Gas exchange, ionoregulation and acid-base balance in fish; their interactions and the evolution of complex physiological systems.

点击翻译按钮获取中文摘要

The long-term goal of my research program remains to understand the interaction between gas-exchange, ion regulation and acid-base balance in fish (that represent half of all vertebrates) during environmental acclimation/adaptation and development. In this proposal I will investigate three areas: 1) Teleosts (95% of all fishes) possess a very pH-sensitive hemoglobin (Root effect), where a reduction in pH in specialized structures greatly enhances O2 delivery to the eye and swimbladder which is thought to be associated with the extensive adaptive radiation of teleosts. However, we have discovered a mechanism where a mild acid-base disturbance in the presence of a Root effect and plasma accessible carbonic anhydrase (CA) can double or even triple tissue O2 unloading. We will further investigate the mechanisms involved to permit this system, it's ubiquity among species and its functional significance on whole animal performance. 2) While the gills are the primary site for blood pH regulation in fish, they become limited in this capacity at high CO2 levels. Fish that can tolerate high CO2 appear to abandon blood pH regulation and instead completely defend pHi of important tissues, a fundamentally different pattern from other vertebrates which we have termed preferential pHi (ppHi) regulation. We will investigate the cellular mechanisms for preferential pHi regulation and investigate the hypothesis that it is an embryonic trait in vertebrates that was retained in many fish species (which we propose represents an exaptation for air-breathing in fish) but lost in other adult vertebrates. 3) The vertebrate gill is generally thought to have evolved primarily to enhance gas exchange and secondarily for other processes, such as ionoregulation, acid-base balance and ammonia excretion. However, we have shown that during early development in rainbow trout and lamprey, the gills take on a dominant role for ionoregulation long before gas exchange. We will characterize gill function in basal developing fishes (sturgeon and lamprey), basal chordates (amphioxus and larval tunicates) and a protochordate (acorn worm) at rest and in environments that challenge gas exchange (hypoxia and temperature), ionoregulation (altered water ion levels) and acid-base challenges (elevated water CO2) to shed insight on the plasticity of gill function and provide potential insight into the early evolution of the physiological (non-feeding) role of the chordate gill. The proposed experiments are interdisciplinary, spanning the range of molecular, cellular, and whole animal. They are designed to test novel hypotheses and findings will add significantly to our understanding of the evolution of complex physiological systems. All 3 areas have the potential to alter textbook dogma. Overall this program will train 1 PDF, 5 Ph D, 5 MSc students and 15 undergraduate students.