Lecture 15: Sexual Selection PDF

Lecture 15: Sexual selection In many animals, members of one sex (usually males) have exaggerated and costly traits that may reduce survival “The sweet strains poured forth by many male birds during the season of love, are certainly admired by the females... On the whole, birds appear to...

Lecture 15: Sexual selection In many animals, members of one sex (usually males) have exaggerated and costly traits that may reduce survival “The sweet strains poured forth by many male birds during the season of love, are certainly admired by the females... On the whole, birds appear to be the most aesthetic of all animals, excepting of course man, and they have nearly the same taste for the beautiful as we have... [Male birds] charm the female by vocal and instrumental music of the Darwin 1871 most varied kinds.” Competing for access to mates, or, individuals of the choosy sex select mates Intrasexual selection Intersexual selection (direct competition) (choice) Usually, but not always, males are the competing sex and females are the choosy sex… why? The Mating Game Moore et al. 2012. Am. Biol. Teach 74: 648-651.  How to play The Mating Game 9 males (quality 1-5; each with many gametes) 9 females (quality 1-5; each with a few gametes) Male and female agree to mate Female accepts one sperm at a time, pairs with an egg, brings both gametes to me, then back to breeding area Males stay in breeding area (keep mating!) Person with the most fitness points (number and quality of offspring) wins Selective forces on males & females How can males best increase their fitness? Does this also work for females? Which sex is fitter, ON AVERAGE? which sex has higher POTENTIAL  Why be choosy? Direct benefits (attractive mates are good parents) – food, territory, protection Indirect benefits (attractive mates have good genes) – offspring survival Sexy sons/ a taste for the beautiful (attractive mates produce attractive offspring)  Sex differences in parental investment and potential fitness determine which sex competes and which sex chooses red phalaropes seahorse What if both sexes invest heavily in parental care? Mating preferences in humans: What qualities are attractive in a partner?  Females may have different priorities for long-term vs short- term mates Males may have different standards for long-term vs short-term mates  Take-homes: Sexual selection Why does it happen? Which sex competes, and which sex chooses? When both sexes invest heavily in offspring, both sexes compete and both sexes choose