BIOL2007 TUTORIAL EXERCISE: Due tomorrow, Fri. 4:30 Kevin in office 2:30-4:00 pm TODAY

1. BIOL2007 TUTORIAL EXERCISE: Due tomorrow, Fri. 4:30Kevin in office 2:30-4:00 pm TODAY May be some help if you are having problems with game theory exercise

2. BIOL2007 EVOLUTION OF SEX AND SEXUAL SELECTION EVOLUTIONARY QUESTIONS ABOUT SEX Today:A) The evolution of sex 1) What is the advantage of sex? B) Ev. of sexual dimorphism - sexual selection 2) Why are there "secondary sexual characteristics"

3. OTHER interesting questions could be asked: 4) Why meiosis?5) Why mitochondria &c asexual?6) Why only 2 sexes? 7) What is the optimal sex ratio? (Kevin) 8) Why does the Y chromosome become degenerate (non-coding)?9) How does sex determination evolve? 10) Sexual conflict – why and how? See: BIOL2011 (Behavioural Ecology & Sociobiol) and BIOL3012 (Sex, Genes and Evolution).

4. WHAT IS SEX? ·Recombination – all of life ·Meiosis - eukaryotes only·Anisogamy - unequal gamete size - multicell eukaryotes·Dioecy - Separate sexes - vs. hermaphrodites and monoecy These are complex energy-requiring traits ADAPTATIONS Recombination seems to be a lowest common denominator of all sex.

5. EVOLUTION OF SEX Costs of sex Recombination and sex is complicated, costly, predation-prone (even if fun).

6. Two-fold cost of sex Populations grow faster if parthenogens. Suppose each female produces 2.4 progeny: ... and so on (but it works for any reprod. rate)

7. Males contribute little; males are useless! SO: parthenogens should outdo sexual females and increase in frequency. (But advantage not always twofold…) If such strong disadvantages to dioecy, …must be some pretty hefty advantages. Recombination is the primary feature of sex. Advantages of sex must have something to do with recombination.

8. Advantages of sex a) recombination increases evolutionary rate Muller: Recombination allows advantageous mutations to combine in the same individuals.

9. D'you know what dandelions are? Higher evolutionary rate can be adaptive for a species. May work against individual disadvantages for sex within populations: so group selection. Asexual "cheats" gain individual advantage, spread to fixation within species, not to other species. Asexual species do exist (e.g. dandelions). Why do they not take over? If other species evolving/adapting faster, competition may cause extinction of asexuals one of the few cases where group selection may actually be operating. (Conversely, why don't dandelions die out?)

11. Evidence: asexual species trapped on “twigs” in phylogenies.

12. b) Individual selection Survival in a coevolutionary "arms race“ Environment of offspring may be very different from that of their parent, parent’s adaptations may not be sufficient (e.g. Daphnia, aphids). Sex as a lottery: at least some progeny with reshuffled adaptations - direct individual selection advantage to parents in producing recombined, variable offspring. Other ideas. There are plenty, but we will leave that to other courses.

13. EVOLUTION OF SEXUAL DIMORPHISM - SEXUAL SELECTION Darwin: secondary sexual characteristics due to a struggle for genetic representation between members of the same sex. Sexual selection (struggle for mating success) vs. natural selection (struggle for survival and reproduction after mating). Nowadays: sexual selection a special form of natural selection, but a very important one.

14. Birds of paradise (Paradiseidae)

15. Western grebe Aechmophorus occidentalis

16. Jackson’s widowbird Euplectes jacksoni

17. Satin bowerbird Ptilinoorhynchus violaceus

18. Stag beetle Lucanus cervus

19. Stalk-eyed fly Cyrtidopsis dalmanii (Diopsidae)

20. Why are males more extreme? Males usually more flamboyant than females, with horns, bright colours, or displays. Why?  Darwin's view: males are more "passionate" than females. So females can be more choosy. Males have to“sedulously display their charms before the females” Maybe (!); but why are males more passionate?

21. Males: cheap gametescan produce lotslittle parental investmentpotentially father many offspring Females: expensive gametesproduce few often show more parental care, at least as far as nutrients in the eggmore limited no. offspring than males

22. Males: compete for access to females more indiscriminate, less to lose Females: plenty of willing males around worthwhile to be choosy, because number of matings doesn’t limit offspring number

23. Elephant seals: > 90% males father no offspring; fittest fathered 93. But > 50% females have 1 offspring.  Males: higher variance in offspring number.

