Chen Hwei-Yen, Maklakov Alexei A
Ageing Research Group; Department of Animal Ecology; Evolutionary Biology Centre; Uppsala University; Uppsala, Sweden.
Worm. 2013 Jul 1;2(3):e23704. doi: 10.4161/worm.23704. Epub 2013 Oct 1.
Organisms age because of the "selection shadow"-the decline of the force of natural selection with age. Seemingly straightforward corollary of this theory is the Medawar-Williams prediction, which maintains that increased extrinsic (non-aging) mortality will result in the evolution of accelerated aging and decreased longevity. Despite its centrality to modern thinking about the ultimate causes of aging, this prediction ignores the fact that mortality is often a non-random process depending on individual condition. Increased condition-dependent mortality inescapably results in increased selection for resistance against the agent of mortality. Provided that resistance to various stressors is commonly associated with increased longevity, the evolutionary outcome is no longer certain. We recently documented this experimentally by showing that populations of Caenorhabditis remanei evolved to live shorter under high extrinsic mortality, but only when mortality was applied haphazardly. On the contrary, when extrinsic mortality was caused by heat-shock, populations experiencing the same rate of increased mortality evolved greater longevities, notwithstanding increased "selection shadow." Intriguingly, stress-resistant and long-lived worms were also more fecund. We discuss these results in the light of recent theoretical developments, such as condition-environment interactions and hyperfunction theory of aging.
生物体衰老的原因是“选择阴影”——自然选择的力量随着年龄增长而下降。该理论看似直接的推论是梅达沃-威廉姆斯预测，即外部（非衰老）死亡率的增加将导致加速衰老和寿命缩短的进化。尽管这一预测在现代关于衰老终极原因的思考中占据核心地位，但它忽略了死亡率往往是一个取决于个体状况的非随机过程这一事实。与个体状况相关的死亡率增加必然会导致对死亡率因素的抵抗力选择增加。假设对各种应激源的抵抗力通常与寿命延长相关，那么进化结果就不再确定。我们最近通过实验证明，秀丽隐杆线虫种群在高外部死亡率下进化出较短的寿命，但前提是死亡率是随机施加的。相反，当外部死亡率由热休克引起时，尽管“选择阴影”增加，但经历相同死亡率增加速率的种群进化出了更长的寿命。有趣的是，抗应激且长寿的蠕虫繁殖能力也更强。我们根据最近的理论进展，如状况-环境相互作用和衰老的功能亢进理论，来讨论这些结果。
