Lecture #11 Date ________Lecture #11 Date ________

• Chapter 24 ~ Chapter 24 ~ The Origin of The Origin of SpeciesSpecies

Macroevolution: Macroevolution: the origin of new taxonomic groupsthe origin of new taxonomic groups

• Speciation: Speciation: the origin of new speciesthe origin of new species

• 1-1- Anagenesis Anagenesis (phyletic evolution): (phyletic evolution): accumulation of heritable changesaccumulation of heritable changes

• 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

MacroevolutionMacroevolution

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What is a species?What is a species?

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

Reproductive Isolation (isolation of gene pools), IReproductive Isolation (isolation of gene pools), I

• Prezygotic barriers:Prezygotic barriers: impede mating impede mating between species or hinder the fertilization between species or hinder the fertilization of the ovaof the ova

• Habitat (snakes; water/terrestrial)Habitat (snakes; water/terrestrial)

• Behavioral (fireflies; mate signaling)Behavioral (fireflies; mate signaling)

• Temporal (salmon; seasonal mating)Temporal (salmon; seasonal mating)

• Mechanical (flowers; pollination Mechanical (flowers; pollination anatomy)anatomy)

• Gametic (frogs; egg coat receptors)Gametic (frogs; egg coat receptors)

Reproductive Isolation, IIReproductive Isolation, II• Postzygotic barriers: Postzygotic barriers: fertilization occurs, but fertilization occurs, but

the hybrid zygote does not develop into a the hybrid zygote does not develop into a viable, fertile adultviable, fertile adult

• Reduced hybrid viability (frogs; zygotes Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)fail to develop or reach sexual maturity)

• Reduced hybrid fertility (mule; horse x Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)donkey; cannot backbreed)

• Hybrid breakdown (cotton; 2nd Hybrid breakdown (cotton; 2nd generation hybrids are sterile)generation hybrids are sterile)

Modes of speciation Modes of speciation (based on how gene flow is interrupted)(based on how gene flow is interrupted)

• Allopatric:Allopatric: populations segregated by a populations segregated by a geographical barrier; can geographical barrier; can result in adaptive radiation result in adaptive radiation (island species)(island species)

• Sympatric:Sympatric: reproductively isolated reproductively isolated subpopulation in the midst of subpopulation in the midst of its parent population (change its parent population (change in genome); polyploidy in in genome); polyploidy in plants; cichlid fishesplants; cichlid fishes

Punctuated equilibriaPunctuated equilibria

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