对第一项预测已有大量实证支持，但针对第二项预测的证据则薄弱得多。本研究以斑翅果蝇（Drosophila serrata）体内一类被称为“表皮碳氢化合物（cuticular hydrocarbons, CHCs）”的接触信息素组合构成的多变量性展示为对象，对该项预测开展了定量检验。我们通过半同胞繁育设计，对个体条件状态（即可用于分配至适合度提升性状的代谢资源池）开展了膳食操控，由此也为条件依赖性的遗传基础提供了新认知。正如预测所示，在种群内的其他CHC组合中，受雌性配偶偏好介导的最强性选择作用的CHC线性组合，其条件依赖性显著高于其余组合（P=0.049）。不同CHC混合物的条件依赖性强度与性选择强度之间，也存在显著的正相关关系（r=0.482，P<0.001）。最后，父本对膳食操控的响应存在个体差异，表明条件依赖性存在显著的遗传方差。本研究结果与“性展示的条件依赖性会随持续性性选择的作用而增强”这一演化假说相符。