120.4 Saturday, Jan. 7 The apical sensory organ is not required for the initiation of metamorphosis in larvae of Hydroides elegans NEDVED, B.T.*; ASAHINA, A.Y.; HAFIELD, M.G.; Univ. Hawaii; Univ. Hawaii; Univ. Hawaii firstname.lastname@example.org
Larvae of the serpulid polychaete Hydroides elegans, like most lophotrochozoans, possess an anteriorly-positioned apical sensory organ (ASO). Larvae of H. elegans are induced to metamorphose by bacterial biofilms and, prior to settlement, explore inductive surfaces by repeatedly touching the ASO and surrounding tissue onto biofilms. Due to this behavior it has been assumed that the ASO acts as a chemosensory organ and its stimulation is required for the initiation of metamorphosis. However, there is little evidence to support this hypothesis. In this study, a targeted laser-ablation system was utilized to destroy the ASO in competent larvae of H. elegans. After ablation, larvae were split into three treatment groups: (1) larvae challenged with bacterial biofilm; (2) larvae challenged only with filtered seawater (FSW); and (3) larvae kept to assess cellular damage within the ASO. The percentage of metamorphosis was determined for larvae in treatments 1 and 2 after 24 h. For larvae in treatment 3, FMRF-amide antibodies and confocal laser scanning microscopy (CLSM) were used to assess the damage caused by the laser ablations. There are numerous FMRF-amide immunoreactive cells in the ASO and surrounding tissues. The presence or absence of these cells was used to estimate damage caused by the laser. Five or six laser pulses caused extensive damage to the ASO and surrounding cells but did not inhibit metamorphosis. These data suggest that the ASO is not the site for the perception of stimulatory cues and that other chemosensory cells in the episphere of larvae must act as the receptors of metamorphic cues.