Sea hares—soft-bodied, football-shaped relatives of snails that live underwater—protect themselves from predators by ejecting a chemical cocktail that tastes like a seafood platter, a new study shows. The finding is the first demonstration of such food-mimicking, dubbed phagomimicry, used as a defense, though the tactic may be widespread.
When threatened, some sea hares release two secretions: ink, which has a deep red or purple hue, and opaline, a sticky white substance. One theory holds that the ink acts as a smokescreen, blinding predators' senses. Another posits that the opaline, colored by the ink, serves as a crude physical mimic of the hare, distracting the predator.
The new study, led by neuroethologist Charles Derby of Georgia State University in Atlanta, shows that in addition to those potential other functions, the secretions mimic food. To test the secretions' effects on a predator, the researchers put Aplysia californica sea hares into tanks with spiny lobsters. After nabbing the sea hares, the lobsters appeared dazed and confused by the secretions and allowed the hares to creep away. The lobsters often tried to grab and ingest the surrounding water—the same reaction they showed to squid juice—or would dig in the soil, as if looking for food, the researchers report today in Current Biology.
Chemical analysis showed that both the ink and opaline have high levels of urea, ammonium, and amino acids—especially taurine, which is found in some energy drinks and is also a potent stimulator of hunger in crustaceans. The mixture's stimulation of the lobsters' chemical-sensing neurons may even be strong enough to completely overload the predator's nervous system, the researchers speculate.
Derby says the defense is so effective, "I would be surprised if phagomimicry did not show up in other animals." His group is now looking for similar tactics in snails, octopuses, and squids.
Neuroethologist Heather Eisthen of Michigan State University in East Lansing agrees that the defense may be widespread, adding that it may serve as a new model for examining the neurological component of predator-prey interactions.