Evolutionary rescue and the limits of adaptation

• Published in: Philosophical transactions of the Royal Society of London. Series B. Biological sciences Vol. 368; no. 1610; p. 20120080
• Main Author: Bell, Graham
• Format: Journal Article
• Language: English
• Published: England The Royal Society 19.01.2013
• Subjects: Adaptation, Biological; Alleles; Biological Evolution; Biota; Cost Of Selection; Deteriorating Environment; Environment; Evolutionary Rescue; Extinction, Biological; Extreme Value; Gene Frequency; Genetic Fitness; Genetic Variation; Genostasis; Population Density; Population Dynamics; Review; Selection, Genetic; Stress, Physiological
• ISSN: 0962-8436; 1471-2970; 1471-2970
• 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.