Last One!

It's the last blog! My last entry will be a discussion about a masters thesis regarding the dexterity of forelimbs and the reason for this dexterity (Iwaniuk, 1997). The thesis is sectioned into several different research projects, all of which relate to the common theme of forelimb dexterity. The paper starts by defining the methods which will be used to determined dexterity, a scale method created by the author. He goes through and rates a variety of species. He then uses this data to determine which factors are influencing dexterity. This is what he found:

With regard to brain size, there is little relationship between larger brains and increased dexterity, the theory behind this being that evolution has more subtle ways of manipulating dexterity other than increasing the size of the brain. This makes sense. Many small animals (rats, lizards, squirrels) have quite a bit of dexterity for climbing, opening nuts, digging for food, and yet their brain size is constrained by the size of their skulls.

The second factor analyzed was body size. The author predicted that an animal with a large body would have more dexterity. This turned out not to be true, for many of the same reasons as stated above. But also, body size is dependent on many different factors (diet, habitat, phylogeny) and a small animal is just as likely to develop dexterity on the basis of these as a large animal.

Phylogeny was next on the list. It turned out to be correlated strongly with dexterity. Phylogeny refers to the evolutionary history of an animal and which other animals it is related to. The study found that more closely related animals tended to show more similar forelimb use patterns.

It was also predicted that those animals that lived in trees would be more dextrous. This was only related in terms of proximal dexterity. The author claimed that this is because grasping forepaws are not related to climbing trees.

Vertebrate predation is a factor that many claim gives rise to forelimb dexterity. But this study found that it was actually negatively correlated. This is possibly due to the fact that animals that prey on vertebrates also have to chase these animals down (the lion and the antelope, lynx and snow hares, polar bears and seals). Thus these animals forepaws must strike a balance between finally tuned dexterity and raw running power. The result is not always the most dextrous.

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Iwaniuk, Andrew N., 1997. "The Evolution of Skilled Forelimb Movements in Carnivoran." Masters Thesis, University of Lethbridge, Lethbridge. 151 p.  

Lions, Tigers, and Crocodiles

So the article for the week is about Crocodylian forelimb musculature. You may be asking yourself how that is related to iguanas, and well ... it's not really, other than it is yet another comparison. My interest of this article relates to its focus on why anybody is even studying Crocodylian forelimbs. The article, "Crocodylian Forelimb Musculature and its Relevance to Archosauria," discusses the forelimb of archosaurs as a functionally diverse anatomical unit, but one that has remained nearly the same through its evolutionary path (Meers, 2003).

Archosaurs are a group of creatures that evolved in the late Permian or early Triassic period. They are diapsid amniotes (meaning they have two holes in their skull, one on each side) and the most modern representatives are crocodiles and birds. This gives you a clue as to why their forelimbs are so interesting. The front limbs of an alligator (arms) vary quite significantly from the front limbs of birds (wings). But though they may look different, their musculature isn't all that distinct.

The author dissected 4 Alligator mississippiensis, 1 Crocodylus siamensis, 2 Crocodylus acutus, 2 Osteolaemus tetraspis, and 1 Gavialis gangeticus. They then compiled in depth muscle descriptions for all of the muscles in the forelimbs of the specimens. The muscles don't vary all that much from the iguanas. A part of this is because crocodylians are squamates, like iguanas, and hence their posture is very similar as are the muscles required to maintain this posture. The species dissected did have more extrinsic muscles on the ventral side. This means that they had more chest muscles (extrinsic meaning the muscles originate on the trunk and insert on the front limbs, and ventral being the side with the animal’s heart.) Also, the study named the deep muscles of the back differently than my sources did, but they were relatively the same.

The conclusion of the study was basically that the American alligator is representative of most Crocodylian species (re-enforcing that the forelimb musculature of Archosaurs has not changed much).

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Meer, Mason. "Crocodylian Forelimb Musculature and its Relevance to Archosauria." The Anatomical Records Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology (2003) 274A.2: 891-916. Web. 28 Apr 2012.

Updates

Okay, here are the updates for the week. I've finished both iguanas, photographed them completely, and I'm now on to completing my findings for the project. As I have explained before, this involves drawing comparisons between the iguanas, pigs, and cats. Obviously these are all quadrupeds, and therefore their muscles have a certain amount of similarities, but they are all different animals. Iguanas have a sprawling posture, their legs and arms extending beyond their bodies. Pigs are ungulates; the muscles are focused on keeping their bodies supported and allowing them to move forward and backward, in a single plane. Cats are carnivores, and hence their forelimbs are involved in prey capture and require a more specialized form. 

Hopefully within the next week I will be dissecting and photographing a fetal pig, which will allow me to show direct muscle comparisons between the iguanas and the pig, including a weight difference analysis as well as how their muscles differ with response to locomotion. 

I'm working on the first slides of the slide show right now, detailing the objective (which has changed several times), and the materials and methods. I'm also going through sources looking for information I can use for comparison. This is enormously frustrating because whenever you do a lit search, you seem to never find exactly what you want. I would like to find studies that are similar to what I've done -- a dissection, followed by detailed muscle descriptions, weights, and a locomotion analysis. Unfortunately, I haven't yet stumbled upon the perfect article, so I am just pulling bits and pieces from everything. 

Really?

