Vertebral bone microarchitecture and osteocyte characteristics of three toothed whale species with varying diving behaviour

Abstract

Although vertebral bone microarchitecture has been studied in various tetrapods, limited quantitative data are available on the structural and compositional changes of vertebrae in marine mammals. Whales exhibit exceptional swimming and diving behaviour, and they may not be immune to diving-associated bone pathologies. Lumbar vertebral bodies were analysed in three toothed whale species: the sperm whale (Physeter macrocephalus), orca (Orcinus orca) and harbour porpoise (Phocoena phocoena). The bone volume fraction (BV/TV) did not scale with body size, although the trabeculae were thicker, fewer in number and further apart in larger whale species than in the other two species. These parameters had a negative allometric scaling relationship with body length. In sperm whales and orcas, the analyses revealed a central ossification zone (“bone-within-bone”) with an increased BV/TV and trabecular thickness. Furthermore, a large number of empty osteocyte lacunae was observed in the sperm whales. Quantitative backscattered electron imaging showed that the lacunae were significantly smaller and less densely packed. Our results indicate that whales have a unique vertebral bone morphology with an inside-out appearance and that deep diving may result in a small number of viable osteocytes because of diving depth-related osteocyte death.

Trabecular architecture in the sciuromorph femoral head: allometry and functional adaptation

“…The trabecular microstructure reflects lifestyle-related functional signals. Similar results have been documented in a few mammalian clades (primates [ 13 , 21 , 22 ], Odontoceti [ 27 ], Xenarthra [ 26 ]) and thus suggest to provide important insight into the functional morphology of mammals in general.…”

“…Since research on lifestyle-related functional adaptation of bone microstructure mainly focuses on primates, little has been done in non-primate mammals so far. Recent studies in Xenarthra [ 26 ] and Odontoceti [ 27 ] expanded the sampling of mammalian 3D trabecular architecture in context of lifestyle. In rodents, however, the functional role of trabeculae is mostly studied experimentally.…”

Ultra-high matrix mineralization of sperm whale auditory ossicles facilitates high sound pressure and high-frequency underwater hearing

“…The auditory ossicles were taken from three sperm whales of 12, 13 and 15 years of age [16,17]. All specimens were transferred with special documentation of no commercial or trading interests according to the environmental authority of Schleswig-Holstein (Germany) and approved by the Institute for Terrestrial and Aquatic Wildlife Research (ITAW) on behalf of the Schleswig-Holstein Wadden Sea National Park.…”

“…For comparison, we have analysed the bones of human iliac crest and murine vertebral bones (wild-type C57BL/6 mice) as well as sperm whale vertebral bone regarding the bone mineral density (BMD) using bone specimens from previous studies and our archive [16,20] (n ! 3 per group).…”

Age-related changes in size, bone microarchitecture and volumetric bone mineral density of the mandible in the harbor seal (Phoca vitulina)

“…So far, HR-pQCT imaging has only rarely been used to study bones of marine mammals [46, 47]. A number of previous studies [16–18, 20,21] used dual-energy X-ray absorptiometry (DXA), a method providing aBMD data [48].…”