Meeting Abstract
Among cetaceans, species with rigid, torpedo-shaped bodies are considered as the fastest and most active swimmers. Interspecific variation is encoded in the axial skeleton, where vertebral morphology varies among species with different locomotion modes. Here, we categorized 10 species of cetaceans (Families Delphinidae and Kogiidae) into functional groups determined by swimming modes (rigid vs. flexible body) and diving behavior (shallow vs. deep). We quantified trabecular bone mechanical properties and structure among cetacean functional groups and regions of the vertebral column. We hypothesized that trabecular bone would be stronger, stiffer, and thicker in shallow-diving, rigid-bodied swimmers and in the caudal vertebral column. Vertebrae were obtained from necropsies and dissected from four regions of the vertebral column (thoracic, lumbar, and two caudal). Vertebrae were µCT scanned in a Bruker SkyScan 1173, and trabecular thickness was quantified. After scanning, 6mm3 bone cubes were sawed from vertebrae and compression-tested at 2 mm/min using an Instron E1000 material tester. Yield strength and toughness were calculated using stress-strain curves. Rigid-bodied, shallow-diving cetaceans had the strongest, toughest, and thickest trabecular bone in the caudal region of the vertebral column, and had the greatest values of all functional groups. Conversely, flexible deep-divers showed no regional variation in trabecular mechanical properties and structure and had overall less strong, tough, and stiff bone. These data suggest that in addition to whole body rigidity, animals that habitually overcome surface drag and wave turbulence have increased skeletal loading during active swimming than those that incorporate prolonged glides during deep descents in the water column.
