Sperm competition games: sperm selection by females

Area of Science:

• Evolutionary biology
• Sexual selection
• Game theory

Background:

• Sexual conflict arises from differing reproductive interests between males and females.
• Sperm competition (male-male fertilization competition) and cryptic female choice (female post-mating selection) are key components of sexual conflict.
• Understanding the evolutionary dynamics of these processes requires theoretical modeling.

Purpose of the Study:

• To analyze a co-evolutionary sexual conflict game involving sperm competition and cryptic female choice.
• To investigate how female sperm selection evolves under varying male strategies and costs.
• To compare outcomes between models where males are consistently perceived (constant-types) versus inconsistently (random-roles).

Main Methods:

• Developed a game-theoretic model of sexual conflict.
• Analyzed evolutionary stable strategies (ESS) for female sperm selection and male sperm allocation.
• Compared two male role scenarios: random-roles (males equally likely to be favored) and constant-types (males consistently favored or disfavored).

Main Results:

• Females evolve sperm selection as unfavorable ejaculate viability decreases.
• In the random-roles model, sperm selection can decrease if males conserve sperm for favored roles.
• In the constant-types model, sperm selection does not relax at low viabilities, and male sperm allocation patterns differ significantly between models.

Conclusions:

• The evolutionarily stable strategy for sperm selection depends on male role consistency and the costs of selection for females.
• Male sperm allocation strategies adapt to the perceived likelihood of being favored or disfavored.
• Empirical studies must distinguish between consistent and inconsistent female sperm selection to fully understand cryptic female choice and sperm allocation.