Raoult, V., Howell, N., Zahra, D., Peddemors, V.M., Howard, D.L., de Jonge, M.D., Buchan, B.L. and Williamson, J.E., 2018.  Localized zinc distribution in shark vertebrae suggests differential deposition during ontogeny and across vertebral structures. PLoS ONE 13(1):  e0190927.

Summary

Shark vertebrae are used to examine life-history traits related to trophic ecology, movement patterns, and the management of fisheries. Understanding of their development is beneficial to research that obtain biological information from calcified structures, eg growth. This study used scanning X-ray fluorescence microscopy at the Australian Synchrotron to quantify zinc distribution within vertebrae of ten shark species. Species examined included the White Shark; Smooth Hammerhead; Dusky, Spinner and Blacktip whaler sharks; the Port Jackson Shark; plus two species each of Sawsharks and Angel Sharks. Zinc was not evenly distributed throughout the vertebral structure, with concentration an order of magnitude lower in the outer region known as the corpus calcareum. In most species, zinc concentrations were also higher pre-birth, indicating a high rate of pre-natal zinc deposition. These results point to inter-specific differences in elemental deposition within vertebrae. Since the deposition of zinc is physiologically-driven, these differences suggest that the processes of growth and deposition are potentially different in the intermedialis and corpus calcareum parts of the vertebra, and that caution should be taken when extrapolating information such as annual growth bands from one structure to the other. Together these results imply that the high inter-specific variation in vertebral zinc deposition and associated physiologies may explain the varying effectiveness of ageing methodologies applied to elasmobranch vertebrae.