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Ap Chapter 24 The Origin Of Species


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Ap Chapter 24 The Origin Of Species

  1. 1. The Origin of Species Chapter 24
  2. 2. Microevolution vs macroevolution <ul><li>Microevolution – changes in gene frequencies within population </li></ul><ul><li>Macroevolution – origin of new taxonomic groups, ie – species level and above </li></ul>
  3. 3. <ul><li>Speciation is at the boundary between microevolution and macroevolution. </li></ul>
  4. 4. What is a species? <ul><li>Species is a Latin word meaning “kind” or “appearance.” </li></ul><ul><li>Traditionally, morphological differences have been used to distinguish species. </li></ul><ul><li>Today, differences in body function, biochemistry, behavior, and genetic makeup are also used to differentiate species. </li></ul>
  5. 5. 4 approaches to species concept <ul><li>Biological – reproductive isolation </li></ul><ul><li>Morphological – anatomical differences </li></ul><ul><li>Ecological – unique roles in environment </li></ul><ul><li>Phylogenetic – based on evolutionary lineage with distinct morphology and molecular sequences </li></ul>
  6. 6. Mayr’s concept of species <ul><li>1942 </li></ul><ul><li>Potential to interbreed and produce fertile offspring </li></ul>
  7. 7. Figure 24.2a The biological species concept is based on interfertility rather than physical similarity
  8. 8. Figure 24.2b The biological species concept is based on interfertility rather than physical similarity
  9. 9. Barriers to speciation <ul><li>Prezygotic – prevent mating or successful fertilization </li></ul><ul><li>Postzygotic - prevent the hybrid zygote from developing into a viable, fertile adult. </li></ul>
  10. 10. Prezygotic barriers <ul><li>Habitat isolation </li></ul><ul><li>Temporal isolation – different breeding times </li></ul><ul><li>Behavioral isolation </li></ul><ul><li>Mechanical isolation </li></ul><ul><li>Gametic isolation </li></ul>
  11. 11. Mechanical Isolation Fig. 24-4h (f) Bradybaena with shells spiraling in opposite directions
  12. 12. Temporal Isolation Fig. 24-4e (c) Eastern spotted skunk (Spilogale putorius) Western spotted skunk (Spilogale gracilis)
  13. 13. Behavioral Isolation Fig. 24-4g (e) Courtship ritual of blue- footed boobies
  14. 14. Gametic isolation in sea urchins Fig. 24-4k (g) Sea urchins
  15. 15. Postzygotic Barriers <ul><li>Reduced hybrid viability - Genetic incompatibility between the two species may abort the development of the hybrid at some embryonic stage or produce frail offspring. </li></ul><ul><li>Reduced hybrid fertility - Even if the hybrid offspring are vigorous, the hybrids may be infertile and the hybrid cannot backbreed with either parental species. </li></ul><ul><li>Reduced hybrid breakdown – In some cases, first generation hybrids are viable and fertile. </li></ul><ul><ul><li>However, when they mate with either parent species or with each other, the next generation is feeble or sterile. </li></ul></ul>
  16. 16. Reduced Hybrid Fertility Fig. 24-4m (i) Donkey
  17. 18. Interfertility concept does not apply to <ul><li>Asexually reproducing organisms </li></ul><ul><li>Extinct species </li></ul>
  18. 19. Modes of speciation <ul><li>Allopatric – geographical separation </li></ul><ul><li>Sympatric – biological barriers prevent gene flow in overlapping populations as in autopolyploidy, allopolyploidy, mate preference, etc. </li></ul>
  19. 20. Figure 24.6 Two modes of speciation
  20. 21. Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon
  21. 22. Figure 24.8 Has speciation occurred during geographic isolation?
