F Flashcards
What is Sexual Selection?
A type of natural selection where traits provide a mating advantage, even if they reduce survival.
How does sexual selection fit into natural selection?
It is a subset of natural selection because traits that increase reproductive success are passed on.
What are the two main forms of sexual selection?
- Intrasexual Selection (Competition with the same sex)
- Intersexual selection (Mate choice by the opposite sex).
Why was Darwin puzzled by some sexually selected traits?
He noticed some traits (ex, bright colours and large antlers) made individuals more vulnerable to predators.
How did Darwin resolve his dilemma?
He proposed sexual selection as a separate force from survival selection, explaining why some traits persist.
Why do some traits appear only in males?
Males often elaborate traits due to sexual selection, as seen in peafowl, bettas, and jeweled geckos.
What are two problems with sexually selected traits?
1) If traits like antlers improve survival, why dont females have them?
2) Bright colours or large ornaments increase the predation risk.
What is intrasexual selection?
Competition within one sex (often males) for access to mates.
Give an examples of intrasexual selection?
- Male stag beetles fighting
- Male elephant seals battling for dominance
- Male red deer using vocalizations to assess strength
Why are elephant seal battles more lethal than elk battles?
Elephant seals have fewer chances to reproduce, so competition is more intense.
Why is it intersexual selection?
When only one sex (usually females) chooses mates based on traits like bight colours or elaborate displays.
How do sage grouse use intersexual selection?
Males gather in “leks” and display their air secs to attract females.
What are primary sex characteristics?
Gonads (ovaries/testes) and associated reproductive structures.
What are secondary sex characteristics?
Traits that influence mating success but aren’t directly part of reproduction. (ex: antlers, coloration).
How can traits be sexually selected without being survival traits?
If they proved a mating advantage, they persist even if they decrease survival.
What is the bateman Principle?
- Males should be promiscuous because sperm is cheap
- Females should be expensive because their eggs are expensive
Why is Batemans principle not always true?
- In some species, sperm is not cheap (ex: spiney moss stick insects provide sperm packets).
- Some males provide parental care, making them selective (ex: seahorses, jawfish).
Why might females mate with multiple males?
- Genetic diversity in offspring
- Insurance against infertility
- More resources from multiple males
- Better parental c are
- Access to “Good genes”
How does male-male combat affect evolution?
Stronger, more dominant males pass on their genes, reinforcing competitive traits.
How does female choice drive evolution?
Males with preferred traits reproduce more, passing on attractive characteristics.
What’s an example of a species where females actively choose mates?
Wilson’s bird of paradise - males perform elaborate courtship displays.
How did Victorian society react to Darwin’s ideas on female choice?
They accepted male-male combat but struggled with the idea of female-driven evolution.
