Pregnant and Wicked Fast

This is a wallaby. Well, two actually. 

     Alright, so Friday was my second day in the lab and I split my time between dissection and research. In the morning I spent time with my clawed friend, finishing skinning his left hindlimb and separating the muscles on all four limbs. I then used my handy dandy lab binder to start identifying the muscles in the limbs. It's rather bizarre when you look at something on an animal far unrelated to you, and notice how similar everything is. The major differences I noted were that many of the muscles in the thigh were oriented differently and there were some I had never seen before. Also, because the lizard was heavily preserved, it was sometimes hard to tell if a section of muscle was in fact more than one muscle, or all the same. For those of you who have never dissected, muscle appears similar to ... well, fish actually. You know when you cut into a piece of raw or uncooked fish and it all sort of flakes away? Those are fish muscles-and iguana muscles behave similarly under a scalpel. I had to rely heavily on the diagrams to determine where to cut and separate. 

     I spent the rest of the day taking advantage of ASU's massive online library, searching for more papers on iguana ecology, morphology, and anatomy. Literature searches are often frustrating to me because I know in my head exactly what I want, but it is usually not what I find. Compromise isn't my favorite word, so I tend to wade through massive amounts of sources searching for the perfect one, only to reach the end with nothing. But today I found two sources that I really liked. The first was on pregnant or gravid iguanas and how they are capable of increasing their acceleration even while carrying the extra mass of their clutch of eggs. This was made possible with more force produced by the muscle as well as a longer length of time the foot was left on the ground. The scientists actually theorized that female iguanas who were not pregnant did not have enough mass to fully "load" their muscles and hence were not reaching their potential (Scales, 2007). 

     The second source was regarding the amount of stress the bones in the iguanas hindlimbs underwent due to their more sprawling orientation. Iguanas have higher limb bone safety factors than most mammals. A limb bone safety factor demonstrates how much extra force a bone can take beyond normal. For a bending motion, iguanas have a limb bone safety factor of 5.5 - 10.8. This means that a lizard bone can receive up to 10 times more force than it normally receives. This is abnormally high and unnecessary. This may indicate an evolutionary drawback (Blob, 1999). 

     An afternoon of research was lightened when Dr. Fisher took out some specimens from the freezer.  Today, the wallaby came out of the freezer and moved to the fridge to thaw. It was a little wrapped up in itself, with its tail wrapped around it's body. We also saw the ringtail and it, according to Dr. Fisher, was "cute" and "soft." Personally, I thought it looked a little feral, but in a lovable, endearing way :) We had lab meeting at four and discussed some articles written by Dr. Fisher and her colleagues on red pandas and pygmy hippos.  Did you know hippos have four fingers, not hooves like horses and cows? I didn't either. 

AA


Scales, Jeffrey and Marguerite Butler. "Are powerful females powerful enough? Acceleration in gravid green                iguanas (Iguana iguana)." Integrative and Comparative Biology (2007) 47.2: 285-294. Web. 2 Mar 2012.

Blob, Richard W. and Andrew A. Biewener. "In Vivo Locomotor Strain In The Hindlimb Bones Of Alligator Mississippiensis And Iguana Iguana: Implications For The Evolution Of Limb Bone Safety Factor And Non-Sprawling Limb Posture." The Journal of Experimental Biology (1999) 202.9: 1023-1046. Web. 2 Mar 2012.