Dissertation Research: Behavioral and Genetic Investigations of Reproductive Isolation between Two Electric Fish Signal Morphs

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A diverse group of mormyrid fishes has recently been discovered in Gabon. These fishes produce weak electric pulses to communicate with one another. Past studies indicate that they can detect differences between pulse waveforms and use this information for same-species recognition. Each species emits a distinct electric signature, with one notable exception. Two signal forms ("normal polarity" and "reversed polarity") are produced by co-occurring individuals that cannot be distinguished by sex, shape, or preliminary comparisons at five genetic markers. These forms may be alternate morphs within a single interbreeding species or two nascent species caught in the process of divergence. These alternatives will be investigated by (1) playing back signals to breeding fishes and observing their preferences during two field trips to Africa and (2) surveying hundreds of genetic regions for differences using the new Amplified Fragment Length Polymorphism technique.If the evidence supports reproductive isolation between forms, the fact that they cannot be distinguished by external measurements or preliminary genetic data would indicate species formation to be extremely recent or still in progress. Such cases are difficult to find in nature. They yield important insights into the conditions that give rise to new species. A lack of reproductive isolation between forms, on the other hand, would demand a re-thinking of the importance of electric signals as mating barriers for all members of this group. The results of this project will also be significant to neurobiologists studying electrosensory coding in mormyrid fishes -- a field that has contributed to work on other time-coding sensory systems such as hearing.