| Abstrakt: |
This study quantified the electrosensitivity of a euryhaline elasmobranch, the Atlantic stingray (Dasyatis sabina) across a range of salinities. Specimens from a permanent freshwater (FW) population in the St Johns River system, FL, USA, were compared with stingrays from the tidally dynamic Indian River Lagoon in east Florida, USA. Behavioral responses of stingrays to prey-simulating electric stimuli were quantified in FW (Op.p.t., p=2026 Ωcm), brackish (15p.p.t., p=41 Ωcm) and full strength seawater (35p.p.t., p=19Ωcm). This study demonstrated that the electrosensitivity of D. sabina is significantly reduced in FW. In order to elicit a feeding response, stingrays tested in FW required an electric field 200-300X greater than stingrays tested in brackish and saltwater (median FW treatments=1.4μVcm[sup-1], median brackish-saltwater treatments=6nVcm[sup-1]), and the maximum orientation distance was redUced by 35.2%, from 44.0 cm in the brackish and saltwater treatments to 28.5 cm in FW. The St Johns River stingrays did not demonstrate an enhanced electrosensitivity in FW, nor did they exhibit reduced sensitivity when introduced to higher salinities. Stingrays from both populations responded similarly to the prey-simulating stimulus when tested at similar salinities, regardless of their native environment. The reduction in electrosensitivity and detection range in FW is attributed to both an environmental factor (electrical resistivity of the water) and the physiological function of the ampullary canals. The plasticity of this sensory system to function across such a wide environmental range demonstrates its adaptive significance. [ABSTRACT FROM AUTHOR] |
