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Home , Reproductive isolation, Species

10 What Is a ? investigation • 3–4 c l a s s s e s s i o n s

OVERVIEW Materials and Advance Preparation In this activity students learn about the biological species For the teacher concept in defining species and how it provides information transparency of Scoring Guide: GROUP INTERACTION (GI) about where new species are in the process of separation transparency of Scoring Guide: UNDERSTANDING from closely related species. Students then investigate the ­CONCEPTS (UC) factors that lead to of species. For each group of four students set of 14 Species Pairs Cards Key Content set of 8 Reproductive Barrier Cards 1. Species evolve over time. The millions of species that live chart paper* (optional) on the today are related by descent from common markers* (optional) ancestors. For each student 2. Taxa are classified in a of groups and sub- Student Sheet 10.1, “Supporting a Scientific Argument” groups based on genealogical relationships. (optional) 3. The broad patterns of behavior exhibited by Scoring Guide: GROUP INTERACTION (GI) (optional) have evolved by as a result of reproduc- Scoring Guide: UNDERSTANDING CONCEPTS (UC) tive success. (optional) 4. Scientists have found that the original definition of spe- *Not supplied in kit cies as groups of with similar Decide in advance if you will hand out Student Sheet does not reflect underlying evolutionary processes. 10.1,“Supporting a Scientific Argument,” or have students 5. The biological defines a species as a pop- record this information in their science notebooks. ulation of individuals that actually or can potentially Masters for Scoring Guides are in Teacher Resource IV: interbreed in to produce fertile offspring. Assessment. 6. Scientific explanations must adhere to such criteria as the application of appropriate evidence, consistently log- ical reasoning, and basis in accepted historical and cur- rent scientific knowledge.

Key Process Skills 1. Students communicate and defend a scientific argument. 2. Students apply evidence and reasoning to formulate a logical claim for where are in the process of .

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Teaching Summary • (Literacy) Students write definitions in their own words Getting Started for the types of isolation, and conduct an Informal Meet- ing of the Minds to discuss their definitions. • Students write their understanding of the concept of a species. Follow-up

Doing the Activity • (UC ASSESSMENT) Discuss the biological species concept as providing a snapshot of where two populations are in the • Review the claim-evidence-and-reasoning approach of process of separation. the activity and, with the , apply it to examples in the Student Book. • The class discusses factors that might lead to speciation. • Students make claims based on evidence and reasoning about where in the process of separation species are from one another.

• (GI ASSESSMENT) Students sort pairs of species based on the barriers to that isolate them and pre- vent flow.

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Getting Started 1 Begin the activity by writing the following three questions on the chalkboard or an overhead 1 0 What Is a Species? transparency.

a. What is a species? INK ABOUT THE many different types of organisms you see in a typical day. 1 TIn addition to , you might see such as dogs and ; such as robins and pigeons; such as and fl ies; and ranging from b. Some examples of species are: dandelions to trees. On a farm or at the or aquarium, you would see even ______. more examples. The original idea of different types, or species, of organisms was based on the c. How do biologists decide if two observable differences in their appearances. A species was defi ned as a group of organisms with similar physical characteristics. Beginning in the late 1700s, spe- populations are of the same or cies became the basic unit of classifi cation. different species? As scientists learned more about evolution and the causes of differences among groups of organisms, their ideas about species changed. Scientists now know that some populations of organisms that appear identical are in fact different species, Tell students to write the questions and others that appear different are the same species. The original species concept and their answers in their science was replaced by concepts that focus on evolutionary relationships. notebooks or, if you would like to There are now several alternative defi nitions for species. In this activity, you will explore the biological species concept. This method of defi ning a species is based collect and read their answers, on on whether the organisms actually or can potentially with each other to produce fertile offspring. If they can, they are of the same species. This approach an index card or piece of paper. Stu- gives evolutionary biologists and conservationists a snapshot of where species are dents’ answers will provide you with in the process of separation from one another. The classifi cation of populations into the same or separate biological species may affect their . formative assessments for you to For example, if two populations are determined to be in separate species, it is more likely that both will be considered for protection. The pickerel (a) and moor determine what students already frog (b) are two species of know and to adjust your instruction in the . if necessary. For example, if most students were introduced to tax- onomy in middle school and know that a species is the most funda- mental unit of classification, you need not emphasize this concept. a b Some students are likely to say a

