Regulation of Ureotely in Batrachoidid Fishes

蝠鲼科鱼类中尿素的调控

• 批准号: 0455904
• 负责人: M. Danielle McDonald
• 金额: $ 49.64万
• 依托单位: University of Miami
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-02-01 至 2010-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0455904&HistoricalAwards=false
• 关键词: Regulation; Ureotely; Batrachoidid; Fishes

Regulation of Ureotely in Batrachoidid Fishes Patrick J. Walsh, M. Danielle McDonald University of MiamiUntil recently, it has been commonly accepted knowledge that fish and other aquatic species excrete ammonia as their main waste product following a meal. Ammonia is ultimately toxic, primarily to the brain, so fish and other aquatic species rid their bodies of ammonia as soon as it is produced, and its harmful effects are immediately diluted by the "infinite" volume of the surrounding water. However, when animals evolved to live on land, and did not have the diluting effects of a surrounding water environment, they needed to adopt alternate means of ridding their bodies of this toxin. So, terrestrial animals make (from ammonia) and excrete alternative waste products (urea and uric acid), which they can store in their bodies at higher concentrations without harmful effect until they are able to consume enough water with which to excrete them in their urine; the process of making and excreting urea is known as "ureotely". Surprisingly, in recent years, Walsh and colleagues have discovered that a common marine fish living in the bays and estuaries of the Southeastern US, the gulf toadfish (Opsanus beta), is an exception to this rule, opting to excrete urea instead of ammonia under certain stressful circumstances. Even more unusual, the toadfish excretes all of its urea in a single pulse lasting only a few hours across the gills. Thus the goals of this research project are to understand how this fish species is able to make and excrete urea, and to understand the ecological and evolutionary reasons for why it does so, and why it pulses its urea excretion. The ability to make urea requires a great deal of energy, which would otherwise be spent on predator avoidance, reproduction, etc., so it is reasonable to assume that the ability to make and excrete urea is somehow favored by natural selection, and contributes to the fish's ability to survive stressful conditions and propagate.These goals will be approached with several different methods. In one portion of the study biochemical and molecular biology techniques will be used to understand how the fish shifts from making ammonia to making urea during stress, focusing on enzymes of urea production in the liver. In a second part of the study, physiological studies on how urea is excreted at the gill will be performed. In the third part of the study, field experiments will be used to test the hypotheses that urea production is important to the survival of the fish because the fish lives in an environment with high ammonia concentration, and/or that the pulses of urea excretion help it to be better at chemically camouflaging itself from predators. Lastly, studies will be conducted at the level of DNA to see how closely related species are within this family of fishes, and then compare members of the family that either do or do not adopt this mode of coping with stress. Through these "family tree" studies the PIs intend to determine where in the evolution of these species this trait has appeared or not, giving additional clues as to why the toadfish makes and excretes urea. The overall broader importance of the research is that it will help to understand how rapidly aquatic organisms are able to adapt to changing stressful environments on both an individual and generational time scale, and this work may eventually serve as a case study in the evolution of a complex physiological trait. This type of information becomes more and more valuable as our environment changes due to human influence. Furthermore, since ammonia is one of the most important waste byproducts in aquaculture that must be removed by expensive means to keep fish healthy, these studies may potentially suggest more efficient ways to culture fish and other aquatic species. This research will take place with significant international collaboration (with scientists from 5 other countries). Furthermore, since the University of Miami is a Minority Serving Institution, the PI will be able to recruit student researchers from minorities/underrepresented groups.

帕特里克J.沃尔什，M.直到最近，人们普遍认为鱼和其他水生物种在进餐后排出氨是它们的主要废物。氨最终是有毒的，主要是对大脑有毒，所以鱼和其他水生物种一旦产生氨就会排出体内，其有害影响立即被周围“无限”体积的水稀释。然而，当动物进化到生活在陆地上，并且没有周围水环境的稀释作用时，它们需要采用替代方法来消除体内的这种毒素。因此，陆生动物（从氨）制造和排泄替代废物（尿素和尿酸），它们可以以更高的浓度储存在体内而不会产生有害影响，直到它们能够消耗足够的水以将它们排泄到尿液中;制造和排泄尿素的过程被称为“ureotely”。令人惊讶的是，近年来，沃尔什和同事们发现，一种生活在美国东南部海湾和河口的常见海鱼，海湾蟾鱼（Opsanus beta），是这一规则的例外，在某些压力环境下选择排泄尿素而不是氨。更不寻常的是，蟾鱼通过鳃在一次脉冲中排出所有的尿素，仅持续几个小时。因此，本研究项目的目标是了解这种鱼类如何能够制造和排泄尿素，并了解为什么它这样做的生态和进化原因，以及为什么它脉冲尿素排泄。制造尿素的能力需要大量的能量，否则这些能量将用于躲避捕食者，繁殖等，因此，我们有理由认为，制造和排泄尿素的能力在某种程度上受到自然选择的青睐，并有助于鱼类在压力条件下生存和繁殖的能力。2这些目标将通过几种不同的方法实现。在研究的一部分，生物化学和分子生物学技术将用于了解鱼在应激期间如何从制造氨转变为制造尿素，重点是肝脏中尿素生产的酶。在研究的第二部分中，将进行关于尿素如何在鳃处排泄的生理学研究。在研究的第三部分，现场实验将被用来测试的假设，尿素生产是重要的鱼的生存，因为鱼生活在高氨浓度的环境中，和/或尿素排泄的脉冲帮助它更好地从捕食者的化学防御。最后，我们会从DNA的层面研究，看看这一科鱼类的亲缘关系有多近，然后比较采用或不采用这种应激方式的成员。通过这些“家谱”研究，PI打算确定在这些物种的进化过程中，这种特征是否出现过，从而为蟾鱼制造和排泄尿素提供额外的线索。 这项研究的总体重要性在于，它将有助于了解水生生物在个体和世代时间尺度上适应不断变化的压力环境的速度，这项工作最终可能成为复杂生理特征进化的案例研究。这种类型的信息变得越来越有价值，因为我们的环境变化，由于人类的影响。此外，由于氨是水产养殖中最重要的废物副产品之一，必须通过昂贵的手段去除以保持鱼类健康，这些研究可能会提出更有效的方法来养殖鱼类和其他水生物种。这项研究将与来自其他5个国家的科学家进行重要的国际合作。此外，由于迈阿密大学是一个少数民族服务机构，PI将能够从少数民族/代表性不足的群体中招募学生研究人员。