In the sea slug’s defense against lobsters, confusion is key

Like many other marine creatures, Aplysia, a common sea slug, enlists chemical defenses against its predators, but the mechanisms by which such chemical attacks actually work against their intended targets are not well understood by researchers. New work has now shown that such chemical defenses can involve modes of trickery that had not previously been appreciated as components of chemical defense.

When attacked by predatory spiny lobsters, sea slugs (also known as sea hares) release an inky secretion, termed ink and opaline, from a pair of glands. The new findings show that Aplysia’s defensive secretion includes a variety of chemicals that together comprise a multi-pronged attack on the predator’s nervous system, resulting in the usurpation of its normal behavioral control system and a confused response that facilitates the slug’s ultimate escape.

The team of researchers conducting the study, Cynthia Kicklighter, Zeni Shabani, and Paul Johnson, led by Charles Derby of Georgia State University, discovered that in addition to containing unpalatable, aversive chemicals, Aplysia’s inky secretion contains large quantities of chemicals that are also found in the food of spiny lobsters and that indeed these chemicals serve to activate nervous-system pathways that control feeding behaviors of the lobster. The inky secretion also stimulates other behaviors in the lobster, including grooming and avoidance. Ironically, the slug’s ability to trick the lobster’s nervous system into activating feeding-associated behaviors succeeds, in combination with ink and opaline’s other effects, in distracting the lobster sufficiently to enable the slug’s successful evasion.

Because the set of behaviors stimulated by the slug’s secretions resemble activation of a feeding pathway, the researchers named this novel chemical defense “phagomimicry.” The stickiness of the slug’s secretions appears to contribute to long-lasting effects on the target despite the aqueous environment, enhancing the effectiveness of the slug’s defense.

Cynthia E. Kicklighter, Shkelzen Shabani, Paul M. Johnson, and Charles D. Derby: “Sea Hares Use Novel Antipredatory Chemical Defenses”