species is a group of organisms that 472 share some common characteristics. Their examples are likely to vary widely, and some may be at a higher level of classifica- tion than the species level. Oak trees, for example, are members of a genus that includes several hundred species. Everyday examples of two species are the domestic dog and domestic . Another that students might mention is humans and chimpanzees. Students are likely to say that biologists decide whether organisms are in the same or different species based on their appearance. However, some may have been introduced to the idea that members of the same species are able to mate and produce fertile offspring, possibly citing the example of the of and donkeys to produce sterile . Stress that early classification systems focused on the observable characteristics of organisms, but modern systems do not.

723 science and global issues/biology • Evolution

WHAT IS A SPECIES? • ACTIVITY 10

Other species concepts are applied in other fi elds of biology. For example, evolu- tionary biologists use a phylogenetic species concept, which defi nes a species as a distinct lineage and refl ects the evolutionary relationships among taxa.

Challenge � How do new species separate from existing species?

MATERIALS

FOR EACH GROUP OF FOUR STUDENTS set of 14 Species Pair Cards set of eiggpht Reproductive Barrier Cards

BACKGROUND INFORMATION The Biological Species Concept

ACCORDING TO THE biological sexually. The concept also does not spec ies concept, a biological species fi t many species that cross- is all of the populations of individ- breed under natural or artifi cial uals that actually or can potentially conditions. Also, the concept breed with each other in nature cannot be applied to organ- to produce fertile offspring. The isms because their breeding cannot result of this interbreeding is move- be observed. ment of , called gene fl ow, Nevertheless, the biological species through out the species. Members concept gives scientists a snapshot of the same species share a common of the evolution of new species in group of genes—a gene pooll—and many groups of plants and ani- a common evolutionary history. mals. As you review the examples Should members of different popu- on the following pages, keep in lations mate but produce no or no mind that the populations that fertile offspring or very rarely breed share a common are with each other even when present most likely in the early stages of in the same location, they are con- separation from one another. This sidered different biological species. is likely to be the case if individuals in the two populations meet the OTHER WAYS TO CATEGORIZE SPECIES following two conditions: The biological species concept is straightforward, but it turns out • They usually breed together if that there are a number of areas they meet in the wild. where it is not helpful. For • Their breeding produces off- example, many species, such as spring able to produce their own bacterial species, do not reproduce offspring. �

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Doing the Activity SCIENCE & GLOBAL ISSUES/BIOLOGY • EVOLUTION 2 Remind students that they applied the claim-evidence-and- Procedure reasoning approach to scientific Part A: Species Separation argumentation in Activity 5, “Using 1. Read the information on the biological species concept in the box on the 2 previous page. Fossil Evidence to Investigate Whale 2. In your science notebook, prepare an entry like the one below. It should take Evolution.” Review this approach to 3 up about one-fourth of a notebook page. scientific discussion and argumenta- Species Separation tion. Explain to students that they Example number/ name will take this approach in deter- Claim Evidence to support mining where in the process of the claim Reasoning ­separation species are from one

another (early, mid, or late). To do 3. On another page in your science notebook, across the entire page, draw and this, they must first have a working label an arrow like the one shown below. The arrow shows a continuum from early to late for the process of separation of new species from existing species. concept of what a species is. 4. Work as a class with your teacher to complete some of the examples on the 4 following pages. Stress that the biological species con- cept differs from the original concept for defining species, and it stresses the importance of successful repro- duction in the wild and the sharing of a common set of genes, or gene pool.

:6GAN B>9 A6I: [ 3 If you would like students to 5. Following your teacher’s instructions, complete some of the following exam- enter their work on optional ples with your group and some on your own. ­Student Sheet 10.1, “Supporting a Scientific Argument,” distribute it now. If not, have students set up space in their notebooks for Example 1. 474 4 Work through as many examples as necessary with the class until you think students are ready to work on them more indepen- Note that this is a continuum, and students may wish to dently. As you work together, be sure students understand use designations such as early–mid or mid–late if the evi- the following about the parts of scientific argument: dence is incomplete or inconclusive. The evidence portion of argumentation for these examples refers to what hap- The claim portion is a statement about the placement of pens with mating and offspring. In the reasoning setup, species as early, mid, or late in the process of separation as students should include a statement about how the mating follows: and offspring results affect the exchange of genes and • Early means they are either still one species, or that they sharing of a common gene pool, which indicates where in have just begun separation. separation the species are likely to be. This reasoning relies on the biological species concept and ties the evidence • Mid means they are separating. back to the claim. • Late means they are at the end of separation and they have most likely split into two species.

