Regulation of Ureotely in Batrachoidid Fishes

蝙蝠鱼中尿素的调节 Patrick J. Walsh, M. Danielle McDonald 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氨作为其主要废物。氨最终是有毒的，主要是对大脑有毒，因此鱼类和其他水生物种一旦产生氨，就会立即将其排出体内，其有害影响会立即被周围“无限”体积的水稀释。然而，当动物进化到在陆地上生活，并且没有周围水环境的稀释作用时，它们需要采取替代方法来清除体内的这种毒素。因此，陆生动物（从氨）制造并排泄替代废物（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并通过尿液将其排出；制造和排泄尿素的过程被称为“ureotely”。令人惊讶的是，近年来，沃尔什和同事发现，生活在美国东南部海湾和河口的一种常见海洋鱼类——海湾蟾蜍（Opsanus beta）是这一规则的例外，它在某些压力环境下选择排泄尿素而不是氨。更不寻常的是，蟾蜍在一次脉冲中通过鳃排出所有尿素，该脉冲仅持续几个小时。因此，该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，并了解其这样做的生态和进化原因，以及为什么它会脉冲尿素排泄。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，因此可以合理地假设，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。这些目标将通过几种不同的方法来实现。在该研究的一部分中，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，重点关注肝脏中产生尿素的酶。在研究的第二部分中，将对尿素如何在鳃中排泄进行生理学研究。在研究的第三部分中，现场实验将用于测试以下假设：尿素生产对鱼类的生存很重要，因为鱼类生活在氨浓度高的环境中，和/或尿素排泄的脉冲有助于它更好地通过化学伪装自己免受捕食者的侵害。最后，将在 DNA 水平上进行研究，了解该鱼类家族中物种的亲缘关系有多密切，然后比较采用或不采用这种应对压力模式的家族成员。通过这些“家谱”研究，PI 打算确定这些物种的进化过程中是否出现了这种特征，从而为蟾蜍产生和排泄尿素的原因提供了额外的线索。 这项研究总体上更广泛的重要性在于，它将有助于了解水生生物在个体和代际时间尺度上能够以多快的速度适应不断变化的压力环境，这项工作最终可能成为复杂生理特征进化的案例研究。随着我们的环境因人类影响而发生变化，此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，必须通过昂贵的手段去除以保持鱼类健康，因此这些研究可能会提出更有效的鱼类和其他水生物种养殖方法。这项研究将通过重要的国际合作（与来自其他 5 个国家的科学家）进行。此外，由于迈阿密大学是一所少数族裔服务机构，PI 将能够从少数族裔/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.