1. CHAPTER 14 ORIGIN OF SPECIES
Figure 14.3B Habitat isolation: Courtship ritual in blue-footed boobies as a behavioral barrier between species.

2. 14.1 The origin of species is the source of biological diversity
Speciation is the emergence of new 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 3.6 billion years ago
Copyright © 2009 Pearson Education, Inc.

3. Figure 14.1 How speciation increases diversity.

4. 14.2 There are several ways to define a species
Taxonomy is the branch of biology that names and classifies species and groups them into broader categories
Carolus Linnaeus developed the binomial system of naming organisms using physical characteristics to distinguish over 11,000 species
Similarities between some species and variation within species can make defining species difficult
Copyright © 2009 Pearson Education, Inc.

5. 14.2 There are several ways to define a species
The biological species concept defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring
Reproductive isolation prevents gene flow and maintains separate species
Copyright © 2009 Pearson Education, Inc.

6. 14.2 There are several ways to define a species
The morphological species concept classifies organisms based on observable phenotypic traits
It can be applied to asexual organisms, fossils, and in cases when we donít know about possible interbreeding
There is some subjectivity in deciding which traits to use
Copyright © 2009 Pearson Education, Inc.

7. 14.2 There are several ways to define a species
The ecological species concept defines a species by its ecological role or niche
Consider the cichlids, which are similar in appearance but feed at different depths in the lake
Copyright © 2009 Pearson Education, Inc.

8. 14.2 There are several ways to define a species
The phylogenetic species concept defines a species as a set of organisms representing a specific evolutionary lineage
Morphological or DNA similarities or differences can be used to define a species
Defining the amount of difference required to distinguish separate species is a problem
Copyright © 2009 Pearson Education, Inc.

9. 14.3 Reproductive barriers keep species separate
Reproductive barriers serve to isolate a species gene pool and prevent interbreeding
Reproductive barriers are categorized as prezygotic or postzygotic, depending on whether they function before or after zygotes form
Copyright © 2009 Pearson Education, Inc.

10. Table 14.3 Reproductive Barriers between Species.

11. 14.3 Reproductive barriers keep species separate
Prezygotic Barriers
Prezygotic barriers prevent mating or fertilization between species
In temporal isolation, two species breed at different times (seasons, times of day, years)
In habitat isolation, two species live in the same general area but not in the same kind of place
Copyright © 2009 Pearson Education, Inc.

12. 14.3 Reproductive barriers keep species separate
Prezygotic Barriers
In behavioral isolation, there is little or no sexual attraction between species, due to specific behaviors
In mechanical isolation, female and male sex organs are not compatible
In gametic isolation, female and male gametes are not compatible
Copyright © 2009 Pearson Education, Inc.

13. 14.3 Reproductive barriers keep species separate
Postzygotic Barriers
Postzygotic barriers operate after hybrid zygotes are 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
The process of speciation depends on whether reproductive barriers prevent gene flow between populations
Copyright © 2009 Pearson Education, Inc.

14. Figure 14.3E Reduced hybrid fertility: A horse (above left) and a donkey (above right) may produce a hybrid, sterile offspring, a mule.

15. 14.4 In allopatric speciation, geographic isolation leads to speciation
In allopatric speciation, populations of the same species are geographically separated, separating their gene pools
Changes in the allele frequencies of each population may be caused by natural selection, genetic drift, and mutation, unaffected by gene flow from other populations
Copyright © 2009 Pearson Education, Inc.

16. 14.4 In allopatric speciation, geographic isolation leads to speciation
Gene flow between populations is initially prevented by a geographic barrier
The Grand Canyon and Colorado River separate two species of antelope squirrels
Copyright © 2009 Pearson Education, Inc.

17. A. harrisi A. leucurus South North
Figure 14.4 Allopatric speciation of geographically isolated antelope squirrels.
Ask students for other examples of suitable barriers, then make the point that the size and nature of the barrier vary from species to species.
South
North

18. 14.4 In allopatric speciation, geographic isolation leads to speciation
Likelihood of allopatric speciation increases when a population is small and isolated
A small population may have a different gene pool due to the founder effect
Genetic drift and natural selection may have a greater effect in a small population in a new habitat
Copyright © 2009 Pearson Education, Inc.

