Meeting Abstract
Fishes in the gobiid lineage have evolved a specialized pelvic suction disc from the fusion and modification of the pelvic fins. The stream habitats of Hawai’i host a number of gobiid species, some of which have evolved the ability to climb waterfalls. In this study, we tested whether the pelvic fin rays of climbing species exhibit morphological or mechanical specializations compared with fin rays associated with non-climbing structures (caudal rays), or rays of non-climbing species. We compared pelvic and caudal rays from four species: Sicyopterus stimpsoni, an inching climber; Awaous guamensis, a powerburst climber; Stenogobius hawaiiensis, a non-climbing species with a pelvic disc, and Eleotris sandwicensis, a non-climber in the outgroup to gobies, with unfused pelvic fins. We used three-point bending to measure the flexural stiffness (EI) of pelvic and caudal fin rays, and used mixed linear models to examine differences in EI between climbing and non-climbing species, and between pelvic vs. caudal fin rays. The pelvic discs of the two climbing species are relatively smaller and more rounded than those of non-climbers, with highly branched fin rays. In our mechanical tests, we found that the flexural stiffness of pelvic fin rays from climbing species is significantly lower than in pelvic rays from non-climbing species, resulting in more flexible pelvic rays in climbers. The caudal fin rays are more stiff than the pelvic rays for all species, but the those of the climbing species are more flexible than those of the non-climbers. These comparisons indicate that structural adaptations contributing to higher flexibility in the fins may have facilitated the evolution of climbing performance in gobies.
