**REMEMBER: These questions should be answered as you go through the activity, not all together.

 

PART I:

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

2. Define and give examples of the following reproductive isolating mechanisms. (a-f.)

• Pre-zygotic Mechanisms - when two populations are isolated without zygotes forming

            a. Timing (Temporal isolation) –

            b. Behavior (Behavioral isolation) –

            c. Habitat (Ecological isolation) –

            d. Physically Incompatible (Mechanical isolation) –

• Post-zygotic Mechanisms – when two populations are isolated after zygotes form

            e. Hybrids fail to develop (Hybrid Inviability) –

            f. 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 II:

1. Describe the general pattern(s) to the distribution of the Ensatina salamanders that you see.  Explain whether or not the pattern(s) make sense given the information on these salamanders in the background information and why this might be the case. 

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 populations?  Explain.

3. Based on the appearance of the new specimens listed in the table, what general pattern emerges in the

distribution of the Ensatina salamanders? 

4. Does knowing what the salamanders look like compared with their location on the map help you understand why Stebbins created separate subspecies for populations a (yellow), b (blue), and c (orange)?  Explain using your knowledge of reproductive isolating mechanisms.

5. 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.

6. Based on the information you were given about newts and your knowledge of natural selection, explain why the Ensatina salamanders might appear the way they do (both the coastal and more eastern populations).  Be as specific as you can in applying the principles of natural selection. Note: you may want to look up a physical map of California if you are unfamiliar with California land forms to answer this.

 

PART III:

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

2. 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? 

3. 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.

4. Based on the extra collections and your knowledge of speciation in general, do you still ascribe to your original idea about where the Ensatina complex originated? Where is it most likely that speciation is currently occurring?  Explain.

5. Based on your ideas concerning origination and speciation, 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. If you are unfamiliar with making cladograms, there are help links on the class website under “Study Guides/Links.”

6. Stebbins ultimately 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.