1. Chapter 14 The Origin of Species
Bowerbirds, native to New Guinea and Australia, are named for the structure, called a bower, that the male weaves from twigs and grasses to attract females.
After building his bower, the male collects objects such as fruits, seeds, insect parts, rocks, flowers, and leaves and arranges them artfully by color and type.
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2. Females are dull colored (as are males) and tour the bowers
Figure 14.01
Females are dull colored (as
are males) and tour the bowers
of local males, inspecting each
while its owner courts her with
a song and dance.
Vogelkop bowerbird photograph by Barrie Britton

3. DEFINING SPECIES
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4. 14.1 The origin of species is the source of biological diversity
Microevolution is the change in the gene pool of a population from one generation to the next.
Speciation is the process by which one species splits into two or more species.
Every time speciation occurs, the diversity of life increases.
The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.
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5. 14.2 There are several ways to define a species
The word species is from the Latin for “kind” or “appearance.”
Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions.
How similar are members of the same species?
What keeps one species distinct from others?
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6. 14.2 There are several ways to define a species
The biological species concept defines a species as
a group of populations,
whose members have the potential to interbreed in nature, and
produce fertile offspring.
Therefore, members of a species are similar because they reproduce with each other.
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7. 14.2 There are several ways to define a species
Reproductive isolation
prevents members of different species from mating with each other,
prevents gene flow between species, and
maintains separate species.
Therefore, species are distinct from each other because they do not share the same gene pool.
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8. Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right). Similar looking but different songs and mating behavior
Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right) 8

9. Figure 14.2B Diversity within one species9

10. 14.2 There are several ways to define a species
The biological species concept can be problematic.
Some pairs of clearly distinct species occasionally interbreed and produce hybrids.
For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears.
Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild.
Reproductive isolation cannot usually be determined for extinct organisms known only from fossils.
Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually.
Therefore, alternate species concepts can be useful.
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11. Figure 14.2C Hybridization between two species of bears
Grizzly bear
Polar bear
Figure 14.2C Hybridization between two species of bears
Hybrid “grolar” bear 11

12. 14.2 There are several ways to define a species
The morphological species concept
classifies organisms based on observable physical traits and
can be applied to
asexual organisms and
fossils.
However, there is some subjectivity in deciding which traits to use.
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13. 14.2 There are several ways to define a species
The ecological species concept
defines a species by its ecological role or niche and
focuses on unique adaptations to particular roles in a biological community.
For example, two species may be similar in appearance but distinguishable based on
what they eat or
where they live.
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14. 14.2 There are several ways to define a species
The phylogenetic species concept
defines a species as the smallest group of individuals that shares a common ancestor and thus
forms one branch of the tree of life.
Biologists trace the phylogenetic history of a species by comparing its
morphology or
DNA.
However, defining the amount of difference required to distinguish separate species is a problem.
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15. 14.3 Reproductive barriers keep species separate
Reproductive barriers
serve to isolate the gene pools of species and
prevent interbreeding.
Depending on whether they function before or after zygotes form, reproductive barriers are categorized as
prezygotic or
postzygotic.
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16. 14.3 Reproductive barriers keep species separate
Five types of prezygotic barriers prevent mating or fertilization between species.
In habitat isolation, two species live in the same general area but not in the same kind of place.
In temporal isolation, two species breed at different times (seasons, times of day, years).
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17. Habitat isolation (lack of opportunities to encounter each other)
Figure 14.3
Habitat isolation (lack of opportunities to encounter each other)
The garter snake Thamnophis atratus lives mainly in water.
The garter snake Thamnophis sirtalis lives on land.

18. Temporal isolation (breeding at different times or seasons)
Figure 14.3
Temporal isolation (breeding at different times or seasons)
The eastern spotted skunk (Spilogale putorius) breeds in late winter.
The western spotted skunk (Spilogale gracilis) breeds in the fall.

19. 14.3 Reproductive barriers keep species separate
Prezygotic Barriers, continued
In behavioral isolation, there is little or no mate recognition between females and males of different species.
In mechanical isolation, female and male sex organs are not compatible.
In gametic isolation, female and male gametes are not compatible.
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20. Behavioral isolation (different courtship rituals)
Figure 14.3
Behavioral isolation (different courtship rituals)
The blue-footed booby (Sula nebouxii) performs an elaborate courtship dance.
The masked booby (Sula dactylatra) performs a different courtship ritual.

21. Mechanical isolation (physical incompatibility of reproductive parts)
Figure 14.3
Mechanical isolation (physical incompatibility of reproductive parts)
Heliconia latispatha is pollinated by hummingbirds with short, straight bills.
Heliconia pogonantha is pollinated by hummingbirds with long, curved bills.

