Reduced lifespan and increased ageing driven by genetic drift in small populations

Explaining the strong variation in lifespan among organisms remains a major challenge in evolutionary biology. Whereas previous work has concentrated mainly on differences in selection regimes and selection pressures, we hypothesize that differences in genetic drift may explain some of this variation. We develop a model to formalize this idea and show that the strong positive relationship between lifespan and genetic diversity predicted by this model indeed exists among populations of Daphnia magna, and that ageing is accelerated in small populations. Additional results suggest that this is due to increased drift in small populations rather than adaptation to environments favoring faster life histories: First, the correlation between genetic diversity and lifespan remains significant after statistical correction for potential environmental covariates. Second, no trade-offs are observed; rather, all investigated traits show clear signs of increased genetic load in the small populations. ...解释生物体间寿命的显著差异仍是进化生物学中的重大科学挑战。既往研究多集中于选择模式（selection regimes）与选择压力（selection pressures）的差异，而本研究提出假说：遗传漂变（genetic drift）的差异或可解释其中部分差异。我们构建模型将该假说予以形式化，并证实：该模型所预测的寿命与遗传多样性（genetic diversity）间的强正相关关系，确实存在于大型溞（Daphnia magna）的种群之间，且小型种群的衰老进程显著加速。补充结果显示，该现象源于小型种群中增强的遗传漂变效应，而非对偏好更快生活史的环境产生的适应性进化：其一，在对潜在环境协变量（environmental covariates）进行统计校正后，遗传多样性与寿命间的相关性仍具有统计学显著性；其二，未观测到任何生活史权衡（trade-offs）现象，反而所有被检测的性状均明确显示小型种群的遗传负荷（genetic load）显著升高……