Ostariophysan alarm pheromones: Laboratory and field tests of the functional significance of nitrogen oxides

In laboratory and field-trapping studies, we exposed fathead minnows (Pimep hales promelas) and finescale dace (Chrosomus neogaeus) to hypoxanthine-3-N -oxide and a suite of structurally and functionally similar compounds in or der to determine if: (1) hypoxanthine-3-N-oxide functions as a chemical ala rm signal in ostariophysan fishes and (2) the purine skeleton, a structural component, or the nitrogen oxide, a functional component, or both act as t he molecular trigger in this chemical alarm signaling system. Minnows and d ace exhibited significant antipredator responses when exposed to conspecifi c skin extract or hypoxanthine-3-N-oxide (increased shoaling and decreased area use) and the functionally similar pyridine-N-oxide (increased shoaling ) but not to structurally similar molecules lacking a nitrogen oxide functi onal group or to a swordtail skin extract control. Field-trapping studies r evealed similar results. Traps labeled with fathead minnows skin extract, h ypoxanthine-3-N-oxide, or pyridine-N-oxide caught significantly fewer fish than did those labeled with distilled water. These data strongly suggest th at the nitrogen oxide functional group acts as the chief molecular trigger in the Ostariophysan alarm pheromone system and that, contrary to previous research, hypoxanthine-3-N-oxide may be one of several possible molecules t hat function as a chemical alarm signal. Here we report the first example o f a single functional group capable of eliciting a suite of behavioral resp onses.