Summary
The accumulation of deleterious mutations reduces individual and mean population fitness. Therefore, in the long run, population size is affected. This facilitates further accumulation of mutations by enhanced genetic drift. Such synergistic interaction then drives the population to extinction.
This mutational meltdown process is studied primarily for asexual populations. Recombination cannot stop the meltdown in small sexual populations. Independent of the mode of reproduction, the asexual case is relevant for any paternally or maternally inherited trait and for mitochondria and chloroplasts that can be viewed as asexual populations inside cells.
The extinction risk is maximal for an intermediate value of the selection coefficient. Recombination does not destroy this effect, at least for small populations. In the asexual case, group selection is able to overpower individual selection to establish lineages with low repair capabilities, i.e., highly deleterious mutations.
If the expression of deleterious mutations is modified by the environment, changes in the environment can cause an unexpected increase or decrease in the extinction risk because of the pronounced maximum extinction risk at intermediate values of s. It may be that an environmental management treatment that improves individual fitness, counterintuitively enhances the extinction risk of a population.
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Gabriel, W., Bürger, R. (1994). Extinction risk by mutational meltdown: Synergistic effects between population regulation and genetic drift. In: Loeschcke, V., Jain, S.K., Tomiuk, J. (eds) Conservation Genetics. EXS, vol 68. Birkhäuser, Basel. https://doi.org/10.1007/978-3-0348-8510-2_7
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DOI: https://doi.org/10.1007/978-3-0348-8510-2_7
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