BIO 102 Sexual Selection

1. BIO 102 Sexual Selection

2. Sexual dimorphism is very common in nature

3. What is sexual selection?

4. What is sexual selection? Natural Selection: Differential reproductive success due to variation among individuals in survival and reproduction.

5. What is sexual selection? Darwin (1871) defined sexual selection as: Differential reproductive success due to variation among individuals in success at getting mates.

6. What is sexual selection? Darwin (1871) defined sexual selection as: Differential reproductive success due to variation among individuals in success at getting mates. • sexual selection refers to onecomponent of fitness: mating success. Fitness = Viability +Fecundity +Longevity +Mating success

7. What is sexual selection? Fitness = Viability +Fecundity +Longevity +Mating success

8. What is sexual selection? Fitness = Viability +Fecundity +Longevity +Mating success • “trade-offs” between fitness components may occur!

9. What is sexual selection? Fitness = Viability +Fecundity +Longevity +Mating success • “trade-offs” between fitness components may occur! • a trait improving mating success may increase total fitness yet reduce viability!

10. If sexual selection is indeed the explanation for sexual dimorphism, then it will have to act on sexes differently….. And it does! Sexual reproduction creates different selection pressures for males and females. How?

11. If sexual selection is indeed the explanation for sexual dimorphism, then it will have to act on sexes differently….. And it does! Sexual reproduction creates different selection pressures for males and females. • Through asymmetric parental investment!

12. What is parental investment? • Energy and time expended in either or both: • -constructing an offspring • -caring for it.

13. What is parental investment? • Energy and time expended in either or both: • -constructing an offspring • -caring for it. • Producing eggs (or pregnancies) are more expensive than ejaculates.

14. What is parental investment? • Energy and time expended in either or both: • -constructing an offspring • -caring for it. • Producing eggs (or pregnancies) are more expensive than ejaculates. • In more than 90% of mammal species, females provide substantial parental care and males provide little to none.

15. What acts to limit the lifetime reproductive success of males and females? females: limited by no. of eggs and/or pregnancies

16. What acts to limit the lifetime reproductive success of males and females? females: limited by no. of eggs and/or pregnancies males: limited by no. of females mated

17. What acts to limit the lifetime reproductive success of males and females? females: limited by no. of eggs and/or pregnancies males: limited by no. of females mated (access to mates) This sets up a conflict = sexual selection. To understand sexual selection we must quantify the relationship between number of mates and reproductive success for both males and females

18. Sexual selection in rough-skinned newts

19. Sexual selection in rough-skinned newts

20. Sexual selection in rough-skinned newts Access to females increases reproductive success in males

21. What does this mean? • Heritable traits associated with mating success will become common in males

22. What does this mean? • Heritable traits associated with mating success will become common in males tall crests that appear during breeding season

23. What does this mean? • Heritable traits associated with mating success will become common in males • Heritable traits that are not associated with mating success will tend to disappear from the population

24. Sexual selection in pipefish

25. A baby pipefish emerging from Dad’s brood pouch

26. Sexual selection in pipefish

27. Predictions: Based on Parental Investment: females: limited by no. of eggs and/or pregnancies males: limited by no. of mates Members of the sex subject to strong sexual selection will be competitive. Members of the sex subject to weaker sexual selection will be choosy.

28. Predictions: 1. Males should be competitive

29. Predictions: 1. Males should be competitive • they should compete among themselves for access to females.

30. Predictions: 1. Males should be competitive • they should compete among themselves for access to females. • this is “male-male competition” or intrasexual selection.

31. Predictions: 1. Males should be competitive • they should compete among themselves for access to females. • this is “male-male competition” or intrasexual selection. 2. Females should be choosy

32. Predictions: 1. Males should be competitive • they should compete among themselves for access to females. • this is “male-male competition” or intrasexual selection. 2. Females should be choosy • since her investment is larger, she has more to lose by making a bad decision.

33. Predictions: 1. Males should be competitive • they should compete among themselves for access to females. • this is “male-male competition” or intrasexual selection. 2. Females should be choosy • since her investment is larger, she has more to lose by making a bad decision. • this is “female choice” or intersexual selection.

34. Intrasexual selection (male-male competition)

35. Intrasexual selection • • occurs when individual males can monopolize access to females. • -Fight for control of mates and/or control of resources vital to mates

36. Intrasexual selection • • occurs when individual males can monopolize access to females. • -Fight for control of mates and/or control of resources vital to mates • Types of intra-sexual selection: • Combat • Sperm competition • Infanticide • Sneaky strategy

37. Intrasexual selection • occurs when individual males can monopolize access to females. 1. Combat • leads to sexual dimorphism in size http://video.google.com/videoplay?docid=7730341199662689386&ei=OR2DSoK9KY-SqAOPmbijBA&q=male-male+competition+in+animals&hl=en&client=firefox-a

38. Intrasexual selection • occurs when individual males can monopolize access to females. 1. Combat • leads to sexual dimorphism in size Example: northern elephant seal. ♂ ~ 4,000 lbs ♀ ~1500 lbs

39. Intrasexual selection 1. Combat • leads to sexual dimorphism in size Example: northern elephant seal. • can also lead to the evolution of weaponry

40. Intrasexual selection 1. Combat • leads to sexual dimorphism in size Example: northern elephant seal. • can also lead to the evolution of weaponry Example:horns inungulates and beetles.

41. Intrasexual selection 2. Sperm competition

42. Intrasexual selection 2. Sperm competition • If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success.

43. Intrasexual selection • 2. Sperm competition • • If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success. • Ex. of traits needed to be successful • Large ejaculates • More and longer mating occurrences

44. Intrasexual selection • 2. Sperm competition • • If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success. • Ex. of traits needed to be successful • Large ejaculates • More and longer mating occurrences • Other examples include Sperm plugs, scooping out sperm, prolonged copulation, guarding of mate, applying hormones that reduce female’s attractiveness to other males.

45. Sperm competition in damselflies barbed horns on penis

46. Intrasexual selection 3. Infanticide Example: the African lion

47. Intrasexual selection 4. Alternative male reproductive strategies. Example: Sneaky strategy in Pacific salmon. Female Hooknoses (male- 18mon) Jacks (male-6mon)

48. Intersexual selection (female choice)

49. Intersexual selection • • occurs when males “advertise” for mates and females choose among different males. • Elaborate courtship displays: singing, dancing, or showing off bright color • leads to sexual dimorphism in ornate features

50. Intersexual selection:dancing…... http://www.youtube.com/watch?v=bEhAbwCYc1c&NR=1