Local adaptation along an environmental cline in a species with an inversion polymorphism

Area of Science:

• Evolutionary biology
• Population genetics
• Ecological adaptation

Background:

• Polymorphic inversions are common in animals and often correlate with environmental gradients.
• These clines are hypothesized to arise from selection driving local adaptation, but empirical evidence is limited.
• The seaweed fly (Coelopa frigida) exhibits an alpha/beta inversion polymorphism with frequency clines across the North Sea-Baltic Sea gradient, linked to environmental factors.

Purpose of the Study:

• To empirically test the hypothesis of local adaptation in Coelopa frigida populations along an environmental cline.
• To investigate the role of polymorphic inversions in local adaptation across different environmental conditions.

Main Methods:

• A reciprocal transplant experiment was conducted using four populations of Coelopa frigida sampled along the North Sea-Baltic Sea cline.
• Survival rates of transplanted flies were quantified across different native and non-native substrates to assess local adaptation.

Main Results:

• Survival rates varied significantly among treatments, with a notable Location x Substrate interaction.
• Flies from the extreme ends of the cline exhibited higher survival on their native substrates, confirming local adaptation at these points.
• Intermediate populations did not show enhanced survival on native substrates, suggesting gene flow may counteract local selection.

Conclusions:

• Local adaptation is evident in populations of Coelopa frigida at the extremes of the environmental cline, even over short distances.
• The findings support the role of polymorphic inversions in driving direct and significant fitness effects, contributing to local adaptation.
• Gene flow can potentially override selection in intermediate habitats, influencing the maintenance of adaptive variation.