Lecture #11 Date ________

1. Lecture #11 Date ________ • Chapter 24 ~ The Origin of Species

2. Today • Look at the definition of species • How do new species arise • What are ways organisms can be reproductively isolated • Allopatric vs sympatric speciation • Gradualism vs punctuated equilibrium

3. Reminder • Test Wednesday • Multiple choice • Essays (1-2)

4. Macroevolution: the origin of new taxonomic groups • Speciation: the origin of new species • Microevolution – a change in allelic frequencies (p and q) within a population over time • Macroevolution – broad pattern of evolution over long periods of time (involves speciation)

5. 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 that is genetically isolated from other populations)

6. Other definitions of species • Morphological – can include asexual organisms • Ecological • Phylogenetic

7. Reproductive Isolation (isolation of gene pools), I • 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)

8. Videos

11. Reproductive Isolation, II • 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)

12. Liger

13. Zebroid

14. Zonkey

15. Zetland

16. Beefalo

17. Geep

18. Leopon

19. Cama

20. Pumapard

21. Ocelot/Puma

22. Jaglion

23. Modes of speciation (based on how gene flow is interrupted) • 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

24. Speciation • Allopatric speciation – geographic isolation

25. Sympatric speciation – polyploidy in plants, habitat differentiation (clines), sexual selection

26. Cline – a graded change in a character along a geographic axis • Along a mountainside (changing temperature, elevation, precipitation) • In aquatic environments (changing temps., pressure, O2 concentration)

27. Allopatric speciation • http://wps.prenhall.com/esm_freeman_biosci_1/7/1951/499633.cw/index.html

28. Hybrid Zones • Reinforcement – hybrids are less fit • Fusion – gene pools become similar (cichlids) • Stability – continued production of hybrid individuals

29. Patterns of evolution

30. Punctuated equilibria • 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

31. Adaptive Radiation/Mass extinctions

32. Divergent evolution / homologous evolution

33. Convergent evolution /Analogous Structures