For my article
review I chose to write about the sprinting speeds of lizards of varying size
titled “Optimal Body Size with Respect to Maximal size for the Yellow Spotted Monitor
Lizard (Varanus Panoptes; Varanidae)”
In Physiological and Biochemical Zoology
. In middle school I had a pet green iguana and I noticed that as she grew in
size, she lost her ability to sprint as quickly as when she was smaller. I had
always assumed that it was because she was fat and lazy. This article explores
three hypotheses that attempt to explain this phenomenon in varanids. A
correlation between increased body size and maximum speed has been found up to
a point at which as body size continues to increase the sprint speed decreases. The authors (Clemente et. al ) proposed three
options to explain the slowing of larger lizards. The first is that there exist
biochemical restraints of an increased body size. The other two which the authors
found unlikely were that larger lizards tended to be clumped together in
phylogenetic groups and that there is a replaced selection of speed with larger
body size as there are fewer predators (this is the hypothesis that I favored).
To test
the three hypotheses Varanus panoptes
of varying sizes were tested for the maximum sprinting speed. The individuals
varied in size from .09 to 5.75 kg and anatomical measurements were made, such
as the length of the legs, were made to include in the data analysis. The
lizards were tested three times each with one day’s rest in between each trial
such that the average of the three trials could be used. The results of these
test showed that there is an optimal body size in this species in relation to
speed at about 1.7 kg. As this experiment studied the differences in size of
one species it rules out the phylogenetic inertia theory as a possibility as
genetic variations among different species is not applicable to this scenario. The
hypothesis that a change in behavior as lizards increased in size (due to the
absence of the need to escape) occurs could not be ruled out as a significant
influence; however, the experiment was able to demonstrate biological limitations
that are able to account for the differences in sprinting speed. These
limitations include bone structure and muscle requirements to support the extra
mass of the larger lizards. Furthermore the biological limitations theory was
supported by the fact that the larger lizards beyond the optimum had a shorter
stride than those at the optimum. This was explained to be due to a decreased
flexibility of the joints in favor of increased rigidity.
This
experiment proves that the slower sprints of larger lizards is not necessarily
due to their place on the phylogenetic tree, but rather due to either changes
in behavior as they no longer require the need to evade as many predators as
they move towards the top of their food chain, or that due to the increased
size they are required to sacrifice speed as their bodies cannot handle the
strain of running any faster. Personally I believe that it is a combination of
the two. Larger lizards no longer have to sprint and as such will change their
behavior away from doing so as to conserve energy. By the same token the
increased size likely reduces their ability to sprint in the first place, so it
seems that there is a tradeoff between large size and speed.
Resources:
Christofer
J. Clemente, Philip C. Withers, Graham Thompson. Optimal Body Size with Respect to Maximal Speed for the
Yellow-Spotted Monitor Lizard (Varanus panoptes; Varanidae) Physiological and Biochemical Zoology ,
Vol. 85, No. 3 (May/June 2012), pp.
265-273
2 comments:
Interesting read and the results make sense; I'm fat and I don't like to run, either! Did the article mention the speed these animals are capable of reaching?
I'd like to see a study that examines this pattern in smaller animals, to see if the pattern exists when none are large enough to escape predation. My observations suggest that larger frogs aren't as good at jumping as smaller, lighter frogs of the same species.
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