Sexually antagonistic co-evolution: a model and an empirical test

Area of Science:

• Evolutionary Biology
• Sexual Conflict
• Co-evolutionary Dynamics

Background:

• Sexually antagonistic co-evolution, where traits evolve in opposition between sexes, often leads to exaggerated male persistence and female resistance.
• Previous models explored these dynamics, but the role of directional sexual selection against male persistence was less understood.

Purpose of the Study:

• To adapt an existing model of sexual conflict by incorporating directional sexual selection acting against male persistence.
• To investigate how this added selection pressure influences co-evolutionary outcomes and equilibria.
• To test the model's predictions using empirical data from the seaweed fly (Coelopa ursina).

Main Methods:

• Mathematical modeling of co-evolutionary dynamics.
• Inclusion of directional sexual selection opposing male persistence.
• Parameterization and simulation using empirical data for body size in Coelopa ursina, where size functions as both a resistance and persistence trait.

Main Results:

• The adapted model demonstrates that sexual conflict can be limited by counteracting sexual and natural selection, leading to similar equilibria as previous models.
• Simulations using empirical data for Coelopa ursina consistently reached stable evolutionary equilibria, rather than continuous co-evolutionary cycles.
• The model accurately predicts male-biased sexual size dimorphism in C. ursina and indicates male persistence traits are more sensitive to parameter changes than female resistance.

Conclusions:

• Stable evolutionary equilibria may be more prevalent than continuous co-evolutionary cycles in nature, suggesting sexual conflict's limited role in promoting speciation.
• Sexual selection acting against male persistence can effectively constrain the escalation of sexual conflict.
• The findings highlight the interplay between sexual conflict, sexual selection, and natural selection in shaping evolutionary trajectories.