1. Speciation How Species Form

2. Species How are new species defined? Used to be on basis of structure These are different species: –Top: Grevy’s zebra (endangered) –Bottom: Plains zebra (widespread in Africa)

3. Speciation When some members of a sexually reproducing population change so much that they are no longer able to produce viable, fertile offspring with members of the original population

4. Reproductive Isolation Can produce new species if there is no gene flow between two populations Many isolating mechanisms; some which occur before fertilization and some after

5. Pre-zygotic Isolating Mechanisms Behavioural –Any special signals (bird song, pheromones, mating rituals, etc.) prevent interbreeding –Ex. Eastern and Western meadowlark look the same, have overlapping ranges but have very different songs

6. Pre-zygotic Isolating Mechanisms Habitat –Two species may live in the same general area but have different habitats –Eg. The common garter snake is commonly found near water but the Northwest garter snake prefers open meadows

7. Pre-zygotic Isolating Mechanisms Mechanical –Many species are separated by temporal (timing barriers) –Diurnal vs. nocturnal; mate or flower at different times –Eg. Tropical orchids each flower in response to weather stimuli

8. Pre-zygotic Isolating Mechanisms Mechanical –Some species fail to mate because they are anatomically incompatible –Lock and key genitalia (dogs, insects, etc.) –Plant structure may impede pollination –Dog breeding (Great Dane vs. Chihuahua)

9. Post-zygotic Isolating Mechanisms Hybrid Inviability –Genetic incompatibility between two species –Stops development of hybrid zygote –Eg. Sheep/goat crosses usually die in early development (otherwise we’d have shoats…or geep!) –Doesn’t always fail

10. Post-zygotic Isolating Mechanisms Hybrid Sterility –Can mate and produce hybrid offspring which are sterile –Failure of meiosis due to chromosome number –Eg. Horse and donkey make a mule

11. Modes of Speciation 1.Allopatric Most common 2 populations geographically separated from each other (physical barriers) Species evolve separately in reproductive isolation

12. Modes of Speciation 2.Sympatric A population may split into separate gene pools, even within same geographic area

13. There’s a video for that! http://www.youtube.com/watch?v=2oKlKmrbLoU