Important
Note: Dr.
Steve Rissing, Professor in the Department of Evolution, Ecology, and
Organismal Biology and Director of the Introductory Biology program at The Ohio
State University, Dr. Patricia Princehouse of Case Western Reserve
University's multidisciplinary program in Evolutionary Biology,
and others prepared this draft Lesson Plan aligned to Benchmark H, Indicator
23, at the request of President Sheets and other members of the Ohio State
Board of Education present January 13th, at 5 p.m., for consideration as a
replacement lesson for the problematic "Critical Analysis" lesson
originally submitted to the Board. At the February meeting of the Board,
the authors of this alternative lesson were informed that it would not be
considered until next Fall. This delay was attributed to a decision by
the Chairman of the Standards Committee of the Ohio Board of Education.
Also see Dr. Rissing’s comments at the end of this Lesson Plan.
Lesson Title: How do new species form? A critical analysis of current evolutionary concepts Ohio Standards
Connection: Grade: 10 Standard(s): Life Science Benchmark(s): H Describe a foundation of biological evolution as the change in gene frequency of a population over time. Explain the historical and current scientific developments, mechanisms and processes of biological evolution. Describe how scientists continue to investigate and critically analyze aspects of evolutionary theory. (The intent of this benchmark does not mandate the teaching or testing of intelligent design.) Indicator(s): 23. Describe how scientists continue to investigate and critically analyze aspects of evolutionary theory. (The intent of this benchmark does not mandate the teaching or testing of intelligent design.) Lesson Summary This lesson presents examples with experimental data that suggest alternative methods of species formation. The standard "textbook" model of speciation requires some form of geographic isolation of one population into two or more for a long period of time. This standard model is compared with the more controversial explanation that under some circumstances a single population may give rise to one or two new species without geographical isolation and in a short period of time. A "learning cycle" pedagogical approach is used. Students are presented the standard model of species formation with data to support it. Then a counter-example and data are presented which suggest that new species can and do form within a single population. Finally, data suggesting possible formation of new species of economically important insects in Ohio (corn rootworms) are presented for student consideration of the concept of species and discussion of corn rootworm population changes underway in Ohio constitute speciation. Optional/extended applications of this lesson permit discussion of genetic modification of corn in light of material presented regarding speciation processes possibly underway currently in this major Ohio industry. Estimated Duration:
Pre-assessment:
Direct students to respond to the questions in their science notebook in as much detail as possible leaving space to record information from the ensuing dialogue to add to their notes. Scoring Guidelines: A student should show one or more of the following points.
Reference for quotation above: Darwin, C. 1859. On the Origin of Species By Means of Natural Selection. Sixth Edition. (last sentence of last page).
Instructional
Procedures: The Standard Theory for the Formation of New Species: The commonly theory for the formation of new species suggests that individuals in a single population of interbreeding organisms must become isolated into two or more separate populations usually over a long period of time. These separate populations then experience different effects of various evolutionary mechanisms (natural selection, genetic drift, gene flow, mutation) sometimes resulting in the development of new species. If the populations are isolated geographically for a very long time, they may undergo so many physical and behavioral changes that individuals of the two populations may not even recognize each other as possible mates. Even if they do recognize each other as possible mates, they may have accumulated so many genetic changes that they cannot produce any live offspring, or their offspring would not be able to reproduce as, for example, in the case of horses mating with donkeys to produce sterile mules. Diagrammatically, textbooks often present this standard model of speciation like this:
Figure adapted from Strickberger, M. W. 1996. Evolution. Jones and Barlett Publishers, Sudbury, Mass. 670pp (see Fig. 23-8, p. 558).Darwin's finches and many other species are widely considered to have arisen through such processes. Student Engagement A. Consider (or find) two very similar organisms that you think represent different species. How can you tell they are different species? Teacher tip: You may want to have students answer this
question after they have taken a (brief?) field trip outside where they may
collect different leaves (oak and maple or white oak versus black oak). Students might use field guides (available
in libraries) to pick two similar species of flower, insect or bird. Students in agricultural areas could cite
the differences between wheat and oats. Hunters, birdwatchers, and other outdoor enthusiasts could cite differences
in Ohio fish species or game such as gray vs red squirrels or Canada goose
