Ecological Functions and Adaptations of the Elasmobranch Electrosense

Abstract

Shars and rays have a long evolutionary history as mayor pradactor in marine ecosystems, but the biological funcions and selective pressures that shape the evolution af their ampullary electrosensory system are poorly known. The ampolla of Lorenzini is the funcional electrosensory unit thet consists of a small subdermal ampolla and a canal thet projects to a surface pore on the head or pectoral fins. The sensory epithelium of the ampulla wall detects differences between the potencial at the skin pore and internal potencial of the animal, and stimulates neural transmission of information about the physical features of an external field to the brain. Natural weak electric stimuli include polar field from bioelectric sources and induced field from physical sourses in the enviroment. Neurophysiological studies show that the ampullary electrosense responds to electric field gradients as low as 20 nVcm. Elasmobranch fishes show behavioral responses to bioelectric stimuli produced by natural prey, mates, cosexuals and potential predactors. Numerous models exist for electrosensory navigation, but they remain to be rigorously tested. Recent work shows age-dependent cahnges in the response properties of the electrosense among embryo, juvenile and adult stages and are propose to reflect ontogenetic adaptations to their changing enviroments. In addition, the electrosense response properties are seasonally modified by the periodic expression of gonadal steroids and may serve important modulation of sensory functions during reproductive behaviors. Future work should continue to investigate different biological context in wich the electrosense in used by elasmobranch fishes, and to test the selective forces that may have shaped the evolution of this remarkable sensory system.