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5 Next, instruct students to work in groups to complete enough WHAT IS A SPECIES? • ACTIVITY 10 examples to give them adequate 5 6. In your science notebook, record each of the following: practice applying the claims-evi- • The example number and the name of the organisms • Your claim: a statement about what stage of separation the species are in dence-and-reasoning approach to • Place the names of the organisms at the appropriate stage of separation species separation. Circulate around (early, mid, late) along the arrow you drew in Step 3. • Your evidence: the information about the mechanism of the separation the room, and determine whether between species you need to review students’ ideas • Your reasoning: an explanation of the mechanism of separation that sup- ports your claim. Refer to the biological species concept to explain each before they complete the remaining species’ stage in the separation process.

assigned examples independently. 7. Repeat Step 6 for all of your assigned examples. Sample answers follow. The Separation of Species

• Example 1: Red and Purple EXAMPLE 1 Sea Urchins Red and Purple Sea Urchins Claim: Late Red and purple sea urchins live in embryos produced, however, do Evidence: The eggs can be fertilized shallow along the not survive beyond the very early eastern Pacifi c coast from Alaska to stages of development. � in the lab but the embryos do not Mexico. The sperm of one of these organisms fertilizes the eggs of the survive. other only in the laboratory, where scientists mix the eggs with much Reasoning: Even though the eggs higher concentrations of sperm can be artificially fertilized, the off- than are likely in the wild. The spring do not survive. Therefore, they cannot exchange genes and share a common gene pool, and they have most likely split. Red sea urchins

• Example 2: Eastern and

Great Plains Narrowmouth Frogs Purpple sea urchins Claim: Mid Evidence: Even though they might 475 encounter each other, the two frogs usually do not choose to mate with

their own kind based on mating call. • Example 4: Horses and Donkeys Reasoning: Since they usually do not breed, they are not Claim: Late exchanging genes and sharing a common gene pool, and Evidence: They can breed but do not produce fertile off- are further along in separation as a result. spring. Sometimes female mules breed with horses or don- keys and do produce live offspring. • Example 3: Northern and California Spotted Owls Reasoning: If they breed, there are offspring, but the off- Claim: Early–mid spring are always infertile. Therefore, they cannot Evidence: The owls’ ranges overlap, and they can breed to exchange genes and share a common gene pool and have produce fertile offspring, but rarely do so. most likely split. Reasoning: Because they can breed and produce fertile off- spring, they can exchange genes and share a common gene pool, even if rarely. This means they must be early to midway in the separation process.

726 what is a species? • aCtivity 10

• Example 5: Dogs and Reasoning: If the lacewings are mated, they exchange genes Claim: Early and share a common gene pool. But they also have a dif- Evidence: Dogs and wolves do mate and produce fertile ferent mating call, making them likely to be in a relatively offspring. early stage of separation. Reasoning: If dogs and wolves can mate to produce fertile offspring, they can exchange genes and share a common • Example 9: Copper-resistant and Copper-tolerant gene pool, which means they are one species or early in Yellow Monkey separation. Claim: Early–mid Evidence: When scientists cross the plants many die early, • Example 6: Midas and Arrow Cichlid but some live. Claim: Late Reasoning: If some of the plants live, those few can Evidence: The do not mate in the wild, and their off- exchange genes and share a common gene pool, which spring by do not live. means they are not as separated as they would be if they couldn’t. Reasoning: If they do not mate in the wild and the offspring of controlled breeding do not live, they have most likely split, and there is no exchange of genes or common gene pool. • Example 10: Orchids Claim: Late

• Example 7: Blue and Red Cichlid Fish Evidence: The orchids on different days and cannot Claim: Early–mid be bred to produce hybrids. Evidence: The fish do not breed in nature, but can be bred in Reasoning: If the orchids cannot reproduce fertile off- a lab to produce fertile offspring. spring in nature or in the lab they cannot exchange genes or share a common gene pool, which means they have Reasoning: The fish can breed to produce fertile offspring. most likely split. And, they are very similar to each other. This means they share a common gene pool and they are likely to be one spe- A sample response arrow is shown below. cies, or early in the separation process.

