SEXUAL SELECTION BY THE HANDICAP MECHANISM.

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Genetics

Background:

• The handicap mechanism of sexual selection faces criticism for not reinforcing viability selection and explaining mating preference origins.
• Existing models integrating handicap and Fisher's mechanisms require indefinitely heritable fitness, a significant limitation.

Purpose of the Study:

• To develop a novel model of the handicap mechanism that bypasses the need for heritable fitness.
• To investigate the evolutionary dynamics of sexual selection using a haploid model with nonheritable variation in paternal investment.

Main Methods:

• A simple haploid model was developed, focusing on nonheritable variation in paternal investment.
• The model's evolutionary dynamics were compared to existing simple and quantitative genetic models of the handicap mechanism.

Main Results:

• The new model replicates the evolutionary dynamics of models based on heritable fitness.
• When Fisherian runaway selection is absent, the handicap mechanism directs populations along the Fisher line, creating a stable evolutionary trajectory.
• This deterministic convergence eliminates the possibility of rapid population divergence driven by genetic drift.

Conclusions:

• Nonheritable variation in paternal investment provides a viable mechanism for sexual selection.
• The handicap mechanism can stabilize mating systems by guiding evolutionary trajectories, preventing divergence.
• This resolves long-standing criticisms of the handicap principle in sexual selection theory.