Hill Malcolm S, Hill April L
Biology Department, Fairfield University, Fairfield, Connecticut 06430, USA.
Biol Bull. 2002 Feb;202(1):86-95. doi: 10.2307/1543225.
The goal of the research presented here was to examine phenotypic plasticity exhibited by three morphotypes of the common Caribbean sponge Anthosigmella varians (Duchassaing & Michelotti). We were interested in examining the biotic (and, to a lesser extent, abiotic) factors responsible for branch production in this species. We also tested the hypothesis that the skeleton may serve an antipredator function in this sponge, focusing on vertebrate fish predators (i.e., angelfish) in this work. In transplant and caging experiments, unprotected forma varians replicates were immediately consumed by angelfish, while caged replicates persisted on the reef for several months. These findings support the hypothesis that predators (and not wave energy) restrict forma varians to lagoonal habitats. Branch production was not observed in A. varians forma incrustans when sponges were protected from predators or placed in predator-free, low-wave-energy environments. It is not clear from our work whether forma incrustans is capable of producing branches (i.e., whether branch production is a plastic trait in this morph). Additional field experiments demonstrated that A. varians forma varians increased spicule concentrations, compared to uninjured sponges, in response to artificial predation events, and A. varians forma rigida reduced spicule concentrations, compared to uncaged controls, when protected from predators. These findings indicate that spicule concentration is a plastic morphological trait that can be induced by damage, and that A. varians may be able to reduce spicule concentrations when environmental conditions change (e.g., in the absence of predators). The potential significance of inducible defenses and structural anti-predator defenses in sponges is discussed in relation to recent work on sponge chemical defenses.
本文所呈现的研究目标是考察常见的加勒比海绵Anthosigmella varians（迪沙桑与米凯洛蒂）的三种形态型所表现出的表型可塑性。我们感兴趣的是研究导致该物种分支产生的生物因素（以及在较小程度上的非生物因素）。我们还检验了这样一个假设，即骨骼在这种海绵中可能具有反捕食功能，在这项研究中重点关注脊椎动物鱼类捕食者（即神仙鱼）。在移植和笼养实验中，未受保护的forma varians复制品立即被神仙鱼吃掉，而笼养的复制品在珊瑚礁上存活了几个月。这些发现支持了这样的假设，即捕食者（而非波浪能量）将forma varians限制在泻湖栖息地。当海绵受到捕食者保护或放置在无捕食者、低波浪能量的环境中时，在Anthosigmella varians forma incrustans中未观察到分支产生。从我们的研究中尚不清楚forma incrustans是否有能力产生分支（即分支产生在这种形态中是否是一个可塑性特征）。额外的野外实验表明，与未受伤的海绵相比，Anthosigmella varians forma varians在人工捕食事件后增加了骨针浓度，而Anthosigmella varians forma rigida在受到捕食者保护时，与未笼养的对照相比，降低了骨针浓度。这些发现表明骨针浓度是一种可因损伤而诱导的可塑性形态特征，并且Anthosigmella varians在环境条件变化时（例如在没有捕食者的情况下）可能能够降低骨针浓度。本文结合近期关于海绵化学防御的研究，讨论了海绵中诱导性防御和结构性反捕食防御的潜在意义。
