A Quantitative Survey of Cogradient and Countergradient Variation in Nature

Area of Science:

• Evolutionary biology
• Quantitative genetics
• Ecology

Background:

• Gradient variation describes how environmental and genotypic effects covary across locations, influencing local adaptation and eco-evolutionary dynamics.
• Gene-by-environment interactions (G × E) involve nonadditive genetic and environmental influences on phenotypes.
• Debates persist on whether reaction norm patterns accurately reflect spatial covariance in environmental and genotypic effects (CovGE) and its prevalence relative to G × E.

Purpose of the Study:

• To quantitatively assess the prevalence and patterns of CovGE and G × E across diverse biological systems.
• To determine if qualitative reaction norm assessments reliably indicate CovGE.
• To investigate whether CovGE shows distinct patterns across taxonomic groups, environmental gradients, or trait types.

Main Methods:

• Conducted a quantitative survey of 556 phenotypes.
• Measured CovGE and G × E across various phenotypes, taxa, and environmental gradients.
• Compared qualitative reaction norm assessments with quantitative CovGE measurements.

Main Results:

• Qualitative assessment of reaction norms proved unreliable for identifying CovGE.
• CovGE occurred with a frequency comparable to G × E.
• No consistent patterns of CovGE were observed across environmental, taxonomic, or trait-based groups.

Conclusions:

• The findings challenge prevailing assumptions about the drivers and patterns of gradient variation.
• CovGE appears to be a general evolutionary phenomenon, not restricted to specific conditions.
• Broader application of quantitative methods for CovGE is recommended for a comprehensive understanding of its role in nature.