lecture18 - SEXUAL SELCTION SEXUAL SELCTION SEXUAL...

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Unformatted text preview: SEXUAL SELCTION SEXUAL SELCTION SEXUAL SELECTION SEXUAL SELECTION Sexual Selection= Sexual Selection= Competition among individuals of the same sex for reproductive success – Two types of sexual selection: Male competition Female choice Sexual Selection= Sexual Selection= Competition among individuals of the same sex for reproductive success. This is different from natural selection which is a battle for survival. This is a battle for reproductive rights. Male Competition Male Competition 1) Males fighting (“Breeding Rights”) e.g. Elephant seals Male Competition Male Competition Cont.’ 2) Threat Displays Fighting should be avoided Male Competition Male Competition Cont.’ 3) Sperm Competition Fire ant = 3 sperm/egg Honey bee = 25 Human = 450 million Horse = 7 billion Pig = 20 billion Male Competition Male Competition Cont.’ 4) Sperm removal e.g. Insect barbed penises scoop out competitor’s sperm. e.g. Damselfly Male Competition Male Competition Cont.’ 5) Male guarding of female laying eggs e.g. Dragonfly FEMALE CHOICE FEMALE CHOICE e.g. Female blackbirds choose males with good territory FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ e.g. Female Barn swallows choose males with the longest tails Clicker Question for Women Clicker Question for Which of the following traits do you rank most highly for a mate? 1) College graduate 2) Good health 3) Physical attractiveness 4) Desire for children 5) Religious orientation 6) Good earning capacity 0% 1 0% 2 0% 3 0% 4 45 0% 5 0% 6 Clicker Question for Men Clicker Question for Which of the following traits do you rank most highly for a mate? 1) College graduate 2) Good health 3) Physical attractiveness 4) Desire for children 5) Religious orientation 6) Good earning capacity 0% 1 0% 2 0% 3 0% 4 45 0% 5 0% 6 College Survey College Survey e.g. Humans FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ What traits are selected for? Traits selected with potential for reproductive success: – “Health, wealth, & power” Males are less discriminating than females – Males have a low cost of reproduction – Females have a high parental investment FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Traits without apparent survival value: FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Traits without apparent survival value: Possible explanation—”Runaway Selection” ­­Female prefers a character and chooses it. ­­Her sons get the character (e.g. fancy tails) & her daughters get the tendency to prefer it. FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Female chooses males with fancy tails Sons get fancy tails Daughters get tendency to select fancy tails But why would she prefer some traits over others—ones with no apparent advantage? FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ 1) How are mate preferences developed? Some are learned e.g. Imprinting in turkeys FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ How are mate preferences developed? 1) Some are learned e.g. Eye ring in sea gulls FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Swordtail platyfish Some species with swords and some without. Females of the swordtail species prefer individuals with the longest tails. Is this genetic or learned? FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Genetic: Platyfish How would you test the idea that the female swordtails’ preference is genetically determined? How would you test the idea that the swordtails How would you test the idea that the swordtails’ preference is genetically determined? 1) Cut off the tails of males and see what happens to the mating? 2) Add plastic tails to species without tails and see what happens to the mating? 3) See if males of species with sword tails are preferred by females from species without tails. 4) Place males of two species with & without tails together to see who mates with the females? 5) None of the above 0% 1 0% 2 0% 3 45 0% 4 0% 5 FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Genetic: Platyfish FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Genetic: Platyfish ALL female platyfish prefer males with tails regardless of species! FEMALE CHOICE Cont.’ FEMALE CHOICE Cont.’ Genetic: Platyfish Females have a genetic predisposition toward the swordtail condition But why? Is the tail a signal for some other beneficial trait? KIN SELECTION KIN SELECTION KIN SELECTION= KIN SELECTION= = “a form of natural selection that favors traits that increase survival or reproduction of an individual’s kin at the expense of an individual” KIN SELECTION KIN SELECTION It involves altruism or self sacrifice ­­an act by one individual that increases fitness of others at that individual’s expense benefits close relatives But what possible selective advantage would there be to self sacrifice­­­­for that matter, any altruistic act? KIN SELECTION KIN SELECTION “Inclusive fitness”= Sum of the reproductive success of individuals sharing a genotype KIN SELECTION KIN SELECTION An altruistic act may increase the chances your genes will survive. If you save 2 brothers or sisters you will save your genes (They each share ½ of your genes.) How many 1st cousins do you need to save in How many 1 order to compensate for your self sacrifice? 1) 2) 3) 4) 5) Four Six Eight Sixteen None of the above 0% 1) 0% 2) 0% 3) 45 0% 4) 0% 5) KIN SELECTION KIN SELECTION “I would lay down my life for two brothers or eight first cousins” J.B.S. Haldane KIN SELECTION KIN SELECTION Individual fitness= determined by the # of an individual’s offspring. Inclusive fitness= determined by the sum total of reproductive success of all individuals sharing a genotype KIN SELECTION KIN SELECTION e.g. Naked Mole Rats in Africa KIN SELECTION KIN SELECTION e.g. Social Insects: haplo­diploidy Kin Selection in Bees Kin Selection in Bees We can explain the evolution of the sterile castes of altruistic worker bees by natural selection. Workers leave more of their alleles to the next generation by “farming” their queen then by reproducing themselves! ...
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