HSIEH, S.T.; Harvard University: Mechanics of terrestrial locomotion in aquatic, amphibious, and terrestrial blennies

The amphibious Pacific leaping blenny, Alticus arnoldorum, exhibits a diverse terrestrial locomotor repertoire including jumping, crawling, and climbing. All of these movements involve a stereotyped movement of placing the tail beside the head, twisting the tail axially, and then pushing off with the lateral side of the tail to straighten the body. Despite possessing no obvious modifications to its body plan, it moves about effectively and rapidly on land, whereas its fully-aquatic relatives do not. Six genera from a monophyletic clade of blennies were selected for comparison. For ease of analysis, genera were grouped according to the amount of time spent on land into �terrestrial� (Alticus and Andamia), �amphibious� (Praealticus), and �aquatic� (Istiblennius, Entomacrodus, and Blenniella). I expected that axial tail twisting would enhance terrestrial locomotor capability in regards to jump stability; and that terrestrial and amphibious blennies would adhere more readily to smooth surfaces than do aquatic blennies. Blennies were startled to jump and their movements were filmed with a high-speed video camera at 500 fps and 1/2000s shutter. Adhesion was quantified by tilting individual blennies in a clear, Plexiglas box. Results show terrestrial blennies adhered more readily to a smooth surface than did the aquatic blennies. Also, axial tail twisting is limited to terrestrial and amphibious blennies which exhibited greater stability during jumps. Aquatic blennies pushed off the surface with the ventral surface of their tails and tended to spin axially during jumps. Ongoing analyses of body dynamics and ground reaction forces will address how jumping blennies generate force and maintain body stability.