Speciation in the Ensatina Complex

SPECIATION IN THE ENSATINA COMPLEX

Name: ______

Background

When Darwin wrote On the Origin of Species, he believed that speciation, working through the mechanism of natural selection, was to gradual to be witnessed and could only be inferred from the fossil record, the distribution of similar species, and such. In the 1950’s R.C. Stebbins, at the University of California at Berkeley, completed a study on the salamanders in the genus Ensatina, thought at the time to consist of four species.

Salamander’s in the genus Ensatina are plethodontid salamanders that inhabit the terrestrial coniferous forests and oak woodlands from southern British Columbia in Canada, along the coast, to northern Baja, California. Their range extends east to the western slopes of the Cascades, Sierra Nevada, and Peninsular mountain ranges. Stebbins interest in these salamanders arose from observation of patterns existing in separate populations of these salamanders. Stebbins wondered if there were in fact four species, and if a speciation event was being observed in these salamanders.

At the time, species had been defined by Ernst Mayr as “groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups”. Difficulties arise when a species has a large range and appears to be segregated into distinct populations based on their location and the visible variations existing between populations. In such situations, the separate populations may be considered “subspecies”, suggesting that they may be on a trajectory leading them to become distinct species. Unlike the binomials given by Carl Linneaus, subspecies names contain three words (i.e. Homo sapiens neanderthal).

In the following activity, you will simulate observes of the populations of the Ensatina salamanders that Stebbins made in the 1950’s, analyze his and others data, and make conclusions on speciation in these salamanders.

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

Part A: Pre Activity Questions

1. Read section 15.1 beginning on page 324 to answer questions 1-3.

Part B: Original Specimen Collections

1. Imagine that you are working with Stebbins' salamander specimens, some of which are pictured on the colored sheets provided.

a. In the list below, salamander collections are identified by the letters a-g. These letters correspond to pictures of salamanders you will be given later in the activity.

a. Ensatina 1 (15; brown): 32/R, 32/S, 30/T, 31/T b. Ensatina 2 (203; red): 30/M, 32/O, 34/S, 35/V, 36/W, 35/Z, 38/Y, 40/Z c. Ensatina 3 (48; blue): 36/Z, 38/a, 39/a, 40/a d. Ensatina 4 (373; purple): 9/B, 7/E, 6/E, 13/C, 10/C, 7/D, 15/D e. Ensatina 5 (230; yellow): 2/B, 2/C, 3/C, 4/C f. Ensatina 6 (120; green): 8/J, 10/J, 11/M, 13/M, 15/M, 15/O, 17/M, 15/P, 20/Q, 24/S, 21/R, 25/T, 26/U g. Ensatina 7 (271; orange): 17/G, 17/F, 19/H, 19/O, 20/I, 20/J, 21/I

b. The parentheses after each subspecies name contain a number and a color. The number is the total of individuals Stebbins had available for his study. The color is the one you should use for that collection when you plot its collection area on the California map.

c. Following the parentheses is a list of grid codes indicating where (on the map grid) the subspecies was collected. For example, 32/R means that one or more specimens were collected near the intersection of horizontal Line 32 and vertical Line R.

2. Plot each collection area by filling in the corresponding square on the California map grid. Color in the square above and to the left of the point where the specified grid coordinates cross. For example, the square in the upper left-hand corner is 1/A. Use the colors indicated for each subspecies population (listed above) to make a distribution map of Ensatina complex in California.

3. Answer the questions for Part A. Part C: Supplemental Specimen Collections

1. To more fully understand the relationships between the subspecies identified by Stebbins, he made the following supplemental collections.

b. E.e. eschscholtzii (16; red): 36/Z, 41/Z, 33/M, 34/W, 34/U c. E.e. klauberi (23; blue): 40/b, 40/Z, 36/a h. Unidentified population 8 (44; pink): 4/I, 5/H, 7/H, 7/F, 6/J, 9/F i. Unidentified population 9 (13; burgundy): 28/T, 27/T, 26/T, 28/S, 29/T k. Unidentified population 11 (131; turquoise): 23/J, 24/K, 24/I, 29/M, 25/J, 25/I l. Unidentified population 12 (31; black): 6/C, 7/C, 6/B

2. Mark with the color gold the following places that were searched for Ensatina without success (11/I, 14/I, 17/K, 22/N, 26/Q, 5/M, 32/U, 32/a, 35/f). Specimens of populations 8 (specimen h) and 9 (specimen i) are shown in the color pictures. (There are no illustrations for populations 11 and 12).

