Settlement and metamorphosis of Styela canopus Savigny larvae in response to some neurotransmitters and thyroxin

The larvae of ascidian Styela canopus Savigny were treated with epinephrine, norepinephrine, L-DOPA, GABA and thyroxin to test the ability of these compounds to induce or inhibit larval settlement and metamorphosis. The results showed that epinephrine, norepinephrine and L-DOPA at the concentration of 1μmol/dm 3 induced larval settlement and metamorphosis in S. canopus, with short exposure (1 h) to 1 μmol/dm 3 of L-DOPA inducing rapid settlement. In contrast, GABA at the concentrations of 0.1 ～100.0 μmol/dm 3 significantly inhibited the settlement and metamorphosis of S. canopus larvae. In addition, thyroxin at 1～50 μg/dm 3 had no effect on larval settlement and metamorphosis in S. canopus. These results suggest the importance of neurotransmitters in the settlement and metamorphosis of S. canopus larvae.