Darwin Strikes Again

Integrative organismal biology (IOB). Not a term you hear everyday, but it refers to a part of biology that focuses on the ecology, behavior, and evolution of organisms. My paper for today is about the IOB of marine iguanas, a species closely related to the green iguanas I am working on (Wikelski and Romero, 2003). The study used a method of predicting evolution as the basis for its work. The idea is that if you study the performance of specific organisms you can determine which factors play a role in the selective process of evolution and then use these factors to predict how the species will evolve in the future. 

This study, "Body Size, Performance and Fitness in Galapagos Marine Iguanas," used foraging and reproductive performance as the factors to predict evolution. The reason marine iguanas were chosen as the model is because the body mass of iguanas on different islands can vary by one order of magnitude, adult iguanas really have no predators, and they don't compete with other vertebrates for food (iguanas eat the red and green algae revealed at low tide). This means that there is a ... regulated form of evolution occurring. The changes taking place are based on the iguanas alone, not on other species. 

The study found that larger marine iguanas, male or female, had better reproductive success. The females because they could produce larger babies which were more likely to survive and the males because they were able to control a larger territory and put on a better show for thefemales. However, being large comes with draw backs. The larger iguanas had far less foraging success. They had to expend more energy to move their larger masses, it takes more energy to heat a larger body (the whole cold blooded issue), and in the end, they had trouble getting enough food. When times were good, and algae abundant, the larger lizards did fine. However, when times were bad, like after a hurricane, it was the big lizards that died. 

The conclusion that was drawn from this data is that marine iguanas will continue to get bigger. Not only does reproductive success increase, but the world is getting warmer and that's good for the cold blooded species. However, their size will be regulated by the lack of foraging success. Bigger lizards need more food and sometimes it's just not there. Don't expect any giant iguanas anytime soon. 

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Wikelski, Martin and L. Micahael Romero. "Body Size, Performance and Fitness in Galapagos Marine Iguanas." Integrative and Comparative Biology(2003) 43.3: 376-386. Web. 4 Apr 2012. 

Uncertainty

I'm done with Iguana 1! The forelimbs of my first iguana have been completely de-muscled and now ... well they're just kind of bone that is barely attached to anything. I finally removed all of the deep muscles - the pronator teres, supinator manus, teres major, subscapularis, and the others. It was surprising that while some of the deep muscles were quite small, the majority of them were actually larger than the superficial muscles. For example, the teres major, which is a deep muscle of the back (one of the many that originates from the scapula) weighed significantly more than the trapezius and latissimus dorsi (both superficial muscles). With regards to the brachialis/brachioradialis issue I decided that there was only one muscle there and the muscle had been named differently by the different sources. The muscle itself seems to be more similar to the human brachioradialis as it has its insertion point on the radial shaft. It may be a fusion of the two muscles. 
 
Anyway, I can now start on my second iguana. The process for this one will be the same as the first, but I believe it will go much faster due to the experience I gained with the first. Skinning will hopefully only take one day, and then there is superficial identifications and separations, pictures, and then muscle removal. I already have my muscle catalogue complete, so with the second iguana I have to check with the catalogue and ensure that they agree. If they don't, I have to make a note and take further pictures of the area even though the specimen will have already been photographed. There can actually be quite a bit of difference between different samples of the same species. It is important to remember that bodies are adaptive and everything an animal does, eats, hears, sees, etc change its body chemistry and set up. There is a muscle in the human leg that 8% of humans don't have. Don't you just love the uncertainty?
 
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It's All ... Lizard to Me?

This week in the lab was ... not as productive as hoped. On Tuesday, I got a lot done. All the of the superficial muscles on my iguana were removed and weighed, revealing the deeper muscles below. Taking the muscles off was pretty simple. The hardest part was ensuring that the cut was made as close to the bone as possible. Because I am weighing the muscles for comparative purposes, it it important for the entire muscle to come off, and not just part. This was difficult because I was not familiar with the iguana skeleton. First of all, their clavicles extend all the way around their necks like a collar and they have a second interclavicle below acting like the clavicle in humans. Their sternum, instead of being a single line of bone as in humans, is almost a breastplate covering most of the chest. Some of the muscles that must be removed are attached underneath these bones, so it takes some maneuvering to get them out. 

Friday was an off day. I ended up getting sick and leaving early which means I missed out on almost an entire day of work. So next week I have to catch up and remove the deep muscles of the iguana. There really aren't that many, the problem is identifying them. For example, according to my iguana atlas (Oldham et al, 1975), iguanas have a brachialis muscle, but no brachioradialis. However, this source has been weak in identifying deep muscles. Another source on the forelimb muscles of monitor lizards (a species similar to iguanas), claims that there is only a brachioradialis and not a brachialis (Haines, 1939). However, this brachioradialis inserts and originates at almost the same place as the brachialis of the first source. Then there is the veterinary textbook I've been using (Dyce, 2002) that only references a brachialis muscle. But it uses the forelimb of carnivores for this, and iguana are not carnivores. And then there is the iguana itself. There appears to be only one muscle at the juncture of the elbow between the humerus and radius. There are several possible explanations for this. The first being that all the sources are speaking of the same muscle and have just named them differently. The second is that there are two muscles, but the sources all had different focuses and didn't mention them both. The third would be that there is a conflict in the scientific community about this particular muscle and no one really knows if there is one muscle, two muscles, a fused muscle, or some other variation. Welcome to the academic world.



