1. Chapter 24: The Origin of Species

2. Essential Knowledge
1.c.1 – Speciation and extinction have occurred throughout the Earth’s history (24.3 & 24.4).
1.c.2 – Speciation may occur when two populations become reproductively isolated from each other (24.1).
1.c.3 – Populations of organisms continue to evolve (24.2).
2.e.2 – Timing and coordination of physiological events are regulated by multiple mechanisms (24.1).

3. Two Concepts of Species
1. Morphospecies 2. Biological Species

4. Morphospecies
Organisms with very similar morphology

5. Two Schools
1. Splitters - Break apart species into new ones on the basis of small phenotype changes 2. Lumpers - Group many phenotype variants into one species

6. Biological Species
A group of organisms that could interbreed in nature and produce fertile offspring
Don’t identify species based upon similar likeness ALONE!

7. Key Points Could interbreed Fertile offspring
May or may not be similar in phenotype

8. Morphospecies & Biological Species
Often overlap
Serve different purposes

9. Other Concepts of Species
1. Recognition Species Concept 2. Cohesion Species Concept 3. Ecological Species Concept 4. Evolutionary Species Concept

10. Ecological Species Concept
Emphasizes a specie’s role or function in the environment.
Called an organism’s niche

11. Hybridization has been successful in captivity
(Added Slide ) Lions and tigers are ecologically isolated
Live in forest
Live in open
grassland
Tiglon
Hybridization has been successful in captivity
But it does not occur in the wild

12. Evolutionary Species Concept
Emphasizes evolutionary lineages and ecological roles
Used extensively in comparative biology
Popular among paleontologists

13. Speciation Speciation = formation of a NEW species
Caused by disruptive selection (see Ch 23)
3 Requirements for speciation:
Variation in the population
Selection
Isolation

14. Reproductive Barriers
Serve to isolate a populations from other gene pools
Create and maintain “species”

15. Main Types of Reproductive Barriers
Prezygotic –
Prevent mating or fertilization
Postzygotic –
Prevent viable, fertile offspring

16. Prezygotic - Types
1. Habitat Isolation 2. Behavioral Isolation 3. Temporal Isolation 4. Mechanical Isolation 5. Gametic Isolation

17. Habitat Isolation
Populations live in different habitats or ecological niches
Ex – mountains vs. lowlands

18. Behavioral Isolation Mating or courtship behaviors different
Different sexual attractions operating
Ex – songs and dances in birds

19. Temporal Isolation Breeding seasons or time of day different
Ex – flowers open in morning or evening

20. Mechanical Isolation
Structural differences that prevent gamete transfer
Ex – anthers of flower not positioned to put pollen on a bee, but will put pollen on a bird

21. Gametic Isolation Gametes fail to attract each other and fuse
Ex – chemical markers on egg and sperm fail to match

22. Postzygotic - Types
1. Reduced Hybrid Viability 2. Reduced Hybrid Fertility 3. Hybrid Breakdown

23. Reduced Hybrid Viability
Zygote fails to mature or develop
Ex:
When two different species of frogs hybridize
Egg is fertilized (zygote IS formed)
Zygote never develops properly (if at all)

24. Reduced Hybrid Fertility
Hybrids/offspring are living, viable
Offspring cannot reproduce sexually (nonfertile)
Chromosome count often “odd”
Meiosis doesn’t work out
Ex: mules, ligers

25. Hybrid Breakdown Hybrid/offspring are living, viable AND fertile
Offspring cannot compete successfully with the “pure breeds”
Ex:
Most plant hybrids
Plants are “born” and can produce seeds
Blooms/plants may lack certain color or size of petal

26. Their mating calls also differ substantially
Hybrids between them produced defective embryos in the lab
Their mating calls also differ substantially

27. Modes of Speciation 1. Allopatric Speciation 2. Sympatric Speciation
Both work through a block of gene flow between two populations

29. Allopatric Speciation
Allopatric = other homeland
Ancestral population split by a geographical feature.
Comment – the size of the geographical feature may be very large or small

30. Example Pupfish populations in Death Valley
Generally happens when a species range shrinks for some reason

31. Another Example

32. Conditions Favoring Allopatric Speciation
1. Founder's Effect - with the peripheral isolate 2. Genetic Drift – gives the isolate population variation as compared to the original population 3. Selection pressure on the isolate differs from the parent population

33. Result Gene pool of isolate changes from the parent population
New species can form

34. Comment
Populations separated by geographical barriers may not evolve much
Ex - Pacific and Atlantic Ocean populations separated by the Panama Isthmus
Fish - 72 identical kinds
Crabs - 25 identical kinds
Echinoderms - 25 identical kinds

35. Adaptive Radiation
Rapid emergence of several species from a common ancestor
Common in island and mountain top populations or other “empty” environments
Ex – Galapagos Finches

36. Sympatric Speciation Sympatric = same homeland
New species arise within the range of parent populations
Can occur In a single generation

38. Plants
Polyploids may cause new species because the change in chromosome number creates postzygotic barriers
Animals: Don't form polyploids and will use other mechanisms

39. Polyploid Types
1. Autopolyploid - when a species doubles its chromosome number from 2N to 4N
2. Allopolyploid - formed as a polyploid hybrid between two species
Ex: wheat

40. Autopolyploid

41. Allopolyploid

42. Rate of Evolution??

43. Gradualism Evolution Darwinian style of evolution
Small gradual changes over long periods of time

44. Gradualism Predicts: Long periods of time are needed for evolution
Fossils should show continuous links
Problem: Gaps in fossil record

45. Punctuated Evolution New theory on rate/pace of evolution
Elridge and Gould – 1972

46. Punctuated Equilibrium
Evolution has two speeds of change:
Gradualism or slow change
Rapid bursts of change/speciation

47. Predictions Speciation can occur over a very short period of time
Fossil record will have gaps or missing links
New species will appear in the fossil record
Established species will show

49. Comment
Punctuated Equilibrium is the newest, most widely accepted view
Best explanation of timing

50. Summary Identify several concepts of "species".
Recognize reproductive barriers that keep two species from reproducing with each other.
Recognize various mechanisms of speciation and hybrid zones.
Identify the Gradual and Punctuated interpretations of speciation.
Identify genetic mechanisms of speciation.