versus snow goose. B. How do you suppose they can tell they are different species? C. What kind of cellular mechanisms might be involved in plants that appear to result in only pollen from a few individuals (usually in the same species) fertilizing eggs? D. What kinds of things in nature might cause geographic isolation for some populations? Instructional Procedures: Divide students into groups (2-4 individuals) Teacher tip: Be sure to follow standard guidelines for
cooperative learning. Students should
not normally be permitted to form groups haphazardly on their own. 1. However students have chosen at least two similar species to conduct pre-assessment (e.g. a brief field trip on or near school grounds), have each student explain to his/her cooperative group how they consider these two samples to represent different species. 2. Have each student describe how the above "textbook" illustration of the process of speciation may apply to their pair of individuals. 3. Have each
group of students read the following textbook passages. (Teacher
tip: students might also be able to
locate their own textbook passages in a local library or on the internet by
searching for the term "speciation." "Most biologists agree that in the vast majority of cases the initiating factor in speciation is geographical isolation." (Keeton, W.T. 1980. Biological Science; 3rd edition. Norton Publishers, New York, 1080 pp. See p. 795) "…[F]or years theorists have argued over whether sympatric speciation (speciation within a population occupying a single habitat) occurs at all in animals." (Wallace, R. A., G. P. Sanders, R. J. Ferl, 1996. Biology. The Science of Life; 4th Edition. Harper Collins Publisher, 1073 pp; see p. 389. "While sympatric speciation has not been widely accepted, Bush (an evolutionary biologist) has made the strongest case for its existence; it is far from proven." (Powell, J. R. 1982. In: Barigozzi, C.(Ed.) Mechanisms of speciation. Alan R. Liss, New York, 546 pp; see p. 70. "While allopatric speciation (speciation with geographical isolation) is undisputed, whether sympatric speciation is likely and common, or can only occur under restrictive conditions has been controversial." Stearns, S. C. and R. F. Hoekstra. 2000. Evolution: An introduction. Oxford University Press, 381 pp; see p. 222. Answer these questions: 1. Why don't scientists all agree that geographical isolation is required for the formation of new species through natural selection or genetic drift? 2. What does it mean for students taking biology in high school or college to realize that all evolutionary biologists do not agree that all speciation must occur with geographical isolation? 3. Can you or someone in your group consider a circumstance in which a new species may form from another without geographical isolation? Consider this graphical representation of speciation with and without geographical isolation:
While sympatric speciation is generally considered highly unlikely, evolutionary biologist Guy Bush has suggested exactly this type of model for the evolution of the apple maggot fly, an agricultural pest in Ohio and elsewhere in the US. The apple maggot fly originally was found only on wild hawthorn trees. Adult flies mate, and females lay eggs on adult trees. The fly larvae ("maggots" but also called "caterpillars" in moths and butterflies) feed on the wild haw apples and eventually fall off the tree and enter the ground. They spend the winter in the ground as pupae (just like moths and butterflies) and re-emerge from the ground the next year; the cycle then starts all over again. About 160 years ago some flies began to emerge from the ground at a slightly earlier time of the year when no haw apples were available. They began to feed and lay eggs on apples that were available at that time of the year. This resulted in establishment of an annual cycle with different seasonality and dependent upon apple trees not haw thorn trees. This change in annual cycle that influences which flies in the formerly single interbreeding population came to breed at different times of year and on a different species of tree, appears to result from a single mutation in the flies. Even though haw maggot flies and apple maggot flies occurred in the same geographical region, the preference for different hosts by the two populations appears to have provided sufficient isolation for speciation to proceed resulting in a new species (the apple maggot fly found on introduced apples) and the original haw apple maggot fly. Bush argues these represent two separate species that formed without geographical isolation. But under some laboratory conditions individuals of the two species can sometimes mate and produce offspring that are able to reproduce on their own. Because of this, others have argued that while the process of speciation is occurring right before our eyes in these two populations, they are not yet fully separate species. Optional application 1Pre-assessment questions E. Are genes found in all corn plants? F. Have you ever
eaten any genetically modified food? If
so, what and when? Instructional
