The Role of Senescence in Life History Evolution

9707473雷兹尼克关于衰老过程的最新研究评估了环境因素对衰老速度的影响，或表征了两种模式生物-线虫秀丽线虫和果蝇黑腹果蝇-影响寿命的个别基因。我们建议从进化的角度来评估衰老。衰老被认为是因为选择的强度随着年龄的增长而下降；自然选择将对处于生殖寿命早期的个体产生最大的影响，因为他们才刚刚开始将后代贡献给下一代。当个体不再繁殖或照顾后代时，选择的影响就会下降到零。两种遗传机制，突变积累和拮抗多效性，可以解释由于这种特定年龄选择强度的下降而导致的衰老的进化。这两种机制都预测，高的外部死亡率将选择更早的衰老。“外源性死亡”是指被捕食等外因造成的死亡。我们将通过评估来自高捕食性和低捕食性环境的孔雀鱼的寿命和终生繁殖性能来验证这一预测。在我们早期的工作中，我们确定了特立尼达的孔雀鱼自然种群经历了高死亡率与低死亡率，这与存在的捕食者物种有关。与来自低捕食性环境的孔雀相比，来自高捕食性环境的孔雀鱼成熟的年龄更早，体型更小，并将更多的资源用于繁殖。这些差异被证明是有遗传基础的。通过改变自然人口的死亡率，进一步评估了它们，导致这些相同的生活史模式在短至四年的时间间隔内演变。这些联合研究认为，捕食者和死亡率是根据早期生活史的变化而选择的，或者我们在早期生活史中观察到的种群之间的差异代表了对当前死亡率的适应。这些结果为预测捕食也影响了衰老过程的进化提供了理论基础。评估这些鱼的衰老可能会为研究衰老过程提供一个新的模型系统，提供一种识别与衰老相关的基因的新方法，并提供一种手段来回答一个迄今为止所有基于实验室的系统都无法回答的问题，即为什么我们在自然界中的不同物种之间看到寿命存在如此显著的差异？

9707473 Reznick Most current research on the aging process evaluates the influence of environmental factors on the rate of aging or characterizes individual genes that influence lifespan in two model organisms, the nematode Caenorhabditis elegans and the fruitfly Drosophila melanogaster. We propose evaluating aging instead from an evolutionary perspective. Senescence is thought to have evolved because the strength of selection declines with an individual's age; natural selection will have the greatest influence on individuals that are early in their reproductive lifespans because they have only begun to contribute offspring to the next generation. The influence of selection declines to zero when individuals are no longer reproducing or caring for offspring. Two genetic mechanisms, mutation accumulation and antagonistic pleiotropy, can account for the evolution of senescence due to this age-specific decline in the strength of selection. Both mechanisms predict that high extrinsic mortality rates will select for earlier senescence. "Extrinsic mortality" refers to death to external causes, such as predation. We will test this prediction by evaluating the lifespan and lifetime reproductive performance of guppies derived from high and low predation environments. In our earlier work, we established that natural populations of guppies from Trinidad experience high versus low mortality rates, correlated with the species of predators present. Guppies from high predation environments mature at an earlier age, smaller size, and devote more of their resources to reproduction than their counterparts from low predation environments. These differences were shown to have a genetic basis. They were further evaluated by modifying mortality rates in natural populations, resulting in the evolution of these same life history patterns over time intervals as short as four years. These combined studies argue that predators and mortality rates have selected for changes in the early life history, or that the differences that we observed among populations in early life history represent an adaptation to prevailing mortality rates. These results provide the rationale for predicting that predation has also influences the evolution of the aging process.! Evaluating aging in these fish potentially provides a new model system for studying the aging process, a new way of identifying genes associated with aging, and a means for answering a question that is not accessible in all lab-based systems considered thus far, which is "why do we see such dramatic differences in lifespan among species in nature?".