Biology Department, McGill University, 1205 Avenue Docteur Penfield, Montreal, Quebec, Canada.
Philos Trans R Soc Lond B Biol Sci. 2013 Jan 19;368(1610):20120080. doi: 10.1098/rstb.2012.0080.
Populations subject to severe stress may be rescued by natural selection, but its operation is restricted by ecological and genetic constraints. The cost of natural selection expresses the limited capacity of a population to sustain the load of mortality or sterility required for effective selection. Genostasis expresses the lack of variation that prevents many populations from adapting to stress. While the role of relative fitness in adaptation is well understood, evolutionary rescue emphasizes the need to recognize explicitly the importance of absolute fitness. Permanent adaptation requires a range of genetic variation in absolute fitness that is broad enough to provide a few extreme types capable of sustained growth under a stress that would cause extinction if they were not present. This principle implies that population size is an important determinant of rescue. The overall number of individuals exposed to selection will be greater when the population declines gradually under a constant stress, or is progressively challenged by gradually increasing stress. In gradually deteriorating environments, survival at lethal stress may be procured by prior adaptation to sublethal stress through genetic correlation. Neither the standing genetic variation of small populations nor the mutation supply of large populations, however, may be sufficient to provide evolutionary rescue for most populations.
受到严重压力的种群可能会被自然选择拯救，但它的运作受到生态和遗传限制的限制。自然选择的代价表达了一个种群维持死亡率或不育率所需的有效选择的有限能力。遗传稳定性表达了阻止许多种群适应压力的缺乏变异。虽然相对适合度在适应中的作用是众所周知的，但进化拯救强调需要明确认识到绝对适合度的重要性。永久性适应需要绝对适合度的遗传变异性足够广泛，以提供一些极端类型，这些类型能够在压力下持续增长，如果没有这些类型，压力就会导致灭绝。这一原则意味着种群规模是拯救的一个重要决定因素。当种群在持续的压力下逐渐减少，或者逐渐受到逐渐增加的压力的挑战时，暴露于选择下的个体总数将会增加。在逐渐恶化的环境中，通过遗传相关性，先前对亚致死压力的适应可以获得致死压力下的生存。然而，无论是小种群的遗传变异还是大种群的突变供应，都可能不足以提供大多数种群的进化拯救。
