Pteropod abduction as a chemical defence in a pelagic antarctic amphipod

Abstract

THIS study documents an example of an invertebrate that cannot defend itself chemically (an amphipod) increasing its chances of survival by capturing and carrying a species that can (a pteropod). Although chemical defences are found in a wide variety of marine invertebrates^1–4, few studies have established the extent to which these chemicals will deter predators^5–7, and even fewer have investigated how one organism might exploit another's chemical defence to protect itself^8–10. These chemicals are usually ingested or sequestered in the host's tissue^8,9. Several species indiscriminately decorate themselves with potentially toxic organisms or are passively fouled with chemically defended organisms^11,12. These seem to be commensalisms or sometimes mutualisms. Our example has benefits and costs for the carrier, but only costs to the captive. The antarctic marine food web not only has a variety of chemically defended organisms^13–16, contrary to earlier predictions^17–19, but has at least one unusual symbiosis that makes use of noxiousness.