7/31/13 4:47 PMCh 24 HW Page 1 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Ch 24 HW Due: 11:59pm on Tuesday, August 13, 2013 You will receive no credit for items you complete after the assignment is due. Grading Policy Defining Species Scientists have proposed more than two dozen ways to define species. One commonly used definition, called the biological species concept, holds that populations belong to the same species if they can contribute genes to a common gene pool. Reproductive barriers block gene flow between different species. Gene flow between populations tends to hold the gene pool of a species together. Part A - Comparing species definitions Three of the most prominent definitions of species are the biological species concept, the phylogenetic species concept, and the morphological species (morphospecies) concept. Drag each characteristic to the appropriate bin based on the species concept(s) to which it applies. Hint 1. Definitions of phylogeny and phylogenetic trees Phylogeny refers to the evolutionary history of a species or group of species. Phylogenetic trees are branching diagrams intended to show the evolutionary histories of related species. Because it is impossible to directly observe these relationships as they develop, phylogenetic trees are hypotheses and may change over time as new findings come to light. The phylogenetic species concept defines a species as the smallest group of organisms that share a common ancestor. Hint 2. How can the morphological species concept be used in species classification? The morphological species (morphospecies) concept groups organisms into species based on structural features. Which of the following might be used in classifying a species by the morphological species concept? Select all that apply. ANSWER: Hint 3. What are the limitations of the biological species concept? The biological species concept defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. This means that members of a species can contribute to a common gene pool. Which of the following would allow a researcher to determine whether these criteria are met? ANSWER: ANSWER: flower shape plumage pattern presence or absence of leg feathers skeletal features vascular arrangement in plants observation of organisms that reproduce by mating observation of organisms that reproduce by cloning comparison of leaf structures study of fossilized skeletons 7/31/13 4:47 PMCh 24 HW Page 2 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct Evolution has produced a continuum of life on Earth. To classify organisms at the species level within that continuum, biologists have proposed a variety of ways to define species. Species concept Criteria Advantages Disadvantages biological ability to create viable, fertile offspring objective criteria, meshes well with gene flow concept not applicable to extinct or asexual species morphological similarities in body structures easy to apply, works for asexual and extinct species researchers may disagree on which structures are important phylogenetic common evolutionary history based on actual relationships, works for asexual and extinct species requires good evolutionary histories Part B - Classifying reproductive barriers According to the biological species concept, individuals belong to the same species if they can interbreed in nature and produce viable, fertile offspring. Prezygotic and postzygotic barriers ensure that members of different species do not reproduce with one another. This diagram shows some of these barriers along with examples of the barriers at work. Complete the diagram by following these steps: 1. Drag blue labels onto blue targets only to identify the two main types of reproductive barriers. 2. Drag pink labels onto pink targets only to identify specific barriers. 3. Drag white labels onto white targets only to identify examples of barriers. Hint 1. Definitions of prezygotic and postzygotic 7/31/13 4:47 PMCh 24 HW Page 3 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Recall that the prefix "pre-" means before and the prefix "post-" means after. The term "zygotic" refers to the formation of a zygote from the fusion of gametes. Therefore, a prezygotic barrier is one that occurs before (and prevents) fertilization of the egg, and a postzygotic barrier is one that occurs after (and does not prevent) fertilization of the egg. Hint 2. Definitions of hybrid viability and hybrid fertility Reduced hybrid viability and reduced hybrid fertility are two types of postzygotic reproductive barriers. That is, the offspring of a mating do not pass on their genes. With reduced hybrid viability, the offspring produced by mating are unable to survive to adulthood or are frail and cannot compete for mates. With reduced hybrid fertility, the offspring produced by mating are sterile, preventing continued gene flow. For example, the hybrid offspring of a male donkey and a female horse is a mule, which is sterile. Hint 3. What are the types of reproductive barriers? Drag the terms on the left to the appropriate blanks on the right to complete the sentences. ANSWER: ANSWER: 7/31/13 4:47 PMCh 24 HW Page 4 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct According to the biological species concept, species remain separate because gene flow does not occur between them. Some barriers to gene flow prevent mating or fertilization, whereas others ensure that hybrids (the offspring of a mating between