Variables determining buoyancy in juvenile mink frogs, Rana septentrionalis, with comparisons to boreal chorus frogs, Pseudacris triseriata maculata, and wood frogs, Rana sylvatica

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Rondeau, Sylvie L.
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Aquatic organisms must optimize buoyancy to minimize energy expenditure in locomotion and in holding position. This study examined the hydrostatic role of lungs in the buoyancy regulation of larval 'Rana septentrionalis' in relation to its mode of life. Wet weights in air and water, gas volume, gas-free volume and dry weight were determined in various larval stages. A newly-defined, dimensionless buoyancy index was then calculated in terms of the animal's gas-free specific gravity and gaseous lift factor (ratio of included gas volume to gas-free volume). Field and laboratory observations showed larval and early metamorphic stages to be benthic, inactive, and resident in shallow water near shore in dense vegetation. In summary, buoyancy is closely linked to mode of life. For species inflating their lungs during early larval stages and inhabiting permanent ponds with an abundance of predators, the ability to maintain optimal negative buoyancy levels by regulating lung volume is a highly adaptive trait. (Abstract shortened by UMI.)