Characterization of lecithotrophic propagules in echinoderms

Ferguson-Roberts, Janet M. (2021) Characterization of lecithotrophic propagules in echinoderms. Masters thesis, Memorial University of Newfoundland.

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Abstract

Reproduction often involves use of propagules (e.g. spores, seeds and fruit, fertilized eggs, embryos, and larvae), which are frequently dispersed in a medium such as air or water. These propagules possess characteristics (e.g. size, shape, viscosity, biochemical composition) that may influence their viability. Lecithotrophic (maternally-provisioned) eggs of echinoderms display a diversity of colours and buoyancies worldwide, yet these characteristics are rarely investigated in depth. Much more is known on the biochemical composition of propagules in relation to the ecology of lecithotrophic echinoderms. Thus, the objectives of this thesis were to quantify and find trends in the externally observable biophysical properties (colour and buoyancy) and connect them to trends found in the internal biochemical composition (lipids and pigments) across 1) the oocytes of different species of echinoderms with lecithotrophic development (sea stars: Leptasterias polaris, Henricia sanguinolenta, H. perforata, Crossaster papposus, Solaster endeca, sea cucumbers: Cucumaria frondosa and Psolus fabricii) and 2) across stages of oogenesis and development in the sea cucumber C. frondosa. Using an analytical chemistry technique, thin-layer chromatography with ionization detection, chromaticity, and spectrophotometry, I found 1) a trend in most metrics (density, chromaticity colour coordinates, percentages of glyceryl ethers and triacylglycerols, and pigment concentration) of mature oocytes associated with the phylogeny of the seven focal species, and 2) a bell curve trend in all metrics associated with the eco-physiological constraints of each life stage through the ontogeny (early vitellogenic oocytes to early juveniles) of C. frondosa. An additional contribution of this study was the exploration and development of methods to assess the density and colour of the propagules of seven focal species by reappropriating techniques from the fields of analytical chemistry and colour science (chromaticity x,y coordinates). Future research should extend to other invertebrates or externally fertilizing species, and explore the driving effects of visual predators, ultraviolet radiation, and dispersal on propagule characteristics.

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