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Sperm competition games: external fertilization and "adaptive"' infertility
1Department of Applied Mathematics and Theoretical Physics, University of Liverpool.
Journal of Theoretical Biology
|May 21, 1996
Summary
This study models sperm traits in external fertilization, finding that higher sperm competition increases ejaculate expenditure and reduces infertility. Sperm size and number are optimized based on competition intensity and longevity trade-offs.
Area of Science:
- Evolutionary biology
- Reproductive strategies
- Mathematical modeling
Background:
- External fertilization in species like fish involves simultaneous egg and sperm release.
- Sperm competition intensity varies, influencing reproductive success.
- Sperm traits, including size and longevity, are key factors in fertilization success.
Purpose of the Study:
- To model the evolutionarily stable strategy (ESS) for sperm size and number in ejaculates.
- To predict the ESS level of infertility based on sperm competition.
- To investigate the trade-offs between ejaculate expenditure and future spawning opportunities.
Main Methods:
- Developed a mathematical model of continuous fertilization.
- Incorporated sperm density-dependent fertilization rates.
- Analyzed the influence of sperm size on competitive ability and longevity.
Main Results:
- ESS ejaculate expenditure increases with sperm competition intensity.
- ESS infertility decreases as sperm competition intensity rises.
- Sperm numbers generally increase with sperm competition intensity, but can decrease under specific conditions.
Conclusions:
- Sperm size evolution is contingent on its effect on longevity.
- Optimal sperm size balances travel distance, speed, and number under varying competition.
- The model provides insights into the adaptive evolution of sperm traits in response to sexual selection.