• Example 8: Green Lacewings Claim: Early–mid B^YVhX^X]a^Y Evidence: If mated in a lab, the lacewings gZYhZVjgX]^ch ]dghZh Yd\hVcY Cdgi]ZgcVcY8Va^[dgc^V :VhiZgcVcY9 A6I: Ydc`Znh breed in the wild. dgX]^Yh

()*+H:EJEH<>:kdaji^dcI< ;^\jgZ/()*+:kdI<&%T&+ 6\ZcYVBZY8dcY.$.

Cdgi]ZgcVcY8Va^[dgc^VhediiZY dlah WajZVcYgZYX^X]a^Y \gZZcaVXZl^c\h 727 XdeeZg"gZh^hiVciVcYXdeeZg" idaZgVcibdc`Zn[adlZgh science and global issues/biology • Evolution

SCIENCE & GLOBAL ISSUES/BIOLOGY • EVOLUTION

EXAMPLE 2 Eastern and Great Plains Narrowmouth Frogs

The eastern narrowmouth frog’s because of differences in their range extends along the east coast mating calls. The two groups of the from the Caro- of frogs are distinguished by linas to Florida and west into parts their colors. � of Oklahoma and Texas, where it in moist areas. The Great Plains narrowmouth frog’s range is from Baja California in Mexico to eastern Texas, eastern Oklahoma, and northern Missouri, where it lives in drier regions. These two types of frogs occasionally breed naturally in the areas where they overlap, but the fer- tility of their offspring is not known. Most of the time the frogs select mates of their own , perhaps

Great Plains narrow mouth frog (top), Eastern narrow mouth frog (bottom)

EXAMPLE 3 Northern and California Spotted Owls

Northern spotted owls range from that when birds of each type come northwestern California to western into contact they have bred and Oregon, Washington, and Canada. produced fertile offspring. These California spotted owls are found offspring have a (mixed) in the Sierra Nevada from northern genetic makeup. However, this to southern California. The two cross-breeding is rare. Northern owl populations overlap in parts of and California spotted owls show northern California. Field observa- some differences in appearance tions and genetic evidence suggest and . �

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728 what is a species? • aCtivity 10

WHAT IS A SPECIES? • ACTIVITY 10

EXAMPLE 4 Horses and Donkeys

A female and a male can mate to produce a . Horses have 64 , while donkeys have 62. The mule is born with 63 chromosomes that cannot divide evenly, and this makes mules sterile. Although there are some cases of female mules breeding successfully with male horses or donkeys to produce live but infertile offspring, there are no known cases of male mules breeding successfully with female mules, donkeys, or horses. �

The mule is the sterile offspring of a horse and a donkey.

EXAMPLE 5 Dogs and Wolves

There is great among mate to produce a mixed breed domesticated dogs, which were dog, commonly called a mutt. bred from wolves approximately Dogs can also breed with wolves to 10,000 years ago. Most dogs can produce fertile offspring. These breed with one another and have mixed offspring can reproduce puppies that show a mix of the with similar dogs, other dog traits of the dogs. For , or wolves. Genetic analysis example, a breeder of designer reveals very little difference dogs can mate a boxer and a between dogs and wolves. Wolves poodle to produce a boxerdoodle. are much more similar genetically Dogs from different breeds often to dogs than to . �

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729 science and global issues/biology • Evolution

SCIENCE & GLOBAL ISSUES/BIOLOGY • EVOLUTION

EXAMPLE 6 Midas Cichlid and Arrow Cichlid Fish

Scientists are studying two types of cichlid fi sh in a volcanic lake in Nicaragua. The Midas cichlid is a bottom-feeder, has a wide body, and eats algae. The arrow cichlid has a slender body for swimming and eats winged insects. The two types of fi sh select mates of their own kind, and fail to reproduce live offspring when people try to breed them. �

Arrow cichlid (top), Midas cichlid (bottom)

