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Speciation

Speciation. How Species Form. 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). Speciation.

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Speciation

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  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 • Allopatric • Most common • 2 populations geographically separated from each other (physical barriers) • Species evolve separately in reproductive isolation

  12. Modes of Speciation • 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

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