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Contemporary evolution of the viral-sensing TLR3 gene in an isolated vertebrate population
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  • Charli Davies,
  • Martin Taylor,
  • Martijn Hammers,
  • Terry Burke,
  • J Komdeur,
  • Hannah Dugdale,
  • David Richardson
Charli Davies
University of East Anglia
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Martin Taylor
University of East Anglia Faculty of Science
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Martijn Hammers
University of Groningen
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Terry Burke
The University of Sheffield
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J Komdeur
Groningen Institute for Evolutionary Life Sciences
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Hannah Dugdale
University of Leeds
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David Richardson
University of East Anglia Faculty of Science
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Abstract

Understanding where and how genetic variation is maintained within populations is important from an evolutionary and conservation perspective. Signatures of past selection suggest that pathogen-mediated balancing selection is a key driver of immunogenetic variation, but studies tracking contemporary evolution are needed to help resolve the evolutionary forces and mechanism at play. Previous work in a bottlenecked population of Seychelles warblers (Acrocephalus sechellensis) show that functional variation has been maintained at the viral-sensing Toll-like receptor 3 (TLR3) gene. Here, we characterise evolution at this TLR3 locus over a 25-year period within the original remnant population of the Seychelles warbler, and in four other derived, contained populations. Results show a significant and consistent temporal decline in the frequency of the TLR3C allele in the original population, and that similar declines in the TLR3C allele frequency occurred in all the derived populations. Individuals (of both sexes) with the TLR3CC genotype had lower survival, and males - but not females - that carry the TLR3C allele had significantly lower lifetime reproductive success than those with only the TLR3A allele. These results indicate that positive selection, caused by an as yet unknown agent, is driving TLR3 evolution in the Seychelles warblers. No evidence of heterozygote advantage was detected. However, whether the positive selection observed is part of a longer-term pattern of balancing selection (through fluctuating selection or rare-allele advantage) cannot be resolved without tracking the TLR3C allele in the populations over an extended period of time.

Peer review status:ACCEPTED

08 Dec 2020Submitted to Molecular Ecology
10 Dec 2020Submission Checks Completed
10 Dec 2020Assigned to Editor
06 Jan 2021Reviewer(s) Assigned
23 Feb 2021Review(s) Completed, Editorial Evaluation Pending
24 Feb 2021Editorial Decision: Revise Minor
24 Mar 2021Review(s) Completed, Editorial Evaluation Pending
24 Mar 20211st Revision Received
26 Mar 2021Editorial Decision: Accept