1. CHAPTER 14 The Origin of Species
Modules 14.1 – 14.2

2. Evolution Underground
Evolution has generally been thought of as a very gradual process
However, examples of rapid evolution have been observed

3. One example of rapid evolution occurred among mosquitoes who migrated into the London underground
In less than 150 years, Culex pipiens evolved into a new mosquito species, Culex molestus
The origin of new species is called speciation

4. The isolated mosquitoes adapted to their new underground environment
They altered their prey, mating habits, and breeding patterns
Environmental barriers that isolate populations are just one of many mechanisms in the evolution of species

5. In the United States the two species appeared to hybridize into one species, which transmits West Nile virus
How could the mosquitoes behave like two species on one continent and one species on another?

7. The origin of species is the source of biological diversity
Microevolution, gradual adaptation of a species to its environment, does not produce new species
Speciation, the origin of new species, is at the focal point of evolution
Macroevolution, dramatic biological changes that begin with the origin of new species, has led to Earth's great biodiversity

8. CONCEPTS OF SPECIES 14.1 What is a species?
Taxonomy is the branch of biology concerned with naming and classifying the diverse forms of life
The binomial system was introduced by Linnaeus in the 18th century
Linnaeus used physical appearance to identify species

9. But appearance alone does not always define a species
Example: eastern and western meadowlarks
Figure 14.1A

10. cordilleran flycatcher and Pacific slope flycatcher
FIGURE 16-1 Members of different species may be similar in appearance
(a) The cordilleran flycatcher and (b) Pacific-slope flycatcher are different species.

11. Discovered that the warblers interbreed where their ranges overlap
The myrtle warbler and Audubon’s warbler used to be classified as different species
Discovered that the warblers interbreed where their ranges overlap
Today, considered a single species
FIGURE 16-2 Members of a species may differ in appearance
(a) The myrtle warbler and (b) Audubon's warbler are members of the same species.

12. Similarities between some species and variation within a species can make defining species difficult
Humans exhibit extreme physical diversity
Figure 14.1B

13. The biological species concept
Defines a species as a population or group of populations whose members can interbreed and produce fertile offspring
Reproductive isolation of different species prevents gene flow
Cannot be used as the sole criterion for species assignment
The biological species concept is not applicable to fossils or asexual organisms

14. A ring species may illustrate the process of speciation1
OREGON
POPULATION
Sierra Nevada 2
Yellow- blotched
Yellow- eyed
INLAND POPULATIONS
COASTAL POPULATIONS
Gap in ring
Large- blotched
Monterey 3
Figure 14.1C

15. The morphological species concept
Classifies organisms based on observable phenotypic traits
The ecological species concept
Defines a species by its ecological role
The phylogenetic species concept
Defines a species as a set of organisms with a unique genetic history
The genealogical species concept
defines a species as a cluster of organisms representing a specific evolutionary lineage

16. Reproductive Barriers

17. B. Isolating Mechanisms (Leads to a new species!)
Reproductive Isolation – members of two populations cannot interbreed and produce fertile offspring.

19. specific scents (pheromones of insects).
PRE-Mating Reproductive Isolation – involves mechanisms which do not allow mating to occur in the first place.
1. Behavioral Isolation: Members of two populations are capable of interbreeding but have differences in mating displays or courtship rituals. a. b. c.
specific scents (pheromones of insects).
color patterns/strutting.
specific sounds or calls.

20. Courtship Dance

21. Different Mating Songs

22. 2. Geographic/Ecological Isolation: Two populations are separated by geographic barriers such as rivers, mountains, or bodies of water.

23. When has speciation occurred?

24. 3. Temporal Isolation: Two or more species live in the same habitat but have different mating/reproductive seasons.
a. Brown trout and Rainbow trout are found in the same streams but Rainbow trout spawn in the Spring and Brown trout spawn in the Fall.
b. Three similar species of orchid living in the same tropical habitat each release pollen on different days; therefore, they cannot pollinate one another.

25. Reproductive Isolation
Section 16-3
Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Temporal isolation
Geographic isolation
produced by
produced by
produced by
Behavioral differences
Different mating times
Physical separation
which result in
Independently evolving populations
which result in
Formation of new species

26. NOTE: Several isolating mechanisms can compound one another to insure mating doesn’t occur. This permits two species to occupy the same valuable habitat and prevents wastage of valuable gametes.

