A Mini-Lesson

A STEP IN SPECIATION

The Analysis of Field Observations
Of the California Salamander
Ensatina eschschsoltzii

Adapted from Investigation 9.4 in Biological Science - An Ecological Approach
(BSCS Green Version), 1987, Kendall/Hunt Publishing Co.

EVOLUTION

 SYNOPSIS

 CONCEPTS

1. While natural selection explains evolutionary modifications within lineages, speciation explains evolutionary branching and diversification.

2. Speciation involves genetic differentiation, ecological differentiation (niche separation) and reproductive isolation.

3. Isolation of members of a species in different environments may result in the formation of a number of subspecies.

Nature of Science Skills:
Collaboration, data interpretation, hypothesis formation, predicting.

Student Objective:
Students will relate the distribution of salamanders to the formation of subspecies.

 MATERIALS

Colored pencils (9 different colors, if possible)
Color copies of subspecies of California Salamander: Ensatina eschscholtzii,
(modified from pictures in the source reference) *
Grid map of California *
Handouts with Background, Procedures, and Discussion Questions
Key to Discussion Questions (see PDF version, end of this lesson)

* The best source for top quality images would be the original source (BSCS Green Version text)....see full citation under "Attributions" below.

 STUDENT HANDOUTS

(see end of lesson for the formatted handouts).

TEACHING STRATEGY

Time: Two 50-minute periods

Preparation:
1. Make color copies of the salamander sheets (one per team of 2-4); place these in non-glare transparent plastic notebook sleeves to protect from wear and tear as they are re-used every period and year.

2. Make copies of Grid Map of California. Enlarged copies would work best (one per team). Two versions are provided: one (v.1) is lighter, lower contrast, probably best for student use; v.2 is darker, a little more contrast, probably best for overhead.

3. Make copies of Student Handouts: one or two per team, or one per student; reusable each year.

4. Make three overhead transparencies of the grid-map: one to illustrate the procedure in your class introduction, one for Part A Collection Areas, and one for Part B Collection Areas. Color in the squares on Part A and Part B sheets as per directions on student sheets (do this with permanent markers, or water-based as long as you cover the sheets with plain transparency on which to mark during discussion). These are to be used for class discussion (also for correction keys, if desired).

5. OPTION 1: Make color transparency of the salamanders, possibly reduced in size a bit, then cut them apart to use on the overhead grid map during discussion.

6. OPTION 2: Cut apart the salamanders, keeping names attached (possibly using reduced size color copies), so each team has a set which they can place directly on their grid maps. At least one of these is very useful, which you could use on enlarged grid map to discuss the lesson with students gathered around you, as an alternative to the overhead-discussion. The visual impact and clarity of everyone actually seeing where each salamander type is located makes for a much easier job of pointing out the probable development of the various subspecies from the probable original population in northern California.

7. OPTION 3: Get a large wall map of California, preferably a physical map (showing mountains and valleys, and also vegetation, if possible). Check with the USGS; such a map is very inexpensive. Place cutouts of the salamanders on the map, so all may see. Use a "magnetic" board (behind map) and little magnets behind the salamanders, or use Velcro for attaching salamanders each period.

COMMENT: This lesson demonstrates how speciation occurs and should emphasize for students that a scientist's real work begins when she/he starts to organize and analyze data. Dr. Stebbins' research was published in University of California Publications in Zoology 48 (1949): 377-526.

PRESENTATION:
1. This lesson is probably best presented near the end of your unit on genetics, especially if you have covered population genetics. It helps at this time to see some visible features of real populations and how they are distributed as different subspecies in a particular region. Discussion of the pattern of distribution, in terms of how they may have come to be this way, brings you nicely full circle to the process of evolution again (which, hopefully, was introduced early in your course), showing how a broad concept (evolution) can help make sense out of an interesting pattern of distribution, and also how this pattern provides a strong bit of evidence, and compelling experience, that evolution has occurred. This lesson provides and excellent opportunity to show how biology is so nicely integrated by the themes of evolution and the nature of science. Be sure to point these things out to your students.

2. Set up your teams (probably best to work in pairs at first, coloring in the appropriate squares on their grids). Teams can combine to answer the discussion questions. (say into groups of 4).

