Aboral localization of responsiveness to a metamorphic neuropeptide in the planula larva of Acropora tenuis

Abstract

Planula larvae of the coral genus Acropora ini-tiate metamorphosis in response to microorganisms on the undersea substrate. Since planulae move forward in the direction of the aboral side, it is supposed that initial metamorphic signaling localizes on this side of planula. We dissected planulae of Acropora tenuis into fragments perpendicularly to the oral-aboral axis, and tested their response to a metamorphosis-inducing neuropeptide. Aboral 1/3 fragments metamorphosed in response to the neu-ropeptide with high efficiency while most oral 2/3 frag-ments did not. The results suggest that the tissue in the aboral 1/3 region receives the metamorphic neuropeptide and releases downstream signals to complete metamor-phosis of the oral side in A. tenuis larvae. In addition, oral fragments gained a metamorphic ability in several days, revealing regeneration of the aboral tissue.