Meeting Abstract
Neuromuscular junctions (NMJ) connect an animal’s nervous system to its muscular system, and are a critical component in the behaviors that result from muscle contractions. Yet, little is known about how the size of NMJs (which determines the extent of the motoneuron’s connection to a muscle fiber) varies in association with behavioral use of a muscle. In this study, we examine whether variation in the use of a muscle is positively correlated with variation in NMJ size. We studied 27 Anolis lizard species from the Dominican Republic, Puerto Rico, the Bahamas, and the southeastern USA. First, we observed their use of two muscles: the ceratohyoid (CH), which controls the movement of the dewlap, a throat fan used in courtship and aggressive displays; and the retractor penis magnus (RPM), the muscle that controls movement of the hemipenes during copulation. Then, we dissected the CH and RPM from adult males of each species, and then stained the muscles for acetylcholinesterase, an enzyme that is concentrated in the NMJ. We then measured the cross-sectional area of the NMJs in each muscle. Results show that NMJs in the CH (a muscle used multiple times per min) are much larger than NMJs in the RPM (a muscle used, at most, several times per day). Our preliminary analyses of a subset of 15 species suggest that the size of NMJs in the CH is associated with CH fiber size, but not dewlap display behavior, and that the size of NMJs in the RPM is not associated with RPM fiber size or copulation rate. This comparative study of NMJ size, which varies widely among species and even among muscles within an individual, contributes to our understanding of the evolution of muscle physiology and behavior.
