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Natural Selection and Speciation

Natural Selection and Speciation. Another way to look at it…. Directional Selection. Fitness. Trait. Trait. Negative Directional Selection. Positive Directional Selection. Stabilizing selection. Fitness. average trait value. Egg laying wasp that eventually kills the cactus.

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Natural Selection and Speciation

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  1. Natural Selection and Speciation

  2. Another way to look at it… • Directional Selection Fitness Trait Trait Negative Directional Selection Positive Directional Selection

  3. Stabilizing selection Fitness average trait value

  4. Egg laying wasp that eventually kills the cactus

  5. Disruptive Selection Fitness average trait value

  6. Black-bellied seed cracker (Pyrenestes ostrinus)

  7. Smith, T. B. 1990. Evolution. 44(4):832 • Black-bellied seed crackers (Pyrenestes) in Cameroon

  8. Same birds different studyOpen portion of bar – Number hatchedBlack portion of bar – Number survived

  9. Two more types of selection • Correlational – working on combinations of traits at once. (body size) (Wing length)

  10. Frequency Dependent Selection – Level of selection dependent upon most common phenotype (at the time) Genyochromis Scale eater

  11. Scalebiters – frequency dependent selection Right “mouthedness” Left “mouthedness”

  12. Frequency of left “mouthedness” Frequency of right “mouthedness” Time

  13. Selection can lead to speciation • Speciation: • Splitting of one species into two or more species • Transformation of one species into a new species over time

  14. B B A TIME TIME A A PHENOTYPIC VARIATION PHENOTYPIC VARIATION Anagenetic (gradual) versus Cladistic (punctuated) Speciation

  15. Species • Many, many definitions • Biological species definition: A group of actually or potentially breeding individuals which are reproductively isolated from all other groups. • Doesn’t work in all situations • Fossils • Asexual organisms

  16. Isolating mechanisms • Prezygotic – • Postzygotic -

  17. Pre-zygotic barriers include • Temporal isolation • Behavioral • Mechanical • Gametic

  18. Prezygotic I.M.s • Habitat isolation • Dendroica warblers in Eastern US

  19. Modes of speciation • Allopatric – allo = different, patri = fatherland • Sympatric – sym = together • Has to do with location or habitat

  20. Speciation only occurs with reproductive isolation

  21. Sympatric speciation • Polyploidy in plants • Hybrids

  22. Adaptive Radiation • Evolution of ecological (& morphological) diversity within a rapidly speciating lineage.

  23. Hawaiian honeycreepers

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