1. The Origin of Species
Chapter 24

2. YOU MUST KNOW The biological concept of species
Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations
A description of similar species that are maintained separate by each type of isolating barrier
How allopatric and sympatric speciation are similar and different
How a change in chromosome number can lead to sympatric speciation
Why speciation rates are often rapid in situations when adaptive radiation occurs or in times of ecological stress
The connection between a change in gene frequency, a change in the environment, natural selection, or genetic drift and speciation
How punctuated equilibrium and gradualism describe two different tempos of speciation

3. I. Speciation and Reproductive Isolation
Speciation – process by which new species arise
Biological Species Concept – a species is a group of populations whose individuals have the potential to interbreed in nature and produce viable (healthy and fertile) offspring

4. Microevolution – change in the genetic makeup of a population from generation to generation (confined to a single gene pool)

5. C. Macroevolution – broad pattern of evolutionary change
C. Macroevolution – broad pattern of evolutionary change above the species level, such as the appearance of feathers, used to define higher taxa

6. Reproductive Isolation – biological barriers that prevent members of two species from producing viable offspring

7. Prezygotic Mechanisms– occur before a zygote can be created
Geographic/Habitat isolation – do not live in the same place

8. b. Behavioral isolation – mating signals are not the same

10. c. Temporal isolation – different mating seasons

11. Mechanical isolation – anatomically incompatible
Gametic isolation – gametes will not fuse together (common in sea creatures that use external fertilization – sea cucumbers, sea urchins, etc.)
Damsel Fly Penises

12. Postzygotic barriers – zygote may be formed, but offspring does not develop into a fertile adult
Reduced hybrid viability – zygote forms but does not develop

13. b. Reduced hybrid fertility – zygote develops, but is sterile

14. c. Hybrid breakdown – offspring develop into adults, can mate, but produce weak or sterile offspring

15. II. Types of Speciation
Allopatric speciation – new species forms because it is geographically isolated from parent population
1. Can occur because of geologic events – emergence of a mountain range, formation of a land bridge, evaporation of a lake

16. Smaller populations more likely to undergo speciation
3. Speciation confirmed when individuals from new population cannot mate successfully with individuals from parent population

17. Sympatric Speciation
Small portion of the population forms a new species without being geographically isolated from parent population

18. 2. Change in habitat, food source, or accident in cell division resulting in change in chromosome number a. Polyploidy – nondisjunction resulting in extra sets of chromosomes – can no longer breed with diploid plants

19. Each one fills its own niche
Adaptive Radiation
Many new species arise from one ancestral species
Each one fills its own niche

20. III. Rate of Speciation
Gradualism – species descend from a common ancestor and gradually diverge more and more in morphology

21. B. Punctuated Equilibrium – describes periods of apparent stasis punctuated by sudden change observed in the fossil record