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Abstract:
Many planktonic invertebrates can reproduce by immediately developing subitaneous eggs, which allow fast reproduction, and by resting eggs, which enable the survival of eggs in unfavorable environmental conditions. Since resting eggs can stay viable for decades or even centuries, they are likely to be richer in essential, easily degrading biochemicals than subitaneous eggs. Using the freshwater cladoceran Daphnia pulicaria we test whether the switch between these two qualitatively different reproductive modes is influenced by the availability of essential polyunsaturated fatty acids (PUFAs) in the food. We show that (1) when raised on a PUFA-poor diet, resting eggs of D. pulicaria contain much more PUFAs than subitaneous eggs, and unlike subitaneous eggs, contain considerable amounts of eicosapentaenoic acid (EPA), which was not present in their diet; (2) supplementation with EPA or using EPA-rich algae as food results in dramatically increased resting egg production; (3) when resting eggs are induced by starvation, their increased frequency in the presence of EPA-rich food can be entirely explained by maternal effects. Since dormancy is a ubiquitous phenomenon among invertebrates, our result that its onset can be severely limited by the availability of essential biochemicals may hold for a variety of taxa.
