Aging-related histomorphometric changes in cortical bone tissue of bottlenose dolphins (Tursiops truncatus)

Abstract

Morphological characteristics of bones have shaped as a result of adaptation to life in the aquatic environment and whale diving habits. This study deals with the postnatal bone development and microscopic characteristics of bones of bottlenose dolphins (Tursiops truncatus). Bone sections of the right humerus and the fifth right rib of 106 dolphins aged less than 1–21 years were used to determine the density of the primary, secondary and remodelling osteons, the magnitude of the area occupied by the osteons, and the number of osteon lamellae. Bone sections were analysed using a compound microscope with standard and polarized light. Our study showed the primary osteons of bones to occupy a smaller area than the secondary ones. The secondary osteon area in the humerus is significantly larger than that in the rib. All rib osteons are significantly denser than those of the humerus. In both bones, the number of osteon lamellae is higher in secondary than in primary osteons. The number of secondary and remodelling osteons and the areas occupied by them increase with age, as opposed to primary osteons in which a decrease was noted. The number of lamellae in primary osteons decreases with age, while in secondary osteons their number increases. Within the study frame, morphometric osteon values of the bottlenose dolphin were determined, to the best of our knowledge, for the first time ever as concerns the aquatic mammals.