Paucity of Genetic Variation at an MHC Class I Gene in Massachusetts Populations of the Diamond-backed Terrapin (<i>Malaclemys terrapin</i>): A Cause for Concern?

McCafferty, S. Shawn; Shorette, Amanda; Simundza, Julia; Brennessel, Barbara A.

doi:10.1670/11-069

Cited by 2 publications

(2 citation statements)

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“…However, this polymorphism is potentially overestimated, as the alleles we recovered come from multiple unidentified loci. By comparison, studies of Testudines that were able to assign MHC class I alleles to loci found that across 18 populations of Gopher tortoise ( Gopherus polyphemus ) at MHC class I exon 3, there were 13% segregating sites and nucleotide diversity was 0.03 [53]; furthermore, in a population of Diamondback terrapins ( Malaclemys terrapin ), the MHC class I locus was fixed for a single allele [50]. By contrast, our conservative criteria for retaining alleles means we are probably underestimating total alleles, and additional sea turtle MHC studies will almost certainly reveal further MHC class I α diversity.…”

Section: Discussionmentioning

confidence: 99%

“…To date, MHC studies in reptiles have mainly characterized gene diversity and evolutionary history, finding evidence of shared alleles between closely related species, high levels of polymorphism and evidence of positive selection in antigen-binding sites [47–49]. Even within reptiles, few immunogenetic studies examine turtles [50,51], and only one study has investigated MHC in sea turtles, describing two allele lineages recovered in a single loggerhead sea turtle ( Caretta caretta ) nesting population [52]. Here, we advance knowledge of MHC genetic variation and adaptive evolution in sea turtles by sampling juvenile Ca.…”

Section: Introductionmentioning

confidence: 99%

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Adaptive evolution of major histocompatibility complex class I immune genes and disease associations in coastal juvenile sea turtles

2022

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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 the α 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 of Ch. 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 in Ch. 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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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Adaptive evolution of major histocompatibility complex class I immune genes and disease associations in coastal juvenile sea turtles

2022

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Neutral Genetic Processes Influence MHC Evolution in Threatened Gopher Tortoises (Gopherus polyphemus)

Elbers

Clostio

Taylor³

2017

Journal of Heredity

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Levels of adaptive genetic variation influence how species deal with environmental and ecological change, but these levels are frequently inferred using neutral genetic markers. Major histocompatibility complex (MHC) genes play a key role in the adaptive branch of the immune system and have been used extensively to estimate levels of adaptive genetic variation. Parts of the peptide binding region, sites where MHC molecules directly interact with pathogen and self-proteins, were sequenced from a MHC class I (95/441 tortoises) and class II (245/441 tortoises) gene in threatened and nonthreatened populations of gopher tortoises (Gopherus polyphemus), and adaptive genetic variation at MHC genes was compared to neutral genetic variation derived from 10 microsatellite loci (441 tortoises). Genetic diversity at the MHC class II locus and microsatellites was greater in populations in the nonthreatened portion of the gopher tortoise's range (MHC class II difference in mean A = 8.11, AR = 0.79, HO = 0.51, and HE = 0.16; microsatellite difference in mean A = 1.05 and AR = 0.47). Only MHC class II sequences showed evidence of positive selection (dN/dS > 1, Z = 1.81, P = 0.04). Historical gene flow as estimated with Migrate-N was greater than recent migration estimated with BayesAss, suggesting that populations were better connected in the past when habitat was less fragmented. MHC genetic differentiation was correlated with microsatellite differentiation (Mantel r = 0.431, P = 0.001) suggesting neutral genetic processes are influencing MHC evolution, and advantageous MHC alleles could be lost due to genetic drift.

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Paucity of Genetic Variation at an MHC Class I Gene in Massachusetts Populations of the Diamond-backed Terrapin (Malaclemys terrapin): A Cause for Concern?

Cited by 2 publications

References 36 publications

Adaptive evolution of major histocompatibility complex class I immune genes and disease associations in coastal juvenile sea turtles

Adaptive evolution of major histocompatibility complex class I immune genes and disease associations in coastal juvenile sea turtles

Neutral Genetic Processes Influence MHC Evolution in Threatened Gopher Tortoises (Gopherus polyphemus)

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