Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 19 Speciation and Macroevolution

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Reproductive isolating mechanisms Prevent gene flow between species Prezygotic barriers –Prevent mating or fertilization Postzygotic barriers –Reproductive failure after fertilization

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Temporal isolation Mating at different times of year Mating at different times of day

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Habitat isolation Different habitats in the same area Gametic isolation Incompatible egg and sperm Molecular recognition on the surface of the cells

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Behavioral (sexual) isolation Required courtship behaviors The male satin bowerbird builds a bower of twigs (a dark tunnel) to attract females

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Mechanical isolation Incompatible genital organs Only small bees can land on the petal of the black sage Only large bees brush against the stamens of the white sage

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Postzygotic barriers Hybrid inviability –hybrid embryos die when genetic regulation fails during development Hybrid sterility –problems during meiosis cause abnormal gametes

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Postzygotic barriers Hybrid breakdown –Hybrid cannot reproduce because of some defect

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Speciation A population becomes reproductively isolated The separated gene pools diverge Genetic exchange stops

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Allopatric speciation Geographically separated populations Most common form of speciation Genetic drift in small populations

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Squirrel species separated by the Grand Canyon have diverged in fur color

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Sympatric speciation Divergence of two populations in the same geographic region Other reproductive isolating mechanisms at work Especially common in plants

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Allopolyploid Hybrid with multiple sets of chromosomes from two species Autopolyploid Hybrid with multiple sets of chromosomes from a single species

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Sympatric speciation by allopolyploidy in plants

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Sympatric speciation in animals Population occupies a new ecological niche No gene flow even though species live in the same area

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Two species of maggot flies are sympatric in the northern half of one fly’s range

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Rate of evolutionary change Fossil record often lacks transitional forms between two species Is the fossil record simply incomplete? Or does it accurately reflect evolution as it really occurs?

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Punctuated equilibrium Long periods of stasis (~2 My) Punctuated by periods of rapid speciation (~100,000 y) Triggered by changes in the environment Abrupt appearance of new species in the fossil record

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Gradualism Continuous evolution over long periods The traditional view Populations gradually accumulate adaptations Different selective pressures in different environments

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Gradualism

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Punctuated Equilibrium

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Macroevolution Large-scale phenotypic changes in populations, classified at the species level or higher Appearance of evolutionary novelties Adaptive radiation Mass extinction

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Preadaptations Features that fulfilled one role but later became adaptive in a different role –Feathers originally provided thermal insulations –After gradual change they served a new function in flight

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Allometric growth Varied rates of growth for different parts of the body A change in development can result in a new species when the change is adaptive

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Allometric growth

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Paedomorphosis Retention of juvenile characteristics in the adult A change in the timing of development

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Paedomorphosis in an axolotl salamander

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Adaptive radiation Speciation fills new ecological niches New adaptive zones may appear when the environment changes One species colonizes an island and diversifies into new species

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Adaptive radiation

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Extinction Facilitates evolution by opening adaptive zones Background extinction at a steady rate

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Mass extinctions Five or six mass extinctions of many species and higher taxonomic groups –Major climate changes –Catastrophes such as asteroid impacts

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 19 Speciation and Macroevolution Mass extinction of the archosaurs