© 2014 Pearson Education, Inc. (a) Similarity between different species(b) Diversity within a species 1

© 2014 Pearson Education, Inc. Prezygotic barriersPostzygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown MATING ATTEMPT FERTILI- ZATION VIABLE, FERTILE OFF- SPRING (a)(c)(e)(f)(g)(h)(i)(l) (j) (k) (d) (b) 2

© 2014 Pearson Education, Inc. Grizzly bear (U. arctos) Polar bear (U. maritimus) Hybrid “grolar bear” 3

© 2014 Pearson Education, Inc. Allopatric speciation: forms a new species while geographically isolated. (a) (b) Sympatric speciation: a subset forms a new species without geographic separation. 4

© 2014 Pearson Education, Inc. Under low predation: body shape that favors long, steady swimming (b)Under high predation: body shape that enables rapid bursts of speed (a) 5

© 2014 Pearson Education, Inc. A. formosus A. nuttingi ATLANTIC OCEAN PACIFIC OCEAN A. panamensis A. millsae Isthmus of Panama 6

© 2014 Pearson Education, Inc. Experiment Mating experiments after 40 generations Some flies raised on starch medium Results Some flies raised on maltose medium Initial population of fruit flies (Drosophila pseudoobscura) Female StarchMaltose Starch population 1 Starch population Male Maltose Starch population 1 Starch population 2 Number of matings in experimental group Number of matings in control group 7

© 2014 Pearson Education, Inc. Cell division error Tetraploid cell 4n  12 New species (4n) 2n  6 2n2n Gametes produced by tetraploids 8

© 2014 Pearson Education, Inc. Species A 2n  6 Species B 2n  4 Normal gamete n  3 Normal gamete n  3 Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Unreduced gamete with 4 chromosomes New species: viable fertile hybrid (allopolyploid) 2n  10 Meiotic error; chromosome number not reduced from 2n to n 9

© 2014 Pearson Education, Inc. Normal light Monochromatic orange light Experiment P. pundamilia P. nyererei 10

© 2014 Pearson Education, Inc. Fire-bellied toad range Fire-bellied toad, Bombina bombina Yellow-bellied toad range Hybrid zone Hybrid zone Fire-bellied toad range Yellow-bellied toad range Distance from hybrid zone center (km) Frequency of B. variegata-specific allele Yellow-bellied toad, Bombina variegata

© 2014 Pearson Education, Inc. Isolated population diverges. Possible outcomes: Reinforcement Fusion Stability Hybrid zone Hybrid individual Barrier to gene flow Gene flow Population 12

© 2014 Pearson Education, Inc. Pundamilia nyerereiPundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water 13

© 2014 Pearson Education, Inc. (a) Punctuated model (b) Gradual model Time 14

© 2014 Pearson Education, Inc. (a) Mimulus lewisii M. lewisii with M. cardinalis allele (b) (c) Mimulus cardinalis M. cardinalis with M. lewisii allele (d) 15