24. Sexual selection can lead to increased matings at the expense of reduced survival. Darwin : sexual selection might outweigh natural selection, and explain conspicuous coloration in the animal kingdom. e.g. sexual selection may antagonize natural selection for camouflage.

25. Two major types of sexual selection: Intrasexualselection - male-male competition in which males compete by fighting other males for females And … Intersexualselection - sexual selection by female choice in which males compete to obtain the most interest from females.

26. Intrasexual selection - male-male competition • a) Selection for fighting ability • Examples: • Red deer males: harems of females, defend by roaring, displaying, and finally fighting; injuries and death may result • Salmon: males fight to the death with enlarged hooklike jaws, useless for feeding. • ·Fig wasps: specialized males with huge jaws hatch out and kill other males, then mate with all other females in the fig.

27. b) Sperm competition Male-male competition: after mating. Sexual selection between sperm of rival males for fertilization in reproductive tract of females. In primates, males from species with polyandry have larger testes than males from monandrous species.  e.g. Gorillas monandrous, chimps polyandrous. See also: other courses

28. RA Fisher: his analyses rehabilitated female choice Today, explosion of work showing: 1) females do indeed choose, and 2) sexually selected traits often costly.

29. Widowbird Euplectes progne Before Elongated Control I Control II Shortened 0.0 0.5 1.0 1.5 2.0 After Elongated Control I Control II Shortened 0.0 0.5 1.0 1.5 2.0 Average no. mates

31. Why SHOULD females choose males with exaggerated and costly traits? • Three major theories: • Sensory bias.Exaggeration is a supernormal sign stimulus. • Pre-existing preferences: Physalaemus frog phylogeny shows that "chuck" sound has evolved in a terminal branch of the genus. • Females of related spp. which lack "chuck" still like it. (Mike Ryan).

32. a) Sensory bias b) Direct benefits of female choice e.g. avoiding disease by mating with uninfected males. Or getting help at the nest c) Indirect benefits of female choice Indirect benefits are passed on to the offspring via genetic contribution from male.

33. i) “sexy sons” Mathematical models, by Russ Lande and Mark Kirkpatrick (1980s): runaway models of sexual selection.

34. Imagine male trait evolution and female choice; females can choose whatever they want; males have a natural-selection optimum. Coevolutionof male trait and female response  potential runaway process of evolution.

35. ii) "good genes" hypothesis Exaggerated, costly traits  high fitness. Parasite hypothesis of Hamilton and Zuk Male birds and mammals: bare patches of skin (e.g. baboons’ bottoms, wattles on cockerels) Diseases, parasites: alters blood colour  Bare flesh: honest signals of overall health. Hamilton & Zuk: sexually dimorphic species of birds suffer more from parasites.

36. Zahavi’s "handicap principle". Not very costly male badges prone to cheating Zahavi: only very costly traits uncheatable A costly "handicap" is selected, paradoxically, because it guarantees "honest signalling".

37. Which is correct? Direct selection? Clearly this occurs "Good genes" some evidence, easy to test Non-adaptive "sexy sons" idea appealing, but difficult to prove Evolutionists haven’t yet resolved these arguments, but they are fun to think about

38. Sexual selection in humans Darwin: "The Descent of Man and Selection in Relation to Sex". Sexual selection may explain the extraordinary racial differences in animals and humans

39. Desmond Morris, Jared Diamond, • “evolutionary psychologists”: • similar conclusions • Peculiarly human features such as: • bare skin, hairlessness • lips • hair colour, skin colour • enlarged breasts in females • beard in males • copulation when not in oestrus • weapons, war? • ornaments, jewellery? • music? • art? ... etc.

40. TAKE HOME POINTS • Evolution of sex: • The basis of sex is recombination • Sex is usually costly • Separate sexes may exist because of: • asexual lineages die out (group selection) • offspring variability (individual selection)

41. TAKE HOME POINTS (contd.) • Sexual selection/sexual dimorphism: • Male-male competition • fighting • sperm competition • Female choice • sensory bias • direct benefit to self/offspring • indirect (inherited benefits) • sexy sons • good genes

42. FURTHER READING FUTUYMA, Evolution. Ch 14: 329-339, Ch 17: 417-426. Science Library: View B242 Teaching Collection by going to eUCLid; use Keyword, Basic Search, All Fields: B242