3. Demonstrate (using overhead) how they should color in the squares on the grid map, pointing out where the colors are recommended, so that class comparisons will be easier. Ask them to take turns coloring in the squares for each subspecies.

4. Hand out the materials (easiest to have them in trays for easy pickup by rep from each team). Students read and proceed as directed in handouts.

5. Do Part A on first day (including the Part A Discussion), then Part B on second day. Monitor their progress; if time, you can go to CLASS discussion if most teams have finished the part B Discussion. Class discussion can continue into the third day. Be sure to use the overheads, or wall map (or salamander cutouts on enlarged map to the gathered-around class) during discussion.

6. For class discussion, you can simply go over their discussion questions, calling on reps from each team randomly or in succession. Be sure you have thoroughly familiarized yourself with the questions, and the answers provided in the key (PDF format, end of this lesson), before doing this lesson. The conclusions / interpretations provide powerful evidence for evolution, but can be subtly tricky at first.

RECENT DEVLOPMENTS AND CURRENT STUDIES OF ENSATINA at http://www.santarosa.edu/lifesciences2/ensatina2.htm.
Questions and evidence discussed regarding whether this is one species with several varieties, or several species. The dynamic evolutionary significance of Ensatina is also discussed. This site is maintained by Santa Rosa Junior College. (Added 6/18/07)

EXTENSIONS AND VARIATIONS

1. ANOTHER EXCELLENT SPECIATION LESSON:
For another excellent lesson which addresses the geographical aspects of speciation, on the UCMP web site, look for the lesson entitled: "Island Biogeography and Evolution: Solving a Phylogenetic Puzzle With Molecular Genetics" by R.P. Filson. All needed materials can be downloaded directly.

2. SPECIAL NOTE: Click here to explore many of the different lines of evidence pointing to speciation and macroevolution.

3. MACROEVOLUTION DIAGRAM: See the Microevolution to Macroevolution and Classification diagram and a page of directions for using that diagram on an overhead projector. This nicely shows how accumulated speciations can eventually form all the groups and subgroups of organisms. It also shows how classification is related to evolution. A very nice colorful version of this can be found on page 32 of that most useful resource: Teaching About Evolution and the Nature of Science, by the National Academy of Sciences (1998) (see our Resources section). A particularly interesting alternative diagram is the one Darwin included in The Origin of Species (chapter IV), the only diagram in that book! Darwin recommended that biological taxonomy be based on evolutionary relationships. His discussion there of that diagram should be required reading for any biology teacher. Darwin's Tree makes a great overhead transparency for discussing his concept of evolution by natural selection, as well as how classification reflects that evolution.

4. A QUICKIE SPECIATION ACTIVITY
Here's an effective and quick way to get across to students different ways new populations can emerge, be reproductively separated from the parent population, and eventually evolve into a new species. It is the basis for the genetic drift and "bottleneck" speciation, as well as a vivid application of the point of the Hardy-Weinberg formula - without calculations!

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: Biological Science - An Ecological Approach (BSCS Green Version), 1987, Kendall/Hunt Publishing Co., pages 296-299. Also,1992 edition, pp. 230-233.

2. Modifications for ENSI presentations by:
pre 1992 Participants: ?
1992 Participants: Cheryl (George) Garcia, Steve Harness, Judy Loundagin, and Carol-Anne Piehl
1993 or 1994 Participants: ?

3. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 12/15/97

4. Edited / Revised for website by L. Flammer 5/99

5. Item 4 added 29 Oct. 2009.

 The following pages are in Adobe Acrobat pdf format in order to maintain their intended layout for easy printing of handouts. Only a "thumbnail" reduced size image of the first page is showing (if more than one page is in that file). For enlarging and copying, (and seeing other pages in that file), you will need to download the free Acrobat Reader from Adobe (unless it's already installed in your system). Then just click on the blue file name above, below, or next to the first page. You may see the "Acrobat Exchange" (Reader application) loading, then the pages will display. You might need to shift-click and drag the lower left corner of the page to enlarge it, or click the magnifying glass on the menu bar.

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