IOS-0818390 Collaborative Research: Mechanisms of Signal Diversity in Electric Fish Communication
In this collaborative project, researchers from Cornell University in Ithaca and Washington University in St. Louis will explore the mechanisms responsible for the large-scale diversification of animal communication signals. The mormyrids are a diverse group of fishes from Africa that communicate using species-specific electric organ discharges (EODs) that are essential for species recognition. However, some species are polymorphic, with different individuals having distinct EOD forms and correspondingly different electric organ morphology. This project will focus on the polymorphic species Paramormyrops kingsleyae as a microcosm of electric signal evolution throughout the mormyrids. The researchers will use a combination of field work, molecular genetic techniques, electrophysiology, and behavioral playback experiments to determine the genetic basis for electric signal diversity in P. kingsleyae, and the importance of this diversity in driving reproductive isolation between populations and adapting different populations to their particular environments. The results of these studies will lead to specific hypotheses about the root causes of electric signal diversification throughout the mormyrids, which the researchers will test using similar techniques across a wide range of species. This research will prove broadly applicable by providing a mechanistic understanding of how animal communication signals diversify, as well as insight into the ultimate causes for this diversification and the resulting consequences for speciation and the evolution of communication behavior. Broader impacts: The project includes an educational outreach program for public school students, which uses electric fish to provide hands-on demonstrations for linking basic concepts in the physical sciences and biology. In addition, the researchers will create an online searchable database of electric signals that researchers, students, and the general public will be able to access. This database will be used to archive and catalogue thousands of EODs collected during more than 20 years of field work in Africa.
Signal Diversity in Communication Weakly electric fishes have long been used as a model system for understanding the physiological basis for animal communication. These fishes have many advantages to their study: their electric signals are simple pulses that can be accurately recorded, reproduced, and analyzed; the signal modality is used by comparatively few species that can be well characterized; and the evolutionary relationships of the fishes are well known from our previously published molecular phylogenies. In this project we have explored patterns of signal diversity among the mormyrid electric fishes (family Mormyridae) of West-Central Africa in order to understand the importance of signals for the evolution of biological diversity. Our focus was on Paramormyrops kingsleaye, whose electric signals vary geographically (Fig. 1A) because of gain and loss of structures in electrocytes – the cells making up the electric organs. In most populations of P. kingsleyae, electrocytes have penetrating stalks that receive synaptic inputs from the nervous system which initiates the action potentials in the electric organ discharge (EOD). We discovered several populations of these fish where electrocytes have non-penetrating stalks resulting in EODs that lack a small initial head-negative phase, P0, prior to the main positive peak, P1, and negative peak, P2. The EODs of this species are illustrated in Fig. 1A. This pattern of EOD variation is significant because it is similar to the pattern we have reported in other clades in the genus Paramormyrops, and other genera within the family Mormyridae (Fig. 1B) (Gallant et al., 2011; Gallant et al in preparation). We now have behavioral and population genetic data supporting the conclusion that divergence in electric signals in the Paramormyrops species flock arose in advance of divergence in size, morphology, or trophic ecology. These results lead to the conclusion that sexual selection may be the driving force behind the adaptive radiation of weakly electric fishes of West-Central Africa (Arnegard et al, 2010). Figure 1. Paramormyrops kingsleyae EOD variation is a microcosm of EOD variation in Paramormyrops. (A) P. kingsleyae signals are variable in the presence of a small initial head negative phase (P0) of the EOD. (B.) Twelve sympatric Paramormyrops species captured from the same locality in the Ivindo River of Gabon shows EOD variation within Paramormyrops, which differ in terms of duration and polarity, as well as in the number of phases to the discharge. All Paramormyrops on the left have P0-absent EOD waveforms, and lack penetrating stalked electrocytes, while all Paramormyrops on the right have P0-present waveforms and also have penetrating stalked electrocytes. References Arnegard, M., E., McIntyre, P., B. , Harmon, L. J., Zelditch, M. L., Crampton, W. G. R., Davis, J. K., Sullivan, J. P., Lavoué, S. and Hopkins, C. D. (2010). Sexual signal evolution outpaces ecological divergence during electric fish species radiation. American Naturalist 176, 335-356. Gallant, J. R., Arnegard, M. E., Sullivan, J. P., Carlson, B. A. and Hopkins, C. D. (2011). Signal variation and its morphological correlates in paramormyrops kingsleyae provide insight into the evolution of electrogenic signal diversity in mormyrid electric fish. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 197, 799-817. Gallant, J. R., Deitcher, D. L. and Hopkins, C. D. (2012). Differential expression of genes and proteins between electric organ and skeletal muscle in the mormyrid electric fish brienomyrus brachyistius. J. Exp. Biology 215, 2479-2494. Gallant, J. R., J. Sperling, et al. (in preparation). "Microevolutionary processes underlying macroevolutionary patterns of electric signal diversity in mormyrid fish."
