Travels to Rockefeller State Refuge

Alligator hanging out along Route 82

Rockefeller State Refuge is an expansive area of the western end of Louisiana’s swampy coast which prides itself as being one of the key DNR sites to aid in the rescue of American Alligators when they were endangered several decades ago (Link to Map and Location).  Today, besides maintaining a large wildlife management area full of birds, fish, herps, and sporting enthusiasts, they manage the region’s alligator population, work with commercial farmers and supply most of the alligators used in research in North America. If you didn’t already know, research in alligators is booming. There is strong interest in alligator and crocodilian genomics, hematology and disease resistance, biomechanics (for example…the death roll..), cardiopulmonary and developmental physiology, let alone our persistence in using them as a comparative anatomical model for vertebrate paleontology, functional anatomy and evolution.

Early morning Sun, Rockefeller Jan 31, 2011

 In February 2011, Henry Tsai and I drove down to collect alligator cadavers and made it back to Columbia at 3am, about 1hour before a blizzard hit and snowed us in for 2 days. It was a drive of legend in which we threaded the needle between two separate winter storms driving up through Western Arkansas. The alligators were quite comfy in the back of the truck, in my driveway while  we were snowed in.

The morning after picking up gators, after a 15hr drive through winter weather, Feb 1, 2011.

Needless to say, there are few contrasts in weather than experiencing sunrise over a balmy swamp one morning, and then 24 inches of snow the next.  The gators were used for research as well as a fairly popular high school workshop “Inside Alligators”we put on a week or so after we returned.

This June, I was accompanied by Ohio U/Witmer lab alum and current Mizzou Lecturer Dave Dufeau, and two undergraduates, Cortaiga Gant and Julie Tea. Cortaiga has been part of Project Gator Chin for a while whereas Julie is a Visiting Summer Fellow from University of Houston. This trip made for a good experience for them–none of whom had ever visited a place like Rockefeller and everyone got a chance to see, hold, and work with alligators. We stopped in Baton Rouge on the way down, stuffed our faces with shrimp and oysters at The Chimes and had a relatively leisurely drive down the coast the next day to get to Rockefeller. We then drove the entire way back to make sure the eggs and cadavers were taken care of.

Beach West of Cameron, LA

We visited Rockefeller this trip to load up a bunch of eggs we are currently incubating in the lab. Alligator eggs typically take about 65 days to hatch and are laid in a large, mother-guarded, mounded nest in late May/Early June. The Refuge staff use helicopters and airboats to identify and flag nests every season. They also collect recently-laid eggs and keep them in large outdoor incubators. The eggs are given to researchers or are hatched and raised until they are released into the wild or used otherwise.

Julie, Dave, and Cortaiga at Rockefeller, June 2012

Rockefeller has something different going on every time I visit. I’ve seen other students there collecting blood and gut bacteria. This time they had a number of alligator gar carcasses being prepped for someone’s study. Rockefeller received some serious damage from Hurricanes Rita and Katrina in 2005. One the “major” losses was their large outdoor, walk-in freezer, which had dozens of frozen specimens including the head of a gator that must have been pushing 10feet long…all swept away. None of this would be possible without the support and effort of Supervisor Ruth Elsey. Ruth has championed research and made the resources of the Refuge available to researchers and students from around the world. Ruth is always keen to help out people with research projects and educational materials and is always a welcoming host at Rockefeller.

Holding Gators

Alligator gar heads

Ruth showing Julie and Cortaiga a local gator nest. Momma is just under the reeds at the bottom of photo.

Cartilage Fusion in Gator Chins

Mandibular joints and Meckel’s cartilage in Alligator.

Summer in the Holliday Lab is getting exciting. A busy Spring has resulted in a couple new projects coming out later in the Fall (more later) but we’re deep in new directions in the lab including our first stint into Evo-Devo. Some students and I traveled to Louisiana to retrieve about 100 Alligator eggs to run an experiment this summer on the development of the Alligator chin. We’re keen to understand when and how the chin, or mandibular symphysis develops and pinpoint particular mechanisms and events that occur during its in ovo transformation.

Meckel’s cartilage is the cartilaginous rod that provides the scaffold for the ossifying mandible and 1st Branchial arch derivatives in the vertebrate skull. So, in reptiles, it promotes the ossification of the bones of the lower jaw and quadrate and remains as a persistent cartilage throughout life (Top Figure). This is in stark contrast to the mammalian condition in which the cartilage cavitates, aids in the formation of the dentary, 2 middle ear ossicles, and the tympanic ring. This caudal end of the system is better known-with questions involving the evolution and development of the mammalian ear driving many research directions. If you want to read more, I point you to the research of Abigail Tucker and  Zhe-Xi Luo, among many others.

Cross-section through suture and Meckel’s cartilage and CT-based 3D model of mandibular symphysis with bone, and without showing Meckel’s cartilage and sutural ligament.

At the rostral end of Meckel’s cartilage, out at the mandibular symphysis, we find animals doing a couple of different things. More often than not, the two cartilage rods (Left and Right) remain independent of one another and the symphysis is solely a membranous, ligamentous syndesmodial joint that fully fuses in primates, oviraptors, neoavians and a handful of other vertebrates, or may be sutured but unfused (dogs, crocodyliforms) (Middle Fig), or even mobile as in snakes, some lizards, possums and other animals probably. Second, research into the development of the human chin has found that the two cartilaginous rods stick together during development and eventually recede, occasionally leaving small nodular cartilages. Although the 2 cartilages stick to one another, the perichondral layer remains patent. We found a similar pattern in Iguana chins in our 2010 Anat Rec paper on lizard mandibular symphyses. Third, and now to the point. In alligators and geckos, Meckel’s cartilage not only sticks to its opposite member, but it obliterates the perichondral borders between the two cartilaginous rods, forming a continuous cartilaginous rod from the left articular all the way around the chin and back to the right articular.

That’s cool! Buy why? Is it adaptive? We’ve got some ideas. How? we’re working on it. Why do we care? working on that too :) but in general, mandibular symphyses are important cranial joints functionally, so understanding their development and evolution are key goals if you want to understand the how the vertebrate head works. Meckel’s cartilage is often entwined in craniofacial defects that affect branchial arch development. Archosaur chins are really cool and quite diverse and thus may shed light on form, function, and ecology of feeding during their evolution.  Also, paleontologists have started to wiggle chin joints with more frequency these days, what with various animation and modeling applications,  despite there being what I consider a total lack of published research on how the joint is built (my fault I guess) and functions (in the works!)  in living reptiles.

Cleared and Double-stained alligator embryo showing the incipient double fusion and spatulate process of Meckel’s cartilage at the symphysis.

I digress… Fourth…Alligators take this cartilage fusion one step further in that a spatulate structure extends rostrally from the main body of Meckel’s cartilage  and forms a second fusion which eventually seals up with the caudal, main body of the cartilage. This spatulate form persists throughout life in alligators, leaving a large, flat trough within the bony symphysis. Is this fusion similar to those fusions we see in the hyoid skeleton, or the chondrocranium? probably. We’ll find out.

This summer we’re growing up Alligators to capture the time during development when this fusion occurs–I’ll post about that next.