PERNET, B.*; JAECKLE, W.: Egg size and energy content in polychaete annelids: a comparison with echinoderms

Eggs of many polychaete species are smaller than the smallest echinoderm eggs. In addition, polychaete eggs greater than about 100 µm in diameter typically develop without a feeding larval stage, but among echinoderms the transition between feeding and non-feeding development occurs at a larger egg diameter (ca. 200 µm). These patterns may be explained by between-taxon differences in energy content of eggs of equivalent diameter. To evaluate this hypothesis, we estimated volume, energy content, and dry organic weight (DOW) of eggs from 13 species of polychaetes (P) and compared these data with existing data for eggs of echinoderms (E, n = 15 species). Scaling coefficients for egg energy content and volume (1.05 ± 0.07 (P), 1.07 ± 0.05 (E)) and egg energy content and DOW (1.10 ± 0.03 (P), 0.99 ± 0.00 (E)) were similar in the two taxa. Variation in other traits (e.g., size at metamorphosis) must explain differences in egg volume and developmental mode between polychaetes and echinoderms. In contrast, weight-specific energy content did differ between eggs of the two taxa: polychaete eggs (16.4 ± 1.14 J/mg, mean ± SE ) contained less energy per mg DOW (t-test, p<0.001) than did echinoderm eggs (33.0 ± 0.68 J/mg). These results suggests that eggs of the two taxa differ in biochemical composition. Such differences may influence potentially ecologically important traits such as egg and embryo buoyancy and rate of development.