1. 1 How does sexual selection influence animal behavior? A (male) sage grouse

2. 2 6/10/08: Reproduction: Sexual Selection Lecture objectives: 1.Be able to define sexual selection and use the theory to generate hypotheses and predictions 2.Understand why and how male-male competition can select for reproductive- related behaviors and traits 3.Understand why and how female choice can select for reproductive-related behaviors and traits

3. 3 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: 2. (males compete; females choose) 1.

4. 4 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

5. 5 Male-male competition can select for traits related to aggression over mating

6. 6 Male-male competition can select for alternative mating strategies alphabetagamma Marine isopod males # females

7. 7 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

8. 8 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: - - - -

9. 9 Elaborate male genitalia: Females have the opportunity to mate with >1 male Females are mostly monogamous Elaborate male genitalia: Females have short periods of receptivity Females have longer periods of receptivity

10. 10 Female choice can select for males that advertise paternal effort (“I’ll be a good dad!”) signal: Song as an honest signal of paternal effort in sedge warblers signal: Body shaking as an honest signal of paternal effort in 15-spined sticklebacks

11. 11 Female choice can select for nuptial gift-giving A transferred by a male to a female just prior to or during mating Gift of a ____: Male hangingflies * Males that give larger gifts will have a higher reproductive success… because the female leaves as soon as she’s done eating!

12. 12 Gift of __________ (as a meal): Sexual cannibalism in male redback spiders Nuptial gifts (continued)… - Males have a 20% chance of finding a mate - Eaten males fertilize more eggs than uneaten males (full female is less likely to mate again soon)

13. 13 Utetheisa ornatrix I like a man…er, moth, with high levels of PA! Gift of _______________: Transfer of alkaloids in spermatophores of moths Nuptial gifts (continued)… Hypothesis: PA (-) females will develop after mating with a PA (+) male

14. 14 Nuptial gifts (continued)… Gift of ___________ Sex is thirst-quenching for female Bruchid beetles 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 Gift of … __________________

15. 15 Jumping spider courtship Female choice can select for male ornaments and courtship that provide no material benefits Widowbird

16. 16 1. Healthy mate theory: females choose males who are likely to have good health

17. 17 2. Good genes theory: females choose males who are likely to have good genes

18. 18 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) Male: Time before mating Son: Time before mating What might make a trait “sexy”?

19. 19 Intra and Intersexual selection often go hand-in-hand Function of display? Done in presence of males and females Elephant sealsAmazonian river dolphins

20. 20 Sexual conflict arises when males and females have different interests __________________ in orangutans ________________ in Panorpa scorpionflies