Speciation

1. Speciation

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. 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

6. 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

7. Reproductive Isolation Activity • Eagle and Tom: • Explain temporal isolation (time) • Tony and Anna: • Explain behavioral isolation • Linda and Gina: • Explain mechanical isolation • Melody and Ammy: • Explain postzygotic isolation (hybrid) • YOUR TURN!!! • I’m done talking. Your turn to teach each other. • Discuss your topic in pairs • teach your topic to the group • Prepare examples and bring in visual material • Here are the pairs and topics:

8. The Evolution of Species Speciation • The evolution of new species • Members of similar populations no longer interbreed to produce fertile offspring within their natural environment • 4 Isolating Mechanisms: • Geographical Isolation: • Physical separation of two groups; often have different environmental factors

9. Causes of Speciation 2) Reproductive Isolation: • Species no longer can physically mate or offspring are sterile 3)Behavioral Isolation: • populations have different mating behaviors 4) Temporal Isolation: • Two groups reproduce at different times

10. Patterns of Evolution Divergent evolution • species that once were similar to an ancestral species diverge, or become increasingly distinct. Adaptive Radiation • Ancestral species evolves into many species to fit a number of diverse habitats Convergent evolution • distantly related organisms evolve similartraits

11. 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

12. Types of Geographic Speciation 2) 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; now separated they start their path towards speciation • Polyploidy plants typically experience this type of speciation

13. 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

14. Genes and Speciation 2) Polyploidy extra copies of chromosomes can reproductively isolate populations • Autopolyploidy “self”; homologous chromosomes don’t separate; unreduced gamete (diploid sex cell) • Grass, violets, chrysanthemums • Unreduced gametes mix to make tetraploid offspring • Can self-pollinate or mate with othertetraploidplants • Reproductively isolated from all non-polyploidy populations

15. Genes and Speciation 2) Allopolyploidy “other”; 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

16. 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