The products of sexual selection
Impressive displays in manakins
Intense contest competition
Anisogamy
Female limitation: Number of eggs producedMale 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
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
Female mate choice: Why be choosy?
1) Direct benefits- Offspring provisioning (or mate
provisioning)- Territory quality/access to resources- Protection/safety
2) Indirect benefits- Good genes- Sexy sons
Why is there such strong selection for elaborate traits in males that provide little or no
parental investment?
Number of eyespots predicts survival of offspring
Number of eyespots is also negatively correlated with white blood cell count (an indicator of fighting infection)
• 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?
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