HERBIVORE RESISTANCE TO SEAWEED CHEMICAL DEFENSE - THE ROLES OF MOBILITY AND PREDATION RISK
HERBIVORE RESISTANCE TO SEAWEED CHEMICAL DEFENSE - THE ROLES OF MOBILITY AND PREDATION RISK
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DOI：
10.2307/1937456
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发表时间：
1994-07-01
期刊：
影响因子：
4.8
通讯作者：
HAY, ME
中科院分区：
文献类型：
--
作者：
DUFFY, JE;HAY, ME
许多小型定居食草动物（中食动物，如片足类，小螃蟹，腹足类）是耐海藻次生代谢物，阻止更大，更移动的食草鱼类。此外，专门的中食动物在生活在产生这些化合物的海藻上时，减少了鱼类的捕食。在这项研究中，我们测试的假设，通才，而不是专家，中食草动物也可以受益于减少捕食时，他们占据化学防御植物。其次，通过比较三种同域分布的通才端足类动物对具有化学防御能力的褐海藻网地藻的反应，我们评估了这样一种假设，即不受草食动物大小或专门摄食的干扰，草食动物的低移动性选择了对海藻化学防御的耐受性（长鳍钝头鱼，和Gamamruts mucronatus）。对网地亚门化学防御的反应在这三种端足类动物之间的差异与先前研究的远缘鱼类和中食动物之间的差异一样大，并支持了这种假说认为，移动的较少的食草动物应该对植物的化学防御最有耐受力。在实验室实验中，A. longimana移动很少，优先消耗网地藻超过其他海藻，并不受所有网地藻次生代谢产物测试。与此相反，G. mucronatus是活跃的，它不吃网地藻，和三个网地藻次生代谢产物中的两个阻止它的放牧。在该领域的片足类的分布表明，这些喂养模式影响片足类的捕食风险。A.在鱼类最丰富的季节，longimana在网球藻上达到最高丰度，而网球藻对杂食性鱼类捕食者来说是不好吃的。同时，高活性的C. mucronatus减少到几乎灭绝。就像G。mucronatus、尖吻拟谷盗A. valida被两种Dictyota次级代谢产物所阻遏，不吃Dictyota，在鱼类丰富时消失。longimana在占据具有化学防护的海藻时比占据可口的海藻时更不容易受到鱼类捕食。这种减少捕食主要是由于减少了频率遇到捕食者时，片足类动物的化学防御植物。当我们实验均衡遇到率之间的杂食性pinfish（Lagodon rhomboides）和海藻Dictyota pedialis和石莼curvata（不好吃和可口，分别为pinfish）在实验室中，端足类动物占据这两种植物以类似的速度被吃掉。与此相反，当活的端足类动物被贴在石莼和网壳藻上并部署在固定的位置时，端足类动物只在网壳藻上存活。在后一个实验中，大量的鱼在石莼上吃草，表明石莼上的片足类动物的生存状况不佳，这可能是由于鱼类频繁光顾，导致了对这种植物的片足类动物的更大的检测和/或偶然摄入。觅食的鱼类很少光顾网藻也可以解释A. longimana的持久性通过这个化学防御海藻的夏天，而两个石莼相关的端足类动物急剧下降。这些结果（1）证实了与化学防御植物的联系可以减少对通才以及专门食草动物的捕食，（2）表明，对化学防御植物的优先摄食最有可能是定居的中食动物，因为低流动性增强了利用化学防御海藻作为鱼类捕食避难所的能力。
Numerous small sedentary herbivores (mesograzers such as amphipods, small crabs, and gastropods) are resistant to seaweed secondary metabolites that deter larger, more mobile herbivorous fishes. In addition, specialist mesograzers experience reduced predation from fishes when living on seaweeds that produce these compounds. In this study we tested the hypothesis that generalist, as opposed to specialist, mesograzers can also benefit from reduced predation when they occupy chemically defended plants. Secondly, we assessed the hypothesis that low herbivore mobility, unconfounded by herbivore size or specialized feeding, selects for tolerance of seaweed chemical defenses, by comparing responses to the chemically defended brown seaweed Dictyota menstraulis of three sympatric, generalist amphipods that differ in mobility (Ampithoe longimana, Ampithoe valida, and Gamamruts mucronatus).Responses to Dictyota's chemical defenses varied as much among these three amphipods as among the phylogenetically distant fishes and mesograzers studied previously and supported the hypothesis that less mobile herbivores should be most tolerant of plant chemical defenses. In laboratory experiments, A. longimana moved little, preferentially consumed Dictyota over other seaweeds, and was unaffected by all Dictyota secondary metabolites tested. In contrast, G. mucronatus was active, it did not feed on Dictyota, and two of three Dictyota secondary metabolites deterred its grazing. Distribution of amphipods in the field suggested that these feeding patterns affected amphipod risk of predation. A. longimana reached its highest abundance on Dictyota, which is unpalatable to omnivorous fish predators, during the season when fish are most abundant. At the same time, the highly active C. mucronatus decreased to near extinction. Like G. mucronatus, A. valida was deterred by two Dictyota secondary metabolites, did not eat Dictyota, and disappeared when fishes were abundant.Experiments confirmed that A. longimana was less vulnerable to fish predation when occupying a chemically defended seaweed than when occupying a palatable seaweed. This decreased predation resulted primarily from a decreased frequency of encounter with predators when amphipods were on chemically defended plants. When we experimentally equalized encounter rates between omnivorous pinfish (Lagodon rhomboides) and the seaweeds Dictyota menstrualis and Ulva curvata (unpalatable and palatable, respectively, to pinfish) in the laboratory, amphipods occupying these two plants were eaten at similar rates. In contrast, when live amphipods were affixed to Ulva and Dictyota and deployed in the held, amphipods survived only on Dictyota. Heavy fish grazing on Ulva in the latter experiment suggests that poor survival of amphipods on Ulva may have resulted from greater detection and/or incidental ingestion of amphipods on this plant, due to frequent visitation by fishes. Infrequent visitation of Dictyota by foraging fish also may explain A. longimana's persistence through the summer on this chemically defended seaweed while the two Ulva-associated amphipods declined precipitously. These results (1) confirm that association with chemically defended plants can reduce predation on generalist, as well as specialist, herbivores and (2) suggest that preferential feeding on chemically defended plants is most likely for sedentary mesograzers because low mobility enhances the ability to exploit chemically defended seaweeds as refuges from fish predation.