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Parallelism and historical contingency during rapid ecotype divergence in an isopod
F Eroukhmanoff1, A Hargeby, N N Arnberg
1Section for Animal Ecology, Lund University, Lund, Sweden. fabrice.eroukhmanoff@zooekol.lu.se
Journal of Evolutionary Biology
|April 5, 2011
Summary
Selection strongly drives rapid adaptive divergence in freshwater isopods, with historical factors playing a minor role. This study reveals how new environments trigger significant phenotypic changes in Asellus aquaticus populations.
Area of Science:
- Evolutionary biology
- Ecology
- Genetics
Background:
- Parallel evolution research often debates the interplay of selection and historical contingency in adaptive divergence.
- Freshwater isopods (Asellus aquaticus) in geographically isolated lakes provide a model for studying rapid adaptation.
- Colonization of novel habitats by source populations presents opportunities to observe adaptive changes.
Purpose of the Study:
- To investigate the relative contributions of selection and historical contingency to rapid phenotypic divergence in Asellus aquaticus.
- To quantify phenotypic variation attributed to habitat, lake-specific history, and their interaction.
- To understand the mechanisms driving rapid adaptation in newly colonized environments.
Main Methods:
- Studied genetically independent lake populations of Asellus aquaticus in southern Sweden.
- Analyzed phenotypic variation (pigmentation, size, sexual behavior) in source and newly colonized habitats.
- Partitioned phenotypic variation using statistical methods to assess contributions from selection, history, and unique diversification.
Main Results:
- Habitat-specific selection explained a significant portion of phenotypic variation (81–94%).
- Historical contingency (lake-specific effects) played a limited role (0.1–6%) in phenotypic divergence.
- Higher phenotypic variation was observed in source populations compared to colonized ones.
- Rapid phenotypic changes in pigmentation, size, and behavior were linked to differing predatory regimes.
Conclusions:
- Divergent selection is a primary driver of rapid phenotypic changes in Asellus aquaticus adapting to new habitats.
- Historical contingency has a minimal influence on the observed adaptive divergence in these populations.
- Phenotype sorting and strong divergent selection are key mechanisms facilitating rapid adaptation during colonization events.
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