Meeting Abstract

P1.82  Thursday, Jan. 3  Phototactic Responses of Larvae from the Marine Sponge Xestospongia proxima MOBLEY, A.S.*; BUSUTIL, L.; LEYS, S.P.; DIAZ, M.C.; COLLIN, R.; THACKER, R.W.; Univ. of Alabama at Birmingham; Instituto de Oceanolog�a, Cuba; Univ. of Alberta, Canada; Museo Marino de Margarita, Venezuela; STRI Bocas del Toro Research Station, Panama; Univ. of Alabama at Birmingham thacker@uab.edu

In August 2007, the Training in Tropical Taxonomy program at the Smithsonian Tropical Research Institute’s Bocas Research Station sponsored a two-week course on the Taxonomy and Ecology of Caribbean Sponges. During the course we examined the phototactic behavior of larvae from the marine sponge Xestospongia proxima. Previous studies suggest that negative phototaxis in sponge larvae is generated by the responsiveness of a tuft of long posterior cilia. While other sponge larvae are known to be positively phototactic, the mechanism by which swimming direction is coordinated in those species is not yet understood. Since X. proxima hosts large populations of photosynthetic, unicellular cyanobacteria, we hypothesized that the larvae would be positively phototactic, and that the ciliary response would be opposite to that of negatively phototactic larvae. We incubated X. proxima larvae in petri dishes, with half of the dish covered by black plastic, and placed a light source over the uncovered half of the dish. Initially, all larvae were positively phototactic; however, the percentage of larvae displaying negative phototaxis increased steadily to 50% after 36 hours. As predicted, larval cilia quickly responded to changes in light intensity, straightening as light diminished, and bending as light increased. These results demonstrate that larvae of diverse sponge species coordinate behavioral responses to light using the same mechanism.