Prof. Carl Hopkins researches Mormyrid fish, which are known as weakly electric fish because they produce small electric currents and use electric fields for communication and location purposes. His specific field of study is neuroethology — which is a branch of neurobiology and behavior that emphasizes comparative methods. The fish’s electric system gave scientists comparative insight into understanding the hearing system of other animals.
In addition to the many specimens preserved in exhibits for the public to enjoy, the American Museum of Natural History in New York City also holds many behind-the-scenes collections for scientists to study. One such specimen concealed in a jar and stored away in a room dedicated to fish is Paramormyrops hopkinsi, an electric fish belonging to the Mormyrid family. The scientist studying this specimen is Prof. Carl Hopkins, neurobiology and behavior, who also discovered the species in the Ivindo River in Gabon, western Africa.
Hopkins researches Mormyrid fish, which are known as weakly electric fish because they produce small electric currents and use electric fields for communication and location purposes. Mormyrid fish are not to be confused with the likes of electric eels, which are characterized as strongly electric fish that use electricity to shock their prey.
Both weakly and strongly electric fish use an electric organ to create electricity and surface receptors to receive signals. Hopkins researched the behavior of the fish as well as the mechanisms that underlie their behaviors.
Hopkins’ field of study is neuroethology — which is a branch of neurobiology and behavior that emphasizes comparative methods. The fish’s electric system gave scientists comparative insight into understanding the hearing system of other animals. Much like bats, which use echolocation to identify their surroundings, Mormyrid fish use electrolocation as a way to interpret their environment.
“Their brains are specialized for receiving signals from the electric sense,” Hopkins said. “It is an ideal system because it is doing one thing very well.”
Similar to how the hearing system helps facilitate communication, the electric system also plays a part in sending signals from fish to fish. Male fish have a certain signal for mating; female fish have a certain signal to indicate they are receptive to males. Dominant males have a different signal than subordinate males. There are also different signals for threats and alarms.
Current research at the Hopkins lab has indicated that Mormyrid fish can distinguish between different species of Mormyrid fish. The fish can tell there are differences in electric signal, but the extent to which the fish can perceive the differences in species is hard to tell.
“If we use a very general behavior, like time spent next to an electrode playing signal 1 versus signal 2, we can see differences, but we can’t actually ascribe these to ‘species’ specific signal,” Hopkins said.
The electric signals also appear to be one of the first things that change when a species evolutionarily diverges, according to a paper he helped publish in 2010. Although Hopkins said scientists are not sure exactly how signal divergence comes about, he hypothesized that divergence happens because the signal change leads to altered mating behavior, preventing different species from cross mating.
Another hypothesis is that hybridization, producing offspring by mating between fish with different signals, is less desirable than producing offspring by mating between fish with identical signals. This leads to reinforcement, mating between fish with the same signal. Speciation has happened in Gabon “explosively” because it occurred over a relatively short period of time. A whole new number of species emerged in one place, much like Darwin’s finches in the Galapagos, Hopkins said.
Hopkins is currently on sabbatical at the Museum of Natural History where he is working on classifying and describing new species. Hopkins is also teaching other scientists how to differentiate between the species, which are often nearly identical.
Hopkins will return to Cornell this fall. In addition to continuing his research, Hopkins will also resume teaching his course BioNB 4240: Neuroethology: Neural Circuits and Animal Behavior. “The bottom line: Neuroethology is an approach to studying the nervous system that embraces the comparative method and evolution as part of its motivation,” Hopkins said. “It has resulted in the discovery of a lot of interesting model systems that have been helpful to the general field of neuroscience.”