PORTER, S.S.; University of Washington: Bacteria as cues for metamorphosis in the colonial ascidian Botrylloides violaceus

The viviparous colonial ascidian Botrylloides violaceus (Styelidae) releases non-feeding tadpoles which rapidly acquire competence. Within seconds after release, swimming larvae are capable of attachment to a substrate and the initiation of metamorphosis, though the process can be delayed for hours. The average time to metamorphosis of larvae in sterile-filtered seawater was compared between larvae exposed to a suspension of a purified bacteria or left untreated. Two species of bacteria isolated from adult ascidian tunics decreased the average time to metamorphosis as compared to untreated larvae, one species of bacteria isolated from decomposing algae increased the average time to metamorphosis and six bacterial species from various sources did not influence the time to metamorphosis. KCl-elevated seawater (50 mM) was also found to decrease the average time to metamorphosis. Despite the rapid initiation of metamorphosis in B. violaceus, the bacterial species present on a substrate may mildly induce or inhibit metamorphosis and may therefore affect the distribution of new recruits.