1. Chap.06 Sexual selection 鄭先祐 (Ayo) 教授 國立台南大學 環境與生態學院 生態科學與技術學系 環境生態研究所 + 生態旅遊研究所

2. Ayo 2010 Ethology2 Sexual selection  Intersexual and intrasexual selection  Evolutionary models of mate choice  Learning and mate choice  Cultural transmission and mate choice  Male-male competition and sexual selection

3. Ayo 2010 Ethology3 Intersexual and intrasexual selection  Intersexual selection  Individuals of one sex choose which individuals of the other sex to take as mates.,  Intrasexual selection  members of one sex compete with each other for access to the other sex

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6. 6 Bateman’s principle  Work on fruit flies  Females should be the choosier sex because eggs are expensive and because a female’s reproductive success is limited compared with that of a male, and this should translate into greater variance in the reproductive success of males.  Until about 30 years ago, much of work on mate selection focused almost exclusively on intrasexual competition, rather than mate choice, or intersexual selection.

7. Ayo 2010 Ethology7 (A) Male deer battle with their antlers (B) male horses compete for females.

8. Ayo 2010 Ethology8 Pulse song in fruit flies  During courtship, male fruit flies would make pulse song, and the interval between pulses appears to be critical in terms of the mate choice of female fruit flies.  Recent work suggests that the genetics of song appear to involve three loci that account for a good deal of variance in courtship song.

9. Ayo 2010 Ethology9 Evolutionary models of mate choice 1 2 3 4

10. Ayo 2010 Ethology10 1. Direct benefits  Direct benefits and nuptial gifts in scorpionflies  Female scorpionflies choose their mates using a very basic rule  Choose male that bring relatively large prey items during the courtship process (Fig. 6.5)  These nuptial gifts, which are consumed during courtship, provide females with a direct tangible benefit, food.  There is a positive relationship between prey size and copulation time.

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15. Ayo 2010 Ethology15 2. Good genes  Females get more than direct resources such as food and shelter from their mates, they also get sperm, and with it genes that are passed on to offspring.  For example, in pronghorn antelopes, male provide female with no direct benefits.  Most females end up mating with a small subset of males in their population.  Attractive males vs. nonattractive males (Fig. 6.7)

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17. Ayo 2010 Ethology17 Parasite resistance and good genes  Honest indicators, should be generally costly to produce,  The costlier the trait, the more difficult it is to fake, and hence the more likely it is that this trait is a true indicator of good genes. (Fig. 6.8 Peacock ’ s tail)  If information on internal parasitization is unavailable, using some other trait that correlates well with the one of interest.  One such proxy cue appears to be body coloration (Fig. 6.9)

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20. Ayo 2010 Ethology20 One reason stickleback females may prefer the most colorful (red) males is that color indicates resistance to parasites.

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23. Ayo 2010 Ethology23 MHC and good genes  MHC = major histocompatibility complex  Animals may prefer mating with others who have a dissimilar MHC.  Such a preference could arise because offspring resulting from a mating between individuals with very different MHCs will have a new combination of MHC genes.  Females rats or mice use odors to determine if another individual is a good MHC match.

24. Ayo 2010 Ethology24 a negative correlation between pleasantness and MHC similarity. a negative correlation between pleasantness and MHC similarity. MHC that as dissimilar from their own to be the most pleasant.

25. Ayo 2010 Ethology25 MHC allele counting hypothesis  Individuals should prefer mates with many MHC alleles, rather than choosing a mate that is dissimilar in MHC-related genes.  Using wild-caught stickleback fish from three populations.  When females were given a choice between males, some of whom had few MHC alleles and some of whom had many such alleles, they consistently preferred males with a greater number of MHC alleles (Fig. 6.13)

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28. Ayo 2010 Ethology28 Symmetry and good genes  Developmental stability, is a measure of how well an organism handles changing environment as it matures.  Symmetry is a measure of the similarity of the left and right sides of an organism.  Females may select more symmetric males. (Fig. 6.15) (Fig.6.16)

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31. Ayo 2010 Ethology31 Smell, attraction, and fertility in women  College females smelled T-shirts worn by males for two days, and then the women rated the attractiveness of the scent of forty –one T-shirts worn by the men. (Fig. 6.17)  (A) women who were closed to ovulation in their menstrual cycle preferred the scent of more symmetric males, while  (B) women at a low fertility point I their cycle showed no such preference.

