Meeting Abstract
Sea urchin behavioral reactions to light are more complex than previously thought. These animals have a diffuse photoreceptive system with at least two types of opsins expressed throughout their epidermis. Essentially, each urchin functions as a large compound eye. Their dermal light sense facilitates behavioral tasks that even include coarse spatial vision. This is novel, as diffuse dermal photoreception is generally assumed to mediate non-visual tasks. It has been suggested that urchins inhabiting rocky reefs use spatial vision to locate dark crevices to hide from predators. It is commonly thought that animals have photoreceptive and visual abilities that correlate to the complexity of their light-guided behaviors. The goal of this investigation was to determine the thresholds of urchin photoreception and spatial vision in the context of environmental relevance. Laboratory behavioral trials were conducted to establish the lower limits of intensity required for spatial tasks, action spectra, and image resolution of several Southern California urchin species that vary in depth range and habitat. Results indicate that each species has visual abilities relatively suited to its environment. Intensity thresholds correlate to naturally occurring irradiance levels for different species: for example, deeper dwelling species can perform spatial tasks under dimmer light than intertidal ones. Additionally, reef dwelling species reliably move towards a dark target, while sandy flat dwelling species do not. Describing the function of the urchin as a compound eye allows us to understand how these animals perceive their environments and make choices based on visual cues.