Procedures (optional application 1): Every major agricultural crop, not just apples, are vulnerable to some kind of organism(s) that we consider "pests" although biologically it might be more appropriate to consider them competitors. In Ohio, corn contributes almost $1 billion in annual revenues. Not surprisingly, corn has an array of pests that compete with farmers for the food value of corn crops. Many agricultural pests, like the apple maggot fly and a number of corn pests, display a natural history trait such as over-wintering in the soil as a pupa and emerging the next growing season to feed on another corn crop planted in the same field. One environmentally safe and economic weapon in Ohio corn growers arsenal to fight such pests is crop rotation: corn is grown in a field one year and a different crop, often soybeans (another billion dollar crop in Ohio), is grown in the same field the next year. Emerging corn pests can’t eat soybeans just as soybean pests emerging in alternate years can’t eat corn plants. Further, most corn and soy pests don't fly far if at all making crop rotation in a given field even more effective. Alas, like any other method designed to combat crop pests, such efforts always result in the development of resistance in the target pest(s) through natural selection. As far as farmers are concerned, pest resistance is inevitable. If they weren’t competing with us for our food and livelihood, we might call some instances of resistance brilliant; understandably, farmers consider them devious at best. Corn root worm, a common and sometimes serious pest for Ohio corn growers, has developed a number of resistance traits to farmers’ attempts to control them. Perhaps the most surprising is the spontaneous appearance of a strain of rootworms that take two years instead of the normal one year to emerge as adults from the soil. This means they stay underground as soybeans are grown in the field above them only to emerge the next year when corn is grown in the field once again. The insects have developed resistance to crop rotation. Questions: 1. Discuss the ability of pest/competitor insects to develop resistance to agricultural practices such as crop rotation and spraying standard pesticides from the perspectives of what you have learned about natural selection acting on populations of pest insects. NOTE: If introduced in the lesson on natural selection, above answer should include: 1.) there must be variance in the trait (resistance), 2.) Some of that variance must be heritable, i.e. be of genetic origin, 3.) Because of that variation, some individuals are more likely to survive and reproduce. 2. In the table below compare and contrast the modified life history traits and other aspects of the haw apple maggot discussed above with that of the crop rotation resistant corn root worm discussed here.
Scoring guideline:
3. Does your discussion group consider the new, crop rotation resistant, corn rootworm population to represent the formation of a new species? 4. What difference, if any, does your answer to the question immediately above make to a corn farmer in Ohio? Scoring guideline: Answers should address the question of whether or not the two possible species are capable of interbreeding and producing viable, fertile offspring. At this point, we don’t know the answer to this question, but there can be pedagogical value in raising questions for which we have no current answers. Students in this class addressing this question may someday answer it.
Instructional
Procedures (optional application 2): Many, if not most, life history traits that can change resulting in the process of speciation often change subtly and slowly. This often occurs because the trait itself in under the control of many genes. In these situations, slight changes in a life history trait likely do not cause speciation. Nonetheless, over many generations and many small changes, dramatic difference can develop between populations of organisms. Not too surprisingly, these have been documented best in agriculturally important crops where farmers and agricultural researchers can select over many generations for individuals that produce the most useable amounts of materials most economically important to their growers and the rest of the society. Once again, we can turn to corn and the economic importance of this crop to address this question about possible speciation. Economic value of most corn crops increases with their oil content. The following graph displays the results of 76 (annual) generations of selection to increase oil content of corn; a simultaneous effort to decrease oil content of corn was also done for comparison: 
Figure modified from: Dudley, J.W. 1977. 76 generations of selection for oil and protein percentage in maize. Pages 459-473. In Pollak, E., Kempthorne, O. and Bailey, jr., T. B. (eds.) Proceedings of the International Conference on Quantitative Genetics; August 16-21, 1976. Iowa State University Press, Ames; 872pp. Consider these questions:
Instructional Procedures (optional application 3): We can now identify and cut out this gene from the Bt genome; it can then be inserted to another organism, especially corn and soybeans. The gene once inserted into a corn or soybean seed acts just as it did in the original bacterium producing a molecule that can kill pest moths or butterflies. Moth or butterfly larvae eating the corn or soybean plant will ingest the molecule produced by the Bt gene inserted into the corn or soybean plant and die. This results in less dependence by soybean and corn growers on chemical pesticide spraying and more economical production of their crops. But these crops are now classified as "genetically modified (GM)," a term that concerns many consumers. Indeed, most of these crops are not eaten directly by people. While only about 9% of the corn grown in Ohio in 2003 was "GM" almost 75% of the soybeans grown in Ohio in 2003 were GM (see following map and table).