27. 14.2 Reproductive barriers keep species separate
Prezygotic and postzygotic reproductive barriers prevent individuals of different species from interbreeding
Table 14.2

28. Premating Isolating Mechanisms
Habitat isolation
In nature, lions (africa) do not mate with tigers (India)- the liger/tigon is an anomaly
Each species of fig wasp breeds in the fruits of a particular species of fig

29. Temporal isolation Bishop pine pollination occurs in summer
Monterey pine pollination occurs in early spring

30. Behavioral isolation
Songs, dances, and plumage of male songbirds are species specific
Attract females of the same species
Females of other species are unresponsive

31. Mechanical incompatibility
snails of species whose
shells have left-handed
spirals may be unable to
successfully copulate with
snails whose shells have
right-handed spirals
Many plant species have
flower structures that are
adapted to specific pollinators

32. Gametic incompatibility
In animals, fluids of the female reproductive tract may weaken or kill sperm of another species
In plants, pollen from one species may fail to germinate when it lands on the stigma of another species

33. Postmating Isolating Mechanisms
Postmating isolating mechanisms include:
Hybrid breakdown
Hybrid inviability
Hybrid infertility

34. Hybrid breakdown = offspring to hybrids are weak or infertile
as witnessed in laboratory crosses of fruit flies, where the offspring of second-generation hybrids are weak and usually cannot produce viable offspring). 

35. Postmating Isolating Mechanisms
Hybrid inviability occurs when hybrid offspring fail to survive to maturity
the hybrid egg formed
from the mating of a
sheep and a goat will
die early in development

36. Postmating Isolating Mechanisms
Hybrid may abort early in development
Hybrid may be unable to reproduce because it display behaviors that are mixtures of the two parental types
Lovebird hybrids have great difficulty learning to carry nest materials during flight

37. Postmating Isolating Mechanisms
Hybrid infertility/Sterility occurs when hybrid offspring are sterile or have reduced fertility
Mule hybrids (a cross between a horse and a donkey) are sterile
Liger hybrids (a zoo-based cross between a male lion and a female tiger) are sterile

38. Hybrid Sterility +
Donkey
Horse =
Mule (sterile)

39. FIGURE 16-8 Hybrid infertility
This liger, the hybrid offspring of a lion and a tiger, is sterile. The gene pools of its parent species remain separate.

40. 14.3 Geographic isolation can lead to speciation
MECHANISMS OF SPECIATION
14.3 Geographic isolation can lead to speciation
Mechanisms of speciation
Allopatric speciation
Isolating mechanism is a physical barrier
Sympatric speciation
Isolation occurs without geographic separation
Figure 14.3

41. ALLOPATRIC SPECIATION
FIGURE 16-9 (part 1) Allopatric isolation and divergence
In allopatric speciation, some event causes a population to be divided by an impassable geographical barrier. One way the division can occur is by colonization of an isolated island. The two now-separated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

42. ALLOPATRIC SPECIATION
FIGURE 16-9 (part 2) Allopatric isolation and divergence
In allopatric speciation, some event causes a population to be divided by an impassable geographical barrier. One way the division can occur is by colonization of an isolated island. The two now-separated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

43. ALLOPATRIC SPECIATION
FIGURE 16-9 (part 3) Allopatric isolation and divergence
In allopatric speciation, some event causes a population to be divided by an impassable geographical barrier. One way the division can occur is by colonization of an isolated island. The two now-separated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

44. Allopatric Speciation
Allopatric speciation occurs when two populations of a species become separated by a geographical barrier
Colonization of remote islands by mainland organisms
Geological changes such as volcanism, earthquakes, continental drift, and rivers changing course

46. Allopatric Speciation
Allopatric speciation occurs when isolated populations diverge genetically

47. Allopatric Speciation
Is believed to be the most common type of speciation, especially among animals
Two allopatric populations, the Abert’s squirrel and the Kaibab squirrel (subspecies of Aberts), may be evolving into two separate species

48. Kaibab Abert FIGURE 16-3 Geographical isolation
To determine if these two squirrels are members of different species, we must know if they are "actually or potentially interbreeding." Unfortunately, it is hard to tell, because (a) the Kaibab squirrel lives only on the north rim of the Grand Canyon and (b) the Abert squirrel lives only on the south rim. The two populations are geographically isolated but still quite similar. Have they diverged enough since their separation to become reproductively isolated? Because they remain geographically isolated, we cannot say for sure.

