1. Chapter 24 ~ The Origin of Species

2. Macroevolution: evolutionary change above the species level:
Speciation: the origin of new species
Results in diversity of life forms
Can be slow(gradualism) or occur in bursts (punctuated equilibrium).
Macroevolution: describes evolution above the level of the species

3. Speciation and extinction:
Mass extinctions are often followed by adaptive radiation
Example: radial expansion of mammals after the extinction of dinosaurs (horse)

4. Two forms of speciation:
1- Anagenesis (phyletic evolution): accumulation of heritable changes
Transforms a species into a species with different characteristics

5. Two forms of speciation:
Cladogenesis:
branching evolution
The splitting of the gene pool into two or more separate pools, which give rise to one or more new species

6. Anagenesis vs. cladogenesis
Which form of speciation is the basis for biological diversity?

7. How does the environment influence speciation
How does the environment influence speciation? (physiological responses)
Examples:
Phototropism(plants and planaria) the response to the presence of light
Photoperiodism(flowering plants, chickens and eggs) response in change in the length of the night

8. More examples: Diurnal/nocturnal
Circadian rhythms: physiological cycle of about 24 hours
Present in all eukaryotes
Can persist in the absence of external cues
Diurnal/nocturnal
Seasonal responses- hibernation, estavation and migration

9. More examples:
Quorum sensing in bacteria: regulation of gene expression in response to cell population and density

10. What is a species? Biological species concept (Mayr):
a population or group of populations whose members have the potential to:
Reproductive compatibility;
Interbreeding, producing viable offspring
Cannot produce viable offspring with members of other populations

11. Alternatives to the biological species concept:
1. morphological species concept
2. paleontological species concept
3. ecological species concept
4. phylogenic species concept

12. Reproductive Isolation (isolation of gene pools)
New species arising when two populations diverge from a common ancestor and become reproductively isolated
Must be maintained for species to remain distinct

13. 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)

14. Reproductive Isolation (cont.)
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)

15. Something to think about:
Can prezygotic and postzygotic reproductive barriers break down?
Are there real world examples of this??

16. Modes of speciation: (based on how gene flow is interrupted)
Allopatric: populations segregated by a geographical barrier
Separated from its parent population
Adaptive radiation (island species)
Occurs when potential to interbreed and produce fertile offspring no longer exists
Examples: flycatchers

17. Modes of speciation (based on how gene flow is interrupted)
Sympatric: reproductively isolated subpopulation in the midst of its parent population
*no geographic isolation but reproductive barriers
*Examples: polyploidy in plants; cichlids

18. Modes of speciation (based on how gene flow is interrupted)

19. Tempo of Speciation: Gradualism vs. Punctuated Equilibria
Gradual divergence from a common ancestor
Change in morphology over a long time as unique adaptations are acquired

20. Tempo of Speciation: Gradualism vs. Punctuated Equilibrium
Sudden change
Evolution in short bursts
New species bud from parent species and then changes little for the rest of its existence