Functional and Evolutionary Ecology Laboratory, Stazione Zoologica Anton Dohrn, Naples, Italy.
Ecotoxicology. 2010 Mar;19(3):493-511. doi: 10.1007/s10646-009-0434-y.
Traditionally, diatoms have been regarded as providing the bulk of the food that sustains the marine food chain and important fisheries. However, this view was challenged almost two decades ago on the basis of laboratory and field studies showing that when copepods, the principal predators of diatoms, feed on certain diatom diets, they produce abnormal eggs that either fail to develop to hatching or hatch into malformed (i.e. teratogenic) nauplii that die soon afterwards. Over the years, many explanations have been advanced to explain the causes for reproductive failure in copepods and other marine and freshwater invertebrates including diatom toxicity, or nutritional deficiency and poor assimilation of essential compounds in the animal gut. Here we review the literature concerning the first possibility, that diatoms produce cytotoxic compounds responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment. The cytotoxic compounds responsible for these effects are short chain polyunsaturated aldehydes (PUAs) and other oxygenated fatty acid degradation products such as hydroxides, oxo-acids, and epoxyalcohols (collectively termed oxylipins) that are cleaved from fatty acid precursors by enzymes activated within seconds after crushing of cells. Such toxins are suggested to have multiple simultaneous functions in that they not only deter herbivore feeding but some also act as allelopathic agents against other phytoplankton cells, thereby affecting the growth of competitors, and also signalling population-level cell death and termination of blooms, with possible consequences for food web structure and community composition. Some oxylipins also play a role in driving marine bacterial community diversity, with neutral, positive or negative interactions depending on the species, thereby shaping the structure of bacterial communities during diatom blooms. Several reviews have already been published on diatom-grazer interactions so this paper does not attempt to provide a comprehensive overview, but rather to consider some of the more recent findings in this field. We also consider the role of diatom oxylipins in mediating physiological and ecological processes in the plankton and the multiple simultaneous functions of these secondary metabolites.
传统上，人们认为硅藻为海洋食物链和重要渔业提供了大部分食物。然而，这种观点在近二十年前就受到了挑战，当时的实验室和实地研究表明，当桡足类动物——硅藻的主要捕食者——以某些硅藻为食时，它们会产生异常的卵子，这些卵子要么无法发育孵化，要么孵化成畸形（即致畸）的无节幼体，随后很快死亡。多年来，人们提出了许多解释来解释桡足类动物和其他海洋和淡水无脊椎动物生殖失败的原因，包括硅藻毒性、营养缺乏以及动物肠道中必需化合物的不良吸收。在这里，我们回顾了有关第一个可能性的文献，即硅藻产生细胞毒性化合物，导致生长抑制和致畸活性，通过诱导不良繁殖，可能破坏未来几代食草动物的生存。导致这些影响的细胞毒性化合物是短链多不饱和醛（PUA）和其他含氧脂肪酸降解产物，如氢氧化物、氧代酸和环氧化醇（统称为氧代脂类），这些化合物是由细胞破碎后几秒钟内激活的酶从脂肪酸前体中切割出来的。这些毒素被认为具有多种同时的功能，不仅阻止草食动物进食，而且一些毒素还作为化感物质对抗其他浮游植物细胞，从而影响竞争者的生长，还发出种群水平的细胞死亡和繁殖结束的信号，这可能对食物网结构和群落组成产生影响。一些氧代脂类也在驱动海洋细菌群落多样性方面发挥作用，根据物种的不同，产生中性、正性或负性相互作用，从而在硅藻繁殖期间塑造细菌群落的结构。已经有几篇关于硅藻-食草动物相互作用的综述文章，因此本文不试图提供全面的概述，而是考虑该领域的一些最新发现。我们还考虑了硅藻氧代脂类在调节浮游生物生理和生态过程中的作用，以及这些次生代谢物的多种同时功能。
