Bio1B Evolution 7 Last lecture Evolutionary processes Selection disruptive stabilizing Directional selection genome signatures Today Coevolution mutualistic antagonistic freq dependent selection SEX Why have sex cost of sex alternatives pathenogenesis proposed advantages Sexual selection pp 295 297 Mating systems Intra vs intersexual selection Female preference Direct benefits resources vs indirect good genes Coevolution pp 428 9 species 1 selection selection species 2 Mutualistic Symbioses mutualisms eg Yucca moths Yucca Yucca moth Antagonistic Host pathogen Predator prey Garter snake and poisonous pacific newt Why have sex Alternatives asexual parthenogenesis in animals pp 639 apomixis in plants pp 568 569 Why not sex Inefficient risky breaks up good gene combinations Daphnia asexual in good times sexual in harsh conditions Cost of sex Parthenogenetic whiptail lizards Apomictic dandelion 1 Hypotheses for advantages of sex 1 Reduces accumulation of disadvantageous mutations Mueller s ratchet 2 Brings together independent mutations that together increase fitness 3 Generates genetically diverse offspring Long term and only if sexual populations are large weak drift Advantage in variable environment Increases ability to resist pathogens parasites coevol arms race Red Queen hypothesis Sex and genetic variation Sexual reproduction produces genetically variable offspring through Random mating Independent assortment across loci Recombination between loci See pp 138 139 Independent assortment Recombination Evolution consequences of parthenogenesis in an Australian gecko Heteronotia binoei Sexual population Parthenogenetic population Mite load Rapid spread but more parasites 2 The things males do Irish Elk extinct And youtube moonwalk bird and dancing bird of paradise Intra v inter sexual selection A few males dominate reproduction Female choice manipulation of taillength in male widowbirds Number nests per male Competition and mating success in male elephant seals Futuyma Evolution 1st Ed See also Fig 15 9 Sperm competition cooperation in Peromyscus mice Fisher Hoekstra 2010 Nature 463 801 Sperm in groups swim faster fertilization advantage In species with multiple mating P maniculatus sperm aggregate with themselves vs sperm from relatives This is not seen in monogamous species P polionotus 3 Benefits of multiple mating sperm competition winner increased survival of offspring Fisher et al 2006 Nature 444 89 92 Antechinus marsupial mouse Stud M multiple polyandry single Wimp M Female choice good gene hypothesis Females prefer males with long calls LC Do females select males based on signals that indicate high fitness of offspring Offspring of LC males have higher fitness Intersexual selection female choice dimorphism displays ornamentation 4 Sensory bias males exploiting pre existing preferences of females Evidence from phylogeny P F preference T M trait Futuyma 5
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