Source for the above map and table: http://pewagbiotech.org/resources/factsheets/display.php3?FactsheetID=2 Consider the following questions:
Learning how to isolate bacterial genes and insert them into agriculturally important plants like corn and soybeans has required years of research at great expense. Not surprisingly, one gene has been developed and inserted into GM plants to cause their seeds, while still nutritious, to be infertile. This acts as a "patent" of sorts on the genetically modified seeds and protects the research costs invested into them. A grower who buys GM seeds from a producer cannot simply save some of this year’s "seed corn" (or seed soybeans) to plant next year—they won’t grow. This gene and the technology to develop it has been given the name of "the terminator gene." Consider these questions: 1.) Are two fields of GM soybeans planted next to each other with all plants in both populations containing the "terminator" gene separate species? Scoring guideline: Technically, yes because by definition none of the individual plants are capable of producing offspring at all with any other individual of their "species." This question takes the arbitrary definition of the concept of a "species" to the ultimate limit and shows the useful limits of species concept in some areas of biology. 2.) Is it ethical to sell GM plants containing terminator genes? Scoring guideline: This is a wide open question designed for student appreciation of the complexities and opportunities deriving from our ongoing revolution in understanding of the molecular genetics of the speciation process and bioagricultural techniques of identifying and inserting genes from one organism (or biological kingdom) into another. Most bioethicists seem to think that the marketing of terminator gene seeds in developed countries is acceptable, while their position regarding the sale of GM plants with terminator genes in third world countries where people produce crops just to subsist and may not understand the implications of growing GM and "terminator" is much less clear. Additional
questions for possible discussion or expansion of this lesson:
NOTE: Identify science indicator that discusses the impact of technological advances on all aspects of society? As a conclusion, point out that most research creates more questions, and scientists rarely learn all the answers. Understanding the process scientists use to determine how a specific organism evolved and by what mechanisms is the scientific goal behind the indicator "Describe how scientists continue to investigate and critically analyze aspects of evolutionary theory." This is still an unresolved issue in 2003. Web links cited in this lesson (NOTE: All websites are *.edu, *.oh)
Darwin's finches: http://www.dnr.state.oh.us/dnap/rivfish/default.htm Red vs. gray squirrels in Ohio: http://www.dnr.state.oh.us/news/jan02/0125squirrelcolumn.htm Canada goose: http://www.ducks.org/waterfowling/gallery/index.asp?duck=4 Snow goose: http://www.ducks.org/waterfowling/gallery/index.asp?duck=17 Apple maggot fly: http://ohioline.osu.edu/hyg-fact/2000/2041.html Hawthorn trees: http://ohioline.osu.edu/b700/b700_40.html Economic impact of corn: http://ohioline.osu.edu/eso-fact/2578/2578_3.html Soy bean crop rotation: http://www.soyohio.org/agro/nematode.cfm Corn rootworm in Ohio: http://ohioline.osu.edu/ent-fact/0016.html Crop rotation resistant corn rootworms: www.soils.wisc.edu/extension/FAPM/approvedppt2003/ Jensen_Rootworm.pdf Economic value of corn oil content: http://www.oardc.ohio-state.edu/hocorn/hoc_index.htm Ethanol from corn in Ohio: http://www.state.oh.us/agr/Ethanol/ethanoloped.htm Jumping genes: biocrs.biomed.brown.edu/Books/Essays/JumpingGenes.html Ensatina salamanders (ring species) http://www.pbs.org/wgbh/evolution/library/05/2/l_052_05.html Note regarding the development of this draft lesson. In early 2000 I was asked to join the advisory committee for the development of the Ohio science content standards. In that capacity I was involved directly in the preparation of the tenth grade indicators for evolutionary theory. When those indicators were considered and modified by the Ohio state board of education, I testified against having students understand that scientists critically analyze aspects of evolutionary theory only. Rather, I argued that such understanding should be expected for all scientific theories. Since this did not occur and evolution was the only theory in science treated thusly in the indicators, I decided to follow the development of model lessons aligned to this indicator (# 23 in the 10th grade life sciences standards). In Fall 2003 I volunteered to act as an outside reviewer for lessons developed for indicator 23. I eventually received two draft lessons not associated with this indicator and requested all lessons associated with it specifically. I then received two additional lessons: L10H20 (Scientists, wolves and the United States government) and L10H23 (Critical analysis of evolution) and provided complete reviews for them and one of the first pair I was sent as well. I observed the writing committee meeting on 4-5 December where all outside reviews were considered. I made a public request for records to see final versions of the two lessons pertaining to indicator 23 on 16 December and received those documents on 8 January 2004. On 13 January I testified to the state board of education that many points in L10H23 remained false and uncorrected even after the outside review process and that in general, the lesson was hopelessly flawed. I was asked by board members (Hovis and others) during my testimony and after to develop a new lesson that might better prepare teachers and students to meet the requirements of indicator 23. I have used the general format and some of the materials of lesson L10H20 and L10H23 as presented to the board as my starting document for the draft lesson presented above.
Dr. Steve Rissing Department of Evolution, Ecology and Organismal Biology The Ohio State University 26 January 2004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
