Surface sequestration of chemical feeding deterren

Authors: F Bruce Furrow Charles D Amsler James B McClintock Bill J Baker

Publish Date: 2003/06/12

Volume: 143, Issue: 3, Pages: 443-449

PDF Link

Abstract

Latrunculia apicalis is a spherically shaped demosponge that previous investigations have shown is rarely preyed upon by sea stars which are the dominant spongivores in antarctic benthic communities Prior studies have also demonstrated that L apicalis produces organic compounds that elicit a tube foot retraction response in the keystone spongivorous sea star Perknaster fuscus that can be used as a reliable assay for feeding deterrence L apicalis is known to contain discorhabdin alkaloids which serve among other roles as the source of its green coloration To assess the defensive nature of the discorhabdin alkaloids toward P fuscus we have determined discorhabdin G concentrations in discrete sponge layers and evaluated those concentrations in the P fuscus bioassay In discorhabdin Gbearing sponges we found a gradient of discorhabdin G that falls off rapidly toward the center of the sponge On average 52 of total discorhabdin G in a given sponge was found within 2 mm of the sponge surface Tube foot retraction responses to extracts from the surface tissues 0–2 mm depth of L apicalis were compared to those of an inner layer 8–10 mm depth and to a sample comprised of the same inner layer spiked with discorhabdin G at a concentration equivalent to that of the surface tissues Tube foot retraction response times to extracts of the surface layers and the spiked inner layers were not statistically different but were significantly greater than responses to the unaltered inner layer and controls These results support the predictions of the optimal defense theory as L apicalis sequesters its defensive chemistry discorhabdin G in its most vulnerable surface tissues where the likelihood of predation from sea stars is highest As antarctic sponges are generally preyed upon by extraoral feeding sea stars rather than deeper biting predators such as fish surface sequestration may be uniquely adaptive in sessile macroinvertebrates occurring in antarctic marine benthic environmentsField and laboratory assistance from Andy Mahon Katrin Iken Joanna Hubbard and Jill Baker is gratefully acknowledged Maggie Amsler provided valuable editorial assistance We are also grateful to Dr Robert Angus for advice on statistical analyses We wish to acknowledge Antarctic Support Associates Raytheon Polar Services Company and the Antarctic support services of the National Science Foundation for providing logistical support This research was facilitated by the generous support of the Office of Polar Programs of the National Science Foundation to CDA and JBM OPP9814538 to JBM OPP9530735 OPP0125181 and to BJB OPP9526610 OPP9901076 OPP0125152 The experiments in this paper comply with the current laws in the United States

Keywords: