Blubber morphology in wild bottlenose dolphins (Tursiops truncatus) from the Southeastern United States: Influence of geographic location, age class, and reproductive state

Abstract

This study investigated blubber morphology and correlations of histological measurements with ontogeny, geography, and reproductive state in live, wild bottlenose dolphins (Tursiops truncatus) from the southeastern United States. Surgical skin-blubber biopsies (N=74) were collected from dolphins during capture-release studies conducted in two geographic locations: Charleston, SC (N=38) and Indian River Lagoon, FL (N=36). Histological analysis of blubber revealed stratification into superficial, middle, and deep layers. Adipocytes of the middle blubber were 1.6x larger in Charleston subadults than in Indian River Lagoon subadults (4,590+/-340 compared to 2,833+/-335 microm2 per cell). Charleston subadult dolphins contained higher levels of total blubber lipids than Charleston adult animals (49.3%+/-1.9% compared to 34.2%+/-1.7%), and this difference was manifested in more adipocytes in the middle blubber layer (19.2+/-0.9 compared to 14.9+/-0.5 cells per field). However, dolphins from Indian River Lagoon did not exhibit this pattern, and the adipocyte cell counts of subadults were approximately equal to those of the adults (16.0+/-1.4 compared to 13.4+/-0.8 cells per field). The colder year-round water temperatures in Charleston compared to Indian River Lagoon may explain these differences. Adipocytes in the deep blubber layer were significantly smaller in lactating and simultaneously pregnant and lactating animals compared to pregnant dolphins (840+/-179, 627+/-333, and 2,776+/-586 microm2 per cell, respectively). Total blubber lipid content and adipocyte size in the deep blubber of mothers with calves decreased linearly with calf length. Lactating females may utilize lipids from the deep blubber during periods of increased energetic demands associated with offspring care. This study demonstrates that ontogeny, geography, and reproductive state may influence morphological parameters such as structural fiber densities and adipocyte numbers and sizes, measured in bottlenose dolphin blubber.

Seasonal and Ontogenetic Variation in Subcutaneous Adipose Of the Bowhead Whale (Balaena mysticetus)

“…1 and 3). These patterns are similar to those observed in other nonarctic cetaceans; notably, bottlenose dolphins from the southern United States (Struntz et al, 2004;Montie et al, 2008). Deep blubber samples consist of the smallest adipocyte populations.…”

“…In regard to structure, little variation in connective tissue, adipocyte size, and adipocyte number amounts were detected in more external blubber layers, whereas greater variations in these traits were seen in more inner layers of fin whale (Balaenoptera physalus), harbor porpoise (Phocoena phocoena), and bottlenose dolphin (Tursiops truncatus) blubber (Aguilar and Borrell, 1990;Koopman et al, 1996;Struntz et al, 2004). Biochemical stratification in lipid composition occurs in the blubber of harbor porpoises between external and internal blubber layers (Koopman et al, 1996).Taken together, these studies have identified that more internal blubber layers are closely associated with lipid utilization, whereas more external layers are less dynamic and fulfill a primarily insulative and biomechanical function (Ackman et al, 1965;Koopman et al, 2002;Mau, 2004;Struntz et al, 2004;Montie et al, 2008). Histological and biochemical blubber parameters are related to environmental conditions to formulate hypotheses about developmental and environmental correlates of morphology.…”

“…Images were analyzed using ImageJ software (National Institutes of Health, MD) and the cell measurements were completed using the previously published protocols (Struntz et al, 2004;Montie et al, 2008). For each of the six blubber depths examined, a 1 mm 3 1 mm box was positioned over the center of a 2 mm 3 2 mm image.…”

“…Juvenile bowhead whales inhabit cold arctic waters and, owing to their smaller body size, possess a higher surface area to volume ratio. Larger, lipid-rich adipocytes (especially in intermediate and deep blubber layers where the most significant variations were detected) assist in providing adequate insulation Montie et al, 2008). Furthermore, juvenile bowheads feed less efficiently owing to shorter baleen plates after weaning Fig.…”

“…Blubber in most cetaceans is vertically stratified in both structure and lipid composition with variations occurring with depth within the tissue (Ackman et al, 1975a,b;Aguilar and Borrell, 1990;Koopman et al, 1996, Krahn et al, 2004Struntz et al, 2004;Montie et al, 2008). In regard to structure, little variation in connective tissue, adipocyte size, and adipocyte number amounts were detected in more external blubber layers, whereas greater variations in these traits were seen in more inner layers of fin whale (Balaenoptera physalus), harbor porpoise (Phocoena phocoena), and bottlenose dolphin (Tursiops truncatus) blubber (Aguilar and Borrell, 1990;Koopman et al, 1996;Struntz et al, 2004).…”