Sexual Selection, Conflict, and the Evolution of Life Histories
Sexual Selection and Reproductive Success
Sexual selection
Sexual selection is differential reproductive success arising from competition for mates and mate choice. It can produce exaggerated ornaments, weaponry, behavioral displays, and intense dimorphism even when these traits reduce survival.
Sexual conflict
Sexual conflict occurs when the evolutionary interests of males and females diverge, or when traits favored in one sex impose costs on the other. This can drive antagonistic coevolution and rapid trait turnover.
Trade-off logic
Traits often reflect trade-offs among survival, mating success, fecundity, and parental investment rather than simple maximization of one outcome.
Life-history evolution
Life histories describe how organisms allocate resources among growth, maintenance, and reproduction. Theory predicts trade-offs among age at maturity, offspring number, offspring size, lifespan, and iteroparity versus semelparity.
What is a classic outcome of sexual selection?
Sexual selection often exaggerates traits involved in competition or attraction.
Correct answer: Evolution of secondary sexual traits
Why are life-history traits expected to trade off?
Allocation constraints create evolutionary trade-offs.
Correct answer: Because organisms have limited energetic and temporal resources that must be partitioned among growth, survival, and reproduction.
Selection contexts
| Context | Typical trait response |
|---|---|
| Intrasexual competition | Weapons, aggression, body size |
| Intersexual choice | Ornaments, signals, display behavior |
| Parental investment | Brood size, care intensity, timing of reproduction |
| Sexual conflict | Resistance traits and counter-adaptations |
Investigating sexual selection
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1
Quantify variance in mating success and reproductive success.
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2
Measure trait correlations with competitive or choosy contexts.
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3
Distinguish pre- and postcopulatory selection when possible.
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4
Test for sexually antagonistic alleles or conflict signatures.
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5
Relate life-history patterns to ecological and demographic constraints.
Which trait is most directly linked to parental investment theory?
Parental investment theory concerns allocation to current and future offspring.
Correct answer: Offspring number and offspring size
Define sexual conflict.
It can occur before, during, or after mating.
Correct answer: Sexual conflict is evolutionary disagreement between the sexes over optimal trait values or reproductive strategies.