While on the hunt, a supreme awareness of the surroundings can pay off large dividends for an individual. One species that takes advantage of their surroundings is the shark. In Life, a shark quickly reacts to the movements of a school of anchovies by sensing the electrical signals given off by their collective movement, giving the shark an advantage while hunting. Sharks have a “sixth sense” called electroreception, which enables them to sense weak electrical stimuli conducted through ocean water via electrosensory receptors on the surface of their skin [1]. This enables them to hunt precisely underwater, sensing the weak voltage generated by the muscle contractions of their prey [2]. These tiny electrical signals can be picked up by the sharks due to salty ocean water being such a great medium for conduction. Although the exact developmental origin of electroreceptors is still not fully understood [3], electroreception can be seen in a variety of other species, including bees and dolphins. Research has delved into the possibility of the evolution of unique head morphology for the enhancement of these electrosensory capabilities [4], but these studies have proven inconclusive so far. Thus the search continues for the origin of this unique characteristic, and the phenomenon behind its mysterious evolutionary path.
by Gracy Trinoskey-Rice and Jason McCartney
Life, Season 1, Episode 4, Fish, starting at approximately 42:08
References
- Bullock TH. 1973. Seeing the world through a new sense: electroreception in fish: sharks, catfish, and electric fish use low- or high-frequency electroreceptors actively and passively, in object detection and social communication. American Scientist 61(3): 316-325.
- Kalmijn AJ. 1971. The electric sense of sharks and rays. Journal of Experimental Biology 55:371-383.
- Freitas R, Zhang G, Albert JS, Evans DH and MJ Cohn. 2006. Developmental origin of shark electrosensory organs. Evolution & Development 8: 74-80.
- Paulin MG. 1995. Electroreception and the compass sense of sharks. Journal of Theoretical Biology 174(3): 325-339
The Evolution of Planet Earth 