Sexual Selection Shapes Reproductive Success
- Traits that improve mating success, rather than survival, are shaped by sexual selection.
- These traits, such as vibrant feathers or elaborate dances, evolve because they enhance the likelihood of attracting a mate.
Sexual Selection Focuses on Mating, Not Survival
- Sexual selection is a type of natural selection, but its focus is different:
- Natural selection favors traits that improve survival.
- Sexual selection favors traits that increase reproductive success, even if they reduce survival chances.
Two Pathways of Sexual Selection
1. Mate Choice (Intersexual Selection)
- One sex (often females) chooses mates based on traits signaling health or genetic fitness.
Female guppies prefer males with brighter coloration, associating it with good health.
2. Competition for Mates (Intrasexual Selection)
- Individuals of the same sex (usually males) compete for access to mates.
- This can involve physical contests or visual displays of dominance.
Stags use their antlers in battles to win access to females
Why Females Are Picky About Mates
- In many species, females invest more resources in reproduction (e.g., producing eggs, gestation, or raising offspring).
- This makes them selective, choosing mates that maximize the survival and fitness of their offspring.
Male traits, like bright colors or elaborate displays, may increase predator attention but are favored because they boost mating success.
Examples of Sexual Selection in Action
Birds of Paradise: Dancing for Attention
- Male birds of paradise are famous for their extravagant plumage and courtship dances.
- What happens: Males clear a display area and perform intricate dances to showcase their feathers.
- Why it matters: Females evaluate multiple males, choosing the one with the most vibrant and energetic display.
Peacocks: A Tail That Signals Fitness
- The peacock’s tail is a classic example of sexual selection.
- What happens: Males with larger, more vibrant tails attract more mates.
- Why it matters: The tail signals genetic quality but increases predation risk due to its conspicuousness.
Sexual Selection Drives Evolution of Extreme Traits
- Sexual selection changes allele frequencies in populations by favoring traits that enhance mating success.
- Over time, these traits become more common, even if they reduce survival chances.
Always ask, "How does this trait improve the individual's ability to reproduce?"
Challenges and Limits of Sexual Selection
- Trade-offs Between Survival and Reproduction: Traits favored by sexual selection, like bright colors, may reduce survival by attracting predators.
- Environmental Influence on Selection: The strength of sexual selection depends on the environment. In predator-rich areas, traits like bright feathers may lose their advantage.
- Variation Is Key: Sexual selection relies on variation. If all individuals possess similar traits, selection pressures weaken.
- How does sexual selection challenge the idea that evolution always leads to traits that improve survival?
- Consider the ethical implications of human interventions, such as trophy hunting, which can alter natural selection pressures.
Avoid assuming that all traits in animals are the result of sexual selection. Many traits are shaped by other factors, such as natural selection or genetic drift.