EXAMPLE 7 Blue and Red Cichlid Fish

Two very similar types of cichlid where they cannot see the color fi sh live in Lake Victoria in Africa. of the other fi sh, they will freely One is blue, and the other is red. mate with fi sh of the other color. Females of these two types prefer In these lab conditions, the females mates of the same color, and in would now mate with either color nature these two types of fi sh do male, and produce fully fertile not breed. However, in a lab, when offspring. � they are put in lighting conditions

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WHAT IS A SPECIES? • ACTIVITY 10

EXAMPLE 8 Green Lacewings

Two populations of lacewings that look identical and live in the same locations do not mate in the wild because they have different mating signals. Female lacewings exhibit a strong preference in the wild for changes prevent the mating of males with a similar mating call. males and females with different Genetic analysis suggests that mating calls. When mated in the the changes in mating call result laboratory, o ffspring of these two from changes in just a small types of lacewings are fertile. � number of genes, but that these

EXAMPLE 9 Copper-resistant and Copper-tolerant Yellow Monkey Flower

Copper is toxic to most plants. cop per, many However, scientists have observed a of the hybrid few plants that have developed a plants did tolerance for copper. One of those not survive. is the yellow monkey fl ower. When In early growth stages, their scientists crossed copper-tolerant turned yellow and they died soon plants with plants sensitive to after. �

EXAMPLE 10 Orchids

Three populations of orchids each the same tropical forest area, there fl ower at different times of the year is no chance that members of one for just a single day. Therefore, will fertilize the other even though these orchids grow in in the wild. �

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6 (GI ASSESSMENT) Distribute a set of 14 Species Pair Cards to each SCIENCE & GLOBAL ISSUES/BIOLOGY • EVOLUTION group of four students. Inform stu- Part B: The Formation of New Species Evolutionary biologists focus on the question of how new species and other taxa dents that this activity asks them to arise. As you have learned, two populations that have different physical character- demonstrate their ability to work istics might still belong to the same species if they can interbreed to produce fer- tile offspring and do so in nature. This interbreeding allows gene fl ow, with the together in their groups to complete two populations sharing a common gene pool. the Procedure. If necessary, dis- How do new species arise? According to the biological species concept, two popula- tions must be reproductively isolated. Reproductive isolation is caused by several tribute copies of the GROUP INTERAC- kinds of barriers. Once they become reproductively isolated, the two populations will TION (GI) Scoring Guide. Review the no longer share a common gene pool. Each population will change independently of the other. Eventually the two populations could evolve into two separate species. guidelines for the GI Scoring Guide. 6 8. With your group, spread the Species Pair Cards out on a table. 7 Tell students to work through the 9. Examine the information on each card carefully, noting the barriers to repro- 7 duction between the two species described on the card. rest of the Procedure steps. Groups 10. Sort the cards into groups based on the barriers to reproduction. Work with should work together to organize your group to agree on a name that describes each kind of barrier. While doing so, the cards and record the groupings • listen to and consider the explanations of your group members. they have formed. Most impor- • if you disagree, explain how and why you disagree. tantly, they should note the 11. In your science notebook, write the title: Our Groupings. Beneath this title, list the groups that you created and the names you picked to describe each common barrier to reproduction by group. Be sure to record which species pairs belong to each group.

which they formed each of the 12. Following your teacher’s instructions, your team will present your groupings 8 groupings of species. If students are to the class. As you look at other students’ groupings, observe the similarities and differences between their systems and yours. Discuss your observations having problems, suggest that they with your team members. select only one criterion to begin 13. Your group will receive eight Reproductive Barrier Cards from your teacher. Each card represents a barrier that leads to reproductive isolation of related their sorting, but allow them to species. Based on the information described on the Reproductive Barrier Cards, place each Species Pair Card under one of the Reproductive Barrier work as independently as possible. Cards.

14. Record this new set of groupings in your science notebook under the title Sci- 8 Hold a brief class discussion entifi c Groupings.