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Dyce, KM, et al. Textbook of Veterinary Anatomy. St. Louis: Saunders, 2002. Print.

Oldham, Jonathan Clark and Hobart Muir Smith. Laboratory Anatomy of the Iguana. Dubuque: WC Brown,   1975. Print.

Haines, R. Wheeler. "A Revision of the Extensor Muscles of the Forearm in Tetrapods." Journal of Anatomy (1939) 73.2: 211-233. Web. 29 Mar 2012.

Deep

     Todays blog is on deep muscles. These are the muscles that ... well no one really talks about. Everyone knows about the biceps and triceps, pectorals and deltoids, but not many people discuss the teres major or the pronator quadratus. My iguana has been almost completely de-muscled except for these deep muscles, and to be honest, I'm not really sure what to be looking for. So Dr. Zack helped me out with two papers on the homologies of tetrapod forearm extensors and flexors. 

     The first paper (Haines, 1939) details the results of a study that compares the forearm extensor musculature of Chelonia (turtle), Sphenodon (lizard), Salamandra (salamander), Ophiacodon (synapsid), the giant salamander, Eryops (early amphibian), Rana (frog), Varanus (monitor lizard), crocodilians (this seems obvious), monotremes (mammals that lay eggs), and Didelphys virginiana (opposum). It was a pretty extensive study. What I took away from it, is that generally species living in similar environments have similar muscles, which makes sense given that they have to do similar things. Evolution is consistent like that especially because this study was focusing specifically on homologies (something that is shared in present species because it was shared by a common ancestor). I also determined that in my iguana I need to be on the look out for brachioradialis, which allows for the rotation of the forearm, supinator manus, which allows for the supination of the hand, and supinator manus accessorius, which helps in the supination of the hand. I believe I have already found the brachioradialis, but the other two I haven't looked for yet.
     The second paper was slightly less in depth (Haines, 1950). It compared many of the same species as the previous study, but really focused on Varanus (monitor lizards) and Felis (cats). The main take away for me was that I need to be looking for pronator profundus, which in humans is often called pronator teres and allows for the pronation of the hand, and pronator quadratus, which does the same. Keep in mind, the forelimb of my iguana is only maybe three inches in length, and on humans these muscles are only maybe an inch or two long. They're tiny in iguanas. 
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Haines, R. Wheeler. "A Revision of the Extensor Muscles of the Forearm in Tetrapods." Journal of Anatomy (1939) 73.2: 211-233. Web. 29 Mar 2012. 

Haines, R. Wheeler. "The Flexor Muscles of the Forearm and Hand in Lizards and Mammals." Journal of Anatomy (1950) 84.1: 13-29. Web. 29 Mar 2012. 

King of the Jungle

Alright, another lit search turned up a pretty cool article. Though it is not directly related to iguanas, I think it offers some cool insights in to the musculature of the forelimb in a variety of species. The study was conducted to analyze the evolution of pectoral and forelimb muscles from bony fish to non-mammalian tetrapods and then further to monotreme and therian mammals, including humans.
Bony fish or sarcopterygians have very few muscles in their "upper bodies." They have a fin abductor and adductor and then some undifferentiated hypaxial and epaxial muscles. This makes sense when you consider that fish aren't doing a lot of heavy lifting. This also explains why there was a large change upon the evolution of tetrapods (creatures that walk on four legs). Species that walk must support half their weight on their forelimbs and their pectorals and back muscles have to support their entire body weight on their limbs. Many species have heavily developed shoulder and back muscles due to their large body mass. For example, hippos have a huge weight in their trunks and they have to move this when they walk. The muscles around the trunk have to not only stabilize this mass, but also move it against the force of gravity, mud, water, etc. That's a lot of requirements and is the reason that nature went from fish with 2 clear forelimbs muscles to over 40. And these forty muscles has not undergone a large amount of change since then, mainly because the same requirements are still present (Diogo, 2009).
All of the current forelimb muscles -- biceps, triceps, coracobrachialis, extensor carpi ulnaris, flexor carpi radialis, extensor digitorum, and about twenty others -- derived from the first two forelimb muscles in fish, the fin abductor and adductor. Oddly enough, the pectoral muscles developed from the "postcranial axial" muscles. These are the muscles that are below the head and towards the center of the body. I have to say, the whole article was very odd. It is not very often that I think about how I am descendant from fish. Does that strike anyone else as ironic? You know how we now eat fish and consider them fairly low on the food chain, it's very Lion King ;)
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Diogo, R., Abdala, V., Aziz, M. A., Lonergan, N. and Wood, B. A. “From Fish to Modern Humans – Comparative Anatomy, Homologies and Evolution of the Pectoral and Forelimb Musculature.” Journal of Anatomy (2009), 214.5: 694–716. Web. 23 Mar 2012.

