Affiliation:
1. Department of Evolution and Ecology, University of California, Davis, CA 95616
Abstract
Cytoplasmic incompatibility (CI) is the most common reproductive manipulation produced by
Wolbachia
, obligately intracellular alphaproteobacteria that infect approximately half of all insect species. Once infection frequencies within host populations approach 10%, intense CI can drive
Wolbachia
to near fixation within 10 generations. However, natural selection among
Wolbachia
variants within individual host populations does not favor enhanced CI. Indeed, variants that do not cause CI but increase host fitness or are more reliably maternally transmitted are expected to spread if infected females remain protected from CI. Nevertheless, approximately half of analyzed
Wolbachia
infections cause detectable CI. Why? The frequency and persistence of CI are more plausibly explained by preferential spread to new host species (clade selection) rather than by natural selection among variants within host populations. CI-causing
Wolbachia
lineages preferentially spread into new host species because 1) CI increases equilibrium
Wolbachia
frequencies within host populations, and 2) CI-causing variants can remain at high frequencies within populations even when conditions change so that initially beneficial
Wolbachia
infections become harmful. An epidemiological model describing
Wolbachia
acquisition and loss by host species and the loss of CI-induction within
Wolbachia
lineages yields simple expressions for the incidence of
Wolbachia
infections and the fraction of those infections causing CI. Supporting a determinative role for differential interspecific spread in maintaining CI, many
Wolbachia
infections were recently acquired by their host species, many show evidence for contemporary spatial spread or retreat, and rapid evolution of CI-inducing loci, especially degradation, is common.
Funder
HHS | NIH | National Institute of General Medical Sciences
Publisher
Proceedings of the National Academy of Sciences
Cited by
9 articles.
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