Over the first week of our rigorous program, comparisons between species and phylums were repeatedly discernible. Whether these connections took form in a lecture slide about comparative embryology, or a simple bridge was made between the dorsal fin that is characteristic to fishes and also makes an appearance on specific marine mammals (such as the dorsal fin on the Carcharodon carcharias, great white shark, that is also exhibited by the Tursiops truncatus, or the common bottlenose dolphin), the noticings are everywhere.
The most profound example of specialized evolution, I found, is seen among sharks and dolphins and was discussed during lecture. Due to the fact that both sharks and dolphins have far fewer rods and cones in their eyes than humans, they are left with poor eyesight. To adapt to their pelagic, changing environments, sharks and dolphins convergently evolved similar ways of sensing with electrical frequencies and sound, respectively.
Members of the Elasmobranchs, I assume, developed their electrolocation senses, which derive from the ampullae of Lorenzini, due to the electric fields their prey arise. The Negaprion brevirostris, or lemon shark, for example employs their electroreceptor cells most strongly in the presence of its prey, subsequently eliciting a feeding behavioral response. An influx of a positive charge, around prey, causes the shark’s neurotransmitters to elicit a feeding response. The charge dissipates through a membrane once the shark has stopped eating.
Though our echolocation activity yesterday suggested the sense is not terribly helpful, dolphins have a very large melon that produces frequency clicks. Their ears are isolated from the rest of the skull, which heightens this sense for them, as it makes a sonar sound louder. Echolocation bounces off of a nearby food source, and allows the dolphin to interpret the prey’s shape and size.
Despite the fact that echolocation and electrolocation are not explicitly the same, they produce a similar sensory role in fishes and marine mammals.
*On a side note, it is possible that sharks may use Earth’s magnetic field to orient themselves while swimming, an adaptation already exhibited in dolphin species. This finding would connect marine animals with the world above, as many species that fly, such as the Apis mellifera, or European honey bee, use biomolecules to orient themselves during flight.
References: Fields, R. Douglas. 2007. “The Shark’s Electric Sense: An astonishingly sensitive detector of electric fields helps sharks zero in on prey.” Scientific American.
-Isabel McNeill
Adventures in Marine Science 