Salamanders reveal novel trajectories of amphibian MHC evolution

Genes of the Major Histocompatibility Complex (MHC) code for immune proteins that are crucial for pathogen recognition in vertebrates. MHC research in non-model taxa has long been hampered by its genomic complexity that makes the locus-specific genotyping challenging. The recent progress in sequencing and genotyping methodologies allows an extensive phylogenetic coverage in studies of MHC evolution. Here, we analysed the peptide-binding region of MHC class I in 30 species of salamanders from six families representative of Urodela phylogeny. This extensive dataset revealed an extreme diversity of MHC-I in salamanders, both in terms of sequence diversity (ca. 3000 variants) and architecture (2-22 gene copies per species). The signal of positive selection was moderate and consistent between both peptide binding domains, but varied greatly between genera. Positions of positively selected sites mostly coincided with human Peptide Binding Sites, suggesting similar structural properties of MHC...