Reproductive behavior

Bower birds:•Males build elaborate structures •Females are attracted to these structures•Occasionally a female will mate with a male after inspecting his bower•After mating the female leaves never to return

Reproductive behavior

WHY?•Bowers are not nests•They take an incredible effort to build

Reproductive behavior

Boys and bowers: build them bigger build them better

Do human males create displays to attract females?Does the size of the display relate to relate to:

•Commitment?•Resources?•Success?

Do human females really go for the elaborate “bower?”

Differential reproductive investment patterns

copyright © Dennis Kunkel.

1. Potential sexual partners are traders and sex is an exchange• Trades must be equitable • Value is based on supply and demand

2. Male investment in sperm is far lower than female investment in eggs3. Male investment in rearing offspring tends to be low4. Male reproductive potential far higher than female

Therefore: The operational sex ratio is male biased• Males have surplus supply but high demand

Differential reproductive investment equates to different motives/roles/morphs

Sexual selectionThe theory that competition for mates drives the evolution of certain traits.

Because operational sex ratio biases exist there can be selective pressure •Intrasexual selection: within sex pressure•Intersexual selection: between sex pressure

Image: from Darwin’s The Descent of Man and selection in relation to sex Tufted Coquette Lophornis ornatus, female on left, ornamented male on right

Intersexual selectionIntrasexual selection

Test of theory: when operational sex ratio is reversed…males with low reproductive rate or with high parental investment …what should happen?

•Sex role reversals

Male pipefish are selective for more color and fertile females

Male dominance and mating success

Elephant seals: the most dominant males are the most successful

Polygamous mating systems tend to produce selective pressure for size

•Monogamous seals do not exhibit size differences

Dimorphisms in Humans?

Male alternative sexual strategies: When your not the biggest and the best.…or for that matter if your late to the party

Interference DeceptionSneak copulations