49. Sympatric Speciation Sympatric speciation occurs when
Two populations of a species living in the same geographical area become restricted to different habitats
Isolated populations diverge genetically

50. Sympatric Speciation
Two sympatric populations of fruit flies (Rhagoletis pomonella) may be evolving into two separate species

51. Sympatric Speciation
One population lays its eggs in hawthorn fruit, while the other prefers apples
The two populations experience very little interbreeding

52. Sympatric Speciation
Males and females prefer the same type of fruit in which they developed
Apples mature two or three weeks later than hawthorn fruit (flies mature and mate at different times)

53. SYMPATRIC SPECIATION
FIGURE (part 1) Sympatric isolation and divergence
In sympatric speciation, some event blocks gene flow between two parts of a population that remains in a single geographic area. One way in which this genetic isolation can occur is if a portion of a population begins to use a previously unexploited resource, as when some members of an insect population shift to a new host plant species (as has occurred in the fruit fly species Rhagoletis pomonella). The two now-isolated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

54. SYMPATRIC SPECIATION
FIGURE (part 2) Sympatric isolation and divergence
In sympatric speciation, some event blocks gene flow between two parts of a population that remains in a single geographic area. One way in which this genetic isolation can occur is if a portion of a population begins to use a previously unexploited resource, as when some members of an insect population shift to a new host plant species (as has occurred in the fruit fly species Rhagoletis pomonella). The two now-isolated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

55. SYMPATRIC SPECIATION
FIGURE (part 3) Sympatric isolation and divergence
In sympatric speciation, some event blocks gene flow between two parts of a population that remains in a single geographic area. One way in which this genetic isolation can occur is if a portion of a population begins to use a previously unexploited resource, as when some members of an insect population shift to a new host plant species (as has occurred in the fruit fly species Rhagoletis pomonella). The two now-isolated populations may diverge genetically. If the genetic differences between the two populations become large enough to prevent interbreeding, then the two populations constitute separate species.

56. New Species
The above mechanisms of speciation and reproductive isolation lead to forking branches in the evolutionary tree of life, as one species splits into two

57. FIGURE 16-11a Interpreting evolutionary trees
Evolutionary history is often represented by (a) an evolutionary tree, a graph in which the vertical axis plots time. In (b), an evolutionary tree representing an adaptive radiation, many lines may branch from a single point. This pattern reflects biologists' uncertainty about the order in which the multiple speciation events of the radiation took place. With more research, it may be possible to replace the "starburst" pattern with a more informative tree.

58. 14.4 Islands are living laboratories of speciation
On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches
Figure 14.4A

59. Adaptive Radiation
Adaptive radiation is the rise of many new species over a relatively short period of time

60. FIGURE 16-11b Interpreting evolutionary trees
Evolutionary history is often represented by (a) an evolutionary tree, a graph in which the vertical axis plots time. In (b), an evolutionary tree representing an adaptive radiation, many lines may branch from a single point. This pattern reflects biologists' uncertainty about the order in which the multiple speciation events of the radiation took place. With more research, it may be possible to replace the "starburst" pattern with a more informative tree.

61. Adaptive Radiation
Occurs when populations of one species invade a variety of new habitats
Finch colonization of the Galápagos Islands
Silversword plants of the Hawaiian islands
Cichlid fish colonization of Lake Malawi
Tarweed plant colonization of the Hawaiian Islands

62. Adaptive radiation on an island chain
finches 1
Species A from mainland 2 B A B 3 B B 4 C C C C D C D 5
Figure 14.4B

63. SILVERSWORD FIGURE 16-12 Adaptive radiation
About 30 species of silversword plants inhabit the Hawaiian Islands. These species are found nowhere else, and all of them descended from a single ancestral population within a few million years. This adaptive radiation has led to a collection of closely related species of diverse form and appearance, with an array of adaptations for exploiting the many different habitats in Hawaii, from warm, moist rain forests to cool, barren volcanic mountaintops.

