Quantifying maladaptation during the evolution of sexual dimorphism.

Area of Science:

• Evolutionary Biology
• Quantitative Genetics
• Sexual Selection

Background:

• Distinct trait optima in females and males drive selection for sexual dimorphism.
• Strong cross-sex genetic correlations constrain evolutionary divergence, potentially causing maladaptation.
• The fitness costs associated with these constraints during sexual dimorphism evolution are not well quantified.

Purpose of the Study:

• To theoretically derive and empirically quantify the costs of evolving sexual dimorphism.
• To assess the severity of fitness costs imposed by genetic constraints on sexual dimorphism.

Main Methods:

• Developed a theoretical model for the cost of evolving sexual dimorphism, analogous to Haldane's cost of selection.
• Compiled quantitative genetic data from diverse traits and populations via a comprehensive literature search.
• Quantified costs using the derived model and compiled genetic variance-covariance data.

Main Results:

• For approximately 90% of traits examined, the costs of evolving sexual dimorphism were found to be modest.
• These modest costs are comparable to the energetic costs of fixing a few beneficial genetic mutations.
• For the remaining 10% of traits, substantial costs were identified, potentially orders of magnitude higher.

Conclusions:

• While most traits exhibit manageable costs for sexual dimorphism evolution, a subset faces significant evolutionary challenges.
• Understanding these costs is crucial for predicting evolutionary trajectories and population fitness.
• The findings highlight the variable impact of genetic constraints on the evolution of sex differences.