1. Macroevolution: Investigating the Origin of Species *Adapted from Macroevolution lecture at ccbcmd.edu.

2. Learning Targets: Distinguish between anagenesis and cladogenesis. Define biological species (Mayr) and describe limitations of the concept. Distinguish between prezygotic and postzygotic mechanisms of reproductive isolation.

3. Speciation Anagenesis – One species replaces another – No net change in number of species Cladogenesis – One species branches off from an existing species – A net increase in number of species (diversity)

4. Biological Species Concept A species is a group of individuals whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring but cannot successfully interbreed with members of other species Reproductive isolation prevents breeding with other species

5. Problems with the biological species concept… Not helpful in determining species in fossil record Doesn’t account for asexual organisms Scientists can’t observe all potential interbreeding (in nature or in the lab)

6. Reproductive Isolation: Prezygotic Barriers Impede mating or fertilization: 1.Geographical isolation 2.Behavioral isolation 3.Temporal isolation 4.Hybrids

7. Geographical Isolation: Species are separated by physical barriers. Example: Spotted Owl Species Scientists believe that glaciers during the ice age separated the two populations of owls.

8. Behavioral isolation – Species choose mates based on different behaviors – Examples: bird songs or mating dances

9. Temporal Isolation 1.Species mate at different times of year 2.Species mate at different times of day

10. Hybrid Inviability Example: embryos of sheep and goat hybrids usually die in early development, seeds of some hybrids of peanut plant species will not develop

11. Hybrid Sterility Horse (2N=64) X Donkey (2N=62) = Mule - Mule (hybrid of the two species) is sterile

12. Hybrid Breakdown Offspring of hybrid (F2 generation) not able to survive or reproduce Example: sunflower hybrids – 80% of F2 generation are defective in some way and cannot reproduce successfully

13. Allopatric Speciation Allo = other, patric = homeland Speciation in geographically separate populations Example: speciation of squirrels after separation by the Grand Canyon, speciation of reef fish separated by a land bridge

14. Adaptive Radiation Evolution of many diversely adapted species from a common ancestor – common on island chains Example: Hawaiian honeycreepers evolved from one common ancestor

15. Sympatric Speciation Sym = same, patric = homeland Speciation in over-lapping populations Example: speciation of stickleback species in one same lake due to food specialization, speciation of cichlids due to mate choice

16. Polyploidy in Plants Speciation of plants with extra chromosomes due to abnormal cell division, or hybridization of two different species Polyploids may be able self-fertilize or cross with other polyploids

17. Gradualism vs Punctuated Equilibrium Which is which? Small continuous changes over time Rapid change followed by periods of stasis (little or no change)

18. Gradualism vs Punctuated Equilibrium Which is which? Small continuous changes over time = Gradualism Rapid change followed by periods of stasis (little or no change) = Punctuated Equilibrium