Meeting Abstract
Unlike most tadpoles, Xenopus tadpoles feed by hovering mid water and pumping water through the branchial basket to filter food particles out of suspension. This requires lung-breathing to generate positive buoyancy throughout the larval period and tail beating to offset this buoyancy while feeding. In studying the ontogeny of both traits, we observed that Xenopus tails become increasingly whip-like in shape and behavior, meaning that they become tapered vertically, and their lateral undulations increase in both amplitude and wavelength as they travel to the tip. Measurements of fixed specimens indicated that tails usually become curved dorsally, though they can also curve ventrally or remain straight. Observations of living specimens confirmed that tail curvature is largely behavioral, rather than developmental, and that mature tadpoles appear to curve their tails dorsally when feeding to generate a weak but steady propulsive force that is directed more downward and less forward. Straight and ventrally curved tails are usually observed when the body is aligned horizontally at the top or bottom of the water column. Whip-like tails are rare in vertebrates, and are used for defense in lizards and hunting in thresher sharks. Vertical tail movement is also rare in in anamniotes, occurring in syngnathid fish and plethodontid salamanders with prehensile tails. We propose that Xenopus acquired this unique combination of developmental and behavioral traits to support feeding and defense as the whip-like tail is expected to focus predators’ attention on the posterior extremity of the body, and is easily regenerated.
