Lecture #11 Date

Lecture #11 Date

Lecture Date ________ Chapter 24 ~ The Origin of Species Macroevolution: the origin of new taxonomic groups Speciation: the Anagenesis (phyletic evolution):

origin of new species accumulation of heritable changes Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity) What is a species? Biological

species concept (Mayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations) Reproductive Isolation (isolation of gene pools), I

Prezygotic barriers: impede mating between species or hinder the fertilization of the ova EXAMPLES Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling)

Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors) Reproductive Isolation, II Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult

EXAMPLES Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity) Reduced hybrid fertility (mule; horse x donkey; cannot backbreed) Hybrid breakdown (cotton; 2nd generation hybrids are sterile) Modes of speciation (based on how gene flow is interrupted) Allopatric: populations segregated

by a geographical barrier; can result in adaptive radiation (island species) Sympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes Punctuated equilibria

Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the nongradual appearance of species in the fossil record

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