Quantitative Genetic Architecture at Latitudinal Range Boundaries: Reduced Variation but Higher Trait Independence

Area of Science:

• Evolutionary biology
• Ecology
• Population genetics

Background:

• Species distribution limits are often linked to reduced population size and genetic variation.
• Previous research has not fully explored genetic variation in multivariate phenotypes at distribution edges.
• Understanding genetic architecture is crucial for predicting species' adaptive capacity.

Purpose of the Study:

• To investigate if populations at the latitudinal distribution edges of Arabidopsis lyrata exhibit altered quantitative genetic architecture compared to midlatitude populations.
• To assess the evolutionary potential of edge populations under varying environmental conditions (wet and dry).

Main Methods:

• Studied nine Arabidopsis lyrata populations across North America's latitudinal range.
• Assessed 10 ecologically relevant traits (size, development, water balance) under wet and dry conditions.
• Estimated genetic variance-covariance (G-) matrices to analyze quantitative genetic architecture.

Main Results:

• Populations at southern and northern distribution edges showed reduced genetic variation but more spherical G-matrices.
• G-matrix orientation did not correlate with latitude.
• Predicted short-term response to selection was comparable in edge and central populations.

Conclusions:

• Reduced genetic variation at distribution margins does not necessarily limit evolutionary response.
• Genetic drift may erode variation and reduce correlational selection effectiveness at distribution edges.
• Multivariate selection and genetic drift are critical factors influencing species distribution limits, potentially leading to greater-than-expected evolutionary responses at margins.