Data from: The “unguarded-X” and the genetic architecture of lifespan: Inbreeding results in a potentially maladaptive sex-specific reduction of female lifespan in Drosophila melanogaster

Sex differences in ageing and lifespan are ubiquitous in nature. The "unguarded-X” hypothesis (UXh) suggests they may be partly due to the expression of recessive mutations in the hemizygous sex chromosomes of the heterogametic sex, which could help explain sex-specific ageing in a broad array of taxa. A prediction central to the UX hypothesis is that inbreeding will decrease the lifespan of the homogametic sex more than the heterogametic sex, because only in the former does inbreeding increase the expression of recessive deleterious mutations. In this study, we test this prediction by examining the effects of inbreeding on the lifespan and fitness of male and female Drosophila melanogaster across different social environments. We found that, across social environments, inbreeding resulted in a greater reduction of female than male lifespan, and that inbreeding effects on fitness did not seem to counterbalance sex-specific effects on lifespan, suggesting the former are maladaptative. Inter- and intra-sexual correlation analyses also allowed us to identify evidence of an underlying joint genetic architecture for inbreeding effects on lifespan. We discuss these results in light of the UXh and other alternative explanations, and suggest that more attention should be paid to the possibility that the “unguarded-X” may play an important role in the evolution of sex-specific lifespan.

衰老与寿命的性别差异在自然界中普遍存在。‘无防护X染色体假说（unguarded-X hypothesis，UXh）’提出，这类差异可能部分源于异配性别个体半合子性染色体上隐性突变的表达，该假说可解释众多类群中存在的性别特异性衰老现象。该假说的核心预测为：近交对同配性别寿命的缩短作用会强于异配性别，因为仅在同配性别中，近交才会提升隐性有害突变的表达水平。本研究以黑腹果蝇（Drosophila melanogaster）为研究对象，探究不同社会环境下近交对雌雄个体寿命与适合度的影响，以此检验上述核心预测。研究结果显示，无论社会环境如何，近交对雌性寿命的缩短程度均显著高于雄性；且近交对适合度的影响似乎并未抵消其对寿命的性别特异性作用，这表明近交的适合度效应存在适应不良性。性别间与性别内相关性分析还使我们得以发现，近交对寿命的影响存在潜在的联合遗传基础。本研究结合无防护X染色体假说与其他替代假说对上述结果展开讨论，并提出应更多关注‘无防护X染色体’在性别特异性寿命演化中发挥重要作用的可能性。