The evolution of anisogamy: a game-theoretic approach

Area of Science:

• Evolutionary Biology
• Reproductive Biology
• Theoretical Ecology

Background:

• Anisogamy, the difference in gamete size, is a fundamental reproductive strategy.
• The disruptive selection theory proposes anisogamy evolved from isogamy (equal gamete size).
• Recent research highlights other factors potentially influencing anisogamy's evolution.

Purpose of the Study:

• To re-examine the disruptive selection theory for anisogamy's origin.
• To analyze the roles of gamete size-fitness (g(m)) and zygote size-fitness (f(S)) relationships.
• To determine the stability of isogamous and anisogamous strategies using evolutionary game theory.

Main Methods:

• Utilized evolutionary game theory to model gamete and zygote fitness functions.
• Analyzed the functional relationships g(m) and f(S) under various models.
• Investigated the stability of isogamy and anisogamy for two mating types.

Main Results:

• In ancestral unicellular states with similar g(m) and f(S), isogamy is favored.
• Sigmoidal or concave g(m) and f(S) functions support isogamy, with a minimum gamete size consideration for concave functions.
• Multicellularity, potentially altering f(S) without changing g(m), can drive the evolution of anisogamy.

Conclusions:

• The disruptive selection theory provides a robust explanation for the initial evolution of anisogamy.
• The development of multicellularity is a key factor in transitioning from isogamy to anisogamy.
• While disruptive selection is a powerful driver, other selective forces likely contributed to gamete specialization.