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

最近在加蓬发现了一群种类繁多的mormyrid鱼。这些鱼产生微弱的电脉冲来相互交流。过去的研究表明，它们可以检测到脉冲波形之间的差异，并利用这些信息来识别同一物种。每个物种都会发出独特的电子信号，但有一个明显的例外。两种信号形式（“正常极性”和“反向极性”）是由共同发生的个体产生的，这些个体不能通过性别、形状或五种遗传标记的初步比较来区分。这些形式可能是在一个杂交物种内的交替变种，也可能是在分化过程中被捕获的两个新生物种。这些选择将通过(1)在两次非洲实地考察中向繁殖鱼类播放信号并观察它们的偏好(2)使用新的扩增片段长度多态性技术调查数百个遗传区域的差异来研究。如果证据支持不同物种之间的生殖隔离，那么它们无法通过外部测量或初步遗传数据加以区分的事实将表明，物种的形成是极其近期的，或仍在进行中。这种情况在自然界是很难找到的。它们对产生新物种的条件提供了重要的见解。另一方面，不同形式之间缺乏生殖隔离，就需要重新思考电信号作为这一群体所有成员的交配障碍的重要性。这个项目的结果对于研究mormyrid鱼类电感觉编码的神经生物学家来说也很重要——这一领域已经为其他时间编码的感觉系统（如听觉）的研究做出了贡献。

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.