individuals of different species) are unable to reproduce. Reproductive barrier Prezygotic or postzygotic Description Example behavioral isolation prezygotic differences in mating rituals or displays different bird species display feathers of different colors during mating display temporal isolation prezygotic differences in the timing of mating one plant species flowers before dawn; a related species flowers in the late afternoon habitat isolation prezygotic differences in habitat occupied different ticks live on different host species mechanical isolation prezygotic reproductive structure incompatibility differently shaped snail shells prevent alignment of genital openings gametic isolation prezygotic sperm and egg are incompatible different coral species release gametes into the water, but only gametes of conspecifics can fuse reduced hybrid viability postzygotic hybrid offspring are produced but are feeble or unable to compete for mates two species of fish successfully interbreed, but their offspring don't live to maturity reduced hybrid fertility postzygotic hybrid offspring are produced but are sterile horses can be mated with zebras, but their offspring are sterile Part C - Gene flow and the biological species concept Recall that the biological species concept defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. This means that all members of these populations (called conspecifics) can contribute to a common gene pool. Conspecifics are organisms or populations that belong to the same species. Genes are transferred between conspecific populations through both direct and indirect gene flow. 7/31/13 4:47 PMCh 24 HW Page 5 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Biologists studying disease susceptibility in mice used genetic techniques to look for gene flow in 12 wild populations of mice. The populations (designated A through L) were located along a 210-km transect line. The researchers found evidence of gene flow between some, but not all, pairs of populations. In the grid below, a "+" indicates a pair of populations in which direct gene flow was detected, and a "?" indicates a pair that showed no evidence of direct gene flow. For help reading this grid, see Hint 2. The researchers discovered that the 12 populations could be organized into 3 distinct species. Populations A, B, and C each belong to a different species. Use the data in the grid to sort each population to the species to which it belongs. Hint 1. How to approach the problem To understand gene pools and gene flow between populations, you can think about containers of water (X, Y, and Z in the diagram below) as models of populations. If containers X and Y are connected by a pipe, water can flow between them. If container Z is connected to container Y, water can flow between X and Z even though they aren't directly connected. Thus, a container shares water not only with neighboring containers to which it is directly connected, but also with any other container that is connected to its neighbors. Similarly, genes can flow between populations, either directly or indirectly, through other populations. To determine which populations in Part C are conspecifics, use the following steps: 7/31/13 4:47 PMCh 24 HW Page 6 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 1. Use the grid to determine which populations have direct gene flow with population A. 2. Next, determine which populations have direct gene flow with those populations, and thus have indirect gene flow with population A. Populations having direct or indirect gene flow with population A are considered to be conspecific with A. 3. Repeat these steps with populations B and C. Hint 2. How to read the grid To determine whether direct gene flow was detected between populations C and G, for example, find the square where row C intersects column G. There is a ?+? in that square, which means that there is direct gene flow between these two populations. But remember, to answer Part C, you will need to consider both direct gene flow and indirect gene flow between populations. Hint 3. Which populations belong to the same species as population A? Using the data in the grid, find all of the populations that have had direct or indirect gene flow with population A. Start by finding populations that have had direct gene flow with population A, and then find ones that have had gene flow with those populations. Select the five that apply. ANSWER: D E F G H I J K L 7/31/13 4:47 PMCh 24 HW Page 7 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 ANSWER: Correct Based on the gene flow data in the grid, populations A, D, F, H, I, and K belong to one species, populations B, E, and L belong to a second species, and populations C, G, and J belong to a third species. Just as different species are kept separate by barriers to gene flow, species integrity is maintained by gene flow between populations. Even populations that are separated by large distances (such as A and K in this example) may be connected through gene flow. Gene flow can also occur between two populations that do not directly interbreed. As genes are exchanged between some populations, and those populations then exchange genes with other populations, genes can flow throughout all populations of a species. Activity: Overview of Macroevolution Click here to complete this activity. Then answer the questions. Part A Feathers either play a role, or may have played a role, in _____. ANSWER: 