Meeting Abstract
The axial musculature of fishes is characterized by distinctive, “W”-shaped myomeres; however, myomere morphology varies across taxa and little is known about the evolutionary and developmental factors that influence axial morphology. Our long-term goal is to determine if variation in caudal peduncle morphology influences locomotor performance in the killifishes (Cyprinodontiformes). As a first step, we survey axial muscle and vertebral anatomy in the peduncle region of four cyprinodontiform fishes to test the a priori prediction that myomere variation mirrors vertebral column variation. For example, if the neural and hemal spines of the vertebrae form shallower angles (more posteriorly oriented angles) relative to the vertebral column in one species relative to another, then we expect the “W” shaped myomeres will also display shallower angles and form a more compressed “W” shape. We dissected individual myomeres from the axial musculature of the caudal peduncles in Gambusia affinis, Poecilia mexicana, Jordanella floridae and Kryptolebias marmoratus and compared myomere angles to measurements of the vertebral column in cleared and stained individuals. Variation in peduncle morphology is associated with variation in vertebral spine angles: as the neural and hemal spines “bend” toward the posterior vertebral centra (to form a shallower angle), the angle of the anterior cone relative to the vertebral column also decreases. In addition, cyprinodontiform fishes with smaller caudal peduncles appear to have shorter myomeres when normalized to body length. Although there is a point when the sclerotome and myotome separate in embryology, it is likely that the bony and muscular elements of the axial skeleton are linked developmentally because the vertebrae and axial musculature both form during somitogenesis.
