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

Table 1 Number of sites in candidate genes showing the strongest signal of selection in polar bears

Gene	Associated phenotype	Coding length (bp)	Alternative allele in brown bear		Ancestral allele in brown bear
Gene	Associated phenotype	Coding length (bp)	Standing variation	de novo	Standing variation	de novo
ABCC6*	Cardiovascular	4551	12	2	3	2
AIM1*	Pigmentation	5484	23	2	5	2
APOB*	Cardiovascular, metabolism, pigmentation	13,305	49	4	12	4
COL5A3*	Adipose tissue, metabolism	5256	16	4	2	1
CUL7	Adipose tissue, cardiovascular, metabolism	4308	13	0	2	0
FCGBP	NA	8424	10	0	0	0
LAMC3	NA	3957	18	0	2	0
LYST*	Metabolism, pigmentation	11,403	32	7	9	6
POLR1A*	Adipose tissue	5172	16	1	2	1
TTN*	Cardiovascular	102,861	117	20	16	12
XIRP1	Cardiovascular	5541	10	0	0	0

Putative Arctic-associated phenotypes are included for each gene; NA refers to genes in which no associated phenotype appears to be explicitly related to adaptations to the Arctic. Phenotype information was obtained from GeneCards (genecards.org). Sites fixed in polar bears are either biallelic (segregate with two alleles), fixed for an alternative allele, or fixed for the ancestral allele (also found in giant panda), in brown bears. A schematic showing the distribution of alleles (coloured dots) in the polar bear (light blue circle) and brown bear (light brown circle) gene pools has been included to ease interpretation. Blue dots represent the allele fixed in polar bears; brown dots are the alternative allele (with unknown ancestral state) in brown bears; white dots represent the ancestral allele (also found in giant panda). Asterisk indicates the seven genes that have sites putatively indicating de novo mutations: they are fixed in polar bears for the derived allele, and fixed in brown bears for the ancestral allele.

ISSN: 1471-2164