Meeting Abstract
Understanding how modifications of the musculoskeletal system generate variation in body shape is key to understanding the evolution of form and function in teleost fishes. The neural and hemal spines projecting from the vertebral centra define the dorso-ventral margins of the posterior body of most teleosts. How are vertebral spines altered to produce variation in body depth among taxa? We hypothesized that variation in body depth is generated by both changes in spine angle (angle of spine relative to vertebral column) and spine length, with more acute angles and shorter spines creating dorso-ventrally “shallower” body types. We quantified the angle the spines create with the vertebral centra in the posterior 40% of the body and the relative length of the spines (spine length/body length) in multiple cyprinodontiform species (killifishes) and regressed these variables on the relative depth of the caudal peduncle (dorso-ventral depth of peduncle/body length), where a positive slope indicates an association between a spine variable and body depth. We found that changes in body shape just anterior to the caudal peduncle can be generated by variation in spine angle, in spine length, or combination of both factors. However, variation in the dorso-ventral boundary of the caudal peduncle is generated by variation of the relative length of the spines, and not through variation in spine angle: shallow caudal peduncles are the result of short vertebral spines. Caudal peduncle depth is also positively associated with spine length in three non-cyprinodontiform taxa; we suggest that spine angle may be constrained in the peduncle, possibly due to mechanical or developmental selective pressures. We also note that killifishes occupy a morphospace wherein multiple combinations of spine length and angle can generate similar overall body shape phenotypes.
