Lec 12 Sexual Strategies


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Lec 12 Sexual Strategies

  1. 1. Sexual Strategies
  2. 2. Sexual Strategies <ul><li>Sexual strategies </li></ul><ul><ul><li>Intraselection (competition within a gender for mates) </li></ul></ul><ul><ul><li>Interselection (mate choice) </li></ul></ul>
  3. 3. Sexual Strategies <ul><li>Historically intrasexual selection was studied </li></ul><ul><ul><li>(e.g., male male competition) </li></ul></ul><ul><li>Now more attention to interselection </li></ul><ul><ul><li>(e.g., female choice of mates) </li></ul></ul>
  4. 4. Sexual Strategies <ul><li>Both may occur </li></ul><ul><ul><li>For example the peacock feathers </li></ul></ul><ul><ul><ul><li>Intrasexual selection male/male size of feathers </li></ul></ul></ul><ul><ul><ul><li>Intersexual selection female/male – females prefer males with most dense occelli </li></ul></ul></ul>
  5. 5. What will we learn? <ul><li>'Lek Paradox' </li></ul><ul><li>mate choice & genetic diversity </li></ul>Animal Behavior Introduction, BIOL 4518
  6. 6. Sexual Strategies <ul><li>More recently competition between the sexes </li></ul>
  7. 7. Sexual Stragies <ul><ul><li>e.g., strategies that tradeoff fitness of male and female </li></ul></ul><ul><li>What are Sexual strategies? </li></ul><ul><ul><li>Finding a mate, securing reproductive success, reproductive success of males vs females (intersexual conflict) </li></ul></ul><ul><li>This is distinct from “Mating Systems” </li></ul><ul><ul><li>Monogamy </li></ul></ul><ul><ul><li>Polyandry </li></ul></ul><ul><ul><li>polygamy </li></ul></ul>
  8. 8. Sexual strategies: <ul><li>You will need to be able to answer the following questions: </li></ul><ul><ul><li>How have the strategies resulted in positive fitness/evolutionarily beneficial (provide a description)? </li></ul></ul>
  9. 9. Sexual strategies: <ul><li>You will need to be able to answer the following questions (cont): </li></ul><ul><ul><li>What are the costs/benefits that have selected for certain animal characteristics, such as sexual dimorphism, and multiple male morphs? </li></ul></ul>
  10. 10. Sexual strategies <ul><li>You will need to be able to answer the following questions (cont.): </li></ul><ul><ul><li>What are the selective pressures on males and females (e.g., sexual conflict between genders within a species)? </li></ul></ul>
  11. 11. Sexual strategies <ul><li>You will need to be able to answer the following questions (cont.): </li></ul><ul><ul><li>Why have multiple sexual strategies remained in population? </li></ul></ul>
  12. 12. Sexual Strategies <ul><li>Use theoretical models to examine strategies </li></ul>
  13. 13. Topics <ul><li>Intrasexual strategies </li></ul><ul><ul><li>Competition for mates </li></ul></ul><ul><ul><li>Conditional Strategies </li></ul></ul><ul><li>Intersexual competition </li></ul><ul><ul><li>Female choice </li></ul></ul><ul><li>Intersexual conflict </li></ul><ul><ul><li>Honest signalling </li></ul></ul>
  14. 14. Concept behind competition for mates <ul><li>Factors </li></ul><ul><ul><li>Energy investment in reproduction </li></ul></ul><ul><ul><li>Availability of mates </li></ul></ul><ul><li>Concept is that females have greater investment in reproduction therefore tend to be choosier </li></ul><ul><ul><li>Greater gamete size, and typically greater gestation, parental care than males </li></ul></ul><ul><li>Males therefore compete for females; </li></ul>
  15. 15. Conditional strategies <ul><li>A conditional strategy is a strategy only adopted under certain conditions </li></ul><ul><li>Example </li></ul><ul><ul><li>Reverse gender role of aggression with: </li></ul></ul><ul><ul><ul><li>high male parental care, </li></ul></ul></ul><ul><ul><ul><li>low male availability </li></ul></ul></ul><ul><ul><li>Different strategies by Multiple morphs </li></ul></ul><ul><ul><ul><li>Sneaker strategy </li></ul></ul></ul><ul><ul><ul><li>Gender switching </li></ul></ul></ul>
  16. 16. Intraselection Mate selection systems <ul><li>Male dominance hierarchy system established for mating </li></ul><ul><li>Males compete with each other until they win the right to be around a female unmolested by males until she is ready to mate. A losing male may mate with a female if more than one female is in estrous at a time </li></ul><ul><ul><li>E.g., mountain sheep; </li></ul></ul><ul><li>Exception – sneaker role, where very low ranking male mates with a female while more dominant males are fighting for highest rank. </li></ul>
