Speciation in Salamanders
Purpose: Using data collected from an actual field study, you will gain insight into the mechanisms at
work when speciation occurs.
Background information: The small salamanders of the genus are strictly terrestrial. Even their eggs are
laid on land, and there is no aquatic larval stage. Nevertheless, these salamanders require a rather
moist environment and do not thrive in arid regions. In California Ensatina has been intensively studied
by Dr. Robert C. Stebbins of the University of California at Berkeley. He has studied the animals in the
field and has collected specimens of the species Ensatina eschscholtzii in many parts of the state.
Procedure
Part I:
Imagine you have been employed in Dr. Stebbins’ laboratory to interpret the data collected in the field.
Drawings of the specimens collected can be found on the provided posters. Below you will find a list of
the subspecies names, a number and a color. The number is the total number of individuals that Dr.
Stebbins had available for his study, the color is for you to use in designating the subspecies. Following
this is a list of collection localities, indicated by a code that fits the map of California supplied to you. For
example, 32/R means that one or more of the croceator subspecies specimens were collected at the
intersection of line 32 and line R. On the outline map of California marked with the grid, plot the
collection localities for each subspecies by making a small X mark with colored pencil. The number given
before the subspecies data corresponds to the number on the poster for that subspecies.
1. croceator (15; brown): 32/R, 32/S, 30/T, 31/T
2. eschscholtzii (203; red): 30/M, 32/O, 34/S, 35/V, 36/W, 35/Z, 38/Y, 40/Z
3. klauberi (48; blue): 36/Z, 38/a, 40/a, 39/a
4. oregonesnis (373; pink): 9/B, 7/E, 6/E, 13/C, 10/C, 7/D, 15/D
5. picta (230; yellow): 2/B, 2/C, 3/C, 4/C
6. platensis (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
7. xanthoptica (271;orange): 17/G, 17/F, 19/H, 19/O, 20/I, 20/J, 21/I
Conclusion from the First Collection
From your distributional map of the subspecies of Ensatina eschscholtzii in California, and from
the pictures of these subspecies on the poster, you should be able to answer the following
questions on a separate sheet of paper.
1. Based on what you read in the introduction about this species of salamander, explain the
distribution of animals across the state with respect to: valleys, mountains, arid and moist
zones.
2. Give a hypothesis for why some subspecies are found in some areas but not in others.
3. Describe any order to the way color patterns occur in California. Pay particular attention to
where you might find: yellow or orange spots on a black body, plain brown-orange body, small
orange spots on a black background, orange body with some yellow and some small black
blotches, and some of them have white feet and/or yellow eyelids.
4. The subspecies eschscholtzii and klauberi are very different in appearance, what relationship (if
any) is there between their distributions?
Procedure
Part II
At this point in your study you may begin to wonder whether there might not be salamanders in some of
the areas for which you have no records and whether there might by additional subspecies for which
you have no specimens in your collections. The biologist faced with these questions would leave his or
her laboratory and go into the field to collect more specimens. Imagine that you do so too and return
with the following additional data:
Data from Second Collection:
eschscholtzii (16; red, circled X): 36/Z, 41/Z, 33/M, 34/W, 34/U
klauberi (23; blue, circled X): 40/b, 40/Z, 36/a
Unidentified population #8 (44; black and green X): 4/I, 5/H, 7/H, 7/F, 6/J, 9/F
Unidentified population #9, (13; black and red X): 28/T, 27/T, 26/T, 28/S, 29/T
Unidentified population #11, (131; black and blue X): 23/J, 24/K, 24/I, 29/M, 25/J, 25/I
(*Note: there is no illustration for population #11 specimens)
Unidentified population #12 (31; black and yellow X): 6/C, 7/C, 6/B (*no illustration for specimens)
Mark with a pen or plain pencil a 0 at the following places which were searched for Ensatina without
success: 11/I, 14/I, 17/K, 19/K, 22/N, 26/Q, 5/M, 32/U, 32/a, 35/f
Conclusions from the Second Collection
According to Dr. Stebbins, the unidentified populations are not additional subspecies. Consider both the
first collection results and what you have learned from the second collection, and then answer the
following questions:
1. What is the probable genetic relationship of populations #8, #9 and #11 to the other subspecies
already plotted on the map?
2. On this basis make a color drawing of the appearance you would expect specimens of
population #11 to have.
3. Why is it unlikely that you would ever find individuals combining characteristics of picta and
xanthoptica?
4. Now consider eschscholtzii and klauberi. Look at the distribution of the first collections. What
reasons were there for making efforts to collect additional specimens from extreme
southwestern California?
5. How do the results of the additional collections differ from the results in other places where two
different populations approach each other?
6. Bear in mind the biological definition of a species and also the appearance and distribution of
the seven named populations of Ensatina. Which one of these populations could best be
considered a species separate from Ensatina eschscholtzii?
7. Now imagine that while examining another museum collection, you find the specimen marked
#10 on the poster. Compare its characteristics, especially the pattern of spotting with those of
the named populations. Between which two is this specimen most likely a hybrid? On your map
draw a line along which you might expect to collect other specimens like this one.
8. In a paragraph explain why Dr. Stebbins concluded that there is but one species of Ensatina in
California.
9. When we consider the effect of wide valleys and deserts on the distribution of Ensatina, the
collection of xanthoptica at locality 19/0 raised a problem. State the problem and suggest some
possible explanations for it.