Clendenin Heather R, Pollard Matthew D, Puckett Emily E
Department of Biological Sciences University of Memphis Memphis Tennessee USA.
Evol Appl. 2025 Jul 16;18(7):e70133. doi: 10.1111/eva.70133. eCollection 2025 Jul.
Historic and contemporary demography affect deleterious variation and inbreeding depression, meaning that measuring genetic diversity alone does not capture the nuances of genetic erosion. Contrasting genomic signatures generated by long-term evolutionary processes to those generated by contemporary changes may help differentiate between populations more or less likely to persist with low diversity or high genetic load. To better understand these interactions, we examined signatures of inbreeding and genetic load across three species of bears: American black (), brown (), and polar (). We sampled across each species' geographic range to represent intraspecific variation in demographic history and ecology. We found that ROH burden often varied more among populations within lineages of species than between species. Admixed populations generally had higher heterozygosity and lower ROH burden; this pattern reversed in small, isolated populations. Greater diversity, including harmful variation, was found in larger, admixed populations-especially those with higher historical effective population sizes (N). However, this did not necessarily correspond to more realized genetic load. While polar bears had low N and low realized load, brown and American black bears exhibited less realized load as N increased and greater realized load in populations with recent bottlenecks and/or indications of recent consanguineous matings. This vantage offers insight into genetic health and threats of genetic erosion within populations and species, which can meaningfully contribute to assessments of threat status. In American black bears, the composite of these metrics revealed a trend in the Louisiana population that may be diagnostic for management intervention based on contemporary demographic changes. In brown bears, the Apennine bear consistently fell outside of the range of values in other populations, reinforcing previous descriptions of isolation, inbreeding, and purging in this population. In polar bears, there were no regional trends that warranted concern with respect to genetic erosion.
历史和当代人口统计学影响有害变异和近亲繁殖衰退，这意味着仅测量遗传多样性并不能捕捉遗传侵蚀的细微差别。将长期进化过程产生的基因组特征与当代变化产生的特征进行对比，可能有助于区分哪些种群更有可能或更不可能在低多样性或高遗传负荷的情况下持续存在。为了更好地理解这些相互作用，我们研究了三种熊的近亲繁殖和遗传负荷特征：美洲黑熊（ ）、棕熊（ ）和北极熊（ ）。我们在每个物种的地理范围内进行采样，以代表种群在人口统计学历史和生态方面的种内变异。我们发现，ROH负担在物种谱系内的种群之间通常比在物种之间变化更大。混合种群通常具有更高的杂合度和更低的ROH负担；在小的、孤立的种群中，这种模式则相反。在较大的、混合的种群中发现了更大的多样性，包括有害变异，尤其是那些具有较高历史有效种群大小（N）的种群。然而，这并不一定对应着更高的实际遗传负荷。虽然北极熊的N值较低且实际负荷也较低，但棕熊和美洲黑熊随着N值的增加表现出较低的实际负荷，而在近期经历瓶颈和/或有近期近亲交配迹象的种群中则表现出较高的实际负荷。这种视角有助于深入了解种群和物种内部的遗传健康状况以及遗传侵蚀的威胁，这可以为威胁状况评估做出有意义的贡献。在美洲黑熊中，这些指标的综合结果显示路易斯安那州种群存在一种趋势，这可能基于当代人口统计学变化为管理干预提供诊断依据。在棕熊中，亚平宁棕熊一直处于其他种群的值范围之外，这强化了之前对该种群隔离、近亲繁殖和净化的描述。在北极熊中，没有区域趋势表明存在值得关注的遗传侵蚀问题。
