Meeting Abstract
The rheophilic hillstream loaches (Balitoridae) of South and Southeast Asia possess a range of pelvic girdle morphologies which may be attributed to adaptations for locomotion against rapid flow. Specifically, the connectivity of the pelvic plate (basipterygium) to the vertebral column via a sacral rib, and the relative size and shape of the sacral rib, fall within a spectrum of three discrete morphotypes: long, narrow rib sometimes meeting with the pelvic plate; thicker, slightly-curved rib meeting or interlocking with the pelvic plate; and robust, crested rib interlocking with the pelvic plate. Species in the second and third categories with more robust sacral rib connections between the pelvic plate and vertebral column are capable of walking out of water with the third category exhibiting a more tetrapod-like lateral-sequence diagonal-couplets gait; this behavior has not been observed in balitorid species lacking direct skeletal connection between the vertebrae and the pelvis. Here, we present a myological analysis of the three morphotypes of balitorids to further address the functional morphology of walking in these fishes. Phosphotungstic acid (PTA) staining was used to increase the radiopacity of musculature for visualization with µCT scanning, after which individual muscle groups were segmented and analyzed for fiber angle and physiological cross-sectional area, to estimate maximum force production during locomotion. The skeletal and muscular morphological data from µCT scans were considered in a phylogenetic context based on robust sampling of ultraconserved elements (UCE). Future work will use kinematics and electromyography to compare the weight-bearing walking capabilities of balitorid species along the observed spectrum of pelvic girdle morphology.
