Ecological Character Displacement between the Sexes

Area of Science:

• Evolutionary Biology
• Ecology
• Animal Behavior

Background:

• Sexual dimorphism in ecologically relevant traits can evolve through intersexual competition for resources.
• While other hypotheses exist, resource competition's role in sexual dimorphism is often underestimated.
• Linking resource competition directly to sexual divergence is key to understanding its evolutionary impact.

Purpose of the Study:

• To establish criteria for demonstrating resource competition's role in the evolution of sexual dimorphism.
• To investigate the influence of density and sex ratio on sexual divergence in feeding morphology.
• To provide direct evidence for resource competition as a driver of sexually antagonistic selection.

Main Methods:

• Experimental manipulation of population density and sex ratio in a semiaquatic salamander model (Notophthalmus viridescens).
• Analysis of fitness surfaces to assess selection pressures on multivariate sexual dimorphism.
• Quantification of disruptive selection on feeding morphology in relation to density and sex ratio.

Main Results:

• Disruptive selection on multivariate feeding morphology was observed, intensifying with increased density.
• Fitness and divergent selection strength exhibited negative-frequency dependence, consistent with competition-driven divergence.
• Direct evidence linking resource competition to sexually antagonistic selection and divergence was found.

Conclusions:

• Resource competition is a direct driver of sexual dimorphism evolution, particularly in feeding morphology.
• Sexually antagonistic selection, fueled by competition, promotes divergence between sexes.
• Resource competition may act jointly with other selection sources to drive sexual divergence, especially with sex-specific ecological opportunities.