1. Speciation Where do species come from?

2. Two Basic Patterns of Evolutionary Change
Anagenesis
Cladogenesis

3. Definition of a species
Biological species
A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but unable to do so with members of other populations

4. The biological species is based on reproductive isolation
Reproductive isolation - the existence of biological factors
(=barriers*) the impede two organisms from producing viable, fertile offspring
*these barriers are known as reproductive isolating mechanisms or RIM’s

5. What are these ‘barriers’?
2 kinds:
Prezygotic - those that inhibit reproduction before fertilization
Postzygotic - those that inhibit reproduction after fertilization

6. Prezygotic Barriers Habitat Isolation Never meet to breed
Water bugs - Trichocorixa
Brackish
saltmarsh ponds
Freshwater ponds
Never meet to breed

7. Prezygotic Barriers Temporal Isolation Western spotted skunk
Eastern spotted skunk
Area where ranges overlap

8. Prezygotic Barriers Temporal Isolation Mates in late summer
Western spotted skunk
Eastern spotted skunk
Area where ranges can
overlap
Mates in late summer
Mates in late winter

9. Prezygotic Barriers Behavioural Isolation Courtship differences
Prairie grouse
Sage grouse

10. Prezygotic Barriers Mechanical Isolation - damselflies
Mating in Damselflies

11. Prezygotic Barriers Gametic Isolation -reproduction in sea urchins
Red and purple urchins fertilize externally at the same time
Gametes are incompatible and won’t fuse

12. Behavioural Isolation
Prezygotic Barriers
Summary
Habitat Isolation
Temporal Isolation
Behavioural Isolation
Mechanical Isolation
Gametic Isolation
All prevent production of offspring by acting
before fertilization

13. Postzygotic Barriers
- those that inhibit reproduction after fertilization
1. Reduced hybrid viability X
E. eschscholtzi
E. klauberi
Lower viability

14. Postzygotic Barriers
- those that inhibit reproduction after fertilization
1. Reduced hybrid fertility X
Horse
Donkey
Mule
- robust but sterile

15. Postzygotic Barriers
- those that inhibit reproduction after fertilization
1. Hybrid Breakdown - hybrid strains of rice
Fertile hybrid
Fertile hybrid
Infertile offspring of the two hybrids

16. Reduced hybrid viability Reduced hybrid fertility
Postzygotic Barriers
Summary
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
All prevent production of offspring by acting
after fertilization

17. Postzygotic Barriers Prezygotic Barriers Roughly reflect time
Habitat Isolation
Temporal Isolation
Behavioural Isolation
Mechanical Isolation
Gametic Isolation
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Roughly reflect time
since species began to
differentiate

18. Summary from your book

19. Kinds of Speciation
Allopatric (= “different country”)
Speciation that occurs when the gene flow between populations is interrupted by a geographical barrier

20. Populations change independently
Kinds of Speciation
Allopatric - via a vicariance event
Geographical
separation
Original population
Populations change independently
of one another
No interbreeding if barrier is removed

21. Allopatric - via a vicariance event
Kinds of Speciation
Allopatric - via a vicariance event
A real example - antelope squirrels (Ammophilus) on the edges of the Grand Canyon
A. leucurus
A. harrisi

22. Allopatric - Founder effect
Kinds of Speciation
Allopatric - Founder effect
(similar to a bottleneck)
- at least one fertilized female invades a new habitat or geographical location
Several generations
Invasion of new habitat

23. Allopatric - Founder effect - Hawaiian Drosophila
Kinds of Speciation
Allopatric - Founder effect
- Hawaiian Drosophila
Initial invasion
(6-8 million years ago)

24. Allopatric - Founder effect
Kinds of Speciation
Allopatric - Founder effect
Often closely tied with ADAPTIVE RADIATION
Adaptive radiation - the evolution of many diversely adapted species from a common ancestor after introduction to new environments

25. Allopatric - Founder effect
Kinds of Speciation
Allopatric - Founder effect
ADAPTIVE RADIATION - Hawaiian silverswords
Tarweed
ancestor

26. Kinds of Speciation
2. Sympatric (= “same country”)
Speciation that occurs when there is no geographical barrier to interrupt gene flow between population.

27. Kinds of Speciation
2. Sympatric (= “same country”)
Sympatric speciation occurs most frequently by chromosome changes or through non-random mating.

28. 2. Sympatric (= “same country”)
Kinds of Speciation
2. Sympatric (= “same country”)
a. Chromosome changes
Figure 24.8 in your book

29. Kinds of Speciation
2. Sympatric (= “same country”)
a. Chromosome changes
Anemone

30. Introduction of apples
Kinds of Speciation
2. Sympatric (= “same country”)
b. Behavioural differences
Apple maggot flies
-laid eggs on hawthorn
Apple maggot flies
-lays eggs on hawthorn and apple
Introduction of apples
200 years ago
Now

31. 2. Sympatric (= “same country”)
Kinds of Speciation
2. Sympatric (= “same country”)
b. Behavioural differences
“apple” flies
Females prefer to lay eggs on apples
“apple” males prefer “apple” females
Females prefer to lay eggs on hawthorn
“hawthorn” males prefer “hawthorn” females
“hawthorn” flies
“hawthorn” flies

32. Tempo of Speciation
How does it occur over time? T I M E

33. Hybrid Zones
Hybrid Zone
Range of species A
Range of species B

34. Hybrid Zones

35. Reinforcement Fusion Stability Gene flow in hybrid zone
Divergence and speciation
Some barrier to gene flow is established
Normal interbreeding populations
Reinforcement
Fusion
Stability

36. Reinforcement in Hybrid Zones

37. Fusion in Hybrid Zones
Cichlids in Lake Victoria

38. Speciation Rates
Single gene mutant
Euhadra – Japanese land snail

39. Finally, reproductive isolation by a pollinator
Mimulus lewisii
Mimulus cardinalis

40. Finally, reproductive isolation by a pollinator
Mimulus lewisii
yuplewisii gene
yupcardinalis gene
Mimulus cardinalis

41. M. lewisii with cardinalis yup gene M. cardinalis
Visits by pollinator
68x increase
74x increase
M. lewisii
M. lewisii with cardinalis yup gene
M. cardinalis
M. cardinalis with lewisii yup gene