Evolution

Bottleneck Dynamics

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Science  16 Mar 2012:
Vol. 335, Issue 6074, pp. 1281
DOI: 10.1126/science.335.6074.1281-b

Natural or anthropogenic disturbance can reduce the number of individuals in a population very rapidly. When these populations subsequently recover, the individuals in the population will be entirely descended from those that survived the previous disturbance. This process is referred to as a population bottleneck and is a commonly recognized reason for declines in genetic diversity. Long-term monitoring of a small water vole population on an isolated Scottish island allowed Oliver and Piertney to document the impacts of a bottleneck driven by the introduction and subsequent removal of sheep. Every individual water vole on the island was identified before, during, and after the sheep-induced population bottleneck, which reduced the population to just five individuals. Monitoring both neutral genetic diversity (in the form of microsatellite DNA) and adaptive diversity (of an MHC allele known to confer resistance to parasites in the population) showed that although genetic diversity, in general, was greatly reduced by the bottleneck, adaptive diversity loss was countered by apparently strong selection for heterozygotes.

Mol. Biol. Evol. 29, 10.1093/molbev/mss063 (2012).

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