Ultrascale and microscale growth dynamics of the cidaroid spine of Phyllacanthus imperialis revealed by ²⁶Mg labeling and NanoSIMS isotopic imaging

Abstract

Growth dynamics of the primary spine of the cidaroid sea urchin Phyllacanthus imperialis was assessed for the first time using pulsed (26) Mg-labeling and NanoSIMS isotopic imaging. The sea urchin was incubated twice (for 48 h) in artificial seawater with elevated level of (26) Mg. After each labeling event, the sea urchin was returned for 72 h to seawater with natural isotopic abundance of (26) Mg. NanoSIMS ion microprobe was subsequently used to visualize the labeled regions of the spine with submicrometer lateral resolution. The growth of the new skeleton was restricted to the distalmost and peripheral portions of the spine. Skeletogenesis involved mostly the deposition of continuous thickening layers and lateral growth involving bridges between previously formed trabeculae. The timescale of formation of individual thickening layers (ca. 1 µm in width) on the stereom trabeculae was on the order of 1 day. Longitudinal growth occurred mainly at the periphery in the form of small portions of the thickening deposits or more massive microspines that appeared to branch and fuse with those above and below. These microspines were found to grow at about 10 µm/day. These results reveal that the skeletal growth of a juvenile cidaroid spine is complex and highly heterogeneous, with different extension rates depending on the stage of the stereom development and/or direction of the growth fronts. The growth pattern observed here at the submicrometer scale provides direct evidence supporting the earlier suggestions that the lamellar structure of echinoderm stereom is formed by periodic deposition of continuous mineral layers.

Effects of seawater chemistry (Mg2+/Ca2+ ratio) and diet on the skeletal Mg/Ca ratio in the common sea urchin Paracentrotus lividus

“…It has been thus widely assumed that biomineralization of spine is only mediated by the covering epidermis (e.g., Gorzelak et al, 2014). Our data, however, suggest that magnesium from diet (either in the form of ions or already formed Mg-enriched nanograins), which may contribute to Mg-enrichment of the spine, may be transported directly from the coelom to the spines.…”

“…Seawater has been widely considered the only source of Mg 2+ and Ca 2+ ions in echinoderm biomineralization (e.g., Weiner and Addadi, 2011). This is supported by a number of experiments, which showed that labeling seawater with fluorescent markers, radioactive or stable isotopes, results in staining of the newly grown skeleton ( Nakano et al, 1963;Lewis et al, 1990;Ebert, 2007;Gorzelak et al, 2011Gorzelak et al, , 2014.…”

Sea urchin growth dynamics at microstructural length scale revealed by Mn-labeling and cathodoluminescence imaging

“…A number of different methodological approaches have been used to study the growth of echinoderms at different length scales. These include indirect examination of natural growth lines and more direct tagging techniques (via plastic tube slipped over the skeleton, tag inserted into a drilled skeleton, passive integrated transponder tags, coded wire tags, fluorochrome chemical markers and stable isotopes) [ 1 – 3 ]. Among these methods, fluorescent dyes, such as tetracycline and calcein, had attracted considerable attention [ 4 – 11 ].…”

Architecture, Growth Dynamics and Biomineralization of Pulsed Sr-Labelled <i>Katelysia rhytiphora</i> (Mollusca, Bivalvia)

“…Hence, labelling experiments with a Ca substituting trace element offers the potential to study calcification processes down to the sub-micron range with excellent analytical detectability for a wide range of micro-beam techniques and are superior to experiments with fluorescent markers e.g. Calcein that are limited in spatial resolution and, furthermore, are suspected to alter biomineralization processes in some biocalcifiers (Russell and Urbaniak, 2004;Thébault et al, 2006;Allison et al, 2011;Gorzelak et al, 2014).…”