Researchers at the Oceans Institute and the School of Animal Biology at the University of Western Australia, Crawley, reported the first evidence that sharks embryos encased in egg sacks can detect electric fields in the Jan. 9, 2013, issue of the open access peer reviewed journal Public Library of Science.
The ampullae of Lorenzini detect minute electric field gradients via an array of openings or ‘pores’ at the skin’s surface in adult sharks. These structures have been demonstrated to be primarily used for the detection of prey but can be used as for predator detection and avoidance as well.
The researchers found that brown-banded bamboo shark embryos encased in their egg sacks can sense electric fields that mimic a predator, and respond by reducing respiratory gill movements. The cessation of gill movements is immediately followed by a rapid coiling of the tail around the body, with little or no discernible body movement during exposure.
The period of time the embryonic sharks can exhibit this behavior is limited by their need for oxygen.
The researchers found that the predator protection behavior is stimulated by a limited set of electric frequencies and is apparent in vary young embryonic sharks. The youngest shark embryos require a higher frequency of electric stimulation to exhibit the protective behavior.
Ryan M. Kempster *, Nathan S. Hart, Shaun P. Collin
The Oceans Institute and the School of Animal Biology, The University of Western Australia, Crawley, Western Australia, Australia