Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Click to edit Master subtitle style 1/12/13 Chapter 11Sex: causes and consequences1/12/13 Mechanisms of reproduction are diverse1/12/13 Twofold cost of sex1/12/131/12/13 Sex creates new genotypes1/12/13 Red queen effect makes sex beneficial1/12/13 Example of red queen effect1/12/13 Persistence of asexual reproduction in Bdelloid rotifers•Enter dormant phase during difficult conditions–Horizontal gene transfer–Shedding of parasites1/12/13 Key Concepts•Sex is the combining and mixing of chromosomes during offspring production–Meiosis and recombination–Fertilization•Hermaphrodites that self-fertilize reproduce sexually but do not create genetic variation•In models, a strategy is a method of maximizing fitness that is contrasted with alternative methods1/12/13 Key Concepts•Sex creates new genetic variation by mixing parental alleles•The Red Queen effect has been used to explain the advantages of sex and constant coevolutionary arms races•Ecological situations that require rapid evolution are likely to favor sex•Asexual lineages have evolved mechanisms that compensate for lack of sex1/12/13 Anisogamy results in differential investment in reproduction1/12/13 Limitations on reproductive success differ for the sexes•Females are limited by fecundity•Males are limited by the number of mates they can obtain1/12/13 Investment differences can extend past fertilization1/12/13 Uncertain paternity may explain why male parental care is rare•Females have certain paternity•Males have uncertain paternity–Parental care could be directed toward offspring not their own1/12/13 Asymmetrical parental care alters operational sex ratio•Operational sex ratio: ratio of males to females capable of reproducing at a given time•Slower rate of reproduction by females leads to male biased OSR1/12/13 Sexual selection•Differential reproductive success resulting from competition for mates–Intrasexual selection–Intersexual selection•Sexual selection typically stronger on males–Maximize fitness by mating multiply–Male biased OSR1/12/13 Sexually dimorphic result from sexual selection•Ornaments: attractive traits that increase mating success•Armaments: weaponry used to outcompete other individuals1/12/13 Male-male competition leads to extreme variance in reproductive success1/12/13 Competing for mates is costly1/12/13 Males may compete for territory1/12/13 Benefits of female choice•Direct benefits: benefit the female directly–e.g. food, nest sites, protection•Indirect benefits: benefits that affect the genetic quality of the female’s offspring1/12/13 Direct benefits1/12/13 Females may benefit from cannibalism1/12/13 Voluntary self-sacrifice in redback spiders1/12/131/12/13 Males may display elaborate ornaments1/12/13 Female preferences are often consistent1/12/13 Female preferences are often consistentFemale stalk-eyed flies prefer longer stalks1/12/13 Female preferences may arise from preexisting sensory bias1/12/131/12/13 Fisher’s runaway: preference and trait genetically correlated1/12/13 Ornaments can serve as handicaps1/12/13 Development of weapons can involve trade-offs1/12/13 Types of mating systems•Monogamy: one male pairs with one female–Sexual: partners mate with each other exclusively–Social: partner pair but may cheat•Polygyny: males mate with multiple females•Polyandry: females mate with multiple males1/12/13 Polyandry selects for male traits that increase paternity1/12/13 Sperm competition drives evolution of larger testes1/12/13 Discriminating sperm in deer mice1/12/13 Evolution of giant sperm in Drosophila1/12/13 Key Concepts•Polyandry leads to sperm competition among males1/12/13 Sexual conflict results in antagonistic coevolution•Sexual conflict: traits that confer a fitness benefit on one sex but cost to the other–Traits coevolve antagonistically1/12/13 Sexual conflict in ducks1/12/13 Evidence for antagonistic coevolution in Drosophila1/12/13 Key Concepts•Sexual conflict leads to antagonistic coevolution between males and