Short & Sweet Male Intrasexual Competition

1. Short & SweetMale Intrasexual Competition

2. Intrasexual Competition • Selection on mating behavior, either through competition among members of one sex (usually males) for access to members of the other sex • Males tend to invest more of their reproductive effort into mating effort than parenting effort • Finding, attracting, Evaluating potential mates

3. Males Short & Sweet • Male- male competition tends to be more confrontational than in females • Male fitness is more variable

4. Recall Bateman’s Principle • Bateman 1948 • The sex which invests the most in producing offspring becomes a limiting resource over which the other sex will compete • Male strategy • Female strategy • Males should be eager, females… “The female, with the rarest exceptions, is less eager than the male…she is coy, And may often be seen endeavoring for a long time to escape.”

5. Mated drosophila Male fitness depends on maximizing mating frequency Promiscuous males have 3-4X more offspring Females less than 2X as many offspring when mated with multiple males Win big, lose big Bateman’s Experiment

6. Bateman’s Principle • Implications • Males are typically facing • Stronger selection forces • More Intrasexual competition • Greater expression of secondary sexual characteristics • Win big, lose big

7. Bateman’s Principle • Implications • Females are typically facing • Energy is the limiting resource for achieving fitness • Females should be choosier who they mate with • Wasted gametes costlier • Typically invest more in cases of parental care

8. Ave offspring produced by males & females similar Males exhibit more variance in number of offspring produced Male potential reproductive output is higher than females Males Win Big, Lose Big The potential for a big “payoff” results in risky behavior

9. Recall Trivers… • Expanded Bateman’s principle to extend beyond gamete scope to include all aspects of reproductive effort • Gestation, feeding, protection • The sex that invests less should adopt a strategy that maximizes copulatory events • Win big, lose big strategy applies to all aspects of reproductive effort • The sex that invests more should adopt a strategy that maximizes choice.. • Hold back reproduction event until the best male is identified

10. Males Are Riskier

11. Males Are Riskier

12. Males Are Riskier

13. Males Are Riskier http://www.lifeinthefastlane.ca/why-women-live-longer-than-men/humor-humour

14. Males Are Riskier • http://www.youtube.com/watch?v=mCudcVno1gQ

15. Male Survivorship Low Relative to Females • Risky behavior in males leads to lower survivorship relative to females • Risky behavior leads to • More exposure to • Predators • Disease • Increased aggression & violent behavior • Increased energetic cost • High levels of testosterone

16. Sahara Gerbil

18. Soay Rams

19. Low Male Survivorship

20. Short Lifespan Influences Reproductive Effort • Male strategies influenced by future reproductive potential • Probability of dying before next reproduction is high • Since females are the limiting factor, males typically invest more in mating effort • Males in competition for limiting resource • Male can only “Win Big” if he outcompetes other males • Males willing to stress, starve & die for reproduction

21. Sex Can Mean Death for a Male!

22. The things boys have to do to get a date…..

23. Male-Male Competition • Andersson, 1994 “Sexual Selection” • Male reproductive strategy dependent on female strategy • 5 fundamental areas of male-male competition • Scrambles • Endurance Rivalry • Contests • Sperm competition • Mate choice (Female choice)

24. Finding Potential Partners • Scrambles • In some species the females remain in one location • Maintain a territory • Females are dispersed in the environment according to resource availability • The male maximizes his ability to find a mate by maximizing his search area & his ability to search

25. Scramble Competition • Male fitness increased by adaptations that allow him to find mates • Results in adaptations that increase • Sensory systems & structures • Mobility • Increased spatial ability • Early search & Swift location of mates • Early reproduction

26. Moths as Scramblers • Male moths & butterflies have more elaborate antennae than females • Sensory structures • Receptive female will pick a safe location & emit a chemical pheromone (chemical attractant) • Male who first reaches her has greater probability of fertilizing her eggs

27. Aaah.. the better to find you

28. Indian Moon Moth Up to 7 miles away….

29. Elaborate Sensory Structures

30. Wedge-shaped Beetle

31. Golden Saltmarsh Mosquito

32. My What Big Eyes You Have Many fly families males have larger eyes to facilitate mate location

33. Newts As Scramblers • Red spotted newts • Tail fin size correlated with fertilization frequency • Adult newt populations average 2 males for each female • Steep intrasexual competition • Males with bigger fins can get to females more efficiently than his competitors

34. Red Spotted Newt

35. Swim Little Buddy…

36. Sahara Gerbil • Increased spatial acuity & locomotor physiology

37. Male Mammals Have Bigger Hippocampus???

38. Scramble Competition Leads to early Maturation in Males • Males of short lived species exhibit early maturation • The earlier a male matures the less males are around for competition • Selection pressure for males to mature early • Males that mature later encounter fewer non-inseminated females

39. Fig Wasp • Female lays eggs in fig • Male wasps develop & hatch earlier than females • Emerge earlier than females • Allows scramble competition for emerging virgin females • Some species males do not wait for females to emerge • Males chew into fig & mate with females before they hatch

40. Endurance Rivalry • Sexual selection favors traits that improve endurance of males • Male remains reproductively active during a large part of the season • Mating success correlated with length of time spent at breeding sites • Allows male to increase the number of females he mates with • Consequences can decrease survival

41. Endurance Rivalry • Favors adaptations that allow male to persist • Larger body size • Stamina

42. Antechinus sp • Insectivorous marsupial • Big bang reproduction • Remain at mating site without feeding until they die • Stomach ulcers, disease, parasites • http://www.youtube.com/watch?v=zv7b-KPg9hY

43. Endurance Rivalry • Lekking • During mating season males of lekking species gather into small clusters of territories (lek) • Males each defend a territory within the lek via competitive mating display • Meet daily before & during mating season display & spar • Superior males earn prime spots

44. Sage Grouse Lek

45. Sage grouse • http://www.youtube.com/watch?v=m0M8pZnNlnI

46. Contests Competition • Combat Contests • Traits that improve success in fights • Large size • Strength • Weaponry • Agility • Strength signals • Favors Threat signals • Alternate tactics • Alternate mating tactics of inferior competitors, avoiding contests with superior rivals

47. Combat Contests • Males engage in direct combat or other physical contests • Natural selection favors Adaptations such as • Weapons • Strength • Large size • Aggression

48. Kangaroo Boxing • http://www.youtube.com/watch?v=yl7g4GR7kzg

49. Moose Fighting • http://www.youtube.com/watch?v=jLnoPkF_6_w

50. Dendrobates auratus • http://www.youtube.com/watch?v=_8lylgXCEfg&feature=related