Jumping slugs!
Energetics and mechanics of muscle contraction
My major research interests focus on the mechanisms and evolution of animal movement. I am particularly interested in how muscles work in natural behaviors. Muscles are versatile motors. They can pull against each other and against their tendons in complex ways. They can act as accelerators or brakes, and their tendons can act as springs that recycle energy. These mechanisms can also interact in ways that enhance strength and reduce cost.
Most of my current research addresses the relationships among muscle anatomy, mechanics, and energetics in muscles. Snakes are excellent models for studying these things, because the tail muscles in many species can sustain high levels of exercise without becoming fatigued. High-performance muscles such as these can show particularly clear relationships among anatomy, mechanics, and physiology that are difficult to measure in more generalized muscles. Rattlesnake tailshaker muscle, in particular, is a great system for studying anatomy, physiology, and biomechanics because it is specialized for sustaining extremely high-frequency contractions (up to 100 Hz!) without fatigue. Currently I'm working on two major projects that address the function and evolution of high-performance muscles and the rattlesnake rattling system.
In one project, which I hope to finish in the near future, I have been studying the function and evolution of tail muscle physiology and biomechanics in snakes. This work involves measuring muscle contraction frequencies, tail vibration frequencies, the mechanics of tail motion, and the enzymatic capacities of the muscles involved in snakes that vibrate their tails at different frequencies. In particular, I am studying how these features function and how they evolved in the lampropeltine and crotaline snakes, both groups for which we have reasonably well-supported phylogenies. See some of the study species here (opens in new window). This project will help show how tail vibration in snakes currently works, how it evolved, and how changes in muscle physiology, tail morphology, and tail mechanics led to the evolution of the rattlesnake rattling system. This work has been funded in part by the Louisiana Board of Regents, the University of Louisiana at Lafayette, and the Department of Biology at UL Lafayette.
In a second major project, I am studying how tendon length affects the energetics of muscle contraction. Muscle-tendon interactions can affect force output and the cost of contraction. However, our ability to resolve the effects of tendons on the cost of muscle contraction has been severely limited by the fact that muscles that vary in tendon length typically also have different fiber types, and hence would be expected to have different energetics. The inability to separate how fiber type and tendon length affect muscle energetics is probably a major reason why the effects of tendon length on energetics have not yet been measured, even though tendon length is known to affect muscle strain, force, work, and power.
In contrast to the muscles of other species, the shaker muscles of rattlesnakes vary in tendon length along the tail but have a uniform fiber type. The uniformity of fiber type provides a critical natural control for measuring how tendon length affects contractile cost. In previous research, I found that shaker muscles with long tendons shorten less than those without tendons. In this work, I am testing whether muscles with long tendons have a lower contractile cost than muscles that have the same fiber types but lack tendons.
By using a muscle-tendon system that has a single fiber type but different tendon lengths, this work will help answer questions about muscle function that are difficult to answer using more generalized muscle-tendon systems. Stay tuned for updates! This project is funded by the National Science Foundation.
Mechanics of muscle-tendon networks
For many years, I have been studying how the complex muscle-tendon networks of snakes are used to produce and control movements that differ in speed, strength, and duration. The behaviors I have been studying include snake locomotion, constriction, and swallowing. See some of the study species (opens in new window).
Snakes are uniquely interesting models for this kind of integrative research. Their simplified body form constrains their movements to bending and twisting, but their complex musculature supports a diversity movements and behaviors. For example, snakes use at least five distinct kinds of locomotion, as well as a variety of prey capture and feeding movements, such as striking, constriction, and swallowing. These behaviors require different speeds, strengths, and ranges of motion, but are all produced by the axial muscles and skeleton. Snake epaxial muscle-tendon networks are among the longest multi-joint muscle systems known. In many species, these muscle-tendon systems involve three major muscles that pull against one another via intermediate tendons. Typically, muscles that pull against one another have antagonistic functions, such as flexing and extending a joint. However, other functionally important consequences are also likely. For example, seemingly antagonistic contractions in serially connected muscles may increase the speed of joint motion and/or bend more joints. In previous research, I found that the complex anatomy and serial activation patterns of snake spinal muscles are appropriate for enhancing each other's force production via active stretching (see figure above, which came from Moon and Gans, 1998). By inducing active stretching, complex muscle-tendon networks may actively enhance muscle force output and reduce energy use. In this project, I plan to test whether muscle interactions via intermediate tendons enhance force output by inducing active stretching during movement; if they do, then I will also quantify how much force is enhanced.
The results of this project may help explain the function of some poorly understood muscles in other animals, including humans, and could help improve the design and control of flexible robots, such as those used in prosthetics, manufacturing, and search and rescue operations. Stay tuned over the next few years for updates! This project is funded by the National Science Foundation.
Small shrimp, big journey (picture to come...)
My research is not just restricted to vertebrates. With Ray Bauer and Jim Delahoussaye, I am studying the migration of juvenile Ohio shrimp (Macrobrachium ohione) up the Atchafalaya River every fall. These incredible little shrimp hatch in brackish marshes on the Louisiana coast and swim upstream by the millions as far as they can go. We're studying how they do that. Historically, they used to make it from the Gulf Coast to the Ohio River, which pretty remarkable for such shrimpy (inch-long) shrimp! For more information, see Dr. Bauer's website about this project (opens in new window). And stay tuned for more about this project in the near future.
Jumping slugs!
Louisiana is a great place to be a biologist, especially a field biologist (or a lab biologist who likes to go on field trips). Here are links to photographs showing some biology in Louisiana:
Our study species in the lab (opens in new window).
Amphibians of Louisiana (opens in new window).
Birds of Louisiana (opens in new window).
More photo galleries to come soon (Louisiana reptiles, miscellaneous animals, and habitats).
Laboratory facilities
In general, my lab is set up for the following kinds of research:
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Updated May 2010