Meeting Abstract
Diving tetrapods are a biologically diverse group; however, they are all under similar constraints: oxygen limitation and increased hydrostatic pressure at depth. Adipose tissue is an interesting tissue to study, due to its physiologically important roles (e.g. metabolic energy storage, regulation of energy balance and thermoregulation) and because nitrogen (N2) is 5 times more soluble in fat than in blood, creating a potential N2 sink in animals consistently diving to depth. We examined the adipose tissue of diving tetrapods (3 species of seabirds, 3 sp. of sea turtles, 3 sp. of pinnipeds and 10 sp. of cetaceans), focusing on how adipose tissue structure allows these animals to cope with the physiological demands of diving. Adipose tissue microvessel density and diffusion distance were used to evaluate the comparative potential for aerobic activity (i.e. O2 delivery). Long duration divers (i.e. beaked whales, > 120 min.) had relatively lower microvessel density (2.6 ± 0.5%) and greater diffusion distances (44.0 ± 13 µm), compared to short duration divers (e.g. eider ducks, < 2 min.; 4.4 ± 1.7% and 24.7 ± 9.9 µm). We hypothesize that beaked whale adipose tissue characteristics may function to minimize energetic costs during diving. Previous research indicates that lipid composition (lipid classes and short chained fatty acids [FA]) in some whales is an important factor determining N2 solubility. However, there was no relationship between FA profile and N2 solubility in the animals studied; species with similar FA profiles had different N2 solubility values. The 3D structure of intact lipid molecules may elucidate the complex interactions between O2, N2 and lipid. Future studies should consider these interactions to better understand the physiological adaptations in diving animals.
