1. Origin of Species Chapter 24

2. What you need to know!  The biological concept of species.  The difference between microevolution and macroevolution.  Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations.  How allopatric and sympatric speciation are similar and different.  How an autopolyploid or an allopolyploid chromosomal change can lead to sympatric speciation.  How punctuated equilibrium and gradualism describe two different tempos of speciation.

3. Species  A population (or group of populations) who can mate and produce fertile offspring with one another but not with a different group  Speciation: process by which new species arise  Microevolution: A population transforms over time as adaptations add up in its gene pool (changing allele frequency)  Macroevolution: major developmental changes that spawn new branches of species  Spinal cord – vertebrates  Feathers - birds

4. Adaptations  A genetic change that makes an organism better suited to its environment  Natural Selection facilitates adaptation within populations Special adaptations:  Mimicry: mimicking another organism that is potentially dangerous  Camouflage: blending in with the environment

5. Reproductive Isolation A.Prezygotic (before zygote) – prevent mating and/or hinder fertilization) 1.Habitat isolation: same area but not the same habitat 2.Behavioral isolation: different mating practices 3.Temporal isolation: reproduce at different times of day or year 4.Gametic isolation: sperm cannot fuse with egg

6. Reproductive Isolation B.Postzygotic (after zygote) – fertilized eggs don’t develop into fertile adults: 1.Reduced hybrid viability: genetic incompatibility terminates pregnancy 2.Reduced hybrid fertility: viable offspring that cannot reproduce (mule) 3.Hybrid breakdown: viable offspring that grow and reproduce but their offspring are weak or sterile

7. Speciation Allopatric Speciation  Interbreeding becomes impossible due to geographic isolation (rivers, canyons, mountains)  New species evolve on the fringes of large ancestral populations Sympatric Speciation  Sudden mutation within a population leads to new species  Polyploidy plants mutate by altering chromosome number in a non-disjunction error

8. Adaptive Radiation  Colonization of a new habitat  New habitats usually vary from the original habitat Example: 1.Original Species A migrates to an unpopulated island chain 2.A is geographically isolated from the original population and speciates into B 3.B migrates to unpopulated islands 4.B is geographically isolated from the original population and speciates into C 5.& 6. C migrates to other islands 7.C is geographically isolated and speciates into D 8.D migrates to other islands 9.D is geographically isolated and speciates into E

9. Rate of Change  Species that change slowly are K selected  i.e. elephants, humans  Species that change quickly are r selected  i.e. Bacteria, viruses  Gradualism: species descend from common ancestors and gradually diverge  Punctuated equilibrium: period of apparent stasis followed by rapid adaptive radiation