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Adaptive evolution of major histocompatibility complex class I immune genes and disease associations in coastal juvenile sea turtles
Author(s) -
Katherine R. Martin,
Katherine Mansfield,
Anna E. Savage
Publication year - 2022
Publication title -
royal society open science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 51
ISSN - 2054-5703
DOI - 10.1098/rsos.211190
Subject(s) - biology , major histocompatibility complex , allele , genetics , balancing selection , evolutionary biology , mhc class i , phylogenetics , genetic variation , genetic diversity , gene , population , demography , sociology
Characterizing polymorphism at the major histocompatibility complex (MHC) genes is key to understanding the vertebrate immune response to disease. Despite being globally afflicted by the infectious tumour disease fibropapillomatosis (FP), immunogenetic variation in sea turtles is minimally explored. We sequenced theα 1 peptide-binding region of MHC class I genes (162 bp) from 268 juvenile green (Chelonia mydas ) and 88 loggerhead (Caretta caretta ) sea turtles in Florida, USA. We recovered extensive variation (116 alleles) and trans-species polymorphism. Supertyping analysis uncovered three functional MHC supertypes corresponding to the three well-supported clades in the phylogeny. We found significant evidence of positive selection at seven amino acid sites in the class I exon. Random forest modelling and risk ratio analysis ofCh. mydas alleles uncovered one allele weakly associated with smooth FP tumour texture, which may be associated with disease outcome. Our study represents the first characterization of MHC class I diversity inCh. mydas and the largest sample of sea turtles used to date in any study of adaptive genetic variation, revealing tremendous genetic variation and high adaptive potential to viral pathogen threats. The novel associations we identified between MHC diversity and FP outcomes in sea turtles further highlight the importance of evaluating genetic predictors of disease, including MHC and other functional markers.

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