about how groups classified the bar- 15. List the isolating mechanisms you examined in this activity. Write a defi ni- 9 riers to reproduction, and named tion for each mechanism in your own words. 16. List the two types of reproductive isolation in this , and describe them their groupings. Allow members of 10 in your own words. each group to briefly show their classifications and describe the choices they made. You might also 68 provide chart paper and markers for students to their systems. Highlight the similarities and differences between the sys- Suggested Answers tems that the different groups used by listing them on the Isolation: Garter , insects board or overhead. Behavioral Isolation: Meadowlarks, fireflies, blue and red Do not hand out the sets of Reproductive Barrier Cards, cichlids which represent the groupings scientists put together, to Geographic Isolation: each team until Procedure Step 12. Explain that scientists Temporal Isolation: Lacewings, orchids look for patterns in their observations and make the kinds Mechanical Isolation: Flowering plants, damselflies of observations students made to group the barriers to Gametic Isolation: Purple and white sea urchins reproduction that are described on the cards. Reduced Hybrid Viability: Frogs Hybrid sterility: Lions and , horses and donkeys

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9 Suggested definitions for the types of isolation follow. WHAT IS A SPECIES? • ACTIVITY 10 Analysis Behavioral isolation: mating songs 11 1. Why is appearance alone no longer considered suffi cient evidence for classi- are too different for potential mates fying organisms? to recognize, or the animals have 2. Explain how geographic isolation can lead to speciation. different courtship rituals 3. Lions and tigers do not overlap in range and do not breed in nature. In captivity, a male lion may mate with a female and produce offspring. Although more rare, a male tiger may also mate with a female lion to produce offspring. In both Habitat isolation: two species live cases, the male offspring are sterile, while the females might or might not be fer- in the same area but in slightly dif- tile. Explain where lions and tigers are on the speciation continuum, according to the biological species concept. Support your answer with evidence and reasoning.

ferent , such as in or on dif- 4. How did your groupings of the reproductive barriers in Part B resemble or ferent parts of the same plant. differ from those used by scientists as shown by the cards in Step 13? 5. Why do you think you came up with a different set of groups in Part B than Temporal isolation: the two species scientists do in their groupings? breed at different times of the year. 6. Did any of the species pairs in Part B show more than one barrier to repro- duction? List examples, and describe the barriers they display. Mechanical isolation: the two spe- 7. Describe the barriers that are causing reproductive isolation for each of the following from Part A: cies do not have the anatomical a. Red and purple sea urchins structures necessary for mating. b. Eastern and Great Plains narrowmouth frogs c. Northern and California spotted owls Gametic isolation: sperm and eggs 8. Two related species of frogs appear to be very similar, but they have different mat- ing calls. In addition, one species breeds in the fall, and the other breeds in the cannot interact. spring. What mechanisms contribute to reproductive isolation of these species?

9. Two related species of birds appear to be similar, but when they breed, their 10 (Literacy) Sample definitions for offspring rarely survive past a few days old. What mechanism leads to repro- the two types of reproductive isola- ductive isolation of these species? 10. A genetic change occurs in the gene pool of a population of a single fl ower tion follow. species with large white tubular fl owers. This species is normally pollinated by a species of large bee that is attracted to large white tubular fl owers. Polli- Hybrid sterility: members of spe- nation is essential for these fl owers to produce seeds. In some individuals, one genetic change leads to the production of much smaller fl owers. Explain how cies can mate, but their offspring are this could lead to speciation in the population. sterile. KEY VOCABULARY Reduced hybrid viability: two biological species gene pool ­species can mate, but the offspring biological species concept species do not live long enough to repro- duce their own offspring. 481

When students have completed Pro- cedure Step 15, conduct an Informal Meeting of the 11 (UC ASSESSMENT) Analysis Questions 2 and 3 are an Minds. Direct students to find a partner from another opportunity to apply the Understanding Concepts group and to discuss their definitions for the types of bar- (UC) Scoring Guide to assess students’ understanding riers, citing an example or two for each. Circulate around of ­geographic isolation and speciation. Review the the room as students talk. Ask pairs to share their defini- UC Scoring Guide, and tell the class your expectations tions with the class. You may wish to have them learn the for satisfactory work. scientific names for the different barriers, but it is more important that they can describe them, how they work, As you discuss the activity and the answers to the Analysis and give an example or two. If you wish, assign this task as Questions, emphasize to students that for some of the homework. Begin the next class period with a review of examples there is a fair amount of grey area for scientists the information. who are trying to determine where in speciation the popu- lations are. This illustrates why the biological species con- cept is considered just a snapshot of what is going on with speciation. Stress the growing emphasis in the field of clas- sification on the importance of the evolutionary relation-