3. Answer the questions for Part B. Questions

Part A: Pre Activity Questions (15.1 page 324)

1. What is reproductive isolation? Why is it important to speciation?

2. Define and give and examples (when the book gives one) of the following reproductive isolating mechanisms.

Pre-zygotic Mechanisms - isolate two populations without zygotes forming

Timing (Temporal isolation) –

Behavior (Behavioral isolation) –

Habitat (Ecological isolation) –

Physically Incompatible (Mechanical isolation) –

Post-zygotic Mechanisms – isolate two populations when zygotes form

Hybrids fail to develop (Hybrid Inviability) –

Hybrid Infertility –

3. How does geographic isolation lead to speciation and adaptive radiation? How do you know when two or more populations have become distinct species? Part B: Original Specimen Collections

1. Are there any general patterns to the distribution of the Ensatina salamanders? Describe the pattern that you see. Does the pattern make sense given the information on these salamanders in the background information? Expand on your previous answer.

2. How many distinct populations can you observe based on the location of the specimens (disregard the colors for the time being)? Which colored populations appear to be single population? Explain.

Stebbins decided that the Ensatina salamanders were not four separate species as previous biologist had determined but were instead a complex of the seven subspecies given below all of the species Ensatina eschscholtzii. Cut out each of the pictures of the representative Ensatina subspecies, arrange them on your map, and answer the following questions. Identification Stebbins subspecies Map Color Letter a E.e. croceator brown b E.e. eschscholtzii red c E.e. klauberi blue d E.e. oregonensis purple e E.e. picta yellow f E.e. platensis green g E.e. xanthoptica orange

3. Based on the appearance of the specimens, what general pattern emerges in the distribution of the Ensatina salamanders? Another species of salamander, called a newt, exists along the coastal range of California. You can view its appearance by surfing to today’s lesson on my website. Newts have a terrestrial stage called an eft that has rough skin like the toads that you may be familiar with. When they are ready to breed they return to water where they sprout gills and breed. While on land the efts are quite vulnerable to predators, and have developed toxins for protection (toads secrete toxins too through their paratoid glands).

4. Based on the information above and your knowledge of natural selection, explain why the Ensatina salamanders appear the way the do (both the coastal and more eastern populations). Be as specific as you can in applying the principles of natural selection.

5. Does knowing what the salamanders look like help you understand why Stebbins created separate subspecies for populations a (brown), b (red), and c (blue)? Explain using your knowledge of reproductive isolating mechanisms.

6. Assuming that the Ensatina complex expanded it range and radiated from only one of these populations of salamanders (traveling either north or south), which one would you predict was the original population and in which direction did they radiate? Explain your reasoning. Part B: Supplemental Specimen Collections

1. Why do you think it was important to Stebbins to enhance his knowledge by collecting the four separate populations of unidentified specimens?

2. What do the appearances of populations 8 (pink) and 9 (burgundy) suggest about the relationships between the subspecies d (purple) and f (green), and f (green) and a (brown), respectively? Does it support Stebbins identification of subspecies? Or should these three subspecies be considered separate species? Explain.

3. Don’t you imagine that Stebbins thought he would be unable to find specimens in the sites you marked in gold? Why then do you think Stebbins looked for specimens in areas that turned out to have none?

4. Why do you think it was important to Stebbins to enhance his collections of the E.e. eschscholtzii and E.e. klauberi subspecies? What may Stebbins have been looking for? Do these collections support Stebbins identification of two subspecies? Or should these subspecies be viewed as distinct species? Explain. 5. Based on the extra collections and your knowledge of speciation in general, where is it most likely that the Ensatina complex originated and where is it most likely that speciation is currently occurring? Explain.

6. Stebbins decided that the populations of the Ensatina complex are one species because he believed that even though the more southerly populations appear to be pretty distinct, they are still connected genetically via the ring of populations connect these species. If this is the case, hypothesize events that could foster the southerly populations in becoming distinct species.

7. Create a cladogram/phylogenetic tree for the seven subspecies of Ensatina salamanders. Use the third name of the subspecies to label the separate end points.