Figure 14.2a-0 Figure 14.2a-0 Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)

14.2 There are several ways to define a species
How similar are members of the same species? Whereas the individuals of many species exhibit fairly limited variation in physical appearance, certain other species—our own, for example— seem extremely varied. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

Figure 14.2b Figure 14.2b Diversity within one 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 (offspring that themselves can reproduce). Thus, members of a biological species are united by being reproductively compatible, at least potentially. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

Reproductive isolation prevents genetic exchange (gene flow) and maintains a boundary between species. But there are some pairs of clearly distinct species that do occasionally interbreed. The resulting offspring are called hybrids. An example is the grizzly bear (Ursus arctos) and the polar bear (Ursus maritimus), whose hybrid offspring have been called “grolar bears.” Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

Grizzly bear Polar bear Hybrid “grolar” bear Figure 14.2c-0
Figure 14.2c-0 Hybridization between two species of bears Hybrid “grolar” bear

There are other instances in which applying the biological species concept is problematic. There is no way to determine whether organisms that are now known only through fossils were once able to interbreed. Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually. Therefore, alternate species concepts can be useful. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, 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. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

The ecological species concept defines a species by its ecological 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 the depth of water in which they are usually found. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

The phylogenetic species concept defines a species as the smallest group of individuals that share a common ancestor and thus form one branch of the tree of life. Biologists trace the phylogenetic history of a species by comparing its morphology, DNA sequences, or biochemical pathways. However, agreeing on the amount of difference required to establish separate species remains a challenge. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Active Lecture Tips  Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.

14.3 VISUALIZING THE CONCEPT: Reproductive barriers keep species separate
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. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Teaching Tips  Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.

Five types of prezygotic barriers prevent mating or fertilization between species. In habitat isolation, there is a lack of opportunity for mates to encounter each other. In temporal isolation, there is breeding at different times or seasons. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Teaching Tips  Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.

PREZYGOTIC BARRIERS POSTZYGOTIC BARRIERS
Figure PREZYGOTIC BARRIERS Habitat isolation (different habitats) Temporal isolation (breeding at different times) Behavioral isolation (different courtship rituals) Mechanical isolation (incompatible reproductive parts) Gametic isolation (incompatible gametes) Figure Reproductive barriers between species POSTZYGOTIC BARRIERS Reduced hybrid vitality (short-lived hybrids) Reduced hybrid fertility (sterile hybrids) Hybrid breakdown (fertile hybrids with sterile offspring)

In behavioral isolation, there is failure to send or receive appropriate signals. In mechanical isolation, there is physical incompatibility of reproductive parts. In gametic isolation, there is molecular incompatibility of eggs and sperm or pollen and stigma. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Teaching Tips  Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.

Three types of postzygotic barriers operate after hybrid zygotes have formed. In reduced hybrid viability, interaction of parental genes impairs the hybrid’s development or survival. In reduced hybrid fertility, hybrids are vigorous but cannot produce viable offspring. In hybrid breakdown, hybrids are viable and fertile, but their offspring are feeble or sterile. Student Misconceptions and Concerns  Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such groupings exist. Could such groupings represent shared ancestry? Teaching Tips  Identify or have your students find several commonly recognized and related species of plants or animals in your area and find out what reproductive barriers keep these species from interbreeding. Local examples always help to bring a point home.

Mechanisms of Speciation

14.4 In allopatric speciation, geographic isolation leads to speciation
A key event in the origin of a new species is the separation of a population from other populations of the same species. With its gene pool isolated, the splinter population can follow its own evolutionary course. Changes in allele frequencies caused by natural selection, genetic drift, and mutation will not be diluted by alleles entering from other populations (gene flow). Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

In allopatric speciation, the initial block to gene flow may come from a geographic barrier that isolates a population. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Several geologic processes can isolate populations. A mountain range may emerge and gradually split a population of organisms that can inhabit only lowlands. A large lake may subside until there are several smaller lakes, isolating certain fish populations. Continents themselves can split and move apart. Allopatric speciation can also occur when individuals colonize a remote area and become geographically isolated from the parent population. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

