Data from: Sex-specific patterns of aging on sexual ornaments and gametes

Sex differences in age-dependent mortality and reproductive success are predicted to drive the evolution of sexually dimorphic patterns of reproductive investment over life. However, this prediction has not been fully explored because it is difficult to measure primary and secondary sexual traits over the life spans of males and females. Here we studied a population of fowl, Gallus gallus, to gain longitudinal data on a sexual ornament (the comb), quantity of gametes produced, and gamete quality (sperm velocity and egg mass) of males and females. Our results reveal pronounced differences between the sexes in age-specific patterns of reproductive investment. In males, comb size decreased linearly with age, high sperm quality early in life was associated with reduced sperm quality late in life, and high sperm production was related to early death. In contrast, female comb size and egg mass were maximized at intermediate ages, and fecundity was independent of life span. Finally, the way traits were related in males did not change over life, whereas in females the association between fecundity and comb size changed from positive to negative over the lifetime of a female, indicating that aging may lead to trade-offs in investment between traits in females. These results show that males and females differ in reproductive investment with age, in terms of both the expression of individual traits and their phenotypic covariance.

学界此前预测，与年龄相关的死亡率和繁殖成功率的两性差异，会推动生命进程中繁殖投入的两性异形模式演化。然而，这一预测尚未得到充分验证，原因在于难以在雌雄个体的整个生命周期内，对其第一性征与第二性征进行量化测量。本研究以原鸡（Gallus gallus）种群为研究对象，收集了雌雄个体的纵向数据，涵盖性装饰器官（鸡冠）、配子生成量以及配子质量（精子活力与卵重）相关指标。研究结果显示，雌雄个体在繁殖投入的年龄特异性模式上存在显著差异。就雄性而言，鸡冠大小随年龄增长呈线性下降；生命早期较高的精子质量与生命后期精子质量降低相关，而高精子生成量则与早亡存在关联。与之相对，雌性的鸡冠大小与卵重在中等年龄阶段达到峰值，且繁殖力与寿命并无关联。最后，雄性个体各性状间的关联模式并未随生命周期发生改变；而雌性个体的繁殖力与鸡冠大小之间的关联，则从正向转为负向，这表明衰老可能会导致雌性个体在不同性状间的繁殖投入出现权衡。本研究结果表明，雌雄个体在随年龄变化的繁殖投入模式上存在差异，这一差异既体现在单个性状的表达上，也体现在性状间的表型协变关系中。