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Outcomes of Natural Selection

Outcomes of Natural Selection. Changes in a population in response to fluctuating environment Formation of new species. What is a Species?. Species is Latin for “kind” or “appearance” - therefore, we are referring to something that is similar in some way. Why are Species Important?.

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Outcomes of Natural Selection

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  1. Outcomes of Natural Selection • Changes in a population in response to fluctuating environment • Formation of new species

  2. What is a Species? Species is Latin for “kind” or “appearance” - therefore, we are referring to something that is similar in some way

  3. Why are Species Important? • Species fit into the hierarchy of life beginning with the population level • Types of species present over geological time important in understanding gains and losses of diversity

  4. Okay, So What is a Species? • Biological Species Concept (Mayr 1942) • A group of actually or potentially interbreeding individuals that are capable of producing viable offspring and are reproductively isolated from other individuals

  5. Biological Species Concept • Actually or potentially interbreeding? • Viable offspring? • Reproductively isolated?

  6. Limitations of the Biological Species Concept • Does not fit all situations • Depends on sexual reproduction • Some species reproduce asexually or without a mate • How to deal with subspecies? • Subspecies may represent the middle stages of speciation (formation of new species)

  7. See Table 25.1 of your text and related material in the text

  8. Reproductive Isolation • Prezygotic Isolation - mechanisms develop that prevent interbreeding • Postzygotic Isolation - Interbreeding takes place but either the embryo does not develop or sterility of offspring prevents further interbreeding

  9. Fig. 25.2-1

  10. Fig. 25.3 Temporal Isolation – Reproductively active at different times of the year

  11. Fig. 25.4 Behavioral Isolation – Mating behaviors become different over time.

  12. Fig. 25.2-2

  13. Fig. 25.2-3

  14. Speciation • Speciation requires that some members of a population become reproductively isolated in some way • Therefore, any process or action that leads to part of a population to stop interbreeding with the rest of the population (if over long enough period of time) can lead to speciation

  15. See Feature Investigation as an example of reproductive isolating mechanism directly linked to the character on which selective force is acting (p. 515 – 517) Note – book addresses allopatric speciation differently from the way I (and a number of people) do

  16. Allopatric Speciation Distribution of a Species

  17. Geographic Barrier Splits Distribution

  18. No longer interbreeding; therefore, no exchange of genes and could be undergoing different selection pressures

  19. Over time, the gene pool of each group can become quit different

  20. If two groups are brought back together and do not interbreed, they are now two separate species

  21. figure 22-03.jpg

  22. Parapatric Speciation • Members of a population move into a new habitat • No longer interbreed with individuals from the original range

  23. Parapatric Speciation Distribution of a Species

  24. Individuals move into a new habitat

  25. If no interbreeding occurs between individuals in new habitat and those in the old, reproductive isolating mechanisms can develop.

  26. figure 22-05-1.jpg 22.5 – Part 1 Figure 22.5 – Part 1

  27. 22.4 figure 22-04.jpg

  28. Sympatric Speciation • Occurs in same habitat (adaptation to local environments) • Abrupt genetic change • Common in plants • Polyploidy (see Fig. 25.11) • Can occur with balancing selection

  29. Sympatric Speciation Isolating mechanism develops within the existing distribution of a species

  30. Sympatric Speciation Isolating mechanism develops within the existing distribution of a species

  31. Speciation • Speciation involves individuals of an existing species to branch off to form new species • For this to happen, the new species must become reproductively isolated from the original group • If they are not reproductively isolated, they continue to interbreed and are not different species

  32. Evolutionary Developmental Biology • Comparison of development of organisms to understand evolutionary relationship and ancestral linkages • Theory of Recapitulation • Principle of Continuity • Signature Principle

  33. Figure 25-14 • Webbed vs unwebbed feet • Two genes • BMP4 = gene for foot development • Gremlin = gene inhibits BMP4 • Natural selection takes over • Can introduce gremlin gene and produce web-feet in chickens

  34. Hox Genes – Fig. 25-15 • Controller genes • Regulate activation of other genes • Critical in the development of “body plans” • The more Hox genes, the greater the complexity

  35. Genomes and Proteomes • Evolution of eye • Visual eye has evolved independently in a number of animal groups Fig. 25.18

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