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

Abstract

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 cospeciation is rare and restricted to few recently diverged species. While in general each species apparently harbours a single Wolbachia strain, Altica 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 and 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 nuclear phylogeny may best be explained by interspecific hybridization that led to introgression of mtDNA coupled with a different Wolbachia strain. Selective sweeps apparently drove the introgressed haplotypes to widespread distribution. As for effects of Wolbachia on reproduction, infection with wLytA1 appears to be correlated with a substantial sex ratio distortion, which was most prominent in A. lythri.

Preliminary evidence of the horizontal transmission of Wolbachia between Crioceris leaf beetles (Coleoptera: Chrysomelidae) and their Asparagus host plants

“…Regardless of these two hypotheses about the spread of Wolbachia in Crioceris, it is not easy to explain why some species are infected, whereas others are not. Similar patterns in the presence-absence of Wolbachia in a group of closely related species occur in other leaf beetles, for example, in species of the genus Altica (Jäckel et al, 2013), Oreina (Montagna et al, 2014), Chelymorpha (Keller et al, 2004), Diabrotica (Roehrdanz & Sears Wichmann, 2013;Roehrdanz & Wichmann, 2014) and Callosobruchus (Kondo et al, 1999). However, none of these studies investigated infection with respect to susceptibility or resistance of the hosts.…”

Local coexistence and genetic isolation of three pollinator species on the same fig tree species

“…While molecular taxonomy may reveal cryptic lineages, the reliability of mtDNA for species delimitation has been criticised for various reasons (Rubinoff et al, 2006), including the persistence of genetic structure after resumption of gene flow due to lack of mtDNA recombination (for example, Lausen et al, 2008;Ruskey and Taylor, 2016), hybrid introgression (for example, Chen et al, 2009;MachadoSchiaffino et al, 2010) and selective sweeps caused by maternally inherited endosymbionts that can drive divergence and homogenisation across species (for example, Graham and Wilson, 2012;Xiao et al, 2012;Jäckel et al, 2013). These issues raise significant concerns when mtDNA is used in isolation, but they are likely to be resolved with further study of nuclear loci.…”

Do relaxed selection and habitat temperature facilitate biased mitogenomic introgression in a narrowly endemic fish?

“…2010; Jackel et al. 2013). Yet, the lack of any cichlids collected in Cuatro Ciénegas with even close to equal proportions of H. minckleyi and H. cyanoguttatus SNP assignment probabilities suggests that any cichlids we examined were unlikely to be F1 hybrids.…”

“…2010; Jackel et al. 2013). Additionally, there could be selection on the metabolically critical mitochondrial locus due to abiotic factors such as temperature that vary extensively within the many isolated springs of Cuatro Ciénegas (Minckley 1969; Doiron et al.…”