  17. 17. Ritualized aggression in mating systems <ul><li>Aggression in mating systems is often ritualized. </li></ul><ul><ul><li>e.g., weaponry for killing is often not used </li></ul></ul><ul><li>Venomous snakes wrestle without biting, fish lock jaws but do not bite; antelopes push and fence with the probable winner. </li></ul><ul><li>Communication system </li></ul><ul><ul><li>e.g., roaring in red deer and outcome of competition </li></ul></ul>
  18. 18. Intraselection Mate selection systems, Lek: <ul><li>Single area seemingly randomly selected area “matrix” within the territory that all males go to and compete for and defend a spot nearest the center (even when they doen’t stand a chance of mating). </li></ul>
  19. 19. Mate selection systems, Lek: <ul><li>Leks may last for weeks. Area is same year to year. Area offers no food or place to rest. </li></ul><ul><li>Number of copulations is highly skewed to one male with the territory in the center who may do 50-75% of the copulations (e.g., kobs and grouse), and neighbors may account for the remainder while the majority of males do not mate at all. </li></ul><ul><li>Female “honor” the lek system. </li></ul>
  20. 20. Mate selection systems, Lek: <ul><li>E.g., Hawaiian drosophila, 2 species of grouse, 2 species of tropical birds, African antelope (e.g., the Uganda kobs), prairie chicken, kakapo (flightless parrot in New Zealand) </li></ul><ul><li>Some species leks are brothers or half brothers </li></ul><ul><li>Female lek </li></ul><ul><ul><li>(females aggregate and compete for males) </li></ul></ul><ul><ul><li>yellow spotted millipede </li></ul></ul>
  21. 21. Male Competition: Interference <ul><li>Previous examples have been male/male competition before females arrive </li></ul><ul><li>Also, competition during attempt to copulation </li></ul><ul><ul><li>Larger bodied males interrupt copulation between smaller bodied males and females </li></ul></ul><ul><ul><ul><li>Solicitation help by females in elephant seals </li></ul></ul></ul><ul><ul><li>Earwigs, elephant seals </li></ul></ul>
  22. 22. Male Competition: Cuckoldry <ul><li>Bluegill sunfish </li></ul><ul><li>3 male morphs </li></ul><ul><ul><li>Parental male </li></ul></ul><ul><ul><li>Sneaker male </li></ul></ul><ul><ul><li>Satellite male </li></ul></ul><ul><li>Parental – maintain territory, mate with female </li></ul><ul><li>Sneaker - no territory, sneak to fertilize eggs when parental mates with femal </li></ul><ul><li>Satellite – looks like a female; fools male (who tries to mate with satellite) and fertilizes egg </li></ul>
  23. 23. Male Competition: Sperm competition <ul><li>Sperm competition </li></ul><ul><ul><li>Parental male </li></ul></ul><ul><ul><li>Sneaker male </li></ul></ul><ul><li>Sneaker male – </li></ul><ul><ul><li>more sperm per ejaculate </li></ul></ul><ul><ul><li>Short lived sperm </li></ul></ul><ul><ul><li>Increases chance of fertilization </li></ul></ul><ul><li>Parental male – </li></ul><ul><ul><li>less dense longer lived high quality sperm </li></ul></ul><ul><li>When same density, equal fertilization by parental and sneaker sperm </li></ul>
  24. 24. Mate guarding <ul><li>Males guard females from other males </li></ul><ul><li>Monogamous systems </li></ul>
  25. 25. Male mating strategies: Sexual Dimorphism <ul><li>Hypothesize </li></ul><ul><ul><li>Sexual dimorphism is largest when harem size is large and hence when male/male competition is most intense </li></ul></ul><ul><ul><li>38 species of pinnipeds (harbor seals, elephant seals etc.) </li></ul></ul><ul><ul><li>Independent contrasts phylogenetic analysis </li></ul></ul><ul><ul><li>Found support for this hypothesis </li></ul></ul>
  26. 26. Alternative male strategies <ul><li>Sneaker role </li></ul><ul><li>Different strategies by Multiple morphs </li></ul><ul><ul><li>Sneaker strategy </li></ul></ul><ul><ul><li>Gender switching </li></ul></ul>
  27. 27. Alternative male strategies <ul><li>Horseshoe crab </li></ul><ul><ul><li>Males which grasps onto female have higher chance of fertilizing eggs </li></ul></ul>
