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Berkeley BIOLOGY 1B - Lecture Notes

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1 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 species 2 Mutualistic • Symbioses, mutualisms; eg. Yucca moths Yucca Antagonistic • Host pathogen • Predator prey selection selection Garter snake and poisonous pacific newt Yucca moth 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 Cost of sex Apomictic dandelion Parthenogenetic whiptail lizards Daphnia - asexual in good times, sexual in harsh conditions2 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 – Advantage in variable environment – Increases ability to resist pathogens & parasites (coevol “arms race” => Red Queen hypothesis Long-term and only if sexual populations are large (weak drift) 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) Rapid spread, but more parasites Sexual population Parthenogenetic population Mite load3 Irish Elk (extinct) The things males do…. And youtube: moonwalk bird” and “dancing bird of paradise”…. Intra v inter sexual selection Female choice: manipulation of tail-length in male widowbirds Competition and mating success in male elephant seals Number nests per male A few males dominate reproduction 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)4 Benefits of multiple mating: sperm-competition winner => increased survival of offspring (Fisher et al. 2006 Nature 444: 89-92) polyandry single multiple Wimp M Stud M Antechinus - marsupial “mouse” Female choice - good gene hypothesis Do females select males based on signals that indicate high fitness of offspring? Females prefer males with long calls (LC) Offspring of LC males have higher fitness Intersexual selection: female choice => dimorphism, displays, ornamentation5 Sensory bias - males exploiting pre-existing preferences of females Evidence from phylogeny - P = F preference, T = M trait


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Berkeley BIOLOGY 1B - Lecture Notes

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