  22. 23. what is? <ul><li>Autopolyploidy – more than two sets of chromosomes; meiotic failure, in self-pollination in plants </li></ul><ul><li>Allopolyploidy * – interspecific hybrid may become fertile due to nondisjunction </li></ul><ul><li>* more common </li></ul>
  23. 24. Sympatric speciation by autopolyploidy in plants
  24. 25. Figure 24.15 One mechanism for allopolyploid speciation in plants
  25. 26. Fig. 24-UN2 Ancestral species: Triticum monococcum (2 n = 14) AA BB Wild Triticum (2 n = 14) Product: AA BB DD T. aestivum (bread wheat) (2 n = 42) Wild T. tauschii (2 n = 14) DD
  26. 27. <ul><li>Around 1870, a new species of grass turned up at the salt marches near the coast of the English Channel: Spartina townsendii . It was taller than the indigenous Spartina alternifolia . </li></ul><ul><li>Another relative, Spartina stricta, inhabits the North-American east coast. It was brought in to Europe and began to occupy the sites of Spartina alternifolia. </li></ul><ul><li>It was now suspected that Spartina townsendii was a hybrid of the two original species. The fact that Spartina townsendii has 2n = 126 chromosomes, Spartina alternifolia has 2n = 70 and Spartina stricta has 2n = 56 chromosomes makes this suggestion seem likely. </li></ul>
  27. 28. Hybrid zones <ul><li>Where divergent allopatric populations come back and interbreed </li></ul><ul><li>Biologists look for patterns to study reproductive isolation </li></ul>
  28. 29. Hybrid Zones over Time <ul><li>When closely related species meet in a hybrid zone, there are three possible outcomes: </li></ul><ul><ul><li>Strengthening of reproductive barriers </li></ul></ul><ul><ul><li>Weakening of reproductive barriers </li></ul></ul><ul><ul><li>Continued formation of hybrid individuals </li></ul></ul>
  29. 30. Fig. 24-13 EUROPE Fire-bellied toad range Hybrid zone Yellow-bellied toad range Yellow-bellied toad, Bombina variegata Fire-bellied toad, Bombina bombina Allele frequency (log scale) Distance from hybrid zone center (km) 40 30 20 20 10 10 0 0.01 0.1 0.5 0.9 0.99
  30. 31. Reinforcement: Strengthening Reproductive Barriers <ul><li>The reinforcement of barriers occurs when hybrids are less fit than the parent species that is reproduce less successfully. </li></ul><ul><li>Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species </li></ul>
  31. 32. Fig. 24-15 Sympatric male pied flycatcher Allopatric male pied flycatcher Pied flycatchers Collared flycatchers Number of females (none) Females mating with males from: Own species Other species Sympatric males Own species Other species Allopatric males 0 4 8 12 16 20 24 28
  32. 33. Fusion: Weakening Reproductive Barriers <ul><li>If hybrids are as fit as parents, there can be substantial gene flow between species </li></ul><ul><li>If gene flow is great enough, the parent species can fuse into a single species </li></ul>
  33. 34. Fig. 24-16 Pundamilia nyererei Pundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water
  34. 35. Stability: Continued Formation of Hybrid Individuals <ul><li>Hybrids continue to be produced between the two species in the area of their overlap, but the gene pools of both parent species remain distinct. </li></ul>
  35. 36. Fig. 24-14-4 Gene flow Population (five individuals are shown) Barrier to gene flow Isolated population diverges Hybrid zone Hybrid Possible outcomes: Reinforcement OR OR Fusion Stability
  36. 37. Timing of evolution? <ul><li>Gradual (Lyell, Darwin) </li></ul><ul><li>Punctuated equilibrium (Gould) – evolution occurs in spurts and interspersed within long periods of stasis </li></ul>
  37. 39. In the punctuated <ul><ul><li>Species undergo most morpholo- gical modifications when they first bud from their parent population. </li></ul></ul><ul><ul><li>After establishing themselves as separate species, they remain static for the vast majority of their existence. </li></ul></ul>
  38. 40. Speciation Rates <ul><li>The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid </li></ul><ul><li>The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years </li></ul>