Recurrent replacement of mtDNA and cryptic hybridization between two sibling bat speciesMyotis myotisandMyotis blythii

Abstract

The two sibling bat speciesMyotis myotisandMyotis blythiioccur in sympatry over wide areas of Southern and Central Europe. Morphological, ecological and previous genetic evidences supported the view that the two species constitute two well-differentiated groups, but recent phylogenetic analyses have shown that the two species shared some mtDNA haplotypes when they occurred in sympatry. In order to see whether some genetic exchange occurred between the two species, we sequenced a highly variable segment of the mitochondrial control region in both species living in sympatry and in allopatry. We also analysed the nuclear diversity of 160 individuals of both species found in two mixed nursery colonies located north and south of the Alps. MtDNA analysis confirmed that EuropeanM. blythiishare multiple, identical or very similar haplotypes withM. myotis. Since allopatric AsianM. blythiipresents mtDNA sequences that are very divergent from those of the two species found in Europe, we postulate that the mitochondrial genome of the EuropeanM. blythiihas been replaced by that ofM. myotis. The analysis of nuclear diversity shows a strikingly different pattern, as both species are well differentiated within mixed nursery colonies (FST=0.18). However, a Bayesian analysis of admixture reveals that the hybrids can be frequently observed, as about 25% of sampledM. blythiishow introgressed genes ofM. myotisorigin. Contrastingly, less than 4% of theM. myotisanalysed were classified as non-parental genotypes, revealing an asymmetry in the pattern of hybridization between the two species. These results show that the two species can interbreed and that the hybridization is still ongoing in the areas of sympatry. The persistence of well-differentiated nuclear gene pools, in spite of an apparent replacement of mitochondrial genome in EuropeanM. blythiiby that ofM. myotis, is best explained by a series of introgression events having occurred repeatedly during the recent colonization of Europe byM. blythiifrom Asia. The sharp contrast obtained from the analysis of mitochondrial and nuclear markers further points to the need to cautiously interpret results based on a single class of genetic markers.