Genetic variation in populations of the earthworm, Lumbricus rubellus, across contaminated mine sites

Anderson, Craig; Cunha, Luis; Sechi, Pierfrancesco; Kille, Peter; Spurgeon, David ORCID: https://orcid.org/0000-0003-3264-8760. 2017 Genetic variation in populations of the earthworm, Lumbricus rubellus, across contaminated mine sites. BMC Genetics, 18, 97. 13, pp. https://doi.org/10.1186/s12863-017-0557-8

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Abstract/Summary

Background: Populations of the earthworm, Lumbricus rubellus, are commonly found across highly contaminated former mine sites and are considered to have under-gone selection for mitigating metal toxicity. Comparison of adapted populations with those found on less contaminated soils can provide insights into ecological processes that demonstrate the long-term effects of soil contamination. Contemporary sequencing methods allow for portrayal of demographic inferences and highlight genetic variation indicative of selection at specific genes. Furthermore, the occurrence of L. rubellus lineages across the UK allows for inferences of mechanisms associated with drivers of speciation and local adaptation. Results: Using RADseq, we were able to define population structure between the two lineages through the use of draft genomes for each, demonstrating an absence of admixture between lineages and that populations over extensive geographic distances form discrete populations. Between the two British lineages, we were able to provide evidence for selection near to genes associated with epigenetic and morphological functions, as well as near a gene encoding a pheromone. Earthworms inhabiting highly contaminated soils bare close genomic resemblance to those from proximal control soils. We were able to define a number of SNPs that largely segregate populations and are indicative of genes that are likely under selection for managing metal toxicity. This includes calcium and phosphate-handling mechanisms linked to lead and arsenic contaminants, respectively, while we also observed evidence for glutathione-related mechanisms, including metallothionein, across multiple populations. Population genomic end points demonstrate no consistent reduction in nucleotide diversity, or increase in inbreeding coefficient, relative to history of exposure. Conclusions: Though we can clearly define lineage membership using genomic markers, as well as population structure between geographic localities, it is difficult to resolve markers that segregate entirely between populations in response to soil metal concentrations. This may represent a highly variable series of traits in response to the heterogenous nature of the soil environment, but ultimately demonstrates the maintenance of lineage-specific genetic variation among local populations. L. rubellus appears to provide an exemplary system for exploring drivers for speciation, with a continuum of lineages coexisting across continental Europe, while distinct lineages exist in isolation throughout the UK.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1186/s12863-017-0557-8
UKCEH and CEH Sections/Science Areas:	Pollution (Science Area 2017-) Unaffiliated
ISSN:	1471-2156
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	earthworms, RADseq, ecotoxicology, population genomics, adaptation, arsenic, lead
NORA Subject Terms:	Ecology and Environment
Date made live:	11 Jan 2018 11:34 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/518928

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