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Ali Krueger
BIOL 481
TA: Alex Grantham
Wolf Lab Writeup
The largest standard deviation of the mean for the traits we measured was for the
A and B skull lengths. The standard deviation for the Interior wolves was 0.98, while it
was 0.94 for the wolves from Southeast. The standard deviation for skull lengths, width,
and jaw length were larger for the Southeast wolves than for the interior wolves. The
standard errors were greatest in the measurement of the palate. I would assume this
variance was due to the increased error in the larger “caliper”-like tool (it could not
measure in units of mm), and due to the subjectivity of measurement. The measurements
of E and H-J had significantly lower standard errors than A, B, C, D and G because were
able to use calipers that have a lower tool error in measurement and allow for less
operator error (“eyeballing” the measurement).
The average zygomatic height (H) and width (I) for the interior wolves was
significantly larger than for the wolves in the Southeast, as seen in the Figures attached.
The skull width (C) was larger for the Interior wolves than for the Southeast wolves.
There was a significantly smaller error seen in the width measurement when compared to
the measurement of the skull height, as seen in the Figures attached. The width of skull
(C) could have also been selected for in terms of its advantage as it forages. Depending
on the food source, the wolf with the narrower head may have more of an advantage
getting prey out from a narrow hiding place, or a wider head may be more advantageous
in head-to-head combat or killing larger prey. The average jaw height (F) for the wolves
in the interior was slightly larger, at 3.40 versus 3.17 for the Southeast wolves. The
Southeast wolf skulls had a significantly larger standard deviation and standard error than
the Interior wolves for the jaw height measurement (F). This jaw height, and subsequent
jaw strength may have been selected for due to the prey species for the wolves in the
Southeast, or maybe the smaller jaw height was selected for in the Interior because it was
lighter to carry. There was a very small standard deviation for the jaw height
measurement (E) for both wolf groups. This suggests that this trait is not very derived if
it is so similar in all of the skulls. This means that there is a larger trait variance among
individuals in the Interior “population”. The average jaw length (D) was significantly
longer for the Interior wolves, but had a slightly higher standard deviation than the
wolves from the Southeast. The long jaw (D) seemed to correlate with a significantly
larger skull length (B) to the superior dorsal point of skulls of wolves in the interior. A
wider skull and larger jawbones may have also been accompanied by larger jaw muscles
and greater clench force. This clench force would impact the prey available to wolves.
Overall, the wolves from the interior had longer jaws, longer skull lengths (as
measured by both A and B), but only a marginally larger average skull height (J) than
wolves from the Southeast, as seen in the Figures attached. I assume this difference in
morphology is due to the differences in prey species and prey size, combat behavior, and
degree of activity. In the interior there tend to be larger animals like deer, moose, caribou,
elk, etc. than in the Southeast. It is possible that the wolves in the interior adapted to
their prey types, in which larger, stronger jaws and skulls allowed for better hunting and
killing of larger prey. For the (J) skull height, there was a significantly larger standard
deviation than for the Southeast wolves. The data show that a majority of the skulls from
the interior were long and wider, but varied substantially in their height. All of the
average measurements for the wolf skulls in the interior were larger than the average
measurements for the Southeast wolves.
As mentioned above with each measurement, evolutionary forces shaped these
patterns by means of selection and allopatric speciation, or independent evolution due to
geographical distance or barrier. I would have been interested to measure the width of
the most ventral portion of the jaw, because it seemed like some wolves had a wider and
more robust jaw protrusion, while others were narrower. I am curious to see if this would
affect teeth location, and therefore impact predation methods and catch abilities (and
there for be selected for or against). Larger, heavier skulls may be more beneficial for
combat situations, and less beneficial to “carry around”. In each environment, one skull
characteristic may be selected for because it increases the fitness of individuals with that
trait. For example, narrower skulls may allow for individuals to obtain more food
because they can reach farther into crevices that their larger-skull counterparts can not,
therefore allowing them to occupy exploit a niche that others were previously not able to
exploit.
As a whole, our group’s data is consistent with the hypothesis that wolf skulls
from the interior are different than wolf skulls from Southeast. The results of our T-test
for the null hypothesis that the two wolf groups were the same were as follows: 3.69E-07,
6.01E-5, and 4.40E-08 for the measurements of skull length, skull width, and skull
height, respectively. Because all of these p-values are smaller than 0.05, we reject the
null hypothesis that both wolf groups are the same (but, it does not tell us anything about
how they are different). It is possible that these wolves evolved separately, in allopatric
speciation. They are geographically separated, and as individuals within the population
vary, certain traits are selected for and persist better than other traits and some traits
prove to be more advantageous under certain ecological conditions (improving fitness for
those individuals).