1. Speciation & Rates of Evolution
Biology 101B

2. Reproductive Isolation Two Types:
1. Prezygotic Isolation
Prevents reproduction by making fertilization unlikely
Geographic isolation- separated by barrier (river, canyon)
Temporal- mating occurs at different times for different species (trout, fireflies, some flowers)
Behavioral isolation- no sexual attraction or communication- use different mating songs or calls
Mechanical- structural differences- sex organs “don’t fit”
Gametic- gametes fail to unite & create viable offspring

3. Reproductive Isolation Two Types:
Liger
2. Post-zygotic Isolation
Prevents the development of fertile adults
Hybrid inviability- zygote fails to develop
Hybrid sterility- offspring are sterile & cannot produce offspring
EX: Liger: cross between a male lion and a female tiger creates liger which is usually sterile
EX: Mule: cross btwn donkey & horse.
Tigon

4. Reproductive Isolation leads to SPECIATION
Speciation: Process by which some members of a sexually reproducing population change so much that they can no longer produce fertile offspring with members of the original population.

5. Speciation Two Types: Allopatric Speciation (Geographic isolation)
Physical barrier divides one population into two or more populations
Mountain ranges, channels btwn islands, rivers, canyons, lava flows
2 different species evolve from same ancestral species
EX: Kaibab squirrel & Abert squirrel separated by Grand Canyon
Activity 23.2 Allopatric Speciation

6. Speciation Two Types: Sympatric Speciation
Species evolves into a new species without a physical barrier
Some insects and plants evolve this way
Most likely due to mutation.

7. Patterns of Evolution Adaptive Radiation
Many species evolve from a common ancestor
Occurs as a result of formation of new habitat or other ecological opportunities
Also called divergent evolution
May follow mass extinctions
EX: cichlid fish in Lake Victoria
EX: Darwin’s finches

8. Patterns of Evolution Coevolution
Species evolve in close relationships with other species
Mutualism
Ex: flowers & their insect pollinators
Predator-prey
Ex: cheetahs & antelope
Ex: plant chemical defenses & insects

9. Patterns of Evolution Convergent evolution
Unrelated species evolve similar traits even though they live in different parts of the world.
Similarity in environment has led to evolution of similar traits.
EX: Madagascar aye-aye and New Guinea striped opossum both have elongated middle fingers. Live separately but have same structure

10. Rates of Evolution Two Types:
Gradualism
Small, gradual steps
Traits remain unchanged for millions of years
Punctuated Equilibrium
Abrupt transitions
Seen in fossil record
Rapid spurts of genetic change caused divergence quickly

11. What are some current trends in evolution?
1. Natural Selection
Antibiotic resistance in bacteria
Pesticide resistance in insects
Industrial melanism- peppered moths changed due to pollution.
Generally, organisms that are more general in their needs survive. A species that requires a specific food source or habitat will be less able to change.
2. Artificial Selection
Genetically modified foods
Selective breeding in dogs
What are some current trends in evolution?
Antibiotic Use & Evolution

12. HIV and drug resistance