Meeting Abstract

31.9  Tuesday, Jan. 5  Assaying echinoid eggs for evolutionary associations among egg size, egg composition, and egg energy MCALISTER, J/S*; MORAN, A/L; Clemson University; Clemson University jmcalis@clemson.edu

Marine invertebrates with feeding larvae use maternally-derived biochemical constituents (carbohydrate, protein, and lipid) in the egg to fuel larval metabolism and to construct the feeding larva. How then are evolutionary changes in egg size associated with egg biochemical composition and the amount of energy available for larval development? We are investigating these associations using the eggs and larvae of echinoid ‘geminate’ species pairs from tropical America, in which species from the low-productivity waters of the Caribbean have larger eggs (by volume) than their sister taxa in the highly productive Pacific. We analyzed egg biochemical constituents of echinoids in the genera Diadema and Echinometra, and found that eggs of the Caribbean species contained more protein and lipid, but carbohydrate did not differ between oceans. Egg compositions differed between oceans in that eggs of Caribbean species were characterized by a higher lipid-to-protein ratio. Total energy (mJ) in the egg (based on summing energy equivalents of constituents) was greater for all Caribbean species, but when controlled for egg volume, total egg energy density (mJ/nl) was significantly lower in the Caribbean Echinometra sp.. Thus, the large eggs of Caribbean Echinometra sp. are not simply ‘scaled up’ small eggs, but contain less energy per unit volume than eggs of the Pacific species. One possible adaptive advantage to producing large, energy-poor eggs is that females can maintain high fecundity while producing eggs that are better targets for fertilization by sperm. We are currently examining larval growth rates, arm lengths, and energy utilization in these taxa to determine the fate of egg constituents and the downstream effects of egg energy density for larval physiology and growth.