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34. Ayo 2010 Ethology34 Runaway sexual selection  Assume that two genes exist: a gene that codes for a particular trait in males, and a gene that codes for mating preference in females.  The two genes become associated with each other through time.  Stalk-eyed flies and runaway selection (Fig, 6.18, Fig. 6.19)

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37. Ayo 2010 Ethology37 Sensory bias and the emergence of male choice  Sensory exploitation, sensory bias, preexisting bias model of mate choice.  Suppose that, red berries are the most nutritious food source.  Females who are best able to search out and subsequently eat red berries survive and reproduce better.  Once a preference for all things red is in place, if red feathers should suddenly arise in males of this normally blue-feathered species, birds with these red feathers may be chosen as mates because the female’s nervous system is already designed to preferentially respond to red objects.

38. Ayo 2010 Ethology38 Sensory exploitation model  The sensory bias model leads to a clear prediction regarding phylogenetic history.  The female preference trait (P) should predate the appearance of the male trait (T) (Fig. 6.20)  範例： 1.Tricolor vision, fruits, and sensory biases in primates 2.Frogs and sensory biases

39. Ayo 2010 Ethology39 female preference trait (P) male trait (T)

40. Ayo 2010 Ethology40 1. Tricolor vision, fruits, and sensory biases in primates  Whereas other mammals have two types of photoreceptor cones in the eye (dichromatic vision), many, but not all, primate species have three types of cones (trichromatic vision).  Possessing a third type of cone allows some primates to detect red-orange colors, whereas many other mammals are colorblind in this spectrum.  Trichromatic vision allows primates to more easily pick out red-orange fruits and edible ripe red leaves in a complex natural environment.

41. Ayo 2010 Ethology41 Females prefer males with red fur coloration and/or red facial skin.

42. Ayo 2010 Ethology42 Phylogenetic tree  Whether trichromatic vision predated a preference for red fur /face coloration?  If trichromatic vision appeared after red fur/face coloration, the sensory bias hypothesis must be rejected.  If trichromatic vision appeared before red fur/face coloration, then this is consistent with the sensory bias hypothesis.  Phylogenetic analysis found that trichromatic vision evolved earlier than red coloration in males (Fig. 6.22)

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44. Ayo 2010 Ethology44 2. Frogs and sensory biases  兩種青蛙的鳴叫 high frequency “whine”  Physalaemus pustulosus  Physalaemus coloradorum  Pustulosus 雄蛙鳴叫聲會有 ”chuck” (low- frequency) ，對 females 較有吸引力。  Coloradorum 雄蛙鳴叫，沒有 ”chuck”  錄音，人工加上 ” chuck ” ，對 females 同樣 較有吸引力。  Support the sensory bias hypothesis.

45. Ayo 2010 Ethology45 Physolaemus pustulosus male

46. Ayo 2010 Ethology46 Learning and mate choice  Sexual imprinting  Young individuals quickly learn mating preferences from their interaction with adults.  Imprinting is restricted to some small time window during normal development, but the length of this window varied dramatically across species.  Learning and mate choice in Japanese quail

47. Ayo 2010 Ethology47 Experimentally examine sexual imprinting 1.Using the cross-fostering approach. 2.Employing the “novel trait” approach, in which offspring are raised by parents that have some novel trait that an experimenter has introduced.  Using the novel trail approach to studying sexual imprinting on the mannikin bird, Lonchura leucogastroides.

48. Ayo 2010 Ethology48 Four groups  Group 1, served as a control.  Group 2, offspring were raised with their mother and father, each of whom had a red head feather attached to their forehead.  Group 3, father with a red feather  Group 4, mother with a red feather.  Young mannikins imprinted on the red head feather of their parents, and expressed a preference for such adorned birds when they themselves matured.

49. Ayo 2010 Ethology49 Learning and mate choice in Japanese quail  Classical conditioning in adults affects mate choice and that adult male Japanese quail will quickly learn to stay in areas in which they have the opportunity to mate with a female.  While earlier work had demonstrated that sexual imprinting affects Japanese quail mate choice, Nash and Domjan found that learning can also play another role in mate choice.  They examined whether adult classical conditioning might override the effects of sexual imprinting as a juvenile.

