Localized zinc distribution in shark vertebrae suggests differential deposition during ontogeny and across vertebral structures

Abstract

The development of shark vertebrae and the possible drivers of inter- and intra-specific differences in vertebral structure are poorly understood. Shark vertebrae are used to examine life-history traits related to trophic ecology, movement patterns, and the management of fisheries; a better understanding of their development would be beneficial to many fields of research that rely on these calcified structures. This study used Scanning X-ray Fluorescence Microscopy to observe zinc distribution within vertebrae of ten shark species from five different orders. Zinc was mostly localised within the intermedialis and was generally detected at levels an order of magnitude lower in the corpus calcareum. In most species, zinc concentrations were higher pre-birth mark, indicating a high rate of pre-natal zinc deposition. These results suggest there are 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, and that caution should be taken when extrapolating information such as annual growth bands from one structure to the other. Together these results suggest 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.

Ontogenetic Patterns of Elemental Tracers in the Vertebrae Cartilage of Coastal and Oceanic Sharks

“…Similarities also emerged among most of the species in their patterns of Mn and Zn concentrations, with both elements being elevated early in life followed by a decline. A similar pattern was observed for multiple shark species from Australia, including C. brevipinna, where Zn concentrations were very high pre-birth and declined post-birth (Raoult et al, 2018). The elevated Zn concentrations observed in the early life of all species in this study match the post-birth pattern observed by Raoult et al (2018), and we hypothesize that this may be the result of maternal loading.…”

“…Elements that are present in the environment are incorporated into the vertebral hydroxyapatite matrix during the biomineralization process, as the vertebrae grow concentrically over time. Although studies validating elemental uptake pathways into elasmobranch vertebrae are currently limited, concentrations of certain elements are thought to be associated with environmental variables such as salinity (Sr, Ba;Tillett et al, 2011) and temperature (Ba, Mg;Smith et al, 2013), dietary intake (Zn, Mn; Mathews and Fisher, 2009), maternal loading (Zn; Raoult et al, 2018), and unresolved physiological controls (McMillan et al, 2017). Consequently, chemical analysis of vertebrae sampled continuously along their radial growth axis may proxy how environmental conditions changed throughout an individual's life (Scharer et al, 2012;Smith et al, 2013).…”

The Sawshark Redemption: Current knowledge and future directions for sawsharks (Pristiophoridae)

“…Analysis of vertebral chemistry is one potential path forward, with elements such as strontium showing promise as a tool for shark ageing (Raoult, 2015; Raoult et al., 2016). Examination of other elements such as zinc may not be appropriate because the deposition of zinc appears to be highly variable within and between elasmobranch species and does not correlate with age for sawsharks (Raoult et al., 2018).…”

Element composition of shark vertebrae shows promise as a natural tag

“…Several other assumptions also need to be addressed to confirm the suitability of vertebral elements as an environmental tracer, including the need to understand potential ontogenetic and diagenetic effects (see McMillan et al 2017a). In previous studies, vertebral element incorporation was not related to somatic growth or vertebral biomineralisation rates , with the exception of Zn : Ca (Raoult et al 2018). However, ontogeny and biomineralisation have been shown to influence rates of element uptake in otoliths of teleost species in some (but not all) manipulative experiments (Morales-Nin 2000;DiMaria et al 2010;Fablet et al 2011;Loewen et al 2016).…”

“…cervical, thoracic, precaudal;Lewis et al 2017), among vertebrae within similar regions of the vertebral column (e.g. Lewis et al 2017;McMillan et al 2017a), with the exception of Zn (Raoult et al 2018), and little to no variation within similar regions of a vertebra (e.g. Tillett et al 2011;Smith et al 2016;Lewis et al 2017).…”