Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Mutation Load and the Survival of Small Populations

Michael Lynch and Wilfried Gabriel
Evolution
Vol. 44, No. 7 (Nov., 1990), pp. 1725-1737
DOI: 10.2307/2409502
Stable URL: http://www.jstor.org/stable/2409502
Page Count: 13
  • Read Online (Free)
  • Download ($4.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Mutation Load and the Survival of Small Populations
Preview not available

Abstract

Previous attempts to model the joint action of selection and mutation in finite populations have treated population size as being independent of the mutation load. However, the accumulation of deleterious mutations is expected to cause a gradual reduction in population size. Consequently, in small populations random genetic drift will progressively overpower selection making it easier to fix future mutations. This synergistic interaction, which we refer to as a mutational melt-down, ultimately leads to population extinction. For many conditions, the coefficient of variation of extinction time is less than 0.1, and for species that reproduce by binary fission, the expected extinction time is quite insensitive to population carrying capacity. These results are consistent with observations that many cultures of ciliated protozoans and vertebrate fibroblasts have characteristic extinction times. The model also predicts that clonal lineages are unlikely to survive more than 104 to 105 generations, which is consistent with existing data on parthenogenetic animals. Contrary to the usual view that Muller's ratchet does more damage when selection is weak, we show that the mean extinction time declines as mutations become more deleterious. Although very small sexual populations, such as self-fertilized lines, are subject to mutational meltdowns, recombination effectively eliminates the process when the effective population size exceeds a dozen or so. The concept of the effective mutation load is developed, and several procedures for estimating it are described. It is shown that this load can be reduced substantially when mutational effects are highly variable.

Page Thumbnails

  • Thumbnail: Page 
1725
    1725
  • Thumbnail: Page 
1726
    1726
  • Thumbnail: Page 
1727
    1727
  • Thumbnail: Page 
1728
    1728
  • Thumbnail: Page 
1729
    1729
  • Thumbnail: Page 
1730
    1730
  • Thumbnail: Page 
1731
    1731
  • Thumbnail: Page 
1732
    1732
  • Thumbnail: Page 
1733
    1733
  • Thumbnail: Page 
1734
    1734
  • Thumbnail: Page 
1735
    1735
  • Thumbnail: Page 
1736
    1736
  • Thumbnail: Page 
1737
    1737