The physiology of polyploid fish

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The objective of this research is to determine how polyploidy affects physiological processes in vertebrates, using fish as experimental models. Polyploids have more than the normal (diploid) two chromosome sets in their genomes: triploids have three, tetraploids have four, etc. Polyploidy has played an important role in vertebrate evolution by providing redundant genes that can mutate without causing lethality. A consequence of polyploidy is increased cell volume in cells for which the nucleus occupies a relatively large proportion of total cell volume, resulting in reduced cell numbers, reduced cellular and nuclear surface area per unit volume, and increased intracellular diffusion distances. These changes likely impose physiological constraints on individual animals that counterbalance the long-term (evolutionary) genetic benefits of polyploidy. This research aims to determine the nature of such constraints, thereby helping to assess the broader significance of polyploidy as a driver of evolution. The focus of this research is on how polyploidy affects the cardio-respiratory system, by examining red blood cells (RBCs) directly, as well as the capillaries and gill lamellae (the sites of respiratory gas exchange, where RBCs travel through the narrowest passages) and the heart (which needs to provide sufficient pressure to drive blood through the circulatory system). A variety of techniques will be used, including light, electron and confocal microscopy as well as Doppler flow analysis, both in vivo and in vitro. The research will be conducted with both salmonids - relatively large, easily cultured fish of importance for aquaculture and fisheries management - and zebrafish - a popular aquarium fish that has become one of the most important model species for research on vertebrate development. Five undergraduate and two graduate students will be trained with funding from this grant. In addition to the basic knowledge gained from this research, it will benefit aquaculture and fisheries management in Canada, as triploidy is seen as a valuable tool for creating reproductively sterile populations of fish. Understanding the limitations of triploids will lead to improvements in their husbandry and will ensure that their welfare is properly considered.