Collaborative Research: Anti-Predator Defenses of Marine Hydroids: Alternative Strategies, Biogeographic Patterns, and Ecological Implications

最优化理论认为，将资源优先分配给一种形式的防御应该发生在一系列替代防御中，从而产生单一的主流防御战略。尽管这个想法已经被广泛接受，但很少有研究提供严格的证据来支持防御系统之间的权衡概念，特别是在海洋系统中。PI的最新数据表明，由于刺状细胞器(线虫囊)和次生代谢物可能是替代防御措施(Stachowicz和Amp；Lindquist，1997年出版)，海洋水生动物可能提供一个很好的系统，用来测试最优理论及其对海洋生物防御策略演变的影响。使用经过验证的实验方法来区分防御线虫和化学防御水生生物，研究人员将严格检验防御性线虫和次生代谢物不会在海洋水生动物中共存的假设，从而代表替代防御策略。他们还将通过检查整个息肉适口性、线虫囊类型、化学适口性和营养参数之间的相关性来检验第二个假说，即水生动物不会因为低营养价值而受到保护。在化学防御明显的地方，他们将分离和结构特征具有威慑性的代谢物，以便他们可以检查水生动物之间的次生生物合成多样性相对于它们的系统发育、种内化学变异性的模式和规模、化合物定位和元素组成，因为它们与水生生物反捕食者策略和化学防御的潜在成本有关。此外，PIS将进行一套单独的现场和实验室研究，研究外来反捕食者防御对其他营养水平的生态影响。具体地说，他们将测试这一假设，即线虫防御的水生动物的表观动物丰度和多样性将低于化学防御的水生动物，因为刺痛的线虫会损害相关的表观动物。由于水生动物构成了整个表层动物群落赖以生存的“基础”，一些水生动物防御措施对表层动物的负面影响可能会对群落组成和这些生态系统的功能产生重要影响。他们将在三个不同的水生动物群上测试这些假设：(1)温带大西洋(NC)；(2)加勒比海(FL)；(3)温带(但季节性较少)东太平洋(CA北部)，允许对水生动物防御捕食者的生物地理进行比较。这项研究的结果将提供一个概念框架，用于比较目前似乎主要依赖化学防御的更广泛的线虫群体(如柳珊瑚和软珊瑚等八珊瑚)与似乎依赖线囊防御的海葵和硬珊瑚之间化学防御和线囊防御的生态和进化后果。

Optimality theory suggests that preferential allocation of resources to one form of defense should occur among a series of alternative defenses resulting in a single prevailing defense strategy. Although this idea has been widely accepted, few studies provide rigorous evidence to support the notion of trade-offs among defense systems, particularly in marine systems. The PI's recent data indicate that, with stinging organelles (nematocysts) and secondary metabolites as likely alternative defenses (Stachowicz & Lindquist 1997, in press), marine hydroids may provide an excellent system with which to test optimality theory and its implications for the evolution of defensive strategies among marine organisms. Using proven experimental methodologies to distinguish between nematocyst-defended and chemically-defended hydroids, The investigators will rigorously test the hypothesis that defensive nematocysts and secondary metabolites do not co-occur in marine hydroids and thus represent alternative defensive strategies. They will also test a second hypothesis that hydroids are not also defended by low nutritional value by examining correlations among whole polyp palatability, nematocyst types, chemical palatability, and nutritional parameters. Where chemical defenses are apparent, they will isolate and structurally characterize deterrent metabolites so that they can examine secondary biosynthetic diversity among hydroids relative to their phylogeny, patterns and scales of intraspecific chemical variability, compound localization, and elemental composition as they relate to hydroid anti-predator strategies and potential costs of the chemical defense.In addition the PIs will conduct a separate set of field and laboratory studies examining the ecological implications of altemative anti-predator defenses for other trophic levels. Specifically, they will test the hypothesis that epifauna abundance and diversity will be lower among nematocyst defended hydroids than among chemically defended hydroids because stinging nematocysts can harm associated epifauna. Because hydroids form the "foundation" on which an entire epifaunal community depends, negative effects of some hydroid defenses on epifauna could have important consequences for community composition and the function of these ecosystems. They will test these hypotheses on 3 different hydroid faunas: (1) the temperate Atlantic (NC); (2) the Caribbean (FL); and (3) the temperate (but less seasonal) eastern Pacific (northern CA), allowing biogeographic comparisons of hydroid defenses against predators. The results of this study will provide a conceptual framework for comparing ecological and evolutionary consequences of chemical vs. nematocyst defenses among broader groups of cnidarians that presently seem to rely largely on chemical defenses (e.g., octocorals like gorgonians and soft corals) vs. those such as sea anemones and hard corals that seem to rely on nematocysts for defense.