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. 2020 Aug 6;21(1):543.
doi: 10.1186/s12864-020-06940-0.

Analyses of key genes involved in Arctic adaptation in polar bears suggest selection on both standing variation and de novo mutations played an important role

Jose Alfredo Samaniego Castruita  1 , Michael V Westbury  2 , Eline D Lorenzen  3
Affiliations

Analyses of key genes involved in Arctic adaptation in polar bears suggest selection on both standing variation and de novo mutations played an important role

Jose Alfredo Samaniego Castruita et al. BMC Genomics. .

Abstract

Background: Polar bears are uniquely adapted to an Arctic existence. Since their relatively recent divergence from their closest living relative, brown bears, less than 500,000 years ago, the species has evolved an array of novel traits suited to its Arctic lifestyle. Previous studies sought to uncover the genomic underpinnings of these unique characteristics, and disclosed the genes showing the strongest signal of positive selection in the polar bear lineage. Here, we survey a comprehensive dataset of 109 polar bear and 33 brown bear genomes to investigate the genomic variants within these top genes present in each species. Specifically, we investigate whether fixed homozygous variants in polar bears derived from selection on standing variation in the ancestral gene pool or on de novo mutation in the polar bear lineage.

Results: We find that a large number of sites fixed in polar bears are biallelic in brown bears, suggesting selection on standing variation. Moreover, we uncover sites in which polar bears are fixed for a derived allele while brown bears are fixed for the ancestral allele, which we suggest may be a signal of de novo mutation in the polar bear lineage.

Conclusions: Our findings suggest that, among other mechanisms, natural selection acting on changes in genes derived from a combination of variation already in the ancestral gene pool, and from de novo missense mutations in the polar bear lineage, may have enabled the rapid adaptation of polar bears to their new Arctic environment.

Keywords: Adaptation; Arctic; Genomics; Polar bear; Selection.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Relative proportions of genotype frequencies at biallelic sites across nine genes with fixed variants in the polar bear lineage. Only sites which are fixed in polar bears for the derived allele and are biallelic or fixed in brown bears for the ancestral allele are shown. Sites fixed for the derived allele in the polar bear lineage and fixed for the ancestral allele in the brown bear lineage (putative de novo mutations) are indicated with an asterisk. Gene length and the position of each site along the gene is indicated, as are the number of individuals (n = X) with more than 4x coverage at said site
See this image and copyright information in PMC

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