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Sensory Ecology of Elasmobranch Fishes

Christine Bedore, Georgia Southern University

17 February 2017

The sensory systems of chondrichthyan fishes are thought to represent the basal vertebrate condition from which more advanced modalities arose. Additionally, elasmobranch fishes inhabit nearly every marine environment and correspondingly represent a wide range of ecological adaptations. Therefore, elasmobranchs demonstrate an impressive array of sensory adaptations that correspond to their individual niches and provide ideal subjects for studying sensory adaptation to biological and physical environments. For example, most batoids possess duplex retinae comprised of rod and cone photoreceptors, although the potential for a species to have color vision varies with the spectral composition of the habitat. Cownose rays, Rhinoptera bonasus, have two cone pigments with color sensitivity that corresponds to their turbid, green-dominated, estuarine habitat. Similarly, yellow stingrays, Urobatis jamaicensis, have three cone pigments that correlate to their inhabitance in clear, spectrally rich reef-associated waters. Additionally, differences in visual temporal resolution, the ability to track moving objects, differs between these two species with the active, schooling cownose rays suffering a lower reduction in temporal resolution with decreases in ambient light levels and temperature. The reduced thermal sensitivity, combined with possession of a cranial rete, suggests that cownose rays may use cranial endothermy, or “brain warming”, to minimize reductions in nervous and sensory function when challenged with environmental temperature changes. Due to their small size relative to most cranial endotherms, as well as their ease of collection and maintenance in the laboratory, cownose rays make ideal models for testing unresolved hypotheses regarding sensory-driven evolution of cranial endothermy in fishes.