The Ancient Chemistry of Avoiding Risks of Predation and Disease

Abstract

Illness, death, and costs of immunity and injury strongly select for avoidance of predators or contagion. Ants, cockroaches, and collembola recognize their dead using unsaturated fatty acids (e.g., oleic or linoleic acid) as ''necromone'' cues. Ants, bees, and termites remove dead from their nests (necrophoric behavior) whereas semisocial species seal off corpses or simply avoid their dead or injured (necrophobic behavior). Alarm and avoidance responses to exudates from injured conspecifics are widespread. This involves diverse pheromones, complex chemistry and learning. We hypothesized that necromones are a phylogenetically ancient class of related signals and predicted that terrestrial Isopoda (that strongly aggregate and lack known dispersants) would avoid body fluids and corpses using fatty acid ''necromones.'' Isopods were repelled by crushed conspecifics (blood), intact corpses, and alcohol extracts of bodies. As predicted, the repellent fraction contained oleic and linoleic acids and authentic standards repelled several isopod species. We further predicted a priori that social caterpillars (lacking known dispersants) would be repelled by their own body fluids and unsaturated fatty acids. Both tent caterpillars and fall webworms avoided branches treated with conspecific body fluid. Oleic and linoleic acids were also strongly avoided by both species. Necromone signaling appears widespread and likely traces to aquatic ancestors pre-dating the divergence of the Crustacea and Hexapoda at least 420 million years ago.

Do Termites Avoid Carcasses? Behavioral Responses Depend on the Nature of the Carcasses

“…In general, intact conspecific carcasses were thought to elicit weaker responses from healthy nestmates compared to crushed carcasses [25]. However, this notion is not supported by the data from the oven-killed carcasses (with an intact body) from the present study.…”

Predatory cannibalism in Drosophila melanogaster larvae

“…Fourth, although we cannot demonstrate its adaptive nature, the phenotypic plasticity of mouth hooks in response to cannibalistic diet is reminiscent of mouth part plasticity in facultatively cannibalistic amphibian larvae 21 . Finally, in many species cues released by injured conspecifics represent a warning against potential danger (for example, predators) and induce avoidance 48,49 . In contrast, Drosophila larvae show attraction to injured conspecifics; similar behaviour in crickets is associated with cannibalism under natural conditions 7 .…”

Volatile and Semivolatile Compounds in Gray Catbird Uropygial Secretions Vary with Age and Between Breeding and Wintering Grounds

“…Interestingly, in a comparison of C14 to C24 unsaturated carboxylic acids, oleic acid was the most effective ovipositional repellant in Culex quinquefasciatus (Hwang et al, 1984). Oleic acid is sometimes called the "smell of death" because of its role as a molecule that signals death in arthropods thereby eliciting an avoidance behavior (Yao et al, 2009). We suggest that such a signal would be beneficial to catbirds and other songbirds, which are constantly subject to attack by arthropod pests to which they are exposed.…”