7/31/13 4:47 PMCh 24 HW Page 8 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct All of these are, or may have been, functions of feathers. Part B _____ is rapid speciation under conditions in which there is little competition. ANSWER: Correct Adaptive radiation is rapid speciation under conditions in which there is little competition. Part C Mass extinctions create conditions that promote _____. ANSWER: Correct Mass extinctions reduce competition and allow for periods of rapid speciation. Part D The appearance of an evolutionary novelty promotes _____. ANSWER: flight gliding extended hops courtship all of these Paedomorphosis Adaptive radiation Gene flow Microevolution Genetic drift microevolution genetic drift paedomorphosis adaptive radiation gene flow 7/31/13 4:47 PMCh 24 HW Page 9 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct The appearance of an evolutionary novelty may allow for the exploitation of previously unexploited niches. Part E The different finch species found on the Galápagos Islands probably arose as a result of _____. ANSWER: Correct The finches that initially immigrated to the Galápagos Islands experienced little competition, the result of which was the promotion of speciation. Chapter 24 Pre-Test Question 1 Part A What is the most important factor that holds a gene pool of a species together and prevents speciation? Hint 1. Think about what is going on in human populations currently. ANSWER: Correct Gene flow refers to the transfer of alleles among populations. As long as populations are exchanging alleles, speciation is unlikely. Chapter 24 Pre-Test Question 2 mutation mass extinction gene flow paedomorphosis adaptive radiation mass extinction adaptive radiation artificial selection paedomorphosis gene flow gene flow hybridization behavioral isolation sexual selection prezygotic barriers 7/31/13 4:47 PMCh 24 HW Page 10 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Part A Two animals are considered members of different species if they _____. Hint 1. Consider the different species concepts. ANSWER: Correct If two individuals cannot interbreed and produce viable, fertile offspring, they are members of different species. Activity: Allopatric Speciation Click here to view this animation. Then answer the questions. Part A What is genetic drift? Hint 1. What causes genetic variation in populations over time? ANSWER: cannot mate and produce viable, fertile offspring live in different habitats are members of different populations look different are geographically isolated The physical splitting of a habitat A change in allele frequencies caused by random events The production of an evolutionarily independent group of organisms The motion of continental plates over time 7/31/13 4:47 PMCh 24 HW Page 11 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct Genetic drift is a random change in allele frequencies over time. Part B Why are the large finches now living on the Galápagos Islands different from the original source population from a nearby island? Hint 1. How do colonization events trigger speciation? ANSWER: Correct Physical isolation, natural selection, and genetic drift are all events that lead to speciation. Part C True or false? The last ice age produced many different species mainly because populations dispersed and colonized new habitats. Hint 1. What effect did the ice age have on existing habitats? ANSWER: Correct The last ice age produced many different species mainly because of vicariance events; the glaciers physically separated populations from each other. Part D Which of the following statements about reinforcement is true? Hint 1. Consider how reinforcement promotes the divergence of species. ANSWER: Genetic drift occurred in the two populations. The separation of habitats reduced gene flow between the populations. Natural selection favored individuals that were more fit in the new environment. All three answers are correct. True False 7/31/13 4:47 PMCh 24 HW Page 12 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct Reinforcement is a type of natural selection called disruptive selection, which favors extreme phenotypes over intermediate phenotypes. Part E A subset of a population of birds leaves its habitat on the mainland and colonizes a nearby island. The birds, after a period of time, become reproductively isolated. The island sinks and the population of birds that lived on the island returns to its original habitat. Which of the following statements about these bird populations is true? Hint 1. Think about how the birds were separated and what happens when speciation does or does not happen. ANSWER: Correct Different species cannot interbreed. Part F A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time? Hint 1. Consider how the birds have adapted to their new environment. ANSWER: Correct Birds with larger beaks are better able to survive in the new environment. Part G Reinforcement increases the number of intermediate phenotypes. Reinforcement decreases the morphological difference between two incipient species. Reinforcement is also called dispersive selection. Reinforcement is a type of natural selection. The populations will not be able to interbreed because they are different species. The populations will be able to interbreed even though they are different species. The birds were separated by a vicariance event. The populations were sympatric while they diverged. Increased fitness