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(a) Similarity between different species

(a) Similarity between different species. (b) Diversity within a species. Prezygotic barriers. Postzygotic barriers. Habitat isolation. Temporal isolation. Behavioral isolation. Mechanical isolation. Gametic isolation. Reduced hybrid viability. Reduced hybrid fertility. Hybrid

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(a) Similarity between different species

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  1. (a) Similarity between different species (b) Diversity within a species

  2. Prezygotic barriers Postzygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown VIABLE, FERTILE OFF- SPRING MATING ATTEMPT FERTILI- ZATION (a) (c) (e) (f) (g) (h) (i) (l) (d) (j) (b) (k)

  3. Grizzly bear (U. arctos) Hybrid “grolar bear” Polar bear (U. maritimus)

  4. Sympatric speciation: a subset forms a new species without geographic separation. (a) (b) Allopatric speciation: forms a new species while geographically isolated.

  5. (a) Under high predation: body shape that enables rapid bursts of speed (b) Under low predation: body shape that favors long, steady swimming

  6. A. nuttingi A. formosus ATLANTIC OCEAN Isthmus of Panama PACIFIC OCEAN A. millsae A. panamensis

  7. Experiment Initial population of fruit flies (Drosophila pseudoobscura) Some flies raised on starch medium Some flies raised on maltose medium Mating experiments after 40 generations Results Female Female Starch population 1 Starch population 2 Starch Maltose Starch population 1 Starch 22 9 18 15 Male Male Starch population 2 Maltose 8 20 12 15 Number of matings in experimental group Number of matings in control group

  8. Cell division error Tetraploid cell 4n 12 2n 6 2n New species (4n) Gametes produced by tetraploids

  9. Species A 2n 6 Species B 2n 4 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes Normal gamete n 3 Hybrid with 7 chromosomes Normal gamete n 3 Unreduced gamete with 7 chromosomes New species: viable fertile hybrid (allopolyploid) 2n 10

  10. Experiment Monochromatic orange light Normal light P. pundamilia P. nyererei

  11. Fire-bellied toad range Fire-bellied toad, Bombina bombina Hybrid zone Yellow-bellied toad range 0.99 Hybrid zone 0.9 Frequency of B. variegata-specific allele Yellow-bellied toad range Fire-bellied toad range 0.5 Yellow-bellied toad, Bombina variegata 0.1 0.01 40 30 20 10 0 10 20 Distance from hybrid zone center (km)

  12. Isolated population diverges. Possible outcomes: Hybrid zone Reinforcement Fusion Gene flow Population Hybrid individual Barrier to gene flow Stability

  13. Pundamilia nyererei Pundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water

  14. (a) Punctuated model Time (b) Gradual model

  15. (b) M. lewisii with M. cardinalis allele (d) M. cardinalis with M. lewisii allele (a) Mimulus lewisii (c) Mimulus cardinalis

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