1. 15.3 Mechanisms of EVOLUTION

3. The formation of a new species
15.3 Speciation
The formation of a new species

4. What is a species?
A group of organisms with similar characteristics capable of producing fertile offspring

5. What is a species?
Members of a species share the same gene pool (sum of all the genes + their different forms – alleles)

6. Speciation
New species are formed when a population diverges into two populations AND

7. Speciation
New species are formed when a population diverges into two populations AND the gene pools of two populations become reproductively isolated

8. Speciation
New species are formed when a population diverges into two populations AND the gene pools of two populations become reproductively isolated = the populations can’t produce a fertile offsprings

9. There are several different ways speciation can occur...

10. Allopatric Speciation Peripatric Speciation Parapatric Speciation
Modes of Speciation
Allopatric Speciation
Peripatric Speciation
Parapatric Speciation
Sympatric Speciation

11. Allopatric Speciation Is a type of geographic isolation
A population is split in two (or more) by some kind of physical barrier (mountain, river, wall…)

12. Allopatric Speciation
The separated populations undergo changes in their genes as they begin to adapt to different environments or as they undergo mutations.

13. Allopatric Speciation
After that time they are no longer
capable of interbreeding (exchanging the genes)

14. EXAMPLE 1 – Allopatric Speciation
A population of wild fruit flies minding its own business on several bunches of rotting bananas. They also lay eggs inside of bananas.

15. EXAMPLE 1 – Allopatric Speciation
A hurricane washes the bananas and the fruit flies’ eggs out to sea. The bananas eventually wash up on an island off the coast of the mainland

16. EXAMPLE 1 – Allopatric Speciation
The fruit flies mature (eggs became flies) and emerge onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them.

17. EXAMPLE 1 – Allopatric Speciation
At this point, speciation has not occurred yet — any fruit flies that would fly back to the mainland could mate and produce healthy offspring with the mainland flies.

18. EXAMPLE 1 – Allopatric Speciation
The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves differently than the mainland population does.

19. EXAMPLE 1 – Allopatric Speciation
Morphology (eye color), food preferences, and mating behaviours change over the course of many generations of natural selection

20. EXAMPLE 1 – Allopatric Speciation
When another storm reintroduces the island flies to the mainland, they will not be able to mate with the mainland flies since they’ve evolved different mating behaviours.

21. EXAMPLE 1 – Allopatric Speciation
The flies’ lineages has split now that genes cannot flow between the populations

22. EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
Darwin thought that a long time ago there must have been a common ancestor to the finch species.

23. EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
As the Galapagos islands were formed, the common ancestor slowly dispersed and broke away from one another.

24. EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
Genetic variations amongst the finches were then selected for by the environment (natural selection).

25. Darwin’s Finches EXAMPLE 2 – Allopatric Speciation
This resulted in the formation of new species on each island

26. EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow wrasse

27. EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow wrasse
Original population was split by the formation of isthmus of Panama about 3.5 million years ago

28. EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow wrasse
Since that time, genetic changes happened in the both populations. These changes led to creation of different species

29. Hawaiian honeycreepers
EXAMPLE 4 – Allopatric Speciation
Hawaiian honeycreepers
Very similar to Galapagos’ finches

30. EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers
On each island of Hawaii, we can find different species of honeycreeper

31. EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers
It is thought that they all descended from a single species of honeycreeper

32. EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers

33. Peripatric Speciation
a special version of the allopatric speciation
- It happens when one of the isolated populations has very few individuals
- genetic drift (the founder effect) plays a major role in this speciation

34. Peripatric Speciation
A population of wild fruit flies minding its own business on several bunches of rotting bananas also laying eggs inside of bananas.

35. Peripatric Speciation
A hurricane washes the bananas and the fruit flies’ eggs out to sea. The bananas eventually wash up on an island off the coast of the mainland

36. Peripatric Speciation
But only a few eggs have survived the journey to end up colonizing the island.

37. Peripatric Speciation
These few survivors just by chance carry some genes that are very rare in the mainland population.

