Passive electroreception in bottlenose dolphins Tursiops truncatus: implication for micro- and large-scale orientation

For the two dolphin species Sotalia guianensis and Tursiops truncatus, it
was shown that the vibrissal crypts located on the rostrum represent
highly innervated, ampullary electroreceptors and that both species are
correspondingly sensitive to weak electric fields. For a comparative
assessment of the sensitivity of the bottlenose dolphin's
electroreceptive system, we determined detection thresholds for DC and AC
electric fields with two bottlenose dolphins. In a psychophysical
experiment, the animals were trained to respond to electric field stimuli
using the go/no-go paradigm. We show that bottlenose dolphins are able to
detect DC electric fields as low as 2.4 &[mu]V cm -1 and
5.5 &[mu]V cm -1, respectively, a detection threshold in the same
order of magnitude as those in the platypus and the Guiana dolphin.
Detection thresholds for AC fields (1, 5, and 25 Hz) were generally higher
than those for DC fields, and the sensitivity for AC fields decreased with
increasing frequency. Although the electroreceptive sensitivity of
dolphins is lower than that of elasmobranchs, it is suggested that it
allows orientation at micro and large scales. In dolphins pursuing benthic
foraging strategies, electroreception may facilitate short-range prey
detection and target-oriented snapping of their prey. Furthermore, we
discuss that the ability to detect weak electric fields may enable
dolphins to detect the Earth's magnetic field through induction-based
magnetoreception, thus allowing large-scale orientation.