Reproduction

BIOL 3100

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 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

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

Elaborate secondary sexual traits

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)

What happens when males invest heavily?

• 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?