of the large-beaked birds, creating a new species Decreased fitness of the insects, allowing the birds to catch them more easily Decreased fitness of small-beaked birds, creating a new species Increased fitness of large-beaked birds, leading to natural selection 7/31/13 4:47 PMCh 24 HW Page 13 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 True or false? A flood that separates a population of frogs onto opposite sides of a lake is an example of a vicariance event that may result in allopatric speciation. Hint 1. Think about how allopatric speciation can occur. ANSWER: Correct Allopatric speciation may occur when populations are separated geographically; this type of speciation can begin with a vicariance event, in which a geographic barrier such as water isolates a population, or a dispersal event, in which a subset of a population migrates to a different habitat. Interpreting Data: Evolution of Reproductive Barriers in Lab Populations of Fruit Flies Can you interpret the results of mating experiments in fruit fly populations? Part A Of the 59 matings in the experimental groups, how many were between like-adapted flies (flies adapted to the same medium)? ANSWER: True False 7/31/13 4:47 PMCh 24 HW Page 14 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Correct Part B Which of the following statements is best supported by the data on matings in the experimental groups? ANSWER: Correct Part C Which of the following statements is supported by the data from the control group matings? ANSWER: Correct Part D A similar control experiment was performed with flies adapted to maltose, and similar results were obtained. What were these control experiments testing? ANSWER: Correct Chapter 24 Pre-Test Question 7 17 22 30 42 The starch-adapted flies and maltose-adapted flies appear to now be separate species as defined by the biological species concept. There is no evidence of reproductive isolation between the starch-adapted flies and maltose-adapted flies. The starch-adapted flies and maltose-adapted flies are not different species, but a reproductive barrier is forming between the populations. Flies were about as likely to mate with flies from different starch-adapted populations as with flies from their own starch-adapted population. Male starch-adapted flies were less likely to mate with female starch-adapted flies than with female maltose-adapted flies. Female starch flies from population #2 were more likely to mate with male flies from their own population than with flies from a different starch population. These control experiments tested whether in the process of becoming adapted to different food sources, the flies had lost the ability to reproduce. These control experiments tested whether flies were more likely to choose mates from their own population than from another population adapted to the same medium. These control experiments tested whether the starch-adapted flies had a greater preference for like-adapted flies than did the maltose-adapted flies. 7/31/13 4:47 PMCh 24 HW Page 15 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Part A Hybrid zones provide an opportunity to investigate _____. Hint 1. A zone where different species are reproducing together may seem like a paradoxical place to investigate this. ANSWER: Correct A hybrid zone allows researchers to see what happens when closely related species come together. Reproductive barriers may be strengthened or weakened, depending on environmental and genetic factors. Chapter 24 Pre-Test Question 8 Part A A certain species of salamander was split into two populations by a wide, dry valley, and the populations began to diverge from each other. After a period of time, some members of the two populations began to interbreed in a hybrid zone at the southern end of the valley. Only weak reproductive barriers existed by this time, so the two populations could freely interbreed and re-establish gene flow. This outcome in a hybrid zone is known as _____. Hint 1. What are the possible outcomes when different species or populations come together in a hybrid zone? ANSWER: Correct Fusion refers to the weakening of reproductive barriers, allowing the two populations to fuse and remain (or become) one species. Chapter 24 Pre-Test Question 9 Part A According to the _____ model, evolution occurs in spurts; species evolve relatively rapidly then remain unchanged for long periods. allopatric speciation the evolution of reproductive isolation punctuated equilibrium mutations polyploidy fusion reinforcement speciation punctuated equilibrium stability 7/31/13 4:47 PMCh 24 HW Page 16 of 16http://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=2133916 Hint 1. Is this a strictly Darwinian view? ANSWER: Correct This is the definition of punctuated equilibrium. Chapter 24 Pre-Test Question 10 Part A Which of the following has been shown to cause speciation most rapidly? Hint 1. The mechanism of speciation can govern the rate of speciation. ANSWER: Correct Autopolyploidy has been shown to produce nearly instantaneous speciation in plants. Score Summary: Your score on this assignment is 91.4%. You received 9.14 out of a possible total of 10 points. geographic isolation nondisjunction adaptive radiation punctuated equilibrium gradualist autopolyploidy hybridization differential resource exploitation sexual selection punctuated equilibrium Travis Warman Ch 24 HW
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