So this week was pretty productive. I finished dissecting, photographing, and everything else - ing on Tuesday. It's pretty exciting to be done with both specimens. For the rest of the week I worked on putting together my presentation, which right now means analyzing data. Because of how my project has changed, "data analysis" is basically taking the muscle data I have for the iguanas and comparing it to other animals, particularly cats and pigs. These two were chosen because there has been so much research done on them, information is abundant. All three of the animals also have different habitats, and differing forms of locomotion. 

At the lab meeting this week, we read a pretty cool animal about extinct porcupines. Did you know that they can climb trees, along with goats and grey foxes? Well they can, and it is presumed that their ancestors could as well, this being deducted from their fossils. This may perhaps be quite a leap though. Today when we look at a species, we analyze their behavior, relate this to their musculature and then connect this with their bones. With fossils, this processed is reversed. Bones are looked at for robustness, bony landmarks, relative length and composition as well as muscle scars and attachments. These things are used to determine where muscles were and their possible actions, and this is then used to determine locomotion, environment, as well as the phylogeny of its descendants and ancestors. But it's certainly not an exact science, and sometimes things seem just a little far fetched.

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Opposites Attract

The study for this week looked at the distal forelimb musculature of the genus of lizards Liolaemus, which includes a particular species of sand lizard Liolaemus wiegmannii (Abdala and Moro 2006). I thought it would be interesting to compare their analysis with my own of the iguana considering their two very different forms of locomotion -- digging and walking in the sand vs. climb trees and swimming. The study went through all of the muscles in what we would call the forearm -- extensor carpi radialis, extensor digitorum, extensor carpi ulnaris, flexor carpi ulnaris, flexor digitorum (palmaris longus), flexor carpi radialis, as well as the muscles of the manus, which I did not analyze in the iguana. 

The article went through and wrote up muscle descriptions similar to how I wrote up muscle descriptions, commenting on the origin, insertion, and any other features of note. As I went through, I noticed there were slight differences between the two species, but nothing of particular note. I found this a little odd, considering the differences between iguanas and sand lizards, until I got to the conclusion of the article. It basically said that the general morphology of the forelimbs in lizards remains consistent across species. That because the set up is so general, it is easily used for many different forms of locomotion, and nothing is required to specialize over much. This is interesting because often times people study the specialization of species, why their musculature is different from everyone else and why this matters. But in this case, it's really the opposite. 


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Abdala, Virginia and Silvia Moro. "Comparative Myology of the Forelimb of Liolaemus Sand Lizards (Liolaemidae)." Acta Zoologica(2006) 87.1: 1-12. Web. 19 Apr 2012. 

Time Will Tell

Alright, this week in the lab, I started Iguana 2. As expected, it was very similar to the first iguana except for the fact that it was much smaller. This is a little ... off putting. Things don't look much different, but they are much smaller and this makes things slightly more difficult to find. The muscles thus far have weighed about half as much as the first iguana, which makes sense as the lizard is about half as big. Overall, not much to say. 

I'd also like to brief everyone on the changes to my project. Due to the time it took to dissect the first iguana as well as the shortness of time in general, the goals of the project have been modified. As you may have guessed, I am no longer working with anoles at all, as my original proposal suggested. The anoles are significantly smaller than the iguanas and it was easier for me to begin on a larger animal. Though I did have dissection experience prior to this project, I have never done something this in depth and hence was a little unprepared. I will also not be comparing the iguanas to any other lizards. Time just became too short, and it was only practical to dissect two lizards. I will instead be comparing the iguanas to mammals that are well documented - pigs and cats mainly. Lizard musculature differs from these mammals due to their habitat (trees and beaches), their posture (sprawling), and the fact that they are not mammals. I think it's a pretty cool comparison. 

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Means vs. Ends

Alright, the article for this week covers two subjects. The first is, you guessed it, iguanas. Specifically, general iguana ecology (was that an oxymoron?). It covers temperature preference, nesting and feeding habits. The second issue is an ethical one. 

Iguana body temperatures ranged from 34.0 degrees to 37.2 degrees Celsius (Hirth, 1963). This is 93.2 degrees to 98.96 degrees Fahrenheit, which is surprisingly not that far from human body temperatures. The air that they tended to reside in was 28 degrees C (82.4 F) to 32 C (89.6 F). Larger iguanas tended to rest in trees, while younger and smaller iguanas rested on the beach and none of the iguanas were ever far from the river or some other source of water. The scientists in the study believed this all had to do with thermoregulation. The water was a quick way for iguanas to cool down while the tree canopy offered heavy insulation, preventing loss of body heat. Remember that iguanas are cold blooded and hence cannot regulate their body temperature thus many of their adaptive behavior relates to thermoregulation.

Iguanas are herbivores, as mentioned before, surviving mainly on leaves and fruits. It has been found that young iguanas may feed on insects, however. As far as nesting goes, iguanas lay eggs in early spring, the most arid part of the year. The eggs are laid on the beach in spots that it takes the female iguanas some time to find. The scientists were not clear on what exactly the female iguanas were looking for, only that they searched for a significant amount of time to find a nesting site. 

As cool as all this iguana stuff is, the most interesting part of the article for me was the techniques used. In order to determine the body temperatures of the iguanas, the lizards were shot with .22 caliber rifle and then their temperature as well as the temperature of the surrounding area was taken as soon as possible. This seems a little ... out of line to me. The study was published in 1963, a time during which animal cruelty standards may have been different, but I'm not sure whether what was gained justified the shootings. Food for thought. 

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Hirth, Harold F. "Some Aspects of the Natural History of Iguana iguana on a Tropical Strand." Ecology (1963) 44.3: 613-615. Web. 11 Mar 2012.