How large must a geographic barrier be to keep allopatric populations apart? The answer depends on the ability of the organisms to move. Birds, mountain lions, and coyotes can easily cross mountain ranges. In contrast, small rodents may find a canyon or a wide river a formidable barrier. The Grand Canyon and Colorado River separate two species of antelope squirrels. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

South rim North rim A. harrisii A. leucurus Figure 14.4a-0
Figure 14.4a-0 Allopatric speciation of geographically isolated antelope squirrels

Thirty species of snapping shrimp in the genus Alpheus live off the Isthmus of Panama, the land bridge that connects South and North America. Morphological and genetic data group these shrimp into 15 pairs of species, with the members of each pair being each other’s closest relative. In each case, one member of the pair lives on the Atlantic side of the isthmus, while the other lives on the Pacific side. This strongly suggests that geographic separation of the ancestral species of these snapping shrimp led to allopatric speciation. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The isolation of a few individuals from a parent population may result from a catastrophic weather or geological event. Ask your students to think back to news footage of torrential rains, massive debris rocketing down a river, and the struggles of animals to haul themselves onto these rafts. Better yet, show them a short news clip of such events. Dramatic weather and geological events may be rare in our lifetimes but are frequent enough to play a role in speciation. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Isthmus of Panama A. formosus A. nuttingi ATLANTIC OCEAN PACIFIC OCEAN
Figure 14.4b A. formosus A. nuttingi ATLANTIC OCEAN Isthmus of Panama PACIFIC OCEAN Figure 14.4b Allopatric speciation in snapping shrimp A. panamensis A. millsae

14.5 Reproductive barriers can evolve as populations diverge
How do reproductive barriers arise? The environment of an isolated population may include different food sources, different types of pollinators, and different predators. As a result of natural selection acting on preexisting variations (or as a result of genetic drift or mutation), a population’s traits may change in ways that also establish reproductive barriers. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day). Teaching Tips  When discussing Module 14.5, consider referring back to Figure 14.3A. Challenge students to explain how each of the prezygotic barriers might impact the evolution of a new species. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

14.5 Reproductive barriers can evolve as populations diverge
Researchers have successfully documented the evolution of reproductive isolation with laboratory experiments. These studies have included laboratory studies of fruit flies and field studies of monkey flowers and their pollinators. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day). Teaching Tips  When discussing Module 14.5, consider referring back to Figure 14.3A. Challenge students to explain how each of the prezygotic barriers might impact the evolution of a new species. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Initial sample of fruit flies Starch medium Maltose medium
Figure 14.5a 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 Maltose Pop#2 Number of matings in experimental groups Number of matings In starch control groups

Pollinator choice in typical monkey flowers
Figure 14.5b-0 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-0 Transferring an allele between monkey flowers changes flower color and influences pollinator choice Typical M. cardinalis (red) M. cardinalis with pink-color allele

14.6 Sympatric speciation takes place without geographic isolation
Sympatric speciation occurs when a new species arises within the same geographic area as its 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. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The Silvery Salamander, Ambystoma platineum, is a triploid, all-female species living in parts of the U.S. Midwest. It is believed to have formed by the hybridization of two related species thousands of years ago. It is an unusual example of sympatric speciation in animals. A good starting point for learning more about this species is Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Many plant species have originated from sympatric speciation that occurs when accidents during cell division result in extra sets of chromosomes. New species formed in this way are polyploid, in that their cells have more than two complete sets of chromosomes. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The Silvery Salamander, Ambystoma platineum, is a triploid, all-female species living in parts of the U.S. Midwest. It is believed to have formed by the hybridization of two related species thousands of years ago. It is an unusual example of sympatric speciation in animals. A good starting point for learning more about this species is Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Sympatric speciation can result from polyploidy within a species (by self-fertilization) or between two species (by hybridization). Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The Silvery Salamander, Ambystoma platineum, is a triploid, all-female species living in parts of the U.S. Midwest. It is believed to have formed by the hybridization of two related species thousands of years ago. It is an unusual example of sympatric speciation in animals. A good starting point for learning more about this species is Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Viable, fertile tetraploid species
Figure 14.6a-3 1 3 Self- fertilization 2 Parent species 2n = 6 Tetraploid cells 4n = 12 Viable, fertile tetraploid species 4n = 12 Figure 14.6a-3 Sympatric speciation by polyploidy within a single species (step 3) Diploid gametes 2n = 6

