Data from: Heritability of body size in the polar bears of Western Hudson Bay

Among polar bears (Ursus maritimus), fitness is dependent on body size
through males' abilities to win mates, females' abilities to
provide for their young, and all bears' abilities to survive
increasingly longer fasting periods caused by climate change. In the
Western Hudson Bay subpopulation (near Churchill, Manitoba, Canada), polar
bears have declined in body size and condition, but nothing is known about
the genetic underpinnings of body size variation, which may be subject to
natural selection. Here, we combine a 4449-individual pedigree and an
array of 5433 single-nucleotide polymorphisms (SNPs) to provide the first
quantitative genetics study of polar bears. We used animal models to
estimate heritability (h2) among polar bears handled between 1966 and
2011, obtaining h2 estimates of 0.34-0.48 for strictly skeletal traits and
0.18 for axillary girth (which is also dependent on fatness). We genotyped
859 individuals with the SNP array to test for marker-trait association
and combined p-values over genetic pathways using gene-set analysis.
Variation in all traits appeared to be polygenic, but we detected one
region of moderately large effect size in body length near a putative
noncoding RNA in an unannotated region of the genome. Gene-set analysis
suggested that variation in body length was associated with genes in the
regulatory cascade of cyclin expression, which has previously been
associated with body size in mice. A greater understanding of the genetic
architecture of body size variation will be valuable in understanding the
potential for adaptation in polar bear populations challenged by climate
change.

在北极熊（Ursus maritimus）种群中，个体适合度依赖于体型大小——这体现在雄性争夺配偶的能力、雌性抚育幼崽的能力，以及所有个体应对气候变化导致的禁食期延长的生存能力。在加拿大马尼托巴省丘吉尔镇附近的西哈德逊湾亚种群中，北极熊的体型和身体状况均出现下降，但学界对体型变异的遗传基础尚不清楚，而这类变异可能正处于自然选择的作用之下。本研究结合了包含4449个个体的谱系数据与一套包含5433个单核苷酸多态性（single-nucleotide polymorphisms, SNPs）的基因芯片，开展了首个针对北极熊的数量遗传学研究。我们利用动物模型对1966年至2011年间捕获的北极熊个体进行遗传力（h²）估算，结果显示：纯骨骼性状的遗传力估算值为0.34~0.48，而腋围（同时受脂肪含量影响）的遗传力估算值为0.18。我们使用该SNP芯片对859个个体进行基因分型，以检验标记-性状关联，并通过基因集分析整合了遗传通路相关的P值。所有性状的变异均呈现多基因调控特征，但我们在基因组未注释区域内一处推定非编码RNA附近，检测到了一个对体长具有中等偏高效应量的基因组区域。基因集分析结果显示，体长变异与细胞周期蛋白表达调控级联通路中的基因相关，而该通路此前已被证实与小鼠的体型大小存在关联。深入解析体型变异的遗传结构，将有助于理解受气候变化威胁的北极熊种群的适应性演化潜力。