38. Peripatric Speciation
One of these rare genes causes a slight variation in the mating behaviour and changes in sexual organs.
(REMEMBER? it’s an example of the founder effect)

39. Peripatric Speciation
After a few generations, the entire island population ends up having these rare genes.

40. Peripatric Speciation
As the island population grows, flies experience natural selection that favours individuals better suited to the reproductive behaviour, climate and food of the island.

41. Peripatric Speciation
After some generations, the island flies become isolated from the mainland flies.
Peripatric speciation has occurred

42. Peripatric vs Allopatric Speciation
WHAT IS THE DIFFERENCE BETWEEN THEM?

43. Peripatric vs Allopatric Speciation
It is the size of the populations involved!

44. Peripatric vs Allopatric Speciation
In allopatric speciation, a population is separated into two relatively large independent populations.
In peripatric speciation, only a small fraction of the original population becomes geographically isolated.

45. Parapatric Speciation
There is no specific barrier (mountain, river…) to gene flow, but the population does not mate randomly

46. Parapatric Speciation
Individuals are more likely to mate with their geographic neighbours than with individuals in a different part of the population’s area

47. Parapatric Speciation
The two species may come in contact from time to time but (after some time), species can no longer produce offspring together anymore

48. EXAMPLE 1 – parapatric Speciation Anthoxanthum odoratum
A grass species
Anthoxanthum odoratum

49. EXAMPLE 1 – parapatric Speciation
Some of these plants live near mines where the soil has become contaminated with heavy metals.

50. EXAMPLE 1 – parapatric Speciation
Some plants around the mines have experienced natural selection and are now tolerant of heavy metals.

51. EXAMPLE 1 – parapatric Speciation
The neighbouring plants that don’t live in polluted soil have not experienced natural selection for this trait (they have NO tolerance of heavy metals)

52. EXAMPLE 1 – parapatric Speciation
Both plants are close enough that they could fertilize each other (mate with each other)

53. EXAMPLE 1 – parapatric Speciation
However, the two types of plants have evolved different flowering times. This change is the first step in cutting off gene flow between the two groups = SPECIATION

54. Sympatric Speciation
In sympatric speciation, species diverge while inhabiting the same place.

55. Sympatric Speciation
It does not require large area to reduce gene flow between parts of a population

56. Example of Sympatric Speciation
200 years ago, the ancestors of apple maggot flies laid their eggs only on hawthorns
Maggots
Hawthorns

57. Example of Sympatric Speciation
but today, these flies lay eggs on hawthorns and domestic apples (which were introduced to America by immigrants)
Apples
Hawthorns
Maggots

58. Example of Sympatric Speciation
Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in.

59. + So hawthorn flies generally end up mating with other hawthorn flies
Example of Sympatric Speciation
So hawthorn flies generally end up mating with other hawthorn flies +
Hawthorns
Hawthorns

60. + and apple flies generally end up mating with other apple flies.
Example of Sympatric Speciation
and apple flies generally end up mating with other apple flies. +
Apples
Apples

61. + Hawthorn flies and apple flies never mate together
Example of Sympatric Speciation
Hawthorn flies and apple flies never mate together +
Hawthorns
Apples

62. Example of Sympatric Speciation
This means that gene flow between parts of the population that mate on different types of fruit is reduced. +
Hawthorns
Apples

63. Example of Sympatric Speciation
This host shift from hawthorns to apples may be the first step toward sympatric speciation —in fewer than 200 years, some genetic differences between these two groups of flies have evolved +
Hawthorns
Apples

65. Evidence for Speciation?
Speciation is a long process, but we can find evidence for it in PATTERNS OF EVOLUTION

66. PATTERNS OF EVOLUTION Adaptive radiation Coevolution
Convergent Evolution
Rate of Speciation

67. Coevolution
Many species evolve in close relationship with other species.

68. Coevolution
The relationship might be so close that the evolution of one species affects the evolution of other species. This is called coevolution.
For Example: Mutualism - when two species benefit each other.

