Effects of Egg Size Reductions on Development Time and Juvenile Size in Three Species of Echinoid Echinoderms: Implications for Life History Theory

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Life-history models for marine invertebrate animals assume a strong correlation between the size of the egg and the time from fertilization until metamorphosis. This assumption is supported by comparative data across a wide range of phyla. However, the exact form of the relationship between egg size and development time has a strong effect on the predicted outcomes of life-history models and has been the subject of much debate. Comparative data suggest that as egg size increases the effect of egg size reductions on development time will decrease and the effects of size reductions on juvenile size will increase. I used blastomere separations to test the effects of a 50% reduction in egg volume on development time and juvenile size in three species of echinoid echinoderms (Arbacia punctulata, Strongylocentrotus purpuratus, and Dendraster excentricus) that develop from eggs of a range of sizes (80–124 μm). I also manipulated the food level given to developing embryos and larvae to investigate the potential interaction between the effects of egg size reductions and food availability. Larvae from halved zygotes took significantly longer to develop to metamorphosis than their whole size counterparts in all three species. In only one species was I able to detect a significant reduction in juvenile size for offspring developing from halved zygotes. When compared with similar manipulations in species with larger eggs (140–387 μm), egg size reductions have a stronger effect on development time in species with small eggs. As predicted, development time does not change linearly with egg size but instead increases exponentially as egg size is reduced. The relationship between egg size and juvenile size remains unclear. Further investigations into the factors, including egg size, that influence juvenile performance are warranted.