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ships among taxa, using the phylogenetic species concept. Sample Responses Discuss also the importance in science of applying evi- 1. Scientists concluded from evolutionary evidence that dence and logical reasoning in making claims from which some species that look identical are different species and to build arguments and explanations. Discuss some of the others that appear different are the same species. examples. Ask students if they felt the information they 2. (UC ASSESSMENT) A complete and correct response will were given in this activity provided the evidence to make a include a description of the types of geographic features solid claim. Note that in some cases, evidence about that can stop gene flow, prevent the sharing of a gene breeding success was not provided because it is not avail- pool, and lead to the separation of species. able. Missing evidence affects the certainty of a claim. Emphasize the importance of logical reasoning, which Sample Level-3 Response: requires an understanding of the appropriate concept(s), Two populations can get separated by physical features in this case the biological species concept, and the devel- on earth such as the formation of mountains, canyons, opment of reasonable connections and inferences between rivers, or glaciers. Or a population moves far away from the evidence and the concept. the original population. This could stop gene flow between the populations, prevent them from sharing a In regard to species conservation introduce the impor- common gene pool, and lead to speciation. tance of where in the process of separation from one another two populations are. In the United States the 3. (UC ASSESSMENT) A complete and correct response will Act (ESA) protects species and sub- explain the placement of lions and tigers on the specia- species, and in the case of may also protect tion continuum, and cite evidence and reasoning from “distinct population segments” that are considered signifi- the biological species concept to support the answer. cant in relation to the entire species. Thus the species or designation of a population may determine Sample Level-3 Response: whether it gets ESA protection if the is threatened. Lions and tigers are late in the speciation process, but not completely separate. The evidence for this is that they do Ask students to volunteer to list the factors that lead to not produce fertile male offspring even when mated in speciation. They should be able to mention all of the types captivity, while some female offspring are fertile. that were given on the Reproductive Barrier Cards in Part According to the biological species concept, the offspring B. Write those on the board. Ask students what all of these of a biological species are fertile, so lions and tigers, with types of barriers have in common. Discuss the idea that all the exception of some female offspring, do not meet this of these are barriers that keep populations apart and no part of the definition of a biological species. longer able to breed. This means they can no longer exchange genes with one another. As this activity demon- 4. Students’ answers will vary, but should be based on stu- strates, there are more barriers than just geographic isola- dents’ recognition of differences between their systems tion that may keep populations from reproducing. Some and the system illustrated on the Reproductive Barrier barriers occur even if the two populations live in the same Cards. For example, some students may have classified as area. For example, two populations that live in the same behavioral isolation the two species of damselflies as spe- area might have different mating seasons or mating calls. cies that cannot mate because the males cannot hold Also, geographic isolation alone is not always enough to onto the females. These students may have interpreted lead to speciation. Some populations might still mate and the holding on as a behavior that may be part of a court- produce live offspring if they are brought together after ship ritual of some type rather than as a result of being geographically isolated. mechanical isolation. 5. Students may suggest they do not have as many examples as scientists do, or that they lumped or split categories differently than scientists.

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6. Lions and tigers show both geographic isolation and • All species are continually in the process of separation hybrid sterility. from one another. For some species the biological species 7. a. Reduced hybrid viability concept determines a snapshot of where on the contin- uum of separation they are. b. Behavioral isolation • When female offspring of hybrids between two popula- c. Geographic isolation tions are fertile but males are not (as in the case of 8. Behavioral (the different mating calls) and temporal mules), the offspring are not considered to be fully fer- (mating at different times) tile, and the horses and donkeys are considered to be late 9. Reduced hybrid viability in separation. Again, this is because gene flow cannot 10. The change could lead to the need for different pollina- continue freely between the horse and donkey popula- tors because of mechanical isolation. If the pollinator of tions. In this case, the mules are essentially a dead end, one group cannot pollinate the other group (and vice and cannot continue a lineage of offspring. versa) due to differences in the size of the flowers, these • There are a variety of factors that lead to speciation. two groups of organisms will become reproductively iso- lated, even though they grow in the same area.

Revisit the Challenge Review these key points about species separation and the biological species concept:

• To be of the same species two populations must be able to breed and choose to breed when they come in contact. If they do not breed successfully, there cannot be a flow of genes from one population to the other and the popu- lations will not share a gene pool. This means they are reproductively isolated, and therefore, likely to be later in separation from one another.

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