Sperm economy between female mating frequency and male ejaculate allocation

Area of Science:

• Evolutionary biology
• Behavioral ecology
• Reproductive strategies

Background:

• Female multiple mating is common across species, raising questions about its evolutionary drivers.
• When females mate multiply, ejaculates from different males compete for fertilization (sperm competition).
• Existing models often analyze female mating frequency or male ejaculate allocation in isolation, neglecting their coevolution.

Purpose of the Study:

• To investigate the coevolution of female mating frequency and male ejaculate allocation strategies.
• To examine how sperm limitation influences the interaction between male and female reproductive strategies.
• To develop a model where females adjust mating frequency and males adjust ejaculate allocation per mating.

Main Methods:

• Developed game-theoretic models incorporating female mating decisions and male ejaculate allocation.
• Analyzed model predictions under varying sex ratios and levels of sperm limitation.
• Compared model outcomes with existing theoretical frameworks and empirical observations.

Main Results:

• Females were predicted to mate once or less under even sex ratios or extreme female bias (due to female resistance or sperm limitation).
• In moderately female-biased populations, males favor resource partitioning across multiple females.
• Females in moderately female-biased conditions favor multiple matings to ensure sufficient sperm, contradicting some existing models.

Conclusions:

• The study highlights the importance of considering the coevolution of male and female strategies in reproductive biology.
• Model predictions offer new insights into the conditions favoring female multiple mating and male ejaculate allocation patterns.
• Findings provide a framework for re-evaluating empirical data on mating systems and sperm competition across diverse species.