When the Iguana Bites

     Okay, it's Spring Break this week, so I've been occupying my time with more lit searches. Todays piece is on ventilation in iguanas and the muscle involved in this. The study found that only four hypaxial muscles are involved in iguana breathing. (A hypaxial muscle is one located on the ventral trunk or the limbs i.e. the muscles of the abs, pecs, arms, and legs, but not those in the back.) The four muscles are the transversalis, the retrahentes costarum, and the external and internal intercostals. The first two are the muscles that control expiration, while the second two control inspiration, however, lizard respiration is a little different than normal (Carrier, 1989).     Iguanas bring air into their lungs by changing the shape of the thoracic cavity to create a sub-atmospheric pressure. If this sounds uncomfortable (the whole deforming of your body in order to breathe), it may be. Recent studies have shown that lizards cannot run and breathe at the same time. In most mammals, the more arduous the activity, the more oxygen we attempt to bring into our bodies, hence the panting that often accompanies running. But lizards can't do this. The author of this article, David Carrier, believes that this is caused by the opposing demands that the ventilatory and locomotive muscle place on the thorax. Both sets of muscles are pulling in different directions, thus reducing the effectiveness of both. Oddly enough, aspiration in iguanas begins with expiration followed immediately by inspiration, but this cycle is usually followed by a period of breath holding. Many humans do the same thing when they become aware of the sounds of their own breathing, particularly if they are standing close to someone else. It's odd how many of those parallels you find.
     So the transversalis and the retrahentes costarum are responsible for expiration. Pretty straight forward. In an iguana, the transversalis is located on the ventral side of the ribcage deep to the intercostals and obliques, while the retrahentes costarum is located on the dorsal side of the ribcage deep to the intercostals and obliques. When these muscle contract, they increase the pressure in the thoracic cavity and aid in the exhalation of the air in the lungs.
     The intercostals are responsible for inspiration, sort of. The internal intercostal lies superficial to the transversalis and the external intercostal lies superficial to the retrahentes costarum. When either of these muscles are stimulated ventrally, thoracic pressure is decreased. But if they are stimulated dorsally, thoracic pressure is increased. Thus these muscles are partially responsible for both parts of breathing.
     Also, these muscles are all composed of both slow twitch fibers and fast twitch fibers. Slow twitch fibers are what allow a marathoner to run 26.5 miles, or a weight lifter to hold a weight in the air for five minutes. They are the endurance fibers. The fast twitch fibers are the sprinters, the ones that produce a large boost of speed or power and then have to wait to be reactivated. The muscles that were responsible for respiration in iguanas relied mainly on slow twitch fibers to accomplish this. That means that there was a significant delay between the muscle activation (the thought to breathe) and the actual beginning of a breath.

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Carrier, David R. "Ventilatory Action of the Hypaxial Muscles of the Lizard Iguana Iguana: A Function of Slow Muscle." Journal of Experimental Biology (1989) 143: 435-457. Web. 22 Mar 2012. 

Another Day, Another Lizard

     So, this is what I did in the lab this week. Tuesday I continued with my muscle descriptions. My first draft, as usual, was a little scatter-brained and some of the terminology was not what it should have been. Anatomical terminology, which seemed so straight forward earlier this year in anatomy, has complicated infinitely. This is due mainly to the fact that I am no longer dealing only with humans. In humans, you use the terms posterior/anterior, medial/lateral, and superior/interior. However, in quadrupeds, which I'll point out is essentially most of the other creatures on the planet, you use dorsal/ventral, medial/lateral, and cranial/caudal. Originally, when I wrote my muscle descriptions I used a combination of both, which made everything unclear and un-standardized.
     For those of you who don't study biology in your spare time, dorsal and ventral basically mean back and front. In humans, this is very obvious; however, in other species, dorsal is the side of the animal where the backbone lies, and ventral is the side with the ribcage/heart. More like the top and bottom. Medial and lateral are how far away something is from the center of the body. Cranial and caudal refer to distance from the head. Cranial is obviously closer, and caudal is farther away. The terms distal and proximal are also used to describe the distance from the trunk when discussing structures in the limbs. I hope that cleared things up.
     So Tuesday, that is what I did. Today, I started to remove muscles. This seems simple, you just cut it off right? Wrong. To remove a muscle, you follow it to both the insertion and origin. Here you must cut the connecting tendons as close to the bone as possible to avoid losing data. After the muscle is removed, you weigh the muscle, record the weight, and then photograph everything again without that muscle. Then you move to the next one. It is a tedious, but necessary process.

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