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

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6 10 08 reproduction sexual selection l.jpg
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 l.jpg
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 l.jpg
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 alternative mating strategies l.jpg
Male-male competition can select for alternative mating strategies

Marine isopod males

alpha

beta

gamma

# females


Male male competition can select for mate guarding l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 continued13 l.jpg
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 continued14 l.jpg
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 courtship that provide no material benefits l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
Sexual conflict arises when males and females have different interests

__________________ in orangutans

________________ in Panorpa scorpionflies


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