Selection on MHC class II supertypes in the New Zealand endemic Hochstetter's frog.

Mette Lillie,Phillip J Bishop,Katherine Belov,Jolene T Sutton,Robyn Howitt,Dianne Gleeson,Catherine E Grueber

doi:10.1186/s12862-015-0342-0

Abstract

BackgroundThe New Zealand native frogs, family Leiopelmatidae, are among the most archaic in the world. Leiopelma hochstetteri (Hochstetter’s frog) is a small, semi-aquatic frog with numerous, fragmented populations scattered across New Zealand’s North Island. We characterized a major histocompatibility complex (MHC) class II B gene (DAB) in L. hochstetteri from a spleen transcriptome, and then compared its diversity to neutral microsatellite markers to assess the adaptive genetic diversity of five populations (“evolutionarily significant units”, ESUs).ResultsL. hochstetteri possessed very high MHC diversity, with 74 DAB alleles characterized. Extremely high differentiation was observed at the DAB locus, with only two alleles shared between populations, a pattern that was not reflected in the microsatellites. Clustering analysis on putative peptide binding residues of the DAB alleles indicated four functional supertypes, all of which were represented in 4 of 5 populations, albeit at different frequencies. Otawa was an exception to these observations, with only two DAB alleles present.ConclusionsThis study of MHC diversity highlights extreme population differentiation at this functional locus. Supertype differentiation was high among populations, suggesting spatial and/or temporal variation in selection pressures. Low DAB diversity in Otawa may limit this population’s adaptive potential to future pathogenic challenges.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0342-0) contains supplementary material, which is available to authorized users.

Highlights

The New Zealand native frogs, family Leiopelmatidae, are among the most archaic in the world
Our results showed high major histocompatibility complex (MHC) polymorphism with extremely high differentiation between studied Evolutionarily Significant Unit (ESU), a pattern that was not reflected in the microsatellites
We observed eight occurrences where microsatellite allele frequencies deviated from Hardy-Weinberg Equilibrium (HWE) but these were not statistically significant after Holm-Bonferroni correction for multiple comparisons (Additional file 2: Table S1)

Summary

Introduction

The New Zealand native frogs, family Leiopelmatidae, are among the most archaic in the world. Leiopelma hochstetteri (Hochstetter’s frog) is a small, semi-aquatic frog with numerous, fragmented populations scattered across New Zealand’s North Island. The frog family Leiopelmatidae contains four species of the genus Leiopelma [1]. These frogs are among the most archaic in the world [2] and only found in New Zealand. Leiopelma hochstetteri is a small, semi-aquatic species [3]. It is the most widespread and common species within this genus, but populations are fragmented and scattered over an extensive area of the North Island (Figure 1) [4,5]. The introduction of mammalian predators and habitat modifications following human settlement of New Zealand in the 17th century have been major contributors to the modern-day fragmentation and population declines [6]

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