64. FIGURE 16-12 (part 1) Adaptive radiation
About 30 species of silversword plants inhabit the Hawaiian Islands. These species are found nowhere else, and all of them descended from a single ancestral population within a few million years. This adaptive radiation has led to a collection of closely related species of diverse form and appearance, with an array of adaptations for exploiting the many different habitats in Hawaii, from warm, moist rain forests to cool, barren volcanic mountaintops.

65. FIGURE 16-12 (part 2) Adaptive radiation
About 30 species of silversword plants inhabit the Hawaiian Islands. These species are found nowhere else, and all of them descended from a single ancestral population within a few million years. This adaptive radiation has led to a collection of closely related species of diverse form and appearance, with an array of adaptations for exploiting the many different habitats in Hawaii, from warm, moist rain forests to cool, barren volcanic mountaintops.

66. FIGURE 16-12 (part 3) Adaptive radiation
About 30 species of silversword plants inhabit the Hawaiian Islands. These species are found nowhere else, and all of them descended from a single ancestral population within a few million years. This adaptive radiation has led to a collection of closely related species of diverse form and appearance, with an array of adaptations for exploiting the many different habitats in Hawaii, from warm, moist rain forests to cool, barren volcanic mountaintops.

67. FIGURE 16-12 (part 4) Adaptive radiation
About 30 species of silversword plants inhabit the Hawaiian Islands. These species are found nowhere else, and all of them descended from a single ancestral population within a few million years. This adaptive radiation has led to a collection of closely related species of diverse form and appearance, with an array of adaptations for exploiting the many different habitats in Hawaii, from warm, moist rain forests to cool, barren volcanic mountaintops.

68. Unreduced diploid gametes
14.5 New species can also arise within the same geographic area as the parent species
In sympatric speciation, a new species may arise without geographic isolation
A failure in meiosis can produce diploid gametes
Self-fertilization can then produce a tetraploid zygote
Parent species
Zygote
Meiotic error
Self- fertilization
Offspring may be viable and self-fertile
2n = 6 Diploid
4n = 12 Tetraploid
Unreduced diploid gametes
Figure 14.5A

69. Sympatric speciation by polyploidy was first discovered by Dutch botanist Hugo de Vries in the early 1900s
Figure 14.5B

70. 14.6 Connection: Polyploid plants clothe and feed us
Many plants are polyploid
They are the products of hybridization
The modern bread wheat is an example
Figure 14.6A

71. The evolution of wheat AA BB Wild Triticum (14 chromo- somes)
Triticum monococcum (14 chromosomes) AB
Sterile hybrid (14 chromosomes)
Meiotic error and self-fertilization
AABB DD
T. turgidum EMMER WHEAT (28 chromosomes)
T. tauschii (wild) (14 chromosomes)
ABD
Sterile hybrid
Meiotic error and self-fertilization
AA BB DD
T. aestivum BREAD WHEAT (42 chromosomes)
Figure 14.6B

72. 14.7 Reproductive barriers may evolve as populations diverge
This has been documented by
laboratory studies (fruit flies)
Diane Dodd tested the hypothesis that reproductive barriers can evolve as a by-product of the adaptive divergence of populations in different environments
Figure 14.7A

73. Initial sample of fruit flies Starch medium Maltose medium Results of
LE 14-5a
Initial sample
of fruit flies
Starch medium
Maltose medium
Results of
mating experiments
Female
Female
Same
population
Different
populations
Starch
Maltose
Starch
Same 22 9 18 15
Male
Male 8 20
Different 12 15
Maltose
Mating frequencies
in experimental group
Mating frequencies
in control group

74. Geographic isolation in Death Valley led to allopatric speciation of pupfish
By genetic drift or natural selection, the isolated populations evolved into separate species

75. examples in natural populations (pupfish in Death Valley)
Figure 14.7B

76. 14.8 The tempo of speciation can appear steady or jumpy
According to the gradualist model of the origin of species
new species evolve by the gradual accumulation of changes brought about by natural selection
However, few gradual transitions are found in the fossil record
Figure 14.8A

77. The punctuated equilibrium model suggests that speciation occurs in spurts
Rapid change occurs when an isolated population diverges from the ancestral stock
Virtually no change occurs for the rest of the species’ existence
Figure 14.8B

78. 14.9 Talking About Science: Peter and Rosemary Grant study the evolution of Darwin’s finches
The occasional hybridization of finch species adds to the genetic variation of parent populations
This may have been important in the adaptive radiation of finch species
Figure 14.9