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The Origin of Species

The Origin of Species. Macroevolution. Macroevolution: the origin of new taxonomic groups Speciation: the origin of new species Anagenesis (phyletic evolution): accumulation of heritable changes

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The Origin of Species

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  1. The Origin of Species

  2. Macroevolution • Macroevolution: the origin of new taxonomic groups • Speciation: the origin of new species • Anagenesis (phyletic evolution): accumulation of heritable changes • Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

  3. What is a species? Biological species concept • a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring • genetic exchange is possible and that is genetically isolated from other populations • Proposed in 1942 by Ernst Mayer

  4. Prezygotic Reproductive Isolation • Biological factors impede 2 different species from producing viable offspring • Prezygotic barriers: impede mating between species or hinder the fertilization of the ova • Habitat (snakes; water/terrestrial) • Behavioral (fireflies; mate signaling) • Temporal (salmon; seasonal mating) • Mechanical (flowers; pollination anatomy) • Gametic (frogs; egg coat receptors)

  5. Postzygotic Reproductive Isolation • Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult • Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity) • Reduced hybrid fertility (mule; horse x donkey; cannot backbreed) • Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

  6. Reproductive Isolation

  7. Modes of speciation • Allopatric: • populations segregated by a geographical barrier • can result in adaptive radiation (island species) • Sympatric: • reproductively isolated subpopulation in the midst of its parent population (change in genome) • polyploidy in plants • cichlid fishes

  8. Causes of Sympatric Speciation • Polyploidy • Autopolyploid  allopolyploid • Plant cells double their chromosome number (become tetraploid) and are no longer able to reproduce with diploid individuals. • Habitat Differentiation • Different food sources • Sexual Selection • Females select for different characteristics in males

  9. Adaptive Radiation • Evolution of many diversely adapted species from a common ancestor • Introduced to new environments • Ex: Species on the Hawaiian Islands

  10. Tempo of Speciation • Gradual change vs. divergence in rapid bursts • Punctuated Equilibrium • Niles Eldredge and Stephen Jay Gould (1972) • Helped explain the non-gradual appearance of species in the fossil record

  11. Evo-Devo Evolution has affected developmental biology • Heterochrony • Rate of developmental events differs between organisms • Allometric growth (proportioning that gives body its distinct form) • Paedomorphosis • Organism retains characteristics of larval stage in adult body

  12. Heterochrony Paedomorphism

  13. No Goal in Sight • Evolution is not goal-oriented • Branches could end up in a “trend” or in a “dead-end” • Individual species undergo natural selection • “species selection”

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