Genetics, Vol. 168, 2049-2058, December 2004, Copyright © 2004
doi:10.1534/genetics.104.030890

Decreased Diversity but Increased Substitution Rate in Host mtDNA as a Consequence of Wolbachia Endosymbiont Infection

* Department of Entomology, University of Wisconsin, Madison, Wisconsin 53706
{dagger} Department of Biology, University of Rochester, Rochester, New York 14627
{ddagger} Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008

2 Corresponding author: Department of Entomology, University of Wisconsin, 643 Russell Labs, 1630 Linden Dr., Madison, WI 53706.
E-mail: dshoemak{at}entomology.wisc.edu

A substantial fraction of insects and other terrestrial arthropods are infected with parasitic, maternally transmitted endosymbiotic bacteria that manipulate host reproduction. In addition to imposing direct selection on the host to resist these effects, endosymbionts may also have indirect effects on the evolution of the mtDNA with which they are cotransmitted. Patterns of mtDNA diversity and evolution were examined in Drosophila recens, which is infected with the endosymbiont Wolbachia, and its uninfected sister species D. subquinaria. The level of mitochondrial, but not nuclear, DNA diversity is much lower in D. recens than in D. subquinaria, consistent with the hypothesized diversity-purging effects of an evolutionarily recent Wolbachia sweep. The dN/dS ratio in mtDNA is significantly greater in D. recens, suggesting that Muller's ratchet has brought about an increased rate of substitution of slightly deleterious mutations. The data also reveal elevated rates of synonymous substitutions in D. recens, suggesting that these sites may experience weak selection. These findings show that maternally transmitted endosymbionts can severely depress levels of mtDNA diversity within an infected host species, while accelerating the rate of divergence among mtDNA lineages in different species.




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