2/24/14 Collect H-W practice sheet  ??? Evolution Quiz (Chp.15) After Quiz: Start Chp.17 Guided Reading DUE TOMORROW!

AP Biology: 2/25/14 Chapter 17 ~ Speciation

Microevolution Changes in allele frequency of a population over time (changes in single gene pool) What we studied in Chp.15 Ex: H-W Equilibrium

Macroevolution Large Scale changes (Ex: evolution of birds from dinosaurs, evolution of seeds in plants)

Macroevolution: the origin of new taxonomic groups Speciation = the origin of new species 1- Anagenesis (phyletic evolution) = accumulation of heritable changes without branching into new species 2- 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 it is genetically isolated from other populations

Modes of speciation (based on how gene flow is interrupted) Allopatric = populations segregated by a geographical barrier; can result in adaptive radiation (island species) Independent selective pressures Genetic Drift Founder Effect Ex: Darwin’s Finches Allopatric is by far the more common

Sympatric Speciation Sympatric = reproductively isolated subpopulation in the midst of its parent population Change in genome: polyploidy in plants New behavior or food

Reproductive Isolation (isolation of gene pools) Prezygotic barriers = impede mating between species or hinder the fertilization of the ova Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling) Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors)

Postzygotic barriers =fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult 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) ***Hybrid Zone = area of overlap between 2 closely related species.

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

Adaptive Radiation The evolution of many new and diversely adapted species from a single common ancestor on introduction to a new environment Ex: silverswords (Hawaii), Cichlids (Africa), mammals (world, after extinction of dinosaurs) Cambrian Explosion  600 mya, origin of most animal phyla

Speciation Questions for Discussion