Abstract
Xenopus laevis (the African clawed frog), which originated through hybridisation and whole genome duplication, has been used as a model for genetics and development for many years, but surprisingly little is known about immune gene variation in natural populations. The purpose of this study was to use an isolated population of X. laevis that was introduced to Wales, UK in the past 50 years to investigate how variation at the MHC compares to that at other loci, following a severe population bottleneck. Among 18 individuals, we found nine alleles based on exon 2 sequences of the Class IIb region (which includes the peptide binding region). Individuals carried from one to three of the loci identified from previous laboratory studies. Genetic variation was an order of magnitude higher at the MHC compared with three single-copy nuclear genes, but all loci showed high levels of heterozygosity and nucleotide diversity and there was not an excess of homozygosity or decrease in diversity over time that would suggest extensive inbreeding in the introduced population. Tajima’s D was positive for all loci, which is consistent with a bottleneck. Moreover, comparison with published sequences identified the source of the introduced population as the Western Cape region of South Africa, where most commercial suppliers have obtained their stocks. These factors suggest that despite founding by potentially already inbred individuals, the alien population in Wales has maintained substantial genetic variation at both adaptively important and neutral genes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00251-015-0860-3) contains supplementary material, which is available to authorized users.
Highlights
A major concern for conservation is how changing climates and human-mediated habitat alterations affect genetic diversity in increasingly fragmented and isolated populations
We addressed four specific questions: (1) Is there evidence that the Class IIb region of the Major Histocompatibility Complex (MHC) is under diversifying selection? (2) Is there evidence for copy number variation at the MHC? (3) How much diversity and heterozygosity are maintained at the MHC compared to single-copy nuclear genes? (4) What was the likely source of the introduced population?
A total of 14 MHC Class IIb haplotypes were identified among published sequences from laboratory colonies, two of which were shared with the Welsh population
Summary
A major concern for conservation is how changing climates and human-mediated habitat alterations affect genetic diversity in increasingly fragmented and isolated populations. The African clawed frog, is native to subSaharan Africa but has been introduced to multiple locations worldwide. This species was used for human pregnancy tests until the 1970s, as well as a model for developmental biology and genetics (Gurdon 1996). Alien X. laevis populations are established in many parts of the world, attributed to release of individuals originating from the southwest region of the Western Cape Province of South Africa (Lillo et al 2013; Lillo et al 2011; Measey et al 2012; Tinsley and Kobel 1996), which has a Mediterranean climate.
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