Evidence for selective sweeps by Wolbachia infections: phylogeny of Altica leaf beetles and their reproductive parasites

Infections with maternally inherited Wolbachia bacteria may have dramatic influences on reproductive traits and speciation patterns of their hosts. We here show that in the beetle genus Altica, infection has influenced phylogenetic patterns of the host’s mtDNA and different strains led to repeated selective sweeps. By comparing a COI/II based phylogeny of the hosts with a phylogeny of the bacteria based on ftsZ, we show that co-speciation is rare and restricted to few recently diverged species. While in general each species apparently harbours a single Wolbachia strain, A. lythri presents a strikingly different pattern: in the polyphyletic species three highly divergent mtDNA haplotypes (2.1 – 4.6% p-distance) are coupled with three different Wolbachia strains (wLytA1, wLytA2, wLytB). These haplotypes and Wolbachia strains are widely distributed and mostly found in sympatry. A phylogeny based on microsatellite data supports the monophyly of A. lythri. The discrepancy between mtDNA and n...