50. Ayo 2010 Ethology50 Three phases (Fig. 6.25)  Phase 1, a brown male was allowed to see a blond female and was then given the opportunity to copulate with her  Phase 2, the same male could see a brown female quail, but was never in physical contact with her.  A given male learned that, the presence of blond ( 金黃色 ) female meant a mating opportunity, but the presence of a brown( 褐色 ) female did not.  Phase 3, males were tested to see how much time they spent near brown and blond females  Adult-stage learning about who was likely to be a receptive mate overrode the effects of early sexual imprinting.

51. Ayo 2010 Ethology51 B= exposure to a blond female N= exposure to a normal (brown) female

52. Ayo 2010 Ethology52 Cultural transmission and mate choice  Mate-choice copying  When a female ’ s mate-choice preference is affected by the preference of other females in her population.  案例：  Mate-choice copying in grouse  Mate-choice copying I mice

53. Ayo 2010 Ethology53 Once some females have chosen mates, mate-choice copying will play a role in the mating decisions of other female black grouse, as they choose to mate with the males chosen by other females.

54. Ayo 2010 Ethology54 Black grouse and mate-choice copying  A single “top male” grouse obtains about 80 percent of all the mating at an arena (lek).  Older females mated, on average, three days earlier than younger females, suggesting that mate-choice copying, if it occurred, was most common among younger females.  Using stuffed “dummy” females placed randomly on a male territory within a lek.  Males courted these dummy females and even mounted them and attempted numerous copulations.  Females were more interested in mating with a male who had copulated with other females on his territory, even if they were dummy females.

55. Ayo 2010 Ethology55 Sage grouse  Fifty-six days of observation, lek  Computer simulation  Support for the mate-copying hypothesis, as the unanimity of female mate choice increased as more females appeared, and this increase occurred more quickly then expected by chance (Fig. 6.27).  The green points are the observed matings and the orange points are the expected matings if the females had not been copying the mate choices of other females.

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57. Ayo 2010 Ethology57 Song learning and mate choice in cowbirds  Cowbirds  One population from South Dakota (SD)  One from Indiana (IN)  Cowbirds display different social behaviors and sing different songs across populations.  A cross-fostering experiment (Fig. 6.28)

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59. Ayo 2010 Ethology59 Song learning and mate choice in cowbirds  Birds paired up and mated with others who came from the same rearing regime (IN or SD) in which they were raised.  SD birds raised with SD adults preferred SD birds as mates, and SD birds raised with IN birds preferred IN birds as mates – the mating preferences of the SD birds were strongly dependent on the social environment in which the birds were raised.  Males copied the songs of the adults with which they were raised.

60. Ayo 2010 Ethology60 Male-male competition and sexual selection  Red deer roars and male-male competition  male-male competition by interference  Male-male competition by cuckoldry

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62. Ayo 2010 Ethology62 Males in possession of harem (holders) roared much more than males not holding a harem (solitaries), as well as more often then males in the pre- rut( 發情 ) or post-rut periods.

63. Ayo 2010 Ethology63 Male-male competition by interference  An interesting subset of male-male interactions consist of males interfering with another male while that male attempts to mate with a female.  Common in amphibians and insects.  Elephant seal, a species in which males form large harems of females and in which the males are much larger than the females (Fig. 6.31).  Only 8.3% of males mated, but some individual males inseminated 121 different females.

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65. Ayo 2010 Ethology65 Not only did alpha (dominant) males mount females more often, but that the females protested their mounts less often than mounts by nondominant adults or subadults (SA3, SA4).

66. Ayo 2010 Ethology66 Sexual size dimorphism and male-male competition from a phylogenetic perspective  The relationship between sexual size dimorphism and male-male competition in the pinnipeds (seals, walruses, and sea lions), including the elephant seals.  They hypothesized that in species in which harem size is large, and hence where male- male competition is most intense, sexual size dimorphism should be greatest.  The relative size of males increased as harem size increased.  As harem size increased, female body size would remain fairly constant.

67. Ayo 2010 Ethology67 Male-male competition by cuckoldry  In bluegill sunfish, three male morphs– parental, sneaker, and satellite– co-exit within populations.  Parental males are light-bodied in color, build nests, and are highly territorial, chasing off any other males.  Sneaker males are smaller, less aggressive, and do not hold territories.  Satellite males tend to look like females.

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69. Ayo 2010 Ethology69 Parental male Sneaker males A satellite male

70. Ayo NUTN website: http://myweb.nutn.edu.tw/~hycheng/ 問題與討論