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 d N /d S 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.

Microsatellites have proved to be very useful as genetic markers, as they seem to be ubiquitous and randomly distributed throughout most eukaryote genomes. However, our laboratories and others have determined that this paradigm does not necessarily apply to the yellow fever mosquito Aedes aegypti. We report the isolation and identification of microsatellite sequences from multiple genomic libraries for A. aegypti. We identified 6 single-copy simple microsatellites from 3 plasmid libraries enriched for (GA)(n), (AAT)(n), and (TAGA)(n) motifs from A. aegypti. In addition, we identified 5 single-copy microsatellites from an A. aegypti cosmid library. Genetic map positions were determined for 8 microsatellite loci. These markers greatly increase the number of microsatellite markers available for A. aegypti and provide additional tools for studying genetic variability of mosquito populations. Additionally, most A. aegypti microsatellites are closely associated with repetitive elements that likely accounts for the limited success in developing an extensive panel of microsatellite marker loci.