Balanced genetic diversity improves population fitness

Area of Science:

• Evolutionary biology
• Population genetics
• Behavioral ecology

Background:

• Genetic diversity is theorized to enhance population fitness, but empirical evidence and mechanistic understanding remain limited.
• The ecological impact of genetic variation and its underlying mechanisms are poorly understood, leading to controversy regarding its benefits.

Purpose of the Study:

• To investigate the ecological effect of a natural single-gene behavioral polymorphism on population fitness in *Drosophila melanogaster*.
• To determine if genetic polymorphism positively influences population fitness and to elucidate the underlying mechanisms, such as complementarity or selection effects.

Main Methods:

• Developed a numerical model to predict population fitness based on genetic polymorphism under balancing selection.
• Empirically tested the model's predictions using the *Rover* and *sitter* behavioral polymorphism in *Drosophila melanogaster* populations.
• Assessed the contribution of complementarity and selection effects to the observed fitness benefits of genetic diversity.

Main Results:

• The numerical model predicted higher fitness for polymorphic populations compared to monomorphic ones, contingent on balancing selection.
• Empirical tests confirmed the model's predictions, demonstrating a positive effect of the *Rover*/*sitter* polymorphism on *Drosophila melanogaster* population fitness.
• The study identified a complementarity effect, rather than a selection effect, as the primary driver of the positive diversity effect on fitness.

Conclusions:

• Provides direct empirical evidence for a positive ecological effect of genetic diversity on population fitness.
• The fitness benefits of genetic polymorphism are condition-dependent and can be attributed to mechanisms like complementarity.
• Findings underscore the importance of genetic variation for population-level performance and ecological dynamics.