Polymorphism of MHC-I genes annotated in the genomes. Bar heights show polymorphism of each gene expressed relative to the most highly polymorphic gene in the species; MHC-I-like genes are not shown because reliable polymorphism estimates were not available. Polymorphism was estimated based on mapping amplicon variants detected in population samples to genes, as described in the text. Maximum relative expression: the maximum fraction of total MHC-I expression (FPKM) attributable to a sequence across all RNA-seq libraries from postmetamorphic individuals within a species. Species abbreviations: (Lh) L. helveticus, (Lv) L. vulgaris, (Pw) P. waltl, (Tc) T. cristatus.