A model for conditional male trimorphisms.

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Quantitative Genetics

Background:

• Conditional dimorphisms are common in nature and can be modeled using game theory and quantitative genetics.
• Conditional trimorphisms, a more complex form, have recently been identified.

Purpose of the Study:

• To combine game theory (rock-paper-scissors model) and quantitative genetics (environmental threshold model) to create a novel model for environmentally induced trimorphisms.
• To investigate the fitness landscape maintaining alternative reproductive tactics in conditional male trimorphism using scarab dung beetles (Phanaeus triangularis).

Main Methods:

• Developed a novel ternary fitness landscape integrating game theory and quantitative genetics principles.
• Tracked tactic frequency changes in a wild population of Phanaeus triangularis.
• Analyzed fitness intransitivity to confirm rock-paper-scissors dynamics.

Main Results:

• The ternary fitness landscape successfully explains the maintenance of conditional male trimorphism in Phanaeus triangularis.
• Observed fitness intransitivity in the wild population aligns with rock-paper-scissors dynamics.
• Model predictions quantitatively match observed parameters in the beetle population.

Conclusions:

• The developed ternary model provides a framework for understanding environmentally induced trimorphisms.
• Geographic populations of these beetles can evolve between trimorphism and dimorphism.
• Polyphenic systems may evolve between conditional and purely genetic control mechanisms.