Institute of Evolution, HUN-REN Centre for Ecological Research, Budapest, Hungary.
Departament de Genètica i de Microbiologia, Grup de Genòmica, Bioinformàtica i Biologia Evolutiva (GBBE), Universitat Autònoma de Barcelona, Barcelona, Spain.
BMC Biol. 2023 Oct 23;21(1):230. doi: 10.1186/s12915-023-01716-w.
Conventional wisdom in evolutionary theory considers aging as a non-selected byproduct of natural selection. Based on this, conviction aging was regarded as an inevitable phenomenon. It was also thought that in the wild organisms tend to die from diseases, predation and other accidents before they could reach the time when senescence takes its course. Evidence has accumulated, however, that aging is not inevitable and there are organisms that show negative aging even. Furthermore, old age does play a role in the deaths of many different organisms in the wild also. The hypothesis of programmed aging posits that a limited lifespan can evolve as an adaptation (i.e., positively selected for) in its own right, partly because it can enhance evolvability by eliminating "outdated" genotypes. A major shortcoming of this idea is that non-aging sexual individuals that fail to pay the demographic cost of aging would be able to steal good genes by recombination from aging ones.
Here, we show by a spatially explicit, individual-based simulation model that aging can positively be selected for if a sufficient degree of kin selection complements directional selection. Under such conditions, senescence enhances evolvability because the rate of aging and the rate of recombination play complementary roles. The selected aging rate is highest at zero recombination (clonal reproduction). In our model, increasing extrinsic mortality favors evolved aging by making up free space, thereby decreasing competition and increasing drift, even when selection is stabilizing and the level of aging is set by mutation-selection balance. Importantly, higher extrinsic mortality is not a substitute for evolved aging under directional selection either. Reduction of relatedness decreases the evolved level of aging; chance relatedness favors non-aging genotypes. The applicability of our results depends on empirical values of directional and kin selection in the wild.
We found that aging can positively be selected for in a spatially explicit population model when sufficiently strong directional and kin selection prevail, even if reproduction is sexual. The view that there is a conceptual link between giving up clonal reproduction and evolving an aging genotype is supported by computational results.
进化理论中的传统观点认为，衰老是非自然选择的副产品。基于此，人们坚信衰老是不可避免的现象。人们还认为，在野外，生物体往往会死于疾病、捕食和其他意外，而不会到达衰老发生的时间。然而，越来越多的证据表明，衰老是可以避免的，甚至有些生物还会出现负衰老现象。此外，在野外，许多不同的生物体的老年期也会导致死亡。程序性衰老假说认为，有限的寿命可以作为一种适应性（即被积极选择）进化而来，部分原因是它可以通过消除“过时”的基因型来增强可进化性。这一观点的一个主要缺点是，那些没有因衰老而付出代价的、没有衰老的有性个体，通过与衰老个体的重组，可以窃取到好的基因。
在这里，我们通过一个空间明确的、基于个体的模拟模型表明，如果有足够程度的亲缘选择来补充定向选择，衰老就可以被积极选择。在这种情况下，衰老增强了可进化性，因为衰老速度和重组速度发挥着互补作用。在没有重组（克隆繁殖）的情况下，选择的衰老速度最高。在我们的模型中，增加外源性死亡率有利于通过填补空位来进化衰老，从而减少竞争，增加漂移，即使选择是稳定的，衰老水平是由突变-选择平衡决定的。重要的是，在定向选择下，外源性死亡率的增加也不能替代进化衰老。亲缘关系的降低会降低进化的衰老水平；偶然的亲缘关系有利于非衰老基因型。我们的研究结果的适用性取决于野外定向选择和亲缘选择的经验值。
我们发现，在一个空间明确的种群模型中，如果有足够强大的定向选择和亲缘选择，即使是有性繁殖，衰老也可以被积极选择。放弃克隆繁殖和进化衰老基因型之间存在概念联系的观点得到了计算结果的支持。
