Regulation of Ureotely in Batrachoidid Fishes

迈阿密大学直到最近，人们普遍认为鱼类和其他水生物种在进食后排泄的主要废物是氨。氨最终是有毒的，主要是对大脑有害，所以鱼和其他水生物种一旦产生氨就会将体内的氨排出体外，而氨的有害影响会立即被周围“无限”的水所稀释。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，它们需要采用其他方法来清除体内的这种毒素。因此，陆生动物（从氨中）产生和排泄替代废物（尿素和尿酸），它们可以将这些废物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，以尿液的形式排出它们；制造和排泄尿素的过程被称为“尿素排泄”。令人惊讶的是，近年来，沃尔什和他的同事们发现，生活在美国东南部海湾和河口的一种常见的海鱼，海湾蟾鱼（Opsanus beta），是这个规则的一个例外，在特定的压力环境下，它们选择排泄尿素而不是氨。更不寻常的是，蟾蜍鱼在一次脉冲中排出所有的尿素，持续时间只有几个小时。因此，这个研究项目的目标是了解这种鱼类是如何产生和排泄尿素的，并了解它这样做的生态和进化原因，以及为什么它会脉冲排泄尿素。制造尿素的能力需要大量的能量，否则这些能量就会被花在躲避捕食者、繁殖等方面，所以我们有理由认为，制造和排泄尿素的能力在某种程度上是自然选择的青睐，并有助于鱼在压力条件下生存和繁殖的能力。这些目标将通过几种不同的方法来实现。研究的一部分将使用生化和分子生物学技术来了解鱼在压力下如何从制造氨转向制造尿素，重点关注肝脏中生产尿素的酶。在研究的第二部分，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，实地实验将用于测试以下假设：尿素的产生对鱼的生存很重要，因为鱼生活在一个高氨浓度的环境中，或者尿素排泄的脉冲有助于它更好地在化学上伪装自己，不被捕食者发现。最后，研究将在DNA水平上进行，以了解该鱼类家族中物种的亲缘关系有多密切，然后比较该家族中采用或不采用这种应对压力模式的成员。通过这些“家谱”研究，pi打算确定这些物种在进化过程中这种特征出现或不出现的位置，为为什么蟾鱼产生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有多快，这项工作最终可能会成为复杂生理特征进化的案例研究。由于人类的影响，我们的环境发生了变化，这类信息变得越来越有价值。此外，由于氨是水产养殖中最重要的废物副产品之一，必须通过昂贵的方法去除以保持鱼类健康，这些研究可能会提出更有效的养殖鱼类和其他水生物种的方法。这项研究将在重要的国际合作下进行（与来自其他5个国家的科学家合作）。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。

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.