Gene flow relates to evolutionary divergence among populations at the range margin

Area of Science:

• Evolutionary Biology
• Ecology
• Genetics

Background:

• Local adaptation to environmental conditions can increase morphological differentiation in genetically isolated populations.
• Previous observations showed clinal variation in body size in isolated Roesel's bush-cricket (Metrioptera roeselii) populations, but not in continuously distributed ones.
• Gene flow's phenotypic effect on climate-induced selection was previously inferred in this species.

Purpose of the Study:

• To differentiate between genetic and environmental influences on population morphology.
• To investigate the role of gene flow in local adaptation and phenotypic variation.

Main Methods:

• Measured four body traits in wild-caught and lab-reared Roesel's bush-crickets from northern Europe (approx. 60°N).
• Compared individuals from populations with restricted gene flow versus continuous gene flow.
• Utilized latitudinally-matched population pairs to control for climate variables.

Main Results:

• Genetically isolated populations exhibited larger body size (femur, pronotum, genital appendages) compared to continuously connected populations.
• This size difference was consistent in both wild-caught and laboratory-reared individuals.
• Observed size cline variation is attributed to local genetic adaptation, not phenotypic plasticity.

Conclusions:

• Restricted gene flow is critical for allele frequencies involved in climate-induced selection.
• Larger phenotypes are favored in isolated populations adapting to colder northern latitudes.
• Genetic isolation facilitates the evolution of climate-driven morphological adaptations.