Structural fiber reinforcement of keel blubber in harbor porpoise (Phocoena phocoena)

Abstract

This study investigated the functional morphology of the blubber that forms the caudal keels of the harbor porpoise (Phocoena phocoena). Blubber is a pliant biocomposite formed by adipocytes and structural fibers composed of collagen and elastic fibers. Caudal keels are dorsally and ventrally placed triangular wedges of blubber that define the hydrodynamic profile of the porpoise tailstock. Mechanical tests on carcasses demonstrate that when keels are bent, they strain nonuniformly along their lengths, with highest strains just caudal to the dorsal fin and lowest at the insertion of the flukes. Therefore, caudal keels undergo nonuniform longitudinal deformation while maintaining a stable, triangular cross-sectional shape. Polarizing and transmitted light microscopy techniques were used to investigate blubber's 3D fiber architecture along the length of the dorsal keel. The triangular cross-sectional shape of the keel appears to be maintained by structural fibers oriented to act as tensile stays. The construction of the blubber composite is regionally specific :structural fiber densities and diameters are higher in the relatively stiff caudal region of the keel than in the more deformable cranial keel region. The orientations of structural fibers also change along the length of the keel. Cranially, no fibers are oriented along the long axis, whereas a novel population of longitudinally oriented fibers reinforces the keel at the insertion of the flukes. Thus, differences in the distribution and orientation of structural fibers contribute to the regionally specific mechanical properties of the dorsal keel.

Topographical variation in lipid content and morphological structure of the blubber in the striped dolphin

“…A line of division occurring at the level of the anus can separate the blubber into two functional components, with one anterior and one posterior. Both parts have insulator and buoyancy functions, but the posterior section mainly serves as a structural element to streamline the body (Hamilton et al 2004). The blubber from the anterior section functions primarily as an insulator, because the main muscles and organs are concentrated at this site, and secondly as a limited short-term energy reserve (Koopman 1998).…”

“…This subcutaneous layer is recognized as the main tissue for energy storage, in the form of lipids, in this mammalian group (Aguilar and Borrell 1990, Koopman et al 1996, Struntz et al 2004. In addition to serving as a depot of energy, it is also the primary thermal barrier in the aquatic environment (Worthy and Edwards 1990, Dunkin et al 2005, Bagge et al 2012, streamlines the body and facilitates hydrodynamic locomotion (Pabst 2000, Fish 2000, Hamilton et al 2004, and contributes to water balance and provides buoyancy (Dearolf et al 2000, Kipps et al 2002, Dunkin et al 2010.…”

Structure of the integument of southern right whales, Eubalaena australis

“…The lateral samples include measurements taken from a juvenile and the marked decrease in blubber thickness in a craniocaudal direction, especially in Position 5, helps create the laterally compressed, stream-lined tailstock. Unfortunately, the lateral location of these samples makes them incomparable to results from other investigations (Ackman et al, 1975;Lockyer et al, 1985), but the laterally compressed nature of the cetacean peduncle (and the underlying structure of the blubber) has been proposed as a mechanism for creating elastic energy that assists in propulsion (Summers, 2001;Hamilton et al, 2004). The deep-core sampling technique was a successful first attempt at obtaining representative integument samples from a free-swimming balaenid.…”

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

“…Blubber is mostly adipose tissue that is located in the subdermal matrix and is laced with connective tissue fibers. It cloaks the body of marine mammals and has allowed cetaceans to colonize even very cold habitats (Parry, 1949;Koopman, 1998;Pabst et al, 1999;Todet, 2001;Hamilton et al, 2004). Blubber displays great variability in thickness, biochemical composition, stratification, and cell density in all marine mammals: pinnipeds, cetaceans, and sirenians (Iverson, 2002;Best et al, 2003;Struntz et al, 2004;Koopman, 2007;Rosa et al, 2007;Castellini et al, 2009).…”