Chemotactic tube-foot responses of the spongivorous sea star Perknaster fuscus to organic extracts of sponges from McMurdo Sound, Antarctica

Abstract

Studies were continued to investigate the ability of secondary metabolites sequestered in Antarctic sponges to cause feeding deterrent responses (tube foot retractions) in a common predator of Aritarctic sponges, the sea star Perknaster fuscus. Lipophilic (dichloromethane/methanol) and hydrophilic (methanol/water) extracts of 15 new species of Antarctic marine sponges were tested for their ability to induce sustained tubefoot retraction. One additional species, Cinchyra antarctica, was re-tested from a previous study because we discovered a colour morph that was of comparative interest. Employing established protocols, sponge extracts were imbedded in silicone and presented to an extended tube-foot on the tip of a glass rod. Extracts of ten of the 15 new species of sponges (67%) caused significantly longer tube-foot retractions than controls. Among all sponges tested, significant tube-foot retraction activity was primarily associated with dichloromethane/methanol extracts (eleven sponge species or colour morphs), while significant tube-foot retraction activity was less common in response to methanol/water extracts (three sponges species or colour morphs). Both lipophilic and hydrophilic extracts from the sponges C. antarctica (yellow morph) and Scolymastia joubini elicited significant tube-foot retraction activity, suggesting that more than one compound from these speciesmight elicit tube-foot retractions in P. fuscus. Overall these findings lend considerable support to the hypothesis that there has been significant evolutionary selection for chemical defences among Antarctic marine sponges in McMurdo Sound, in contrast to earlier biogeographic selection models that predicted low levels of chemical defences in polar marine invertebrates.