1. Speciation & Macroevolution
Packet #30

2. Reproductive Isolating Mechanisms
Restriction of gene flow between species.

3. Reproductive Isolating Mechanisms Prezygotic Barriers
Reproductive isolating mechanisms that prevent fertilization from taking place
Temporal Isolation
Two species reproducing at different times of the day, season or year
Habitat Isolation
Two closely related species that live and breed in different habitats in the same geographic area

4. Prezygotic Barriers II
Behavioral Isolation
Distinctive courtship behaviors prevent mating between species
Mechanical Isolation
Incompatible structural differences in reproductive organs of similar species
Gametic Isolation
Gametes of different species are incompatible
Due to molecular and chemical differences

5. Postzygotic Barriers Definition Hybrid Inviability Hybrid Sterility
Reproductive isolating mechanisms that prevent gene flow after fertilization has taken place
Hybrid Inviability
Death of interspecific embryos during development.
Hybrid Sterility
Prevents interspecific hybrids that survive adulthood from reproducing successfully
Hybrid Breakdown
Prevents offspring of hybrids that survive to adulthood and successfully reproduce, from reproducing beyond one or a few generations.

6. Speciation The evolution of a new species from an ancestral population
More likely to occur when the population is small.

7. Allopatric Speciation
One population becoming geographically isolated from the rest of the species
Eventually leading to divergent evolution
Death valley pupfish
Kaibab squirrels
Porto Santo rabbits

8. Sympatric Speciation Animals
The genetic divergence of multiple populations (from a single parent species) inhabiting the same geographic region
Plants
Results from allopolyploidy
Polyploid individual (one with more than two sets of chromosomes) is a hybrid derived from two species
Kew primroses and hemp nettles
Animals
How it occurs remain to be determined
Fruit maggot flies and cichlids

9. Pace of Evolution Punctuated Equilibrium Gradualism
Evolution of species that occur in spurts
Short periods of active speciation are interspread with long periods of stasis.
Gradualism
Populations diverge slowly from one another by the accumulation of adaptive characteristics within a population.

10. Macroevolution Definition
Large-scale phenotypic changes in populations that warrant their placement (species) in taxonomic groups at the species level and higher. (new taxons)

11. Macroevolution II
Appearance of evolutionary novelties may be due to changes that occurred during development
Changes in regulatory genes could cause structural changes in the organism.
Novelties may originate from preadaptation.
Structures that originally fulfilled one role but changed in a way that was adaptive for a different role.
Feathers
Allometric Growth
Varied different rates of growth for different parts of the body
Result in a change in the overall shape of an organism
Paedomorphosis
Retention of juvenile characteristics in the adult
Occurs to changes in the timing of development
Adult axolotl salamanders with external gills and tail fins

12. Macroevolution III Adaptive Radiation Extinction
Process of diversification of an ancestral species into many new species.
Extinction
Death of a species
Adaptive zones become vacant
Background extinction
Continuous low level extinction of species
Mass extinction
Extinction of numerous and higher taxonomic groups in both terrestrial and marine environments