COWART, J.D.: Palatability of Pteraster tesselatus (Echinodermata: Asteroidea) Eggs

Risk of offspring mortality is a critical component of models concerning the ecology and evolution of life history traits in marine invertebrates. In these models, predation is generally assumed to be the most important cause of pre-settlement offspring mortality. Although few studies have directly investigated offspring susceptibility to predators, most models evaluating development assume that offspring of most species are palatable. Pelagic nonfeeding offspring are commonly large, conspicuous, energy rich, produced in small numbers, and lack apparent morphological defenses. Interactions between nonfeeding offspring and consumers are not well studied. However, recent studies have shown that pelagic nonfeeding offspring may benefit from the production of chemical defenses. This study investigated offspring palatability of the starfish Pteraster tesselatus. Members of the pterasterid family are unique because the adults secrete mucus over their aboral surface when attacked by predators. In addition, most species of pterasterids brood direct developing offspring within a specialized brood chamber called the nidamental chamber. P. tesselatus is unique because it has re-evolved pelagic development. The eggs of P. tesselatus are large, energy rich, positively buoyant, bright orange, and exposed to pelagic predators. I hypothesize that the re-evolution of pelagic development resulted in the evolution of chemical defenses in the offspring of P. tesselatus. Preliminary results support this hypothesis by showing that the eggs of P. tesselatus are unpalatable to two species of northern pacific fish, Oligocottus maculosus and Gasterosteus aculeatus.