Theory predicts that threatened species living in small populations will experience high levels of inbreeding that will increase their genetic load, but recent work suggests that the impact of load may be minimized by purging resulting from long-term population bottlenecks. Empirical studies that examine this idea using genome-wide estimates of inbreeding and genetic load in threatened species are limited. Here we use individual genome resequencing data to compare levels of inbreeding, levels of genetic load (estimated as mutation load) and population history in threatened Eastern massasauga rattlesnakes (Sistrurus catenatus), which exist in small isolated populations, and closely related yet outbred Western massasauga rattlesnakes (Sistrurus tergeminus). In terms of inbreeding, S. catenatus genomes had a greater number of runs of homozygosity of varying sizes, indicating sustained inbreeding through repeated bottlenecks when compared to S. tergeminus. At the species level, outbred S. tergeminus had higher genome-wide levels of mutation load in the form of greater numbers of derived deleterious mutations compared to S. catenatus, presumably due to long-term purging of deleterious mutations in S. catenatus. In contrast, mutations that escaped species-level drift effects within S. catenatus populations were in general more frequent and more often found in homozygous genotypes than in S. tergeminus, suggesting a reduced efficiency of purifying selection in smaller S. catenatus populations for most mutations. Our results support an emerging idea that the historical demography of a threatened species has a significant impact on the type of genetic load present, which impacts implementation of conservation actions such as genetic rescue.

中文翻译：

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受威胁响尾蛇近交和突变负荷的基因组特征

理论预测，生活在小种群中的受威胁物种将经历高水平的近亲繁殖，这将增加它们的遗传负荷，但最近的工作表明，通过长期种群瓶颈导致的清除，可以最大限度地减少负荷的影响。使用受威胁物种近亲繁殖和遗传负荷的全基因组估计来检验这一想法的实证研究是有限的。在这里，我们使用个体基因组重测序数据来比较受威胁的东部马萨加响尾蛇 ( Sistrurus catenatus )的近交水平、遗传负荷水平（估计为突变负荷）和种群历史响尾蛇 ( Sistrurus tergeminus )。在近亲繁殖方面，年代。 catenatus基因组具有更多不同大小的纯合子运行，表明与S相比，通过重复瓶颈持续近交。 三叉戟。在物种水平上，远交S。 与S相比， tergeminus具有更高数量的衍生有害突变形式的全基因组突变负荷水平。 catenatus，可能是由于长期清除S中的有害突变所致。 链状。相比之下，在S中逃脱了物种水平漂移效应的突变。 链状一般而言，纯合基因型中的种群比S中更常见且更常见。 tergeminus，表明在较小的S中纯化选择的效率降低。 大多数突变的链状种群。我们的研究结果支持一个新兴的观点，即受威胁物种的历史人口统计学对存在的遗传负荷类型有重大影响，这会影响遗传拯救等保护行动的实施。