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Speciation with gene flow in the large white-headed gulls: does selection counterbalance introgression?
L Gay1, G Neubauer, M Zagalska-Neubauer
1CEFE-CNRS, UMR 5175, Montpellier cedex 5, France. L.Gay@exeter.ac.uk
Heredity
|September 25, 2008
Summary
Selection drives species distinctness in large gulls despite gene flow. Phenotypic traits, like plumage and orbital ring color, show divergence exceeding neutral genetic changes, indicating spatially varying and sexual selection pressures.
Area of Science:
- Evolutionary Biology
- Speciation
- Population Genetics
Background:
- Species distinctness is maintained despite gene flow, a phenomenon particularly observed in hybridizing species.
- Understanding the role of selection in maintaining species boundaries is crucial for evolutionary studies.
Purpose of the Study:
- To investigate how natural selection generates and maintains species distinctness in large gull species experiencing secondary contact and ongoing gene flow.
- To compare neutral genetic differentiation with phenotypic differentiation to identify traits under selection.
Main Methods:
- Studied two zones of secondary contact between large gull species in Europe and North America.
- Utilized microsatellite loci (F(ST)) to assess neutral genetic differentiation.
- Compared genetic differentiation with phenotypic differentiation (P(ST)) for traits including size, plumage melanism, and bare-part coloration.
Main Results:
- Interspecific divergence in plumage melanism and orbital ring color between North American gulls exceeded neutral genetic differentiation.
- Melanism of central primaries showed high divergence between European gull species.
- Plumage melanism variation aligned with Gloger's rule, suggesting latitude-driven selection.
- Orbital ring color differentiation likely results from sexual selection.
Conclusions:
- Spatially varying selection and sexual selection contribute to species distinctness in large gulls.
- Species differentiation may be concentrated in specific genomic regions under strong disruptive selection due to phenotypic effects.
- These findings offer insights into the mechanisms maintaining species boundaries in recently diverged, hybridizing species.
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