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Chapter 22

Chapter 22. The Origin of Species. What You Need to Know:. The difference between microevolution and macroevolution. The biological concept of a species. Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populaitons.

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Chapter 22

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  1. Chapter 22 The Origin of Species

  2. What You Need to Know: • The difference between microevolution and macroevolution. • The biological concept of a species. • Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populaitons. • How allopatric and sympatric speciation are similar and different. • How autopolyploid or an allopolyploid chromosomal change can lead to sympatric speciation. • How punctuated equilibrium and gradualism describe two different tempos of speciation.

  3. Speciation = origin of species • Microevolution: changes within a single gene pool • Macroevolution: evolutionary change above the species level • cumulative effects of speciation over long periods of time

  4. Species = population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring • Reproductively compatible • Reproductive isolation = barriers that prevent members of 2 species from producing viable, fertile hybrids

  5. Prezygotic Barriers: • Impede mating/fertilization Types: • Habitat isolation • Temporal isolation • Behavioral isolation • Mechanical isolation • Gametic isolation Postzygotic Barriers: • Prevent hybrid zygote from developing into viable adult Types: • Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown

  6. Types of Reproductive Barriers REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

  7. Types of Reproductive Barriers REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

  8. Other definitions of species: • Morphological – by body shape, size, and other structural features • Ecological – niche/role in community • Phylogenetic – share common ancestry, branch on tree of life

  9. Two main modes of speciation

  10. Two main modes of speciation:

  11. Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon

  12. Sympatric Speciation by Polyploidy • Autopolyploid: extra sets of chromosomes • Failure of cell division (2n  4n) • Eg. Strawberries are 4n, 6n, 8n, 10n (decaploid)! • Allopolyploid: 2 species produce a hybrid • Species A (2n=6) + Species B (2n=4)  Hybrid (2n=10) Autopolyploid Speciation 2n 2n = 6 4n = 12 4n

  13. Allopolyploidy

  14. Many new species arise from a single common ancestor • Occurs when: • A few organisms make way to new, distant areas (allopatric speciation) • Environmental change  extinctions  new niches for survivors • Eg. Hawaiian archepelago Founding Parents

  15. Adaptive Radiation: Hawaiian plants descended from ancestral tarweed from North America 5 million years ago N 1.3 million years Dubautia laxa KAUAI 5.1 million years MOLOKAI MAUI OAHU 3.7 million years Argyroxiphium sandwicense LANAI HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis

  16. Hybrid Zones • Incomplete reproductive barriers • Possible outcomes: reinforcement, fusion, stability

  17. Polar Grizzly “Grolar” or “Pizzly”

  18. Tempo of Evolution Punctuated Equilibium • Eldridge & Gould • Long period of stasis punctuated by short bursts of significant change Gradualism • Common ancestor • Slow, constant change

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