69. Coevolution – EXAMPLE 1
comet orchids and the moths that pollinate them have coevolved an intimate dependency
the foot long flowers of this plant perfectly match the foot-long tongue of the moth

70. Coevolution – EXAMPLE 2
One species can evolve a parasitic dependency on another species.
This type of relationship is often called a coevolutionary arms race

71. Coevolution – EXAMPLE 2
A plant and an insect that is dependent on the plant for food.
The plant population evolves a chemical defense against the insect population.
The insects, in turn, evolve the biochemistry to resist the defense.
The plant then steps up the race by evolving new defences, the insect escalates its response, and the race goes on.

72. PATTERNS OF EVOLUTION Adaptive radiation Coevolution
Convergent Evolution
Rate of Speciation

73. Adaptive Radiation = divergent evolution
can occur in a relatively short time when one species gives rise to many species in response to the creation of new habitat or another ecological opportunity.

74. Adaptive Radiation = divergent evolution
Adaptive radiation often follows large - scale extinctions (such as the extinction of dinosaurs and subsequent rise of mammals)
These different species have homologous structures

75. Adaptive Radiation – EXAMPLE 1
More than 300 species of cichlid fish once lived in Africa’s Lake Victoria.
Data shows that these species diverged from a single ancestor within the last 14,000 years.

76. PATTERNS OF EVOLUTION Adaptive radiation Coevolution
Convergent Evolution
Rate of Speciation

77. Produces Homologous Structures
Adaptive Radiation = divergent evolution
Produces Homologous Structures

78. common adaptations to similar environments
Convergent Evolution
common adaptations to similar environments

79. Convergent Evolution
occurs when organisms that are NOT closely related (they have no common ancestors) live in the SAME environment in different parts of the world.

80. Convergent Evolution – Example 1
all of these animals live or lived in an ocean but they are not closely related

81. Convergent Evolution
These species independently evolved similar traits or structures which are adapted to that same environment
What similar traits or structures these three animals gained during the course of evolution?

82. Flippers, streamlined body, ability to swim
Convergent Evolution
Flippers, streamlined body, ability to swim
What similar traits or structures these three animals gained during the course of evolution?

83. Prickles, thorns and spines
Convergent Evolution
Prickles, thorns and spines

84. Convergent Evolution
They have evolved independently to prevent or reduce herbivory (eating of plants by organisms)

85. Produces Analogous Structures
Convergent Evolution
Produces Analogous Structures

86. Produces Homologous Structures
Adaptive Radiation = divergent evolution
Produces Homologous Structures

87. Homologues Structures
Analogues Structures
VS.
Homologues Structures

88. VS. Analogues Structures Homologues Structures
Different internal structures
Same Function
Similar Environments
Result of Convergent Evolution
Same internal structures
Different Functions
Different Environments
Result of Divergent Evolution

89. PATTERNS OF EVOLUTION Adaptive radiation Coevolution
Convergent Evolution
Rate of Speciation

90. Rate of Speciation
Evolution is a dynamic process: traits might change rapidly OR traits might remain unchanged for millions of years.
Some scientists think that evolution proceeds in small, gradual steps = gradualism. A great deal of evidence favors this theory.
# of
species
Time

91. Rate of Speciation
However, the fossil record contains instances of abrupt transitions.
Certain species of fossil snails looked the same for millions of years, then the shell shape changed dramatically in only a few thousand years = punctuated equilibrium

92. Rate of Speciation
However, the fossil record contains instances of abrupt transitions.
Certain species of fossil snails looked the same for millions of years, then the shell shape changed dramatically in only a few thousand years = punctuated equilibrium
# of
species
Time