Department of Biology, Wake Forest University, Winston-Salem, North Carolina.
J Anim Ecol. 2019 Jul;88(7):986-1000. doi: 10.1111/1365-2656.12944. Epub 2019 Feb 12.
Under life-history theories of ageing, increased senescence should follow relatively high reproductive effort. This expectation has rarely been tested against senescence varying between and within the two sexes, although such an approach may clarify the origins of sex-specific ageing in the context of a given mating system. Nazca boobies (Sula granti; a seabird) practise serial monogamy and biparental care. A male-biased population sex ratio results in earlier and more frequent breeding by females. Based on sex-specific reproductive schedules, females were expected to show faster age-related decline for survival and reproduction. Within each sex, high reproductive effort in early life was expected to reduce late-life performance and accelerate senescence. Longitudinal data were used to (a) evaluate the sex specificity of reproductive and actuarial senescence and then (b) test for early-/late-life fitness trade-offs within each sex. Within-sex analyses inform an interpretation of sex differences in senescence based on costs of reproduction. Analyses incorporated individual heterogeneity in breeding performance and cohort-level differences in early-adult environments. Females showed marginally more intense actuarial senescence and stronger age-related declines for fledging success. The opposite pattern (earlier and faster male senescence) was found for breeding probability. Individual reproductive effort in early life positively predicted late-life reproductive performance in both sexes and thus did not support a causal link between early-reproduction/late-life fitness trade-offs and sex differences in ageing. A high-quality diet in early adulthood reduced late-life survival (females) and accelerated senescence for fledging success (males). This study documents clear variation in ageing patterns-by sex, early-adult environment and early-adult reproductive effort-with implications for the role mating systems and early-life environments play in determining ageing patterns. Absent evidence for a disposable soma mechanism, patterns of sex differences in senescence may result from age- and condition-dependent mate choice interacting with this population's male-biased sex ratio and mate rotation.
根据寿命理论，衰老程度的增加应该与较高的繁殖努力相关。尽管这种方法可以在特定的交配系统背景下阐明性别特异性衰老的起源，但这种预期很少在两性之间和两性内部的衰老变化方面得到检验。纳斯卡海鸟（Sula granti；一种海鸟）实行序贯一夫一妻制和双亲养育。雄性偏向的种群性别比例导致雌性更早、更频繁地繁殖。基于特定于性别的繁殖时间表，预计雌性的生存和繁殖会更快地出现与年龄相关的下降。在每一个性别中，早期的高繁殖努力预计会降低晚年的表现并加速衰老。使用纵向数据：（a）评估繁殖和生理衰老的性别特异性，然后（b）在每个性别内测试早期/晚期生活的适应权衡。基于性别的分析为基于繁殖成本的衰老性别差异提供了一个解释。分析纳入了繁殖表现的个体异质性和早期成年环境的群体差异。雌性表现出稍强的生理衰老和更强的与年龄相关的育雏成功率下降。相反的模式（更早和更快的雄性衰老）出现在繁殖概率上。个体早期生活的繁殖努力与两性的晚年繁殖表现呈正相关，因此，早期繁殖/晚年生活适应权衡与衰老性别差异之间不存在因果关系。成年早期的高质量饮食降低了晚年的生存（雌性）和育雏成功率的衰老速度（雄性）。这项研究记录了性别、早期成年环境和早期成年繁殖努力等方面的衰老模式的明显变化，这对交配系统和早期生活环境在确定衰老模式方面的作用具有重要意义。在没有可丢弃的体细胞机制的证据的情况下，衰老性别差异的模式可能是由于年龄和条件依赖的配偶选择与该种群的雄性偏向性别比例和配偶轮换相互作用的结果。
