Evolution of maternal provisioning in ophiuroid echinoderms: characterisation of egg composition in planktotrophic and lecithotrophic developers

摘要

ABSTRACT: For free-spawning marine invertebrates, the egg is the unit of maternal investment in offspring. For many taxa, there is a major life-history trade-off between production of many small, nutrient-poor eggs in high-fecundity species and fewer large, nutrient-rich eggs in low-fecundity species. In echinoderms, the switch from small eggs in species with ancestral-type feeding larvae to large eggs and non-feeding larvae is a significant change with major consequences for larval ecology and juvenile success. In this first comparative study of maternal investment in the Ophiuroidea across species with a range of egg sizes and larval types, the egg protein and lipid content of 4 species with planktotrophic and 6 species with lecithotrophic larvae were characterised. The planktotrophs produced eggs dominated by protein with triacylglycerol as the main energy storage lipid. The switch to lecithotrophy in the Ophiuroidea is associated with an increase in energy storage lipids to produce an energy-dense egg, as is typical of echinoderms with this mode of development. The eggs of the lecithotrophs, however, contained several novel lipid classes not found in ancestral-type ophiuroid eggs. These eggs also differed from those of other echinoderms with lecithotrophic development in the presence of these novel lipids rather than up-scaling of the ancestral maternal provisioning strategy. Our findings support the hypothesis of independent evolution of lecithotrophy multiple times in the Echinodermata. In the Ophiuroidea, this is seen in the evolution of different lipid provisioning patterns between species with large eggs.