Research


Environmental Physiology

Research in my lab is focused on osmoregulation and respiration in aquatic animals. I am interested in how animals cope with changes in the environment. We study the interaction between the animal and its environment from early development to adults in fish and amphibians. For example, we are interested in how the microenvironment of trout embryos impacts their growth and development. We are exploring how salamander embryos within a jelly mass are influenced by position, as oxygen levels are lower and ammonia levels are higher near the center of the jelly mass. We are particularly interested in how amphibious fish alter their anatomy and physiology to cope with an aerial environment. Specific projects are described in more detail below.

 

Mangrove rivulus in a harsh variable environment

The self-fertilizing, hermaphroditic killifish Kryptolebias marmoratus inhabits mangrove forests of the southern US and South/Central America. These tiny fish (~100mg) tolerate a wide range in water temperature, pH, salinity, oxygen, hydrogen sulfide, as well as prolonged air exposure. We are interested in several aspects of their extremophilic nature. What strategies are used to cope with life out of water? Recently we discovered that killfish excrete gaseous NH3 during air exposure, a nitrogen excretion strategy similar to terrestrial gastropods and isopods. We have used microelectrodes to follow changes in the composition of the cutaneous boundary layer. We have measured cutaneous blood vessel reactivity following air exposure using video microscopy. Blood flow appears to be redistributed when fish leave water. We have discovered that gill morphology is plastic. When air exposed, a cell mass grows between secondary lamellae (interlamellar cell mass, ILCM), but when they return to water the gills shed the ILCM. This reduction in functional gill surface area may prevent excessive water loss and/or help to support the delicate lamellar structures out of water. We have investigated iono- and osmoregulation when mangrove killfish are air exposed, particularly focusing on cell composition of the gills and skin. We are also interested in behavioural differences between genotypically identical fish. Why do some fish emerse more frequently than others? These are just some of the avenues of investigation that are underway to more fully understand the remarkable physiological capabilty of these versatile fish.

 

Physiology of salmonid development

Salmonid embryos generally have a protracted development encased in an egg shell or chorion. During this embryonic development, yolk proteins and amino acids provide fuel for the growing embryo. Protein catabolism yields the potentially toxic end-product ammonia. We have studied ammonia and urea metabolism and excretion in rainbow trout embryos. We have cloned several genes involved in the urea cycle and examinded ontogenic expression. More recently we have followed the metabolic events associated with hatching, as well as studied the influence of hypoxia on embryo movement and metabolism. We have measured oxygen gradients in the water boundary layer next to the chorion and in the perivitelline fluid. Oxygen gradients are influenced by water flow, water oxygen concentrations and developmental stage. We are now interested in the water conditions within natural salmonid redds to understand more fully how local variations in water chemistry impact early development.

 

Ammonia excretion

Although fish generate and excrete ammonia, elevated ammonia in the environment can be a deadly poison. We are studying pathways involved in ammonia detoxification. Brain glutamine synthetase is an important enzyme involved in reducing ammonia levels. Alternative nitrogen excretion pathways may also be effective in reducing the uptake of ammonia and/or eliminating excess tissue ammonia. We have recently isolated a new class of ammonia transporters belonging to the Rh family of proteins. Rh genes are upregulated in the gills and skin of mangrove killfish and trout in response to ammonia stress. Work is underway to understand how these proteins function and if they are involved in ammonia excretion against the gradient.