Persistent selection on size explains micro- and macroevolutionary alignments in fly wings

Area of Science:

• Evolutionary biology
• Developmental genetics
• Quantitative genetics

Background:

• The rate paradox in Drosophila wing shape evolution involves the alignment of mutational variance (M), standing genetic variance (G), and macroevolutionary divergence (R).
• Existing explanations involving pleiotropy or correlational selection lack strong empirical support, particularly regarding fitness costs beyond flight performance.

Purpose of the Study:

• To resolve the rate paradox in Drosophila wing shape evolution.
• To investigate the role of wing size as a primary selection target.
• To propose a minimal model explaining micro- and macroevolutionary patterns.

Main Methods:

• Reanalysis of published data on Drosophila wing shape variation.
• Empirical assessment of the ratio of standing genetic to mutational variance for different wing traits.
• Development and testing of a single-axis selection model.

Main Results:

• Wing size exhibits the lowest ratio of standing genetic to mutational variance, indicating strong selective depletion and identifying it as the primary selection target.
• A single-axis selection model, where only wing size is directly selected, successfully reproduces the observed M-G-R alignment.
• The model explains slower-than-neutral divergence rates and micro- to macroevolutionary patterns in Drosophila wing shape.

Conclusions:

• Wing size is the primary target of natural selection in Drosophila wing evolution.
• Correlated evolution of other wing traits as byproducts of selection on size explains the rate paradox.
• A simple, single-axis selection model adequately explains complex evolutionary patterns without invoking complex adaptive landscapes.