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Abstract The black abalone,Haliotis cracherodii, is a large, long‐lived marine mollusc that inhabits rocky intertidal habitats along the coast of California and Mexico. In 1985, populations were impacted by a bacterial disease known as withering syndrome (WS) that wiped out >90% of individuals, leading to the closure of all U.S. black abalone fisheries since 1993. Current conservation strategies include restoring diminished populations by translocating healthy individuals. However, population collapse on this scale may have dramatically lowered genetic diversity and strengthened geographic differentiation, making translocation‐based recovery contentious. Additionally, the current prevalence of WS remains unknown. To address these uncertainties, we sequenced and analysed the genomes of 133 black abalone individuals from across their present range. We observed no spatial genetic structure among black abalone, with the exception of a single chromosomal inversion that increases in frequency with latitude. Outside the inversion, genetic differentiation between sites is minimal and does not scale with either geographic distance or environmental dissimilarity. Genetic diversity appears uniformly high across the range. Demographic inference does indicate a severe population bottleneck beginning just 15 generations in the past, but this decline is short lived, with present‐day size far exceeding the pre‐bottleneck status quo. Finally, we find the bacterial agent of WS is equally present across the sampled range, but only in 10% of individuals. The lack of population genetic structure, uniform diversity and prevalence of WS bacteria indicates that translocation could be a valid and low‐risk means of population restoration for black abalone species' recovery.
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Loss of genetic diversity, recovery and allele surfing in a colonizing parasite, Geomydoecus aurei
Abstract Understanding the genetic consequences of changes in species distributions has wide‐ranging implications for predicting future outcomes of climate change, for protecting threatened or endangered populations and for understanding the history that has led to current genetic patterns within species. Herein, we examine the genetic consequences of range expansion over a 25‐year period in a parasite (Geomydoecus aurei) that is in the process of expanding its geographic range via invasion of a novel host. By sampling the genetics of 1,935G. aureilice taken from 64 host individuals collected over this time period using 12 microsatellite markers, we test hypotheses concerning linear spatial expansion, genetic recovery time and allele surfing. We find evidence of decreasing allelic richness (AR) with increasing distance from the source population, supporting a linear, stepping stone model of spatial expansion that emphasizes the effects of repeated bottleneck events during colonization. We provide evidence of post‐bottleneck genetic recovery, with average AR of infrapopulations increasing about 30% over the 225‐generation span of time observed directly in this study. Our estimates of recovery rate suggest, however, that recovery has plateaued and that this population may not reach genetic diversity levels of the source population without further immigration from the source population. Finally, we employ a grid‐based sampling scheme in the region of ongoing population expansion and provide empirical evidence for the power of allele surfing to impart genetic structure on a population, even under conditions of selective neutrality and in a place that lacks strong barriers to gene flow.
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- Award ID(s):
- 1445708
- PAR ID:
- 10086426
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Ecology
- Volume:
- 28
- Issue:
- 4
- ISSN:
- 0962-1083
- Page Range / eLocation ID:
- p. 703-720
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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