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Evolution of communication systems in South American Electric Fishes

A large group of South American fishes, the Gymnotiformes, have the unusual ability to both produce and sense very weak electric fields. They use this ability to detect the tiny currents produced by their prey or other animals, and they use this sense to form an electric image of their surroundings (like a kind of radar). Interestingly, these fish also use this ability to communicate with each other by sending tiny pulses in specific patterns. The pattern of pulse spacing seems to be particularly important for communication, but less is known of the significance of pulse structure. We are looking at the structure of the pulse itself, how it differs in different species, and particularly how and why it varies within certain species, but not in others. We have conducted geographic surveys of this variability in Brazil, and we are currently determining if each regional population has a different ‘accent.’ If pulse structure is species-specific, as is thought, it can prevent different species in the same habitat from interbreeding, but if different populations of the same species begin to vary due to geographic barriers, small differences could easily lead to the evolution of new species. So we are comparing the diversity of pulse type to the genetic structure of several populations to determine if animals with different signals are interbreeding. We are also looking at how individuals of the same species, but from different populations, interpret each other’s electric discharge. Can they judge the sender’s species? Sex? Reproductive desirability? All of these questions are important for understanding how this ‘language’ evolves, and for understanding how this may lead to the birth of new species. This research is in collaboration with researchers at the Instituto Nacional de Pesquisas da Amazonas (Brazil — INPA) and Yale University.

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