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Speciation Ch. 21

Speciation Ch. 21. How Do Species Form?. Microevolution promotes change in small population, when does enough change create a new separate species? Speciation  process that forms new species from existing ones 2 forces isolate species: Geographic Lead to reproductive isolation Genetic

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Speciation Ch. 21

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  1. SpeciationCh. 21

  2. How Do Species Form? • Microevolution promotes change in small population, when does enough change create a new separate species? • Speciation process that forms new species from existing ones • 2 forces isolate species: • Geographic • Lead to reproductive isolation • Genetic • Pairing of chromosomes limit mating, etc…

  3. Categorizing Species • Linnaeus system Latin; name made genius and species nomenclature • Base of morphological species concept; connect species by physical traits • What is the major problem with the morphological species concept? • Polymorphic species might be confused as multiple species • More exact methods of classification must be used

  4. Modern Classification • Biological species concept categorizes species on reproductive criteria • If members of two populations cannot breed or produce fertile offspring under normal natural conditions they are not the same species • If two population cannot exchange genetic information they are no longer connected • How do we categorize asexual species? • Genetic markers through DNA technology

  5. Ancient Classification • How do we categorize exist species? • Fossil records combined with modern observations • Phylogenetic species concept using morphological and genetic sequence data fossil records are grouped with similar existing species

  6. Geographic Speciation • Populations of a species spread across a wide range experience different environmental factors • The greater the factors, the great genetic and phenotypic variation can be seen • Subspecies variation in a species population that is easily categorized • Five subspecies of rat snake all have different color patterns • Subspecies can still interbreed when in contact

  7. Ring Species • If two subspecies never come directly in contact and never directly interbreed, are they still the same species? • Yes! They can be connected through other subspecies • Ring species intermediate between two populations that allows for the mixing of their genes • California salamanders • Ring species may be showing the process of two separate populations finally dividing into two species

  8. Reproductive Isolation Activity • Crystal and Donatello: • Explain ecological isolation • Serena and Bruce: • Explain temporal isolation • Nick and Papaya: • Explain behavioral isolation • Alex and Michael: • Explain mechanical isolation • Benjamin and Ezreal: • Explain gametic isolation • Fox and Lyn: • Explain all postzygotic mechanism • YOUR TURN!!! • I’m done talking. Your turn to teach each other. • Use the rest of the class and tonight to research your topic in pairs • Tomorrow we will form two groups (one member from each pair) and you will teach your topic to that group • Prepare examples, bring in visual material, and be ready to answer their questions • Here are the pairs and topics:

  9. Types of Geographic Speciation • Allopatric Speciation • “different homeland” • Physical barrier separates populations • Two steps: 1) Physically separate; stops gene flow 2) Mutate over time to become reproductively isolated • Archipelagos are good examples; produce species clusters close related species from a recent common ancestor; Darwin’s Finches • Test speciation with second contact • Either groups are reproductively isolated or they produce hybrids in hybrids zones • Over time these zones may disappear; reinforcement

  10. Types of Geographic Speciation 2) Parapatric Speciation • “beside homeland” • Speciation between adjacent populations; driven by hybrids having a lower fitness in the environment 3) Sympatric Speciation • “same homeland” • One population produces subgroups that separate with time • Insect species lives on one type of plant (host); a mutation in a part of the population causes a shift in the selected host • New population moves to new host (host race); now separated they start their path towards speciation • Polyploidy plants typically experience this type of speciation

  11. Genes and Speciation • Genetic changes ultimately drive speciation; all other factors just help in the eventual changes in the populations gene pools • Genetic Divergence genetic differences that reproductively isolate populations • Swordtails and Platys hybrids produce lethal tumors; genetics wont let hybrids survive • Snail species mutation reverse the direction shells coil, can no longer physically breed • Sexual selection in birds changes in songs and dances make males of one population not attractive to females of another

  12. Genes and Speciation 2) Polyploidy extra copies of chromosomes can reproductively isolate populations • Autopolyploidy full nondisjunction produces an unreduced gamete (diploid sex cell) • Grass, violets, chrysanthemums • Unreduced gametes mix to make tetraploid offspring • Can self-pollinate or mate with other tetraploid plants • Reproductively isolated from all non-polyploidy populations

  13. Genes and Speciation 2) Polyploidy extra copies of chromosomes can reproductively isolate populations 2) Allopolyploidy two closely related species form a hybrid, which is normally sterile, BUT if self-fertilize after forming gametes through meiosis or gains the needed chromosomes, it can form a new species • Coffee, cotton, potatoes, tobacco • Very fast speciation

  14. Genes and Speciation 3) Chromosome Alteration inversions, translocations, deletions, and duplications can all alter the genome enough to cause speciation • Humans (46) diverged from gorillas and chimps (48) possibly because we lost 2 chromosomes that fused into Chromosome #2 • Inversion at centromere on #2 also points to divergence between chimps/humans and gorillas/orangutans • Humans differ from chimps by 6 other inversions

  15. Homework • Crystal and Donatello: • Explain conditions for making fossils/why so few fossils survive • Serena and Bruce: • Explain relative and absolute dating of fossils • Nick and Papaya: • Explain how we use fossils to map out life millions of years ago • Alex and Michael: • Explain the continental drift and how it effects speciation • Benjamin and Ezreal: • Explain slow gradual changes to the surface of the Earth • Fox and Lyn: • Explain sudden dramatic changes to the surface of the Earth • Suggested Homework: • Test Your Knowledge Ch 21 • Actual Homework (Wednesday): • Discuss the Concepts #3 • Interpret the Data • Apply Evolutionary Concepts • Homework for Tuesday’s class: • Summary of each type of reproductive isolation with examples • Be prepared to do the group sharing again with 22.1 and 22.2

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