22. (Strongylocentrotus purpuratus) Red sea urchin
Figure 14.3
Gametic isolation (molecular incompatibility of eggs and sperm or pollen and stigma)
Purple sea urchin
(Strongylocentrotus purpuratus)
Red sea urchin
(Strongylocentrotus franciscanus)

23. 14.3 Reproductive barriers keep species separate
Three types of postzygotic barriers operate after hybrid zygotes have formed.
In reduced hybrid viability, most hybrid offspring do not survive.
In reduced hybrid fertility, hybrid offspring are vigorous but sterile.
In hybrid breakdown,
the first-generation hybrids are viable and fertile but
the offspring of the hybrids are feeble or sterile.
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24. Figure 14.3
Reduced hybrid viability (hybrid development or survival impaired by interaction of parental genes)
Figure 14.3G Reduced hybrid fertility
Some salamander species can hybridize, but their offspring do not develop fully or are frail and will not survive long enough to reproduce. 24

25. A mule is the sterile hybrid offspring of a horse and a donkey.
Figure 14.3
Reduced hybrid fertility (vigorous hybrids that cannot produce viable offspring)
A mule is the sterile hybrid offspring of a horse and a donkey.

26. Hybrid breakdown (viable and fertile hybrids with feeble
Figure 14.3
Hybrid breakdown (viable and fertile hybrids with feeble
or sterile offspring)
The rice hybrids on the left and right
are fertile, but plants of the next generation (middle) are sterile.

27. MECHANISMS OF SPECIATION
MECHANISMS OF SPECIATION
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28. 14.4 In allopatric speciation, geographic isolation leads to speciation
In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools.
Isolated populations will no longer share changes in allele frequencies caused by
natural selection,
genetic drift, and/or
mutation.
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29. 14.4 In allopatric speciation, geographic isolation leads to speciation
Gene flow between populations is initially prevented by a geographic barrier. For example
the Grand Canyon and Colorado River separate two species of antelope squirrels, and
the Isthmus of Panama separates 15 pairs of snapping shrimp.
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30. South rim North rim A. harrisii A. leucurus
Figure 14.4A Allopatric speciation of geographically isolated antelope squirrels (Ammospermophilus)
South rim
North rim
A. harrisii
A. leucurus
Figure 14.4A Allopatric speciation of geographically isolated antelope squirrels 30

31. Figure 14.4B Allopatric speciation in snapping shrimp (Alpheus)
A. formosus
A. nuttingi
ATLANTIC OCEAN
Isthmus of Panama
PACIFIC OCEAN
Figure 14.4B Allopatric speciation in snapping shrimp
A. panamensis
A. millsae 31

32. 14.5 Reproductive barriers can evolve as populations diverge
How do reproductive barriers arise?
Experiments have demonstrated that reproductive barriers can evolve as a by-product of changes in populations as they adapt to different environments.
These studies have included
laboratory studies of fruit flies and
field studies of monkey flowers and their pollinators.
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33. Initial sample of fruit flies
Figure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sources
Initial sample of fruit flies
Starch medium
Maltose medium
Mating experiments
Female
Female
Results
Population #1
Population #2
Starch
Maltose
Starch 22 9
Pop#1 18 15
Figure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sources
Male
Male 8 20 12 15
Pop#2
Maltose
Number of matings in experimental groups
Number of matings in starch control groups 33

34. Pollinator choice in typical monkey flowers
Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice in Mimulus.
Pollinator choice in typical monkey flowers
Pollinator choice after color allele transfer
Typical M. lewisii (pink)
M. lewisii with red-color allele
Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice.
Typical M. cardinalis (red)
M. cardinalis with pink-color allele 34

35. 14.6 Sympatric speciation takes place without geographic isolation
Sympatric speciation occurs when a new species arises within the same geographic area as a parent species.
How can reproductive isolation develop when members of sympatric populations remain in contact with each other?
Gene flow between populations may be reduced by
polyploidy,
habitat differentiation, or
sexual selection.
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36. 14.6 Sympatric speciation takes place without geographic isolation
Many plant species have evolved by polyploidy in which cells have more than two complete sets of chromosomes.
Sympatric speciation can result from polyploidy
within a species (by self-fertilization) or
between two species (by hybridization). .
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37. Viable, fertile tetraploid species 4n = 12
Figure 14.6A Sympatric speciation by polyploidy within a single species 1
Self- fertilization 3 2
Parent species 2n = 6
Tetraploid cells 4n = 12
Viable, fertile tetraploid species 4n = 12
Figure 14.6A_s3 Sympatric speciation by polyploidy within a single species (step 3)
Diploid gametes 2n = 6 37

