How does the greater investment in eggs than sperm influence animal mating behavior?

The greater investment in eggs compared to sperm significantly shapes animal mating behavior by creating fundamental differences in reproductive constraints and selectivity between the sexes.12

Because females typically produce large, nutritionally costly eggs and often provide more parental care, their reproductive success is limited by time and resources. Consequently, females are generally more selective when choosing mates, often preferring males who demonstrate high genetic quality or provide direct benefits, such as resources or parental assistance.12

In contrast, males typically produce a vast number of inexpensive sperm, meaning their reproductive success is often limited by the number of females they can fertilize rather than by the cost of gamete production. This asymmetry drives several key behavioral patterns:12

• Increased Male Competition: Because females are a limited resource, males often engage in intense competition to secure mating opportunities, leading to the evolution of elaborate sexual ornaments, displays, and aggressive behaviors.123
• Mating Systems: The disparity in investment helps explain the prevalence of polygyny, where males seek multiple partners to maximize their reproductive output.13
• Sex-Role Reversal: In rare cases where males provide the majority of parental investment—such as in sea horses or phalaropes—the pattern reverses: males become more selective, and females become more competitive and colorful.12