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

14.7 EVOLUTION CONNECTION: The origin of most plant species can be traced 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, perhaps because of the adaptive advantage of the diverse genes a hybrid inherits from different parental species. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

plums, apples, sugarcane, coffee, and wheat. Polyploid plants include cotton, oats, potatoes, bananas, peanuts, barley, Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Figure Figure The evolution of bread wheat, Triticum aestivum (photo)

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. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The abundance of polyploid plants used for food facilitates further study for student assignments. Perhaps small groups or individuals can select a polyploid crop and describe its evolutionary history and/or its current method of reproduction. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Sterile hybrid (14 chromosomes) Sterile hybrid (21 chromosomes)
Figure AA BB Domesticated Triticum monococcum (14 chromosomes) Wild Triticum (14 chromosomes) 1 Hybridization AB Sterile hybrid (14 chromosomes) Cell division error and self-fertilization 2 AABB DD T. turgidum Emmer wheat (28 chromosomes) Wild T. tauschii (14 chromosomes) 3 Hybridization Figure The evolution of bread wheat, Triticum aestivum ABD Sterile hybrid (21 chromosomes) 4 Cell division error and self-fertilization AABBDD T. aestivum Bread wheat (42 chromosomes)

14.8 Isolated islands are often showcases of speciation
Isolated island chains are often inhabited by unique collections of species. Islands that have physically diverse habitats and that are far enough apart to permit populations to evolve in isolation but close enough to allow occasional dispersions to occur are often the sites of multiple speciation events. The evolution of many diverse species from a common ancestor is known as adaptive radiation. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.  Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

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 from 5 million to 1 million years ago, 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. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.  Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

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 birds share many finchlike traits, differ in their feeding habits and their beaks, specialized for what they eat, and arose through adaptive radiation. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  An analogy might be made between the specialized functions of finch beaks and the many types of screwdrivers (or pliers) that exist today. Each type of screwdriver (Phillips, flathead, hex, etc.) represents a specialization for a particular job or a generalist approach, useful in a variety of applications.  Numerous examples of adaptive radiations exist in the Hawaiian Islands. Hawaiian honeycreepers (birds), fruit flies, and species of the plant genera Cyrtandra and Geranium are excellent examples for additional illustration. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

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

14.9 SCIENTIFIC THINKING: Lake Victoria is a living laboratory for studying speciation
We can see speciation occurring. The species living today represent a snapshot, a brief instant in this vast span of time. The environment continues to change, sometimes rapidly due to human impact, and natural selection continues to act on affected populations. Researchers have documented at least two dozen cases in which populations are diverging as they exploit different food resources or breed in different habitats. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Sexual selection is a form of natural selection in which individuals with certain traits are more likely to obtain mates. In addition to the bowerbirds already discussed, biologists have identified several other animal populations that are diverging as a result of differences in how males attract females or how females choose mates. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Biologists can also test hypotheses about the process of speciation by studying species that arose recently. Cichlids are a family of fishes that live in tropical lakes and rivers. They come in all colors of the rainbow. They are renowned for the spectacular adaptive radiations that stocked the large lakes of East Africa with more than a thousand species of cichlids in less than 100,000 years. In the largest of these lakes, Lake Victoria, roughly 500 species evolved in about 15,000 years. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Uganda Kenya Lake Victoria Indian Ocean Tanzania Figure 14.9a
Figure 14.9a Map of East Africa showing Lake Victoria

