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Title: Genomic signatures of inbreeding and mutation load in a threatened rattlesnake

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,Scatenatusgenomes had a greater number of runs of homozygosity of varying sizes, indicating sustained inbreeding through repeated bottlenecks when compared toStergeminus. At the species level, outbredStergeminushad higher genome‐wide levels of mutation load in the form of greater numbers of derived deleterious mutations compared toScatenatus, presumably due to long‐term purging of deleterious mutations inScatenatus. In contrast, mutations that escaped species‐level drift effects withinScatenatuspopulations were in general more frequent and more often found in homozygous genotypes than inStergeminus, suggesting a reduced efficiency of purifying selection in smallerScatenatuspopulations for most mutations. Our results support more » 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.

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Award ID(s):
Publication Date:
Journal Name:
Molecular Ecology
Page Range or eLocation-ID:
p. 5454-5469
Sponsoring Org:
National Science Foundation
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