Eicosanoids and Egg-Hatching Synchrony in Barnacles: Evidence Against a Dietary Precursor to Egg-Hatching Pheromone

Abstract

The boreoarctic barnacle, Semibalanus balanoides (= Balanus balanoides) (L.), has the ability to synchronize the release of its nauplii with the spring phytoplankton bloom, thereby ensuring that the larvae can start their planktotrophic development successfully. Hatching is induced by an egg-hatching pheromone (an hydroxy fatty acid) released by the adult. Here, the possibility that the pheromone is an excretory metabolite of dietary eicosapentaenoic acid (EPA) is examined. Egg hatching could be induced by feeding gravid adult barnacles on Skeletonema costatum, but neither a concentrated culture of this diatom nor cell-free culture medium induced egg hatching in vitro. Following a 15-min incubation of EPA in seawater, a product with egg hatching activity was obtained, presumably by autooxidation. Egg hatching was not induced by feeding barnacles with lecithin liposomes containing EPA. Likewise, radiolabeled egg-hatching pheromone was not released by adult barnacles that had been fed with [14C]EPA liposomes. Egg-hatching pheromone was not released by barnacles that were actively feeding on S. costatum prior to egg-hatching. The production of egg-hatching pheromone was inhibited in vitro and in vivo by lipoxygenase inhibitors. Taken together, the results suggest that egg-hatching pheromone is not an excretory metabolite but is derived from EPA released from membrane phospholipid and acted upon by a lipoxygenase. The nature of the stimulus to precursor fatty acid release has yet to be established, but a link with molting appears tenuous.