The products of sexual selection Impressive displays in manakins Intense contest competition
Why do the males compete and the females choose?
Anisogamy Female limitation: Number of eggs produced Male limitation: Number of eggs they can fertilize
A single egg of this splendid fairy-wren may weigh 15-20% of her entire mass This male splendid fairy wren may have 8 billion sperm in his testes at any given moment
Investment starts at the gamete, but can take many forms… In American redstarts, only female incubate the eggs, but both males and females feed and care for the offspring Male katydids provide females with edible spermatophores containing carotenoid pigments Female cicada killer wasps paralyze the cicada with a sting then drag them into a burrow where her offspring will feed on the paralyzed cicada
Ratio of sexually active males to receptive females
Extremely high variance in male reproductive success (one of the three key ingredients to evolutionary change) can lead to exaggerated male traits and displays
Extreme sexual size dimorphism in elephant seals Antlers in bighorn sheep are employed directly in contest competition for access to mates Male dung beetles fight for mates and long horns are advantageous, but come with a cost – tissues that go into horn construction are no longer available for building eyes
In birds, female mating competition is found in ~5% of avian species In all those species, males provide the most parental care Sex role reversal Northern Jacanas are polyandrous – females hold territories that encompass the territories of 1-4 males. Males form bonds with females who exclude other females from his territory. Females provide clutches for the males to incubate and protect males from predators. Any thoughts on survival?