  28. 28. Female Choice <ul><li>Theories behind female choice of mates: </li></ul><ul><ul><li>What are females using to select mates? Does the selection criteria increase females fitness or fitness of offspring? </li></ul></ul><ul><li>Theories: </li></ul><ul><ul><li>Good genes </li></ul></ul><ul><ul><li>Gift </li></ul></ul><ul><ul><li>Runaway selection hypothesis </li></ul></ul>
  29. 29. Female choice <ul><li>Good genes </li></ul><ul><ul><li>Pronghorn harem size as indicator of genes, and correlation with growth rate of offspring </li></ul></ul>
  30. 30. Female Choice <ul><li>Good genes </li></ul><ul><ul><li>MHC complex </li></ul></ul><ul><ul><li>MHC number of alleles </li></ul></ul>
  31. 31. What will we learn? <ul><li>Birth control pills, mice, smelly shirts, MHC and pregnancy... </li></ul><ul><li>Disruption of mate choice in humans? </li></ul>Animal Behavior Introduction, BIOL 4518
  32. 32. Female Choice <ul><li>Good genes </li></ul><ul><ul><li>Number of MHC alleles </li></ul></ul><ul><ul><li>Female sticklebacks </li></ul></ul><ul><ul><li>Number of MHC peptides – smell (proximate mechanism) </li></ul></ul><ul><ul><li>Optimal number - offspring with intermediate MHC diversity </li></ul></ul><ul><ul><li>Experiment </li></ul></ul><ul><ul><ul><li>Female and male fish of known allele number (2-8) </li></ul></ul></ul><ul><ul><ul><li>Supplement water with MHC peptides increasing the apparent number of MHC alleles </li></ul></ul></ul><ul><ul><ul><li>Examine female choice </li></ul></ul></ul>
  33. 33. Female Choice <ul><li>Males have large symbols </li></ul><ul><ul><li>Bower bird – size of the bower and amount of decoration </li></ul></ul><ul><ul><li>Size of antlers </li></ul></ul><ul><ul><li>Density of occelli in peacock’s tail (Size of peacock tail is part of male dominance hierarchy) </li></ul></ul>
  34. 34. Female choice <ul><li>Gifts </li></ul><ul><ul><li>e.g., insects, provide a gift to female </li></ul></ul>
  35. 35. Female choice <ul><li>Males present with gifts </li></ul><ul><li>Example </li></ul><ul><ul><li>Male spider presents a wrapped up fly </li></ul></ul><ul><ul><li>Body of male praying mantis (removal of head removes reproduction FAP inhibitors) </li></ul></ul>
  36. 36. Female Choice: Mate Choice Copying <ul><li>Grouse in leks </li></ul><ul><ul><li>Evidence that young females tend to copy mate choice of older females </li></ul></ul><ul><ul><li>Supported with experiment </li></ul></ul>
  37. 37. Female choice <ul><li>Removal of spermatophore </li></ul><ul><li>Sperm storage </li></ul><ul><li>Choice of stored sperm to use </li></ul>
  38. 38. Female Choice <ul><li>Do females always choose the best mates? </li></ul><ul><ul><li>Choice of non-dominant male </li></ul></ul><ul><ul><ul><li>Primates; females may mate with persistent non-dominant males </li></ul></ul></ul><ul><ul><ul><li>Direct fitness benefits? Indirect? </li></ul></ul></ul><ul><ul><li>Avoid non-dominant male </li></ul></ul><ul><ul><ul><li>Elephant seals, female will increase calls if non-dominant male attempts to mate </li></ul></ul></ul><ul><ul><li>Mate choice copying </li></ul></ul>
  39. 39. Female Choice <ul><li>When is female mate choice not beneficial? </li></ul><ul><ul><ul><li>Example of Drosophila largest males result in a reduced lifespan of the female </li></ul></ul></ul><ul><ul><ul><li>Direct fitness benefits? Indirect? </li></ul></ul></ul><ul><li>This leads us to intersexual (male/female) conflict </li></ul>
  40. 40. Intersexual conflict <ul><li>Conflict between fitness of males and females </li></ul><ul><ul><li>Examples: </li></ul></ul><ul><ul><ul><li>“Dishonest” signaling of health </li></ul></ul></ul><ul><ul><ul><li>“Dishonest” gifts </li></ul></ul></ul><ul><ul><li>Arms race of detection of genetic quality and dishonest signaling </li></ul></ul>
  41. 41. Signaling <ul><li>Healthy male </li></ul><ul><ul><li>Female preferences based on displays of male health </li></ul></ul><ul><ul><li>Males display gene quality </li></ul></ul><ul><li>Runaway selection theory </li></ul><ul><ul><ul><li>Endow offspring with genes to prefer traits mothers prefer </li></ul></ul></ul>
  42. 42. Intersexual conflict: “Dishonest” signaling <ul><li>Dishonest gift to females </li></ul><ul><ul><ul><li>Only exoskeleton of body is presented </li></ul></ul></ul><ul><li>How can this strategy persist in the population? </li></ul>
  43. 43. Summary