Size specific chemoreception and ontogenic responses to food in the brittle star Ophioderma cinerea (Echinodermata: Ophiuroidea)

Abstract

Abstract. Ophioderma cinerea (Müller & Troschel, 1842) is a species of warm water ophiuroid that lives primarily in rocky habitats in the tropical Atlantic. Competition for resources can be high in their habitat. Behavioral observations in aquaria led to a hypothesis that differences in body size may affect feeding strategies, and thus affect survivorship. It is widely accepted that echinoderm ontogenic growth is sigmoidal, with juveniles growing much faster than adults. Yet, it is not understood what affect this has on behavior. Individuals were kept in replicate experimental tanks. After a 3-d starvation period, each individual was exposed to a proteinaceous food stimulus. The animals were observed and a time measurement was taken to determine how long it took the animals to sense the food and to begin moving toward the food during both day and night. Smaller individuals were found to sense food significantly faster than larger ones, while no difference was observed for time-to-motion. Several explanations may support this finding. One of these explanations highlights how the need to compete with larger animals may have selectively adapted ontogenetically more sensitive chemoreceptors in smaller animals.