Collaborative Research: Parasite or partner? Causes and consequences of conditional outcomes in a cleaning symbiosis

几十年来，生态学家在生态系统和食物网的研究中一直关注竞争和捕食等拮抗相互作用。但近年来，物种之间的合作互动，即互惠关系，对生态系统的结构和功能同样重要，这一点已经变得很明显。传粉者和植物之间的互惠关系是一种广泛存在的互惠关系，这对农业系统具有重要的经济意义。然而，其他类型的互惠关系在自然界中普遍存在，但人们对它们知之甚少。该项目将研究一个涉及清洁互助的模型系统，这是一种物种相互作用，其中一种生物通过清洁另一种生物来喂养。这种共生关系涉及小龙虾和生活在小龙虾鳃上的小环节动物蠕虫。这种蠕虫通过吃附着在小龙虾鳃上的生物来清洁小龙虾的鳃；这对蚯蚓和小龙虾都有好处。然而，如果这些蠕虫相对于它们的食物来说数量过多，它们就会变成寄生虫，直接以小龙虾的鳃为食。这种从共生到寄生的转变并不是小龙虾-蠕虫系统所独有的。据推测，这种变化可能在自然界中广泛存在，是对某些环境变化的反应。本项目将通过实地和实验室实验来研究小龙虾-蠕虫模型系统，验证这一一般假设。该项目将研究物种行为和其他特征在维持相互作用在互利水平上的重要性，并探索环境背景如何塑造相互作用。该项目还将探索从共生到寄生对食物网和河流生态系统的其他部分的更广泛的影响。该项目具有广泛的影响；它是三所大学教员之间的合作，其中一所大学主要是本科院校。许多本科生将接受水生生态学方面的培训，并将参与团队结构的多年研究项目。一些研究生也将得到该项目的支持，并将通过与当地流域协会和大学推广项目的合作伙伴关系领导推广工作。

For decades, ecologists have focused on antagonistic interactions such as competition and predation in studies of ecosystems and food webs. But in recent years it has become apparent that cooperative interactions among species, i.e., mutualisms, can be equally important to ecosystem structure and function. One widespread mutualism is that between pollinators and plants, which is of major economic importance to agricultural systems. However, other types of mutualisms are prevalent in nature, but poorly understood. This project will study a model system involving a cleaning mutualism, a species interaction in which one organism feeds by cleaning another. The mutualism involves crayfish and small annelid worms, which live on the gills of crayfish. The worms clean the crayfish gills by feeding on organisms that attach to the gills; this benefits both the worms and the crayfish. However, if the worms become too abundant relative to their food, they can switch to act as parasites, feeding directly on the crayfish's gills. This shift from mutualism to parasitism is not unique to the crayfish-worm system. It has been hypothesized that such shifts may be widespread in nature in response to certain environmental changes. This project will test that general hypothesis using both field and laboratory experiments to study the crayfish-worm model system. The project will examine the importance of species behaviors and other traits in maintaining the interaction at mutually beneficial levels, and explore how the mutualism is shaped by environmental context. The project will also explore the broader consequences of a shift from mutualism to parasitism to the rest of the food web and stream ecosystem. This project has substantial broader impacts; it is a collaboration among faculty at three universities, one of which is a predominantly undergraduate institution. Many undergraduate students will be training in aquatic ecology, and will participate in team-structured, multi-year research projects. A number of graduate students will also be supported by this project, and will lead outreach efforts through partnerships with local watershed associations and university extension programs.