Anatomical Linkage Between Upper and Lower Jaws, and Timing in Feeding and Climbing Motion of a Hawaiian Waterfall-Climbing Goby, Sicyopterus Stimpsoni

Among waterfall-climbing gobies, Sicyopterus species are known to use their mouth as a secondary adhesive mechanism during climbing on the steep rock surface of waterfalls. Using the pelvic fins that are fused together (pelvic sucker) and the mouth as two suction mechanisms, Sicyopterus sp. inch-up the waterfalls and reach their spawning habitat in oceanic islands. The motion of the mouth during rock-climbing (grasping the substrate to gain purchase) is kinematically identical with that during feeding (scraping algae off of the substrate), depicted as an exaptation. However, it is not known how the premaxilla (upper jaw) as part of the mouth precisely moves in relation to the motion of the dentary (lower jaw). In this study, we performed a series of dissection on preserved specimens of Sicyopterus stimpsoni from Hawai’i and examined how the premaxilla is anatomically linked to the dentary. Combined with the motion analysis based on highspeed videos collected previously, we discuss the implication of our findings