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Genetic population structure constrains local adaptation in sticklebacks.

Petri Kemppainen1, Zitong Li1,2, Pasi Rastas1,3

  • 1Ecological Genetics Research Unit, Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.

Molecular Ecology
|January 19, 2021
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Summary

Repeated adaptation in stickleback fish shows varied genetic paths. Pelvic reduction evolved through different genetic regions, influenced by population structure and limited variation.

Keywords:
Pungitius pungitiusPitx1convergent evolutionepistasislocal adaptationpelvic reduction

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Area of Science:

  • Evolutionary biology
  • Genetics
  • Ecology

Background:

  • Independent evolution of similar traits from standing genetic variation is common.
  • Limited genetic variation can restrict or alter evolutionary trajectories for local adaptation.
  • Nine-spined sticklebacks exhibit repeated pelvic reduction (PR) in different populations.

Purpose of the Study:

  • To identify genomic regions underlying repeated pelvic reduction in nine-spined sticklebacks.
  • To investigate the role of genetic variation and population structure in shaping adaptation.
  • To compare the genetic architecture of PR across different stickleback populations.

Main Methods:

  • Quantitative trait locus (QTL) mapping was used in three crosses of nine-spined sticklebacks.
  • Genomic screening for deletions in the Pitx1 regulatory element across 27 populations.
  • Analysis of population structuring and genetic isolation by distance.

Main Results:

  • Pelvic reduction mapped to linkage group 7 (LG7) with the Pitx1 gene in one cross.
  • Two other crosses showed polygenic control of PR with 10 novel QTL, mostly unique to each cross.
  • Pitx1 regulatory element deletions were found only in the LG7-PR population, despite evidence of large-effect QTL elsewhere.

Conclusions:

  • The genetic architecture of pelvic reduction varies significantly across nine-spined stickleback populations.
  • Heterogeneity in standing genetic variation, driven by strong population structuring, likely explains the diverse evolutionary pathways.
  • Nine-spined sticklebacks display more complex population structuring than three-spined sticklebacks, impacting adaptive evolution.