19. 14.5 In sympatric speciation, speciation takes place without geographic isolation
In sympatric speciation, new species may arise within the same geographic area as a parent species
Gene flow between populations may be reduced by factors such as polyploidy, habitat differentiation, or sexual selection
Copyright © 2009 Pearson Education, Inc.

20. 14.5 In sympatric speciation, speciation takes place without geographic isolation
Many plant species have evolved by polyploidy, the multiplication of the chromosome number due to errors in cell division
A tetraploid (4n) plant can arise from a diploid parent
Copyright © 2009 Pearson Education, Inc.

21. Self- fertilization Parent species 2n = 6 Tetraploid cells 4n = 123 1
Self-
fertilization
Parent species
2n = 6
Tetraploid
cells
4n = 12
Viable, fertile
tetraploid
species
4n = 12
Figure 14.5A Sympatric speciation by polyploidy within a single species.
Consider customizing Figure 14.5A with the following labels:
Label “diploid gametes”: A failure of cell division after chromosome duplication doubles a cell’s chromosomes.
Label “viable, fertile tetraploid species”: Self-fertilization produces tetraploid zygotes that can self or mate with other 4n plants.
Point out to your students that the result of polyploidy is instant speciation.
The tetraploids cannot produce fertile offspring by mating with parent plants
The result would be 3n offspring, which are sterile.
Diploid
gametes
2n = 6

22. 14.5 In sympatric speciation, speciation takes place without geographic isolation
Most polyploids arise from hybridization of two different species
Haploid gametes from two different species combine to produce a sterile hybrid
Why is the hybrid sterile? How can it reproduce?
Chromosome duplications may produce a fertile polyploid species
What is the chromosome number of the new species
Copyright © 2009 Pearson Education, Inc.

23. Chromosomes not homologous (cannot pair) Species A Gamete 2n = 4 n = 21 2
Species A
2n = 4
Gamete
n = 2 3
Sterile hybrid
n = 5
Viable, fertile
hybrid species
2n = 10
Figure 14.5B Sympatric speciation producing a hybrid polyploid from two different species.
The hybrid is sterile because its chromosomes cannot pair during meiosis.
The hybrid may reproduce asexually.
The polyploid’s chromosome number is equal to the sum of the diploid chromosome numbers of the parent species.
Point out to your students that the new species is reproductively isolated from both parent species.
Gamete
n = 3
Species B
2n = 6

24. 14.5 In sympatric speciation, speciation takes place without geographic isolation
Sympatric speciation in animals more commonly occurs through habitat differentiation and sexual selection
Remember the cichlids in Lake Victoria!
Copyright © 2009 Pearson Education, Inc.

25. 14.6 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
80% of all living plant species are the descendants of ancestors that formed by polyploid speciation
Hybridization between two species accounts for most of these species
What advantage might there be to hybridization?
Polyploid food plants include oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, and bread wheat
Cotton is also polyploid
Copyright © 2009 Pearson Education, Inc.

26. 14.6 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Wheat has been domesticated for 11,000 years
It is the most widely cultivated plant in the world
Bread wheat, Triticum aestivum, is a polyploid with 42 chromosomes
Copyright © 2009 Pearson Education, Inc.

27. Figure 14.6B The evolution of wheat. AA BB
Wild
Triticum
(14 chromo-
somes)
Triticum monococcum
(14 chromosomes) 1
Hybridization AB
Sterile hybrid
(14 chromosomes) 2
Cell division error
and self-fertilization
AA BB DD
T. turgidum
Emmer wheat
(28 chromosomes)
T. tauschii
(wild)
(14 chromosomes) 3
Hybridization
Figure 14.6B The evolution of wheat.
Uppercase letters represent sets of chromosomes, not genes.
Consider customizing Figure 14.6B with the following labels:
Label first cross: A cultivated wheat (AA) hybridized with a weed (BB).
Label first offspring: The AB hybrid was sterile.
Label emmer wheat: An error in cell division and self-fertilization led to a new species (AABB).
Label 2nd hybridization: The new species hybridized with a wild relative, producing a sterile hybrid (ABD).
Label bread wheat: An error in cell division and self-fertilization led to bread wheat (AABBDD).
ABD
Sterile hybrid
(21 chromosomes) 4
Cell division error
and self-fertilization
AA BB DD
T. aestivum
Bread wheat
(42 chromosomes)

28. 14.8 Hybrid zones provide opportunities to study reproductive isolation
What happens when isolated populations renew contact?
In hybrid zones, members of different species meet and mate to produce hybrid offspring
Copyright © 2009 Pearson Education, Inc.

