Induction of Settlement of Larvae of the Sea UrchinHolopneustes purpurascensby Histamine From a Host Alga

Abstract

Larvae of the Australian sea urchin Holopneustes purpurascens are induced to settle and metamorphose (termed settlement herein) by a water-soluble compound produced by the red alga Delisea pulchra, the main host plant of new recruits. The settlement cue for H. purpurascens had previously been identified as a floridoside-isethionic acid complex, and this paper presents new evidence correcting that finding. The actual settlement cue produced by D. pulchra was isolated from the polar extract by cation-exchange chromatography and identified as histamine, using one- and two-dimensional nuclear magnetic resonance spectrometry. The chemical identity of the cue was confirmed by gas chromatography-mass spectrometry (GC-MS) and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Synthetic histamine and histamine at 4.5 microM isolated from D. pulchra both induced rapid settlement in 80%-100% of the larvae of H. purpurascens. Lower concentrations of histamine (0.9-2.3 micro M) induced larval settlement, but this response varied from 0%-90%. The histamine content of two host plants of H. purpurascens--D. pulchra and Ecklonia radiata--and of four other common species was quantified using GC-MS. D. pulchra had the highest histamine content, which is consistent with H. purpurascens recruiting to this species. Histamine was also detected in the seawater surrounding these host algae. This is the first time that a settlement cue has been quantified in the habitat of a marine organism.

An α 2 -macroglobulin-like protein is the cue to gregarious settlement of the barnacle Balanus amphitrite

“…To the best of our knowledge, the identity of only one inductive cue, histamine in the sea urchin Holopneustes purpurescens (11), is unequivocal. The fact that this cue was originally claimed to be a complex of the sugar floridoside and isethionic acid (12) (with which histamine coeluted) only serves to emphasize the difficulties associated with characterizing invertebrate settlement cues.…”

Chemical Defenses: From Compounds to Communities

“…Relatively few natural settlement cues have been structurally characterized, owing to their low concentrations and the challenges of isolating them from seawater. One of the few ecologically relevant settlement cues that have been isolated for marine invertebrates is histamine, which induces metamorphosis in the sea urchin Holopneustes purpurascens (Swanson et al, 2004) and is a ubiquitous neuralsignaling molecule in many organisms. Molecules found on the benthos that are similar to neurotransmitters such as GABA and L-dopa can act as settlement inducers for molluscan larvae (Morse et al, 1979;Coon et al, 1985;Morse, 1985).…”

Locating the barnacle settlement pheromone: spatial and ontogenetic expression of the settlement-inducing protein complex ofBalanus amphitrite

“…The difficulties associated with identifying such cues have been described (Zimmer & Butman 2000;Hadfield & Paul 2001;Steinberg et al 2001). As a result only one inductive cue has been fully characterized in an ecological context, namely histamine, which induces settlement of the sea urchin, Holopneustes purpurescens, on host algae (Swanson et al 2004). Likewise, the inhibition of surface colonization of algae by halogenated metabolites (Steinberg et al 2001;Paul et al 2006) are the only cases, to our knowledge, where inhibitory compounds have been shown to be released at their site of action at environmentally realistic concentrations.…”