COMPARISON OF METAMORPHIC INDUCTION IN HYDROIDS

摘要

Studies of hydroid metamorphosis have been primarily limited to 3 species: the athecate Hydractinia echinata and 2 thecates, Phialidium gregarium and Mitrocomella polydiademata. To determine if findings from studies on those species can be applied generally, the effects of various agents implicated in hydroid metamorphosis were examined in 2 additional athecates, Halocordyle disticha and Hydractinia symbiolongicarpus. As in all species studied to date, H. disticha and H. symbiodongicarpus can be induced with activators of protein kinase C (PKC) and cannot be induced by the Ca2+ ionophore A23187 (which was actually inhibitory in H. symbiolongicarpus). Unlike H. echinata and H. symbiolongicarpus, H. disticha can be induced by the permeabilizing agents saponin and dimethylsulfoxide. In addition, H. disticha and H. echinata are induced by ammonium chloride, but H. symbiolongicarpus is not. Whereas the thecates respond to PKC-activating phorbol esters in the absence of exogenous Ca2+ and in the presence of Ca2+ channel blockers, H. symbiolongicarpus does not respond to the PKC activator dioctanoylglycerol under these conditions. Further, planulae of thecates induced with CsCl in the presence of Ca2+ channel blockers metamorphose upon release from treatment, whereas those of H. symbiolongicarpus do not. These studies support a central role for PKC in control of hydroid metamorphosis, but suggest that interspecific differences do exist. [References: 33]