Signatures of historical selection on MHC reveal different selection patterns in the moor frog (Rana arvalis)

Abstract

MHC genes are key components in disease resistance and an excellent system for studying selection acting on genetic variation in natural populations. Current patterns of variation in MHC genes are likely to be influenced by past and ongoing selection as well as demographic fluctuations in population size such as those imposed by post-glacial recolonization processes. Here, we investigated signatures of historical selection and demography on an MHC class II gene in 12 moor frog populations along a 1700-km latitudinal gradient. Sequences were obtained from 207 individuals and consecutively assigned into two different clusters (northern and southern clusters, respectively) in concordance with a previously described dual post-glacial colonization route. Selection analyses comparing the relative rates of non-synonymous to synonymous substitutions (dN/dS) suggested evidence of different selection patterns in the northern and the southern clusters, with divergent selection prevailing in the south but uniform positive selection predominating in the north. Also, models of codon evolution revealed considerable differences in the strength of selection: The southern cluster appeared to be under strong selection while the northern cluster showed moderate signs of selection. Our results indicate that the MHC alleles in the north diverged from southern MHC alleles as a result of differential selection patterns.Electronic supplementary materialThe online version of this article (10.1007/s00251-017-1051-1) contains supplementary material, which is available to authorized users.

Latitudinal divergence in a widespread amphibian: Contrasting patterns of neutral and adaptive genomic variation

“…Finding genes and proteins involved in immune defence highlights the role of selection by disease and parasites as a major evolutionary factor. Our results tentatively suggest that their influence varies along latitudinal gradients and agree with earlier studies on major histocompatibility complex (MHC) variation in R. arvalis (Cortázar‐Chinarro et al, , ). While little is known about amphibian parasites along latitudinal gradients, parasite species richness in general decreases with increasing latitude (Schemske, Mittelbach, Cornell, Sobel, & Roy, ).…”

Comparative Analysis of SLA-1, SLA-2, and DQB1 Genetic Diversity in Locally-Adapted Kenyan Pigs and Their Wild Relatives, Warthogs

“…We compared the PBR-encoding sequences across the three suid breeds for each locus studied to infer orthologous relationships despite inherent phenotypic differences. We observed high SLA sequence polymorphisms within the PBR, as reported in previous studies [ 8 , 18 , 72 , 73 ]. PBR-encoding sequences of the east African warthogs grouped with locally-adapted pigs indicated high similarity between the SLA motifs.…”

Hybridization with mountain hares increases the functional allelic repertoire in brown hares

“…Our prime candidates to detect potentially meaningful adaptive introgression in hares included the UCP1 gene, which could have a potential role in adaptation for a colder climate 46 , 47 , MHC class II loci DQA and DQB , which confer general pathogen resistance and are known to be under strong balancing selection favoring genetic diversity in various chordates (e.g. 39 , 48 – 50 ) and TLR2 , required for innate immunity 51 . SDHa was expected to perform as a neutral marker, showing reduced evidence of adaptive introgression and mitochondrial DNA was included to track the maternal lineage hybridization of the individuals.…”