Manuela Zadravec: Postnatal differentiation of bone tissue in the bottlenose dolphin (Tursiops truncatus). Dissertation. Faculty of Veterinary Medicine University of Zagreb. Zagreb. 2014.

Abstract

INTRODUCTION

Previous research on the development and structure of the bones of aquatic mammals has been conducted mainly on fossil bones. They were used for the study of growth dynamics and paleoecology. The development of bone tissue and bone histology of recent whales is still unexplored. In the present research the bones of bottlenose dolphins (Tursiops truncatus) were used to study postnatal bone development and their histomorphometric characteristics. The bottlenose dolphin is the only whale that lives in the Adriatic Sea and has been legally protected in Croatia since 1995.

MATERIALS AND METHODS

For the purpose of this study bone sections of the right humerus and the 5th right rib originating from 105 bottlenose dolphins of all ages were used. The bone sections were used for the histomorphometry and the determination of the intensity and dynamics of bone growth based on the relationship between the thickness of the cortical and cancellous bone parts, the area of the primary and secondary osteon, the number of lamella in the primary and secondary osteon and the features of the osteocytes lacunae. The bone sections were studied with a compound microscope with standard and polarized light. The data were processed in terms of the correlation between the individual parameters by using the statistical software STATA 10.

RESULTS

The rib of a newborn bottlenose dolphin consists of a thick compact bone tissue area, that reduces until 7 years of age. After this age the thickness of compact bone tissue in rib increasis again. The density of primary osteon decreases with the increasing age of the dolphin while the density of secondary osteon and osteon in remodelling increases IIIwith age in the humerus and ribs. Osteon density in the ribs is greater than in the humerus. Secondary osteons in the ribs and in the humerus have a larger area in females than in males. The number of lamellae in the secondary osteon is greater than the number of lamellae in the primary osteon. Osteocyt lacunae are oval-shaped with a long not dense canalicules

CONCLUSION

This study represents the first morphological and morphometrical description of the microstructure of bones such as osteon, lamella and osteocytes lacunae in a cetacean species from a dolphin’s birth to its old ages. The bottlenose dolphin ribs are more compact in structure than the humerus, because of their protective function for thoracic organs. On the other hand, the more cancellous structure of the humerus is supporting the balancing function of the pectoral flippers. This detailed description of bottlenose dolphin bone structures can be applied in species determination, ecology, paleobiology and veterinary medicine.