Wolbachia is considered one of the most common and widespread endosymbiotic bacteria. Wolbacha has varied impacts on the biology and evolution of its hosts. It can obscure true phylogenetic relationships and lead to erroneous mitochondrial-based phylogenetic reconstructions, species misidentification and incorrect taxonomical conclusions.
Our study aimed to shed light on the role of Wolbachia endosymbionts in the evolutionary history, biogeographic patterns and phylogenetic relationships of taxa of the genus Colias, a taxonomically challenging group of butterflies. We analyzed five nuclear (CAD, EF-1a, GADPH, RPS5, wingless) and mitochondrial (COI) genes for a large set of samples per species and conducted PCR screening for three Wolbachia genes (16S, wsp, ftsZ) in order to reveal patterns of Wolbachia infection in Colias taxa.
We discovered several cases of deeply diverged mitochondrial lineages (haplotypes) within the species that were characteristic of the species level. We found that these distinct haplotypes are usually shared by morphologically well-differentiated Colias species. Further investigation revealed the strong association of these diverged lineages with Wolbachia infection. We demonstrated that Wolbachia infection is strongly female-biased and haplotype selective: females bearing deviant haplotypes turn out to be totally infected, while males of these haplotypes, as well as males and females bearing common haplotypes, were either uninfected or had a very low rate of infection (less than 5%). We revealed that females carrying haplotypes shared by morphologically well-differentiated Colias species are always totally infected by the same Wolbachia strain. This fact suggests the transfer of Wolbachia across species through occasional hybridization resulting in mitochondrial introgression.
We conclude that Wolbachia endosymbionts play an essential role in the biology, diversification and evolution of Colias butterflies.
Financial support for this study was provided by the Ministry of Science and Higher Education of the Russian Federation (project FZMW-2023-0006).
