Meeting Abstract
Bonytail (Gila elegans) are an Arizona native endangered species that have unusual morphology thought to have evolved for high flow riverine environments. The shallow peduncle and crescent shaped tail appear to allow them to reduce drag and increase swimming efficiency. We describe the anatomical features associated with body shape in the caudal peduncle region. We compared the peduncle morphology of two closely related native species, Roundtail (Gila robusta) and Humpback chub (Gila cypha), to that of Bonytail. We cleared and stained ten individuals from each species to measure the neural and hemal vertebral spine angles (angle the spine creates with the vertebral centra) and size normalized spine lengths (spine length/standard length of fish) of the last twelve vertebrae. Bonytail have more acute spine angles in the caudal peduncle compared to Humpback and Roundtail. We also examined the soft tissues (muscle and tendon) of the caudal peduncle. Using a tendon-tension test and histological examination, we found evidence for paired lateral tendons in Bonytail that appear to be present in Humpback but absent in Roundtail. The total volume of muscle in the peduncle region of Bonytail appears to be reduced but stronger (tension test) when compared to Roundtail. Loss of musculature and lateral tendons are also seen in scombrid (tunas) fishes, where their long lateral tendons transmit force from the anterior musculature to the tail. Bonytail appear to be converging on this morphology which is likely beneficial during historic seasonal flooding events, where they can maintain position in the flow with relatively low energy expenditure.
