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Ch.24 ~ The Origin of Species

Explore the mysteries of macroevolution and speciation, including anagenesis and cladogenesis, genetic isolation, species emergence, and reproductive barriers. Learn about hybrid zones, reproductive isolation modes, and speciation types like allopatric and sympatric evolution.

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Ch.24 ~ The Origin of Species

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  1. Ch.24 ~ The Origin of Species “That mystery of mysteries – the first appearance of new beings on this Earth.”

  2. Macroevolution: the origin of new taxonomic groups • Speciation: the origin of new species • 1- Anagenesis : accumulation of heritable changes • 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

  3. Macroevolution:Is it different from micro-evolution?

  4. What is a species? • Biological species concept (Mayr):a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and is genetically isolated from other populations)

  5. Biological species concept • Biological species are defined by _____ isolation. • The biological species is the largest unit of a _____ in which _____ is possible.

  6. How do new species emerge?

  7. How do new species emerge? • Physical distinctions • Non-interbreeding populations • Adaptation to a different niche in the environment • Genetic differences

  8. How do new species occur? • At least one gene affecting at least one ____________________ must change for speciation to occur.

  9. Genetics plays a key role in speciation • Reproductive compatibility results in propagation of genetic information to the next generation • Reproductive barriers maintain distinct species • Prezygotic barriers • Postzygotic barriers

  10. Prezygotic barriers prevent mating events • Temporal isolation – separates species by seasons • Habitat isolation – separates species by physical barriers • Behavioral isolation – separates species by patterns of activity

  11. Prezygotic barriers prevent fertilization events • Mechanical isolation – structural differences prohibit interbreeding • Gametic isolation – lack of fertilization even if gametes from different species meet

  12. Closely related frogs of genus Ranaremain distinct species by different reproductive barriers. Males of one species are too small to perform amplexus (action that stimulates ovulation). What type of barrier is this?

  13. Postzygotic barriers eliminate the propagation of mixed genetic material when different species breed • Hybrid offspring of two separate species cannot reproduce • Inviability – offspring never reach maturity • Hybrid sterility – functional gametes not produced in the hybrid offspring • Hybrid breakdown – natural selection acts to eliminate them from the population Cama: camel x llama

  14. A hybrid zone is properly defined as:a – an area where 2 closely related species’ ranges overlapb – an area where mating occurs between 2 closely related species, producing viable offspringc – an area where 2 closely related species intermingle, but experience no gene flow

  15. Reproductive Isolation (isolation of gene pools), I • Habitat (snakes; water/terrestrial) • Behavioral (fireflies; mate signaling) • Temporal (salmon; seasonal mating) • Mechanical (flowers; pollination anatomy) • Gametic (frogs; egg coat receptors) pp. 490-491

  16. Reproductive Isolation, II • 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) pp. 490-491

  17. Modes of speciation (based on interruption of gene flow) • Allopatric:geographic barrier isolates species; 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

  18. A flea species feeds only on antelopes. In the western U.S., antelopes and cattle often mingle. If some of the fleas develop a strong preference, instead, for cattle blood, and mate only with other fleas that prefer cattle blood, then over time, which of these should occur, if the host mammal is considered the fleas’ habitat?1 – reproductive isolation2 – sympatric speciation3 – habitat isolation4 – prezygotic barriers

  19. Punctuated equilibrium • Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record

  20. Present day V W X Y Z Which of the five species in the evolutionary tree originated earliest and appeared suddenly in the fossil record?

  21. Present day V W X Y Z Which species is the extant (not extinct) species that is most closely related to species X and why?

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