Jack Be Nimble, Jack be Quick; Plethodontidae Jumps over the Candle Stick

Hey! Sorry for not posting in a few weeks. The start of the semester has been good, but busy. In this weeks installment of around the lab, I will let you get an over-the should view on what I will be doing for my thesis. I have some “side projects to (all very cool) that I will blog about later on in the semester.
My thesis has three components which look at the molecular, muscle and total body levels of a Plethodontidae (Lungless salamander) jump called a C-start.

Jumping Plethodontids have baffled researchers because their girdles and limbs remain highly underdeveloped for jumping. Their limbs almost always remain in a “pushup” position far away and perpendicular to their body while their ventral side rests in contact with the floor. In contrast, lizards and other higher vertebra that use their more highly developed and specialized hind limbs for jumping. Recent work observed the salamander jump originated in the torso rather than the limbs. This motion, called a C-start jump, mimics what one would see in startle responses observed in Teleosts (boney fish). The salamander, when stimulated by a predator will bend its body into a” C” and then rapidly straighten (unload) its body, propelling the salamander vertically and horizontally. Only the basic movements of the jump have been studies to date.

My studies hope to expand the knowledge of the C-start jump by studying multiple levels of the organism during the C-start.

During the unloading phase of the C-start, a large quantity of energy is expelled to allow the salamander to get off the ground. Where is this potential energy stored?  One idea would be that the muscle contractions of the axial (trunk) muscles themselves could unbend the salamander with enough speed to propel the salamander into the air. This is seen in the lateral bending of salamanders, lizards and fish. If contractions solely played a role in unloading, then the loading phase should have a similar angular velocity. Research shows that the loading velocity is much smaller than the unloading velocity. There may be a storage device at play during the loading phase that allows the storage of energy to be used during the unloading phase, and therefore would account for the extra velocity.

Elastic tissue acts like a rubber band or spring. If elastic elements are in use during the loading phase it is plausible that they are stretched during the loading phase and then released during the unloading phase passing on its stored energy for the jump.

There are a few kinds of elastic elements in vertebrate: passive (Collagen around the muscle cell and titin within the cell) and active (theorized second role of titin). Passive elements are always springy, while active elements work in unison of muscle contractions. I am curious if any or all of these element are at work in the jump. I have lined up three studies to help me answer this.

1) Under high speed, the salamander will be filmed performing the C-start jump. Following, the salamander will be anesthetized and then bent, by hand, into its C-shape and released. A high speed camera will watch the salamander straighten out. The two scenarios will be compared using kinematic analysis. The similarities and differences could help identify if the salamander is only using muscle contractions or elastic elements to gain its straightening speed.

2) EMG studies will be conducted on the salamanders to learn about the muscle control patterns of swimming, running and jumping in this family of salamanders. The knowledge from this will fill a gap in the literature on Plethodontidae and help us learn how these axial muscles work together to make this jump happen.

3) My work is under the premises that active titin exists, but to date it has not been proven. I am working at the molecular level to try and “prove” the leading hypothesis on the subject (Winding Filament Hypothesis) by running several TEM (transmission electron microscopy) studies, as well as RNA studies as well.
Alright, Now that I am sure you are all thoroughly exhausted from reading this long post, I will leave the molecular studies for a later date, but at least you know what I (and therefore the lab) am up too. Expect a weekly post once again, therefore, see you next week. We will discuss some pretty sweet TEM and SEM projects going on in the lab!

-A. Hessel