Cosima Ciuhandu

PhD student, Zoology MSc (Guelph) BSc (Guelph) Contact Info: Department of Zoology University of British Columbia 6270 University Blvd. Vancouver, British Columbia Canada, V6T 1Z4 Tel: (604) 822-5990 FAX: (604) 822-2416 ciuhandu@zoology.ubc.ca

O2 and CO2/H+ Chemoreception in Fish

Air breathing has evolved independently several times and has given rise to phylogenetically diverse groups of bimodally breathing fish. These animals are facultative air breathers that can exchange gases with both water and air. Many are related to lineages that have gone on to give rise to obligate air breathers that now depend solely on air for gas exchange. From the perspective of respiratory control, these developments have been accompanied by the need to control ventilation at multiple sites, utilizing different media (water versus air) and requiring feedback from different groups of receptors. This is compounded by the fact that different sites generally play slightly different roles in O2 uptake (greater in the air breathing organ than the gills) versus CO2 excretion (greater at the gills than the air breathing organ). Finally, with increasing dependence on air breathing for gas exchange comes a switch from the need to acquire oxygen as the primary respiratory drive to a need to eliminate carbon dioxide. Proper control of breathing under these changing circumstances requires feedback from chemoreceptors that monitor the effects of ventilating the different exchange surfaces on oxygen uptake and CO2 excretion and the goal of my research is to determine the location, distribution, stimulus modalities and response characteristics of oxygen and carbon dioxide chemoreceptors in facultative and obligate air breathing fish.

It is our hope that this will provide some phylogenetic insight into the evolution of chemosensory mechanisms associated with the evolution of air-breathing. To begin my investigation, I will examine the magnitude of cardio-respiratory responses in fish subjected to graded and acute hypoxia and hypercarbia to address such questions as 1) Are there O2/CO2 thresholds at which input from one group of receptors switches from stimulating gill ventilation to stimulating air breathing, or is air-breathing stimulated by a different group of receptors? and 2) To what extent are the responses due to input from receptors sensitive to changes in the external versus the internal environment? In this way I hope to document the relative roles of internal- vs. external-sensing oxygen/carbon dioxide receptors in the production of gill versus air-breathing ventilatory responses. In the process I hope to examine evidence for the evolution of central CO2 receptors.