Passive Electroreception in Dolphins

Sharks and other aquatic vertebrates are known to use passive electroreception to detect other organisms in the vicinity. Passive electroreception is the ability of an animal to detect the weak electric field given off by another animal in the vicinity. However, mammals rely primarily on visual, olfactory, touch, and auditory information to perceive their world. Among mammals, only the platypus (Ornithorhynchus anatinus) and echidnas (Tachyglossus aculeatus) uses passive electroreception to detect prey. These mammals use electroreceptors derived from modified mucus glands innervated by the trigeminal nerve.

Researchers from Germany and the United States have now found a novel set of passive electroreceptors in the Guiana dolphin (
Sotalia guianensis). The remnants of vibrissae follicles are still found on the rostrum of Guiana dolphins even though they lack hairs. These vibrissal crypts (Figure 1) act as passive electroreceptors in these dolphins.

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Figure 1. Photograph of the head of a Guiana dolphin showing the location of the vibrissal crypts on the rostrum. Arrows indicate a single vibrissal crypt. (From Czech-Damal et al., 2011)


Detailed histological analysis showed that the vibrissal crypts are similar in structure to the ampullary electroreceptors of other aquatic vertebrates. The crypts contain a hairless lumen filled with keratin fibers and corneocytes, surrounded by approximately 300 axons of the trigeminal nerve (Figure 2). The corneocytes appear to be equivalent to the glycoprotein gel used by fish or the mucus used by the platypus.

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Figure 2. (a) Histology of the vibrissal crypts in the Guiana dolphin. (b) a drawing of the vibrissal crypt showing an ampulla-shaped invagination surrounded by nerve bundles (Nb). (From Czech-Damal et al., 2011)

To determine if these crypts actually serve as passive electroreceptors, the scientists trained a dolphin to respond to weak electrical stimuli similar to those given off by prey species in the natural environment. Guiana dolphins are capable of detecting electric fields at 4.6 microvolts per cubic centimeter. This is similar to detection levels for the platypus despite the fact that the dolphin crypts differ anatomically from the electroreceptors in the platypus. Thus, passive electroreception has evolved at least twice in aquatic mammals.

Interestingly, Guiana dolphins are shallow water benthic feeders; they stir up the mud to flush out buried prey. This behavior is consistent with the use of passive electroreception for close distance prey detection in murky water.

References

Czech-Damal, N., Liebschner, A., Miersch, L., Klauer, G., Hanke, F., Marshall, C., Dehnhardt, G., & Hanke, W. (2011). Electroreception in the Guiana dolphin (Sotalia guianensis) Proceedings of the Royal Society B: Biological Sciences, 279 (1729), 663-668 DOI: 10.1098/rspb.2011.1127