In Lake Victoria, there are pairs of closely related cichlid species that differ in color but nothing else. Breeding males of Pundamilia nyererei have a bright red back and dorsal fin. Breeding males of Pundamilia pundamilia males are metallic blue-gray. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Pundamilia pundamilia
Figure 14.9b Pundamilia nyererei Figure 14.9b Males of Pundamilia nyererei and Pundamilia pundamilia Pundamilia pundamilia

Pundamilia females prefer brightly colored males. Mate-choice experiments performed in the laboratory showed that P. nyererei females prefer red males over blue males, P. pundamilia females prefer blue males over red males, the vision of P. nyererei females is more sensitive to red light than blue light, and the vision of P. pundamilia females is more sensitive to blue light than red light. Researchers also demonstrated that this color sensitivity is heritable. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

As light travels through water, suspended particles selectively absorb and scatter the shorter (blue) wavelengths, so light becomes increasingly red with increasing depth. Thus, in deeper waters, P. nyererei males are pleasingly apparent to females with red-sensitive vision but virtually invisible to P. pundamilia females. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

When biologists sampled cichlid populations in Lake Victoria, they found that P. nyererei breeds in deep water, while P. pundamilia inhabits shallower habitats where the blue males shine brightly. As a consequence of their mating behavior, the two species encounter different environments that may result in further divergence. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  The work of Peter and Rosemary Grant with Darwin’s finches helps to explain to students that the concept of “better” in evolution is relative. As the environment changes, organisms must respond or suffer the consequences. In these circumstances, organisms are reacting, not improving. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

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. Figure 14.10A illustrates the formation of a hybrid zone, starting with the ancestral species. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Three populations of a species
Figure 14.10a Newly formed species Three populations of a species 3 Hybrid zone 2 1 4 Gene flow Gene flow Hybrid individual Figure 14.10a Formation of a hybrid zone Population Barrier to gene flow

Reinforcement When hybrid offspring are less fit than members of both parent species, we might expect natural selection to strengthen, or reinforce, reproductive barriers, thus reducing the formation of unfit hybrids, and that barriers between species should be stronger where the species overlap (that is, where the species are sympatric). The closely related collared flycatcher and pied flycatcher are an example of reinforcement. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Allopatric populations Sympatric populations
Figure 14.10b-0 Allopatric populations Sympatric populations Male collared flycatcher Male pied flycatcher Figure 14.10b-0 Reinforcement of reproductive barriers Pied flycatcher from allopatric population Pied flycatcher from sympatric population

Fusion What happens when the reproductive barriers between species are not strong and the species come into contact in a hybrid zone? So much gene flow may occur that the speciation process reverses, causing the two hybridizing species to fuse into one. Such a situation has been occurring among the cichlid species in Lake Victoria. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Pollution caused by development along the shores of Lake Victoria has turned the water murky. What happens when P. nyererei or P. pundamilia females can’t tell red males from blue males? The behavioral barrier crumbles. Many viable hybrid offspring are produced by interbreeding. The once isolated gene pools of the parent species are combining, with two species fusing into a single hybrid species. Student Misconceptions and Concerns  Students must understand that species do not evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate; it is reactive. Species do not deliberately change. There is no plan. As teachers, we must take care that our descriptions of evolution accurately reflect its process. The use of the passive voice in descriptions of evolution is one way of doing this.  Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  = 31,557,600) or how much money you could spend each day if you spent $1 million a year ($1,000,000/365 = $2,739.73/day).  Students also need to be reminded that 1 billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Teaching Tips  Students might wish to debate whether two cichlid species that fuse into one were previously separate species. If each species retained the natural ability to hybridize with each other, and did so extensively as the environment changed, were they separate species? Such difficult distinctions test our definitions and reveal some of the challenges of biology. Active Lecture Tips  See the Activity Video Review: YouTube – Bang Goes the Theory: Evolution Made Simple at the Instructor Exchange in the MasteringBiology instructor resource area or at the following address.

Animation: Macroevolution

Figure 14.2a-0 Figure 14.2a-0 Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)

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Figure 14.2a-0 Figure 14.2a-0 Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)

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Presentation on theme: "Figure 14.2a-0 Figure 14.2a-0 Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)"— Presentation transcript:

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