THE EVOLUTION OF ASYMMETRY IN SEXUAL ISOLATION: A MODEL AND A TEST CASE.

Area of Science:

• Evolutionary biology
• Speciation research
• Behavioral ecology

Background:

• Sexual selection drives speciation, but the dynamics of sexual isolation remain incompletely understood.
• Existing models, like Kaneshiro's, propose drift and loss of courtship elements as drivers of asymmetric sexual isolation.
• Lande's model provides a foundation for understanding the evolution of sexual selection but requires extension to fully address sexual isolation dynamics.

Purpose of the Study:

• To develop a theoretical model for the evolution of sexual isolation by extending Lande's (1981) model of sexual selection.
• To predict the conditions under which asymmetric sexual isolation arises and its transient nature.
• To test the model's predictions using empirical data on sexual isolation in salamanders.

Main Methods:

• Construction of a mathematical model for sexual isolation evolution, building upon Lande's (1981) framework.
• Empirical testing using experimental data on sexual isolation between 12 allopatric populations of the salamander Desmognathus ochrophaeus.
• Statistical analysis to assess the relationship between sexual isolation asymmetry and the level of trait divergence.

Main Results:

• The model predicts that asymmetric sexual isolation is a transient phase during intermediate stages of divergence in sexually selected traits.
• Significant asymmetry in sexual isolation was found in approximately 25% of the tested population pairs.
• A curvilinear relationship between the degree of isolation asymmetry and the level of divergence was observed, supporting the model's predictions.

Conclusions:

• Asymmetric sexual isolation is a temporary phenomenon in the process of speciation, occurring at intermediate divergence levels.
• The developed model offers an alternative explanation for asymmetric sexual isolation, not relying on genetic drift or loss of courtship behaviors.
• The direction of evolutionary change cannot be inferred solely from the asymmetry of sexual isolation.