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How does sexual selection influence animal behavior?. A (male) sage grouse. 6/10/08: Reproduction: Sexual Selection . Lecture objectives: Be able to define sexual selection and use the theory to generate hypotheses and predictions

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How does sexual selection influence animal behavior?

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How does sexual selection influence animal behavior?

A (male) sage grouse


6/10/08: Reproduction: Sexual Selection

Lecture objectives:

  • Be able to define sexual selection and use the theory to generate hypotheses and predictions

  • Understand why and how male-male competition can select for reproductive-related behaviors and traits

  • Understand why and how female choice can select for reproductive-related behaviors and traits


Darwin recognized that some individuals have a reproductive advantage over others

Sexual selection:

a form of natural selection that occurs when individuals relative to others of the same sex

Sexually selected traits:

1.

2. (males compete; females choose)


Sexually selected traits/behaviors arise from…

Male-male competition(Intrasexual selection)

Female choice(Intersexual selection)

- Aggression- Distinct/Alternative mating strategies- Sperm competition- Mate guarding

- Parental effort- Nuptial gifts- Ornaments & courtship that don’t include material benefits


Male-male competition can select for traits related to aggression over mating


Male-male competition can select for alternative mating strategies

Marine isopod males

alpha

beta

gamma

# females


Male-male competition can select for mate guarding

Benefits of guarding a female (post-mating)_________as the risk that she will mate again increases

Hypothesis: Males millipedes “ride” females as a form of mate guarding

Time riding

Millipede with pair


Male-male competition can select for sperm competition

Females in many species will mate with ______________and use their sperm to fertilize her eggs

Outcome might be determined by:- - - -


Elaborate male genitalia:

Females have the opportunity to mate with >1 male

Females are mostly monogamous

Females have short periods of receptivity

Females have longer periods of receptivity

Elaborate male genitalia:


Female choice can select for males that advertise paternal effort (“I’ll be a good dad!”)

signal:Body shaking as an honest signal of paternal effort in 15-spined sticklebacks

signal:Song as an honest signal of paternal effortin sedge warblers


Female choice can select for nuptial gift-giving

A transferred by a male to a female just prior to or during mating

* Males that give larger gifts will have a higher reproductive success…because the female leaves as soon as she’s done eating!

Gift of a ____: Male hangingflies


Nuptial gifts (continued)…

Gift of __________ (as a meal): Sexual cannibalism in male redback spiders

- Eaten males fertilize more eggs than uneaten males (full female is less likely to mate again soon)

- Males have a 20% chance of finding a mate


Nuptial gifts (continued)…

Gift of _______________:Transfer of alkaloids in spermatophores of moths

Hypothesis: PA (-) females will develop after mating with a PA (+) male

Utetheisa ornatrix

I like a man…er, moth, with high levels of PA!


Nuptial gifts (continued)…

Gift of ___________Sex is thirst-quenching for female Bruchid beetles

Gift of … __________________

Spermatophores: ~10% of male body weight

Dehydrated females were more likely to mate

Once hydrated, a female was less likely to mate with another male


Female choice can select for male ornaments and courtshipthat provide no material benefits

Jumping spider courtship

Widowbird


1. Healthy mate theory: females choose males who are likely to have good health


2. Good genes theory: females choose males who are likely to have good genes


3. Sexy sons theory: females choose males who are likely to have sexy sons

Example: Attractiveness in Drosophila males is __________(sexy males had sexy sons)

Son: Time before mating

What might make a trait “sexy”?

Male: Time before mating


Intra and Intersexual selection often go hand-in-hand

Function of display? Done in presence of males and females

Elephant seals

Amazonian river dolphins


Sexual conflict arises when males and females have different interests

__________________ in orangutans

________________ in Panorpa scorpionflies


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