29. New species Ancestral species Gene flow3
Hybrid
zone 1 2 4
Gene
flow
Gene flow
Figure 14.8A Formation of a hybrid zone.
Four populations are connected by gene flow. A barrier to gene flow separates one population, which has diverged from the other three. Gene flow is reestablished in the hybrid zone.
Hybrid
Population
(five individuals
are shown)
Barrier to
gene flow

30. Reinforcement
Fusion
Stability

31. allopatric population Pied flycatcher from sympatric population
populations
Sympatric
populations
Male
collared
flycatcher
Male
pied
flycatcher
Figure 14.8B Reinforcement of reproductive barriers.
Pied flycatcher from
allopatric population
Pied flycatcher from
sympatric population

32. 14.8 Hybrid zones provide opportunities to study reproductive isolation
What may happen in a hybrid zone?
Reinforcement: If hybrids are less fit than parent species, natural selection strengthens reproductive barriers
Fusion: Weak reproductive barriers between the two species, with considerable gene flow, reverses speciation and two species become one again
Copyright © 2009 Pearson Education, Inc.

33. 14.8 Hybrid zones provide opportunities to study reproductive isolation
Stability: Many hybrid zones are stable, continuing to produce hybrids; this allows some gene flow between populations, but each species maintains its own integrity
Which of these three outcomes—reinforcement, fusion, or stability—is happening to the Pundamilia species of cichlids in Lake Victoria?
Copyright © 2009 Pearson Education, Inc.

34. 14.9 TALKING ABOUT SCIENCE: Peter and Rosemary Grant study the evolution of Darwin’s finches
Peter and Rosemary Grant have worked on medium ground finches on tiny, isolated, uninhabited Daphne Major in the Galapágos Islands for 35 years
Medium ground finches and cactus finches occasionally interbreed
Hybrid offspring have intermediate bill sizes and survive well during wet years, when there are plenty of soft, small seeds around
During dry years, hybrids are outcompeted by both parental types
Copyright © 2009 Pearson Education, Inc.

35. 14.9 TALKING ABOUT SCIENCE: Peter and Rosemary Grant study the evolution of Darwin’s finches
The occasional hybridization between finch species introduces new genes into both populations
During drought years, hybrids die out
This keeps medium ground finches and cactus finches on separate evolutionary paths
Copyright © 2009 Pearson Education, Inc.

36. Tool-using insect-eater (woodpecker finch)
Cactus-seed-eater
(cactus finch)
Figure 14.10A Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet.
Tool-using insect-eater
(woodpecker finch)
Seed-eater
(medium ground finch)

37. 14.10 Adaptive radiation may occur when new opportunities arise
In adaptive radiation, many diverse species evolve from a common ancestor
Adaptive radiations occur
When a few organisms colonize new unexploited areas
After a mass extinction
Adaptive radiations are linked to new opportunities: lack of competitors, varying habitats and food sources, evolution of new structures
Copyright © 2009 Pearson Education, Inc.

38. 14.11 Speciation may 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 and rarely took less than 50,000 years
Copyright © 2009 Pearson Education, Inc.

39. Time
Figure 14.11A Punctuated equilibrium model.

40. Figure 14.11B Gradualism model.
Time

41. You should now be able to
Explain how the diverse assemblage of cichlid species evolved in Lake Victoria; explain why many of these species no longer exist
Compare the definitions, advantages, and disadvantages of the different species concepts
Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations belonging to closely related species from interbreeding
Copyright © 2009 Pearson Education, Inc.

42. You should now be able to
Explain how geographical processes can fragment populations and lead to speciation
Explain how sympatric speciation can occur, noting examples in plants and animals
Explain why polyploidy is important to modern agriculture; explain how modern wheat evolved
Explain how reproductive barriers might evolve in isolated populations of organisms
Copyright © 2009 Pearson Education, Inc.

43. You should now be able to
Explain how hybrid zones are useful in the study of reproductive isolation
Explain the conditions that can lead to adaptive radiation
Copyright © 2009 Pearson Education, Inc.