Collaborative Research: Adaptation of daphniids to digestion resistant resources

无脊椎动物对藻类的消耗是所有水生生态系统--湖泊、溪流和海洋--食物网中一个关键但知之甚少的环节。以前的研究表明，这些无脊椎动物食草动物的生产力，以及包括渔业在内的其他食物网的生产力，往往受到藻类食物质量的限制。在湖泊的开阔水域，藻类食物质量的一个主要决定因素是它们在食草动物的肠道中对消化的抵抗力。虽然人们早就知道，一些藻类可能会毫发无损地穿过小型无脊椎动物的肠道，但这种防御机制与食物网生态和食草动物进化生物学的广泛相关性一直被忽视。这项研究的主要目标将是检查食草动物消化抗性藻类的生理学，量化食草动物物种克服消化防御的能力差异的程度，并通过实验测试这种食草动物-藻类相互作用对水生食物网功能的重要性。一般的研究方法是将重点放在一种容易研究的生物体上，这种生物体也是湖泊开放水域中的主要捕食者：达夫尼虫。利用养殖的和天然的不同消化阻力的藻类，这项研究将测量摄食率、肠道处理、呼吸、同化和生长。从幼年到成年，将在不同的动物年龄对几个物种进行研究，这些物种代表了达夫尼虫中多样性的广度。最后，将通过在一个天然湖泊中的大规模围栏实验来检验放牧动物消化生理变化的生态后果。本实验将对食草动物物种进行操作，并验证食草动物的消化生理影响湖中食草动物和藻类种群动态的假说。本研究在探索生态关键食草动物种群的摄食和肠道加工的多样性，以及这种生理多样性对食物网功能的影响方面具有创新性。尽管它们在湖泊的开阔水域中扮演着主要的食草动物的角色，但人们对甲虫如何消化自然界中的藻类知之甚少。同样，虽然我们知道藻类对消化的抵抗力不同，但对食草动物如何适应这种防御机制却知之甚少。本研究的总体目标是通过研究制约水生生态系统中食草动物和藻类相互作用的生态和进化生理学来解决这两个方面的不足。本研究强调了本科生和研究生在生理学和生态学界面上的培养。拟议的工作还将继续在一个主要是本科生的机构和一个研究密集的野战站之间建立研究和培训伙伴关系，并让本科生全年参与将生物体生理学与食物网的结构和功能联系起来的实验室和实地研究。

The consumption of algae by invertebrates is a critical but poorly understood link in the food webs of all aquatic ecosystems: lakes, streams and oceans. Previous research has shown that the productivity of these invertebrate grazers, and hence the productivity of the rest of the food web including the fisheries, is often limited by the quality of the algal food. In the open water of lakes, a major determinate of algal food quality is their resistance to digestion while in the gut of the grazer. While it has been long known that some algae may pass unharmed through the guts of small invertebrates, the broad relevance of this defense mechanism to food web ecology and to the evolutionary biology of the grazers has been ignored. Major goals of this research will be to examine the physiology of grazer digestion of resistant algae, to quantify the extent to which grazer species vary in ability to overcome digestion defenses, and to experimentally test the importance of this grazer-algae interaction to the functioning of aquatic food webs. The general research approach will be to focus on an easily studied organism that is also a major grazer of algae in the open water of lakes: daphniids. Using both cultured and natural algae that differ in digestion resistance, this research will measure feeding rate, gut processing, respiration, assimilation, and growth of daphniid grazers. Several species, representing the breadth of diversity within the daphniids, will be studied at various animal ages from juvenile to adult. Finally, the ecological consequences of variation in grazer digestive physiology will be examined using a large-scale enclosure experiment in a natural lake. The experiment will manipulate grazer species and test the hypothesis that grazer digestive physiology influences population dynamics of grazers and algae in lakes.This research is innovative in exploring the diversity of feeding and gut processing in an ecologically key group of grazers, and in testing the consequences of this physiological diversity to food web function. Despite their role as dominate grazers in the open water of lakes, there is little understanding of how daphniids digest algae in nature. Similarly, while it is known that algae vary in digestion resistance, there is little understanding of how grazers adapt to such defenses. It is the general aim of this research to address these two deficiencies by studying the ecological and evolutionary physiology that constrains grazer-algal interactions in aquatic ecosystems.Training of undergraduates and graduates at the interface of physiology and ecology is emphasized in this research. The proposed work will also continue a research and training partnership between a primarily undergraduate institution and a research-intensive field station, and provide for year-round undergraduate involvement in laboratory and field studies that link organism physiology to the structure and function of food webs.