HSIEH, S.T.; Harvard University: Comparative locomotor characteristics of two amphibious blennies, Alticus arnoldorum and Praealticus labrovittatus

Amphibious behavior is found in at least 12 families of fishes. Whereas most blennies (family Blenniidae) are fully-aquatic, at least seven of the 53 genera have amphibious species. I have been examining the amphibious locomotor repertoire of the Pacific leaping blenny, Alticus arnoldorum. Found primarily in the tropical Pacific Ocean along the violent surf zones on coastlines, these blennies can leap up to five body lengths between rocks, climb up smooth surfaces such as glass, and appear to skip across the water surface. They routinely use a movement permitting extremely rapid locomotion on land, which involves twisting the tail along its longitudinal axis, curling the tail towards the head and then straightening the body. The ability to actively twist the tail along the longitudinal axis for terrestrial propulsion appears to be unique to this genus. A sister species to A. arnoldorum, Praealticus labrovittatus, the crenulate-lipped rockskipper, also comes onto land to feed, but does not exhibit tail twisting during terrestrial locomotion. Fifteen individuals of A. arnoldorum and five individuals of P. labrovittatus moved freely in a glass aquarium, and were filmed with two orthogonally-oriented high-speed video cameras (250 fps). Midline splines were obtained and the coordinates transformed into three-dimensions using a custom program written in Matlab. Preliminary results suggest that A. arnoldorum utilize a combination of suction and capillary adhesion to stick to smooth surfaces while climbing. I hypothesize that tail twisting significantly increases terrestrial locomotor capability in A. arnoldorum. I will compare crawling locomotion in both species and will also present preliminary results comparing tail morphology between these two species which may permit active tail twisting in propulsive locomotion.