The ontogenetic changes in the thermal properties of blubber from Atlantic bottlenose dolphinTursiops truncatus

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Abstract
In Atlantic bottlenose dolphins Tursiops truncatus, both the thickness and lipid content of blubber vary across ontogeny and across individuals of differing reproductive and nutritional status. This study investigates how these changes in blubber morphology and composition influence its thermal properties. Thermal conductivity (W m–1 deg.–1, where deg. is °C) and thermal insulation (m2 deg. W–1) of dolphin blubber were measured in individuals across an ontogenetic series (fetus through adult, N=36), pregnant females (N=4) and emaciated animals (N=5). These thermal properties were determined by the simultaneous use of two common experimental approaches, the heat flux disc method and the standard material method. Thickness, lipid and water content were measured for each blubber sample. Thermal conductivity and insulation varied significantly across ontogeny. Blubber from fetuses through sub-adults was less conductive (range=0.11–0.13±0.02 W m–1 deg.–1) than that of adults (mean=0.18 W m–1 deg.–1). The conductivity of blubber from pregnant females was similar to non-adult categories, while that of emaciated animals was significantly higher (0.24 ± 0.04 W m deg.–1) than all other categories. Blubber from sub-adults and pregnant females had the highest insulation values while fetuses and emaciated animals had the lowest. In nutritionally dependant life history categories, changes in blubber's thermal insulation were characterized by stable blubber quality (i.e. conductivity) and increased blubber quantity (i.e. thickness). In nutritionally independent animals, blubber quantity remained stable while blubber quality varied. A final, unexpected observation was that heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface, a pattern not observed in control materials. This apparent ability to absorb heat, coupled with blubber's fatty acid composition, suggest that dolphin integument may function as a phase change material.