Sexual Selection, Conflict, and Life-History Evolution
Selection beyond survival
Sexual selection
Sexual selection arises from competition for mates and from mate choice. It can generate extreme traits, rapid divergence, and reproductive isolation. Yet sexual selection is not separate from natural selection; it is a subset of differential reproductive success.
Sexual conflict and antagonistic coevolution
Traits that increase success in one sex can decrease fitness in the other, producing intralocus and interlocus conflict. Such conflicts can accelerate trait diversification, maintain polymorphism, and generate coevolutionary dynamics between male and female traits.
Life-history trade-offs
Which process best describes mate choice favoring conspicuous traits?
Traits favored in mating success can evolve even when they carry survival costs.
Correct answer: Sexual selection
What is sexual conflict?
This conflict can operate at both behavioral and genetic levels.
Correct answer: Selection on one sex for a trait that reduces fitness in the other sex, creating antagonistic evolutionary pressures.
Types of sexual selection
Intrasexual competition
- Competition within a sex, often male-male competition
- Can favor weapons or dominance traits
Intersexual selection
- Mate choice, often by one sex choosing among potential mates
- Can favor ornaments, displays, or signals
Life-history evolution questions
| Question | Typical analysis |
|---|---|
| What is the trade-off? | Resource allocation or survival-fecundity models |
| How heritable is the trait? | Pedigree or genomic estimation |
| Does selection vary by age or environment? | Reaction norms and selection gradients |
| Are there sexual dimorphisms? | Comparative and within-population analyses |
Studying a sexual-selection phenotype
-
1
Measure the trait, mating success, and survival in the same population.
-
2
Estimate selection gradients while controlling for confounding variables.
-
3
Test whether mate preference predicts reproductive output.
-
4
Ask whether the trait is condition-dependent or genetically correlated with fitness.
-
5
Compare results across populations to detect local divergence or conflict.
Why can sexually selected traits persist despite survival costs?
If increased mating success compensates for reduced survival, the trait can still be favored.
Correct answer: Because mating benefits can outweigh viability costs
Give one example of a life-history trade-off.
Life-history theory formalizes such allocation trade-offs.
Correct answer: Investment in current reproduction versus future survival or reproduction.