Ontogenetic changes in the thermal and buoyant properties of Atlantic Bottlenose Dolphin (Tursiops truncatus) blubber

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Robin C. Dunkin (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Ann Pabst

Abstract: The thermal properties of cetacean blubber are influenced by its lipid content and thickness. In Atlantic bottlenose dolphins (Tursiops truncatus), both these features vary across ontogeny and with reproductive and nutritional status and, thus, may result in ontogenetic differences in blubber’s insulative quality. Lipid and water contents, and thermal conductivity and thermal insulation values of Atlantic bottlenose dolphin blubber were measured across fetal through adult life history categories (n = 36), and in pregnant females (n=4) and emaciated animals (n = 5). The thermal conductivities of deep and superficial blubber layers were also measured. Thermal conductivity varied significantly across ontogeny. Fetal through sub-adult life history categories had significantly lower mean thermal conductivity values (0.11 to 0.13 ± 0.01 W/m°C) than adults (0.18 ± 0.02 W/m°C). The conductivity of blubber from pregnant females was similar to non-adult categories, while that of emaciated animals was significantly higher than all other categories. The conductivity of superficial blubber was 37% higher than that of deep blubber. Across life history categories, the conductivity of superficial blubber was similar, while that of deep blubber was significantly greater in emaciated animals. Thermal insulation varied significantly across life history categories. Sub-adults and pregnant females had the highest insulation while fetuses and emaciated animals had the lowest insulation across life history categories. The insulation of neonates and juveniles was similar to that of adult dolphins. Heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface and this difference in heat flux was significantly correlated with blubber thickness. This pattern was not observed in control materials, polystyrene foam and white pine wood. In nutritionally dependant life history categories, changes in blubber’s thermal insulation resulted from changes in blubber thickness (i.e. quantity) and not thermal conductivity (i.e. quality). Conversely, in nutritionally independent animals, blubber quantity remained stable while blubber quality varied. Differences in conductivity through the blubber depth support the characterization of deep blubber as more insulative and metabolically active layer of lipid deposition and mobilization. Finally, blubber’s composition and its ability to absorb heat suggest that it likely is a phase change material. Blubber is the hypertrophied hypodermis of cetaceans composed primarily of adipocytes and structural fibers. Because the density of lipid is less than that of seawater, blubber has the potential to contribute to positive buoyancy. The blubber of Atlantic bottlenose dolphins (Tursiops truncatus) varies both in thickness and lipid content across ontogeny and with reproductive and nutritional status. This variation in blubber’s quantity and quality may significantly influence its contribution to buoyancy. To measure blubber’s buoyant force, its density was measured volumetrically and its volume was calculated at two body sites (trunk and tailstock), across an ontogenetic series of bottlenose dolphins and in pregnant females and emaciated animals. Lipid and water content were measured to correlate compositional changes with differences in blubber’s buoyant force. The density of blubber from the trunk region (mean ± standard error = 1043.1 ± 13.18 kg/m3) was similar to that of the tailstock (mean = 1077.1 ± 24.17 kg/m3) and these were not significantly different than the density of seawater (1026 kg/m3). Density in these regions was also similar between life history categories. Blubber volume in the trunk and tailstock regions increased over two orders of magnitude between fetuses and adults. The buoyant force of trunk blubber was similar across categories (mean = –0.91 ± 8.85N) and was not significantly different from neutral buoyancy (0N). Trunk blubber of emaciated animals was twelve times more negatively buoyant than that of adults. The buoyant force of tailstock blubber was similar between life history categories (mean = –0.30 ± 1.83 N). For groups with a sufficient sample size for statistical analyses (fetus, neonate, and juvenile), mean total buoyant force of blubber was 0.61 ± 7.45 N and was not significantly different between these groups. Despite significant differences in lipid content and volume across life history categories, blubber’s contribution to buoyancy remained neutral. Because this body compartment is nearly 25% of total body mass, it may be essential for this tissue to be neutrally buoyant. Pregnancy and emaciation can significantly influence blubber’s contribution to buoyancy and may impose additional locomotor costs associated with overcoming a positive or negative vertical force. viii

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Adipose tissues--Research, Blubber--Research, Bottlenose dolphin--Physiology, Bottlenose dolphin--Research
Bottlenose dolphin -- Physiology
Bottlenose dolphin -- Research
Blubber -- Research
Adipose tissues -- Research

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