38. Chromosomes cannot pair
Figure 14.6B Sympatric speciation producing a hybrid polyploid from two different species
Chromosomes cannot pair
Species A 2n = 4
Gamete n = 2 3 1
Sterile hybrid n = 5
Viable, fertile hybrid species 2n = 10
Figure 14.6B_s3 Sympatric speciation producing a hybrid polyploid from two different species (step 3)
Can reproduce asexually
Gamete n = 3
Species B 2n = 6 2 38

39. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation.
Hybridization between two species accounts for most of these species.
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40. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Polyploid plants include
cotton,
oats,
potatoes,
bananas,
peanuts,
barley,
plums,
apples,
sugarcane,
coffee, and
bread wheat.
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41. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Wheat
has been domesticated for at least 10,000 years and
is the most widely cultivated plant in the world.
Bread wheat, Triticum aestivum, is
a polyploid with 42 chromosomes and
the result of hybridization and polyploidy.
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42. Figure 14.7 The evolution of bread wheat, Triticum aestivumAA  BB
Wild Triticum (14 chromo- somes)
Domesticated Triticum monococcum (14 chromosomes) 1
Hybridization AB
Sterile hybrid (14 chromosomes) 2
Cell division error and self-fertilization
AABB DD
T. turgidum Emmer wheat (28 chromosomes)
Wild T. tauschii (14 chromosomes) 3
Hybridization
ABD
Sterile hybrid (21 chromosomes) 4
Cell division error and self-fertilization
Figure 14.7 The evolution of bread wheat, Triticum aestivum
AABBDD
T. aestivum Bread wheat (42 chromosomes) 42

43. 14.8 Isolated islands are often showcases of speciation
Most of the species on Earth are thought to have originated by allopatric speciation.
Isolated island chains offer some of the best evidence of this type of speciation.
Multiple speciation events are more likely to occur in island chains that have
physically diverse habitats,
islands far enough apart to permit populations to evolve in isolation, and
islands close enough to each other to allow occasional dispersions between them.
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44. 14.8 Isolated islands are often showcases of speciation
The evolution of many diverse species from a common ancestor is adaptive radiation.
The Galápagos Archipelago
is located about 900 km (560 miles) west of Ecuador,
is one of the world’s great showcases of adaptive radiation,
was formed naked from underwater volcanoes,
was colonized gradually from other islands and the South America mainland, and
has many species of plants and animals found nowhere else in the world.
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45. 14.8 Isolated islands are often showcases of speciation
The Galápagos islands currently have 14 species of closely related finches, called Darwin’s finches, because Darwin collected them during his around- the-world voyage on the Beagle.
These finches
share many finchlike traits,
differ in their feeding habits and their beaks, specialized for what they eat, and
arose through adaptive radiation.
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46. Cactus-seed-eater (cactus finch)
Figure 14.8
Cactus-seed-eater (cactus finch)
Tool-using insect-eater
(woodpecker finch)
Figure 14.8 Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet
Seed-eater
(medium ground finch) 46

47. 14.10 Hybrid zones provide opportunities to study reproductive isolation
What happens when separated populations of closely related species come back into contact with each other?
Biologists try to answer such questions by studying hybrid zones, regions in which members of different species meet and mate to produce at least some hybrid offspring.
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48. 14.10 Hybrid zones provide opportunities to study reproductive isolation
Over time in hybrid zones (Fig 14.10A)
reinforcement may strengthen barriers to reproduction, such as occurs in flycatchers (Fig B), or
fusion may reverse the speciation process as gene flow between species increases, as may be occurring among the cichlid species in Lake Victoria (Fig C).
In stable hybrid zones, a limited number of hybrid offspring continue to be produced.
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49. Figure 14.10A Formation of a hybrid zone
Newly formed species
Three populations of a species 3
Hybrid zone 1 2 4
Gene flow
Gene flow
Figure 14.10A Formation of a hybrid zone
Hybrid individual
Population
Barrier to gene flow 49

50. Figure 14.10B Reinforcement of reproductive barriers
Allopatric populations
Sympatric populations
Male collared flycatcher
Male pied flycatcher
Figure 14.10B Reinforcement of reproductive barriers
Pied flycatcher from allopatric
population
Pied flycatcher from sympatric
population 50

51. Pundamilia pundamilia
Figure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid water
Pundamilia nyererei
Pundamilia pundamilia
Figure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid water
Hybrid: Pundamilia “turbid water” 51

52. 14.11 Speciation can occur rapidly or slowly
There are two models for the tempo of speciation.
The punctuated equilibria model draws on the fossil record, where species
change most as they arise from an ancestral species and then
experience relatively little change for the rest of their existence.
Other species appear to have evolved more gradually = gradualism.
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53. Figure 14.11 Two models for the tempo of speciation
Punctuated pattern
Gradual pattern
Figure Two models for the tempo of speciation
Time 53

54. 14.11 Speciation can occur rapidly or slowly
What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)?
In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years.
Overall, the time between speciation events averaged 6.5 million years.
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