1 Bio1B Evolution 8 Last lecture: Coevolution – mutualism vs antagonistic Why have sex? – advantages v disadvantages of sexual reproduction Sexual selection • Mating systems Today Sexual selection (pp.295-297) • Intra vs intersexual selection Female preference: Direct benefits (resources) vs indirect (good genes) Evolution of sacrifice (altruism) – kin selection… (pp 815-8) Species & speciation (Ch 17). • What is a species anyway? • Speciation processes - introduction & geographic modes 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 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”2 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 Sensory bias - males exploiting pre-existing preferences of females Evidence from phylogeny - P = F preference, T = M trait Futuyma When to sacrifice? - if it helps a relative – lots… • “Kin selection theory” (W. Hamilton) • Help if: rB > C: r = %shared genes, B = benefit, C = cost • Haldane: “I would not lay down my life for a brother, but would do so for 2 brothers or 8 cousins)” • Social insects: inheritance system => higher “r” => increased cooperation Tuco tuco - co-parenting by females in social groups (Eileen Lacey, IB) Belding’s ground squirrels: females more related and give more alarm calls (Fig. 51.29)3 (2005) Nature 434:69 Estimates of relatedness from molecular data What is a species? Typological (pre-evolutionary eg. Aristotle, Linnaeus) Evolutionary Discontinuities: DWM + extinction Morphological SC Reproductive isolation Biological SC Character change Phylogenetic SC NeoDarwinists Systematists Darwin Groups of populations reproductively isolated from others Diagnosable clusters with common ancestry (molecular or morphological) Phenotypically distinct sets of populations Reconciling different perspectives Forms of Reproductive Isolation • Prezygotic – Separation of mating • Habitat, Timing, Behavior, Mechanical • Gamete recognition • Postzygotic – Viability (F1 or later), Fertility General lineage concept: focuses on the process - not how to recognize species Increasing RI & phenotypic divergence Postzygotic RI increases with genetic divergence also Fig. 17.54 Species of Hominidae Pygmy chimp Ensatina eschscholtzii - One ring species? Or 2 biological species? Or >11 Phylogenetic species k-e overlap; no hybrids k-e overlap; hybrids Geographic modes of speciation Futuyma
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