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Small populations with limited range are often threatened by inbreeding and reduced genetic diversity, which can reduce fitness and exacerbate population decline. One of the most extreme natural examples is the Devils Hole pupfish ( Cyprinodon diabolis ), an iconic and critically endangered species with the smallest known range of any vertebrate. This species has experienced severe declines in population size over the last 30 years and suffered major bottlenecks in 2007 and 2013, when the population shrunk to 38 and 35 individuals, respectively. Here, we analysed 30 resequenced genomes of desert pupfishes from Death Valley, Ash Meadows and surrounding areas to examine the genomic consequences of small population size. We found extremely high levels of inbreeding ( F ROH = 0.34–0.81) and an increased amount of potentially deleterious genetic variation in the Devils Hole pupfish as compared to other species, including unique, fixed loss-of-function alleles and deletions in genes associated with sperm motility and hypoxia. Additionally, we successfully resequenced a formalin-fixed museum specimen from 1980 and found that the population was already highly inbred prior to recent known bottlenecks. We thus document severe inbreeding and increased mutation load in the Devils Hole pupfish and identify candidate deleterious variants to inform management of this conservation icon.
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Genomic signatures of inbreeding and mutation load in a threatened rattlesnake
Abstract 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. catenatusgenomes had a greater number of runs of homozygosity of varying sizes, indicating sustained inbreeding through repeated bottlenecks when compared toS. tergeminus. At the species level, outbredS. tergeminushad higher genome‐wide levels of mutation load in the form of greater numbers of derived deleterious mutations compared toS. catenatus, presumably due to long‐term purging of deleterious mutations inS. catenatus. In contrast, mutations that escaped species‐level drift effects withinS. catenatuspopulations were in general more frequent and more often found in homozygous genotypes than inS. tergeminus, suggesting a reduced efficiency of purifying selection in smallerS. catenatuspopulations 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.
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- Award ID(s):
- 1638872
- PAR ID:
- 10360202
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Ecology
- Volume:
- 30
- Issue:
- 21
- ISSN:
- 0962-1083
- Page Range / eLocation ID:
- p. 5454-5469
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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