Amplitude-frequency tradeoffs in the active sensory and communication signal of a weakly electric fish

Abstract

Animal communication signals play an important role in behavioral processes to ensure fitness and survivorship of individuals within a species. Weakly electric fish produce communication signals that could be among the most energetically expensive signals in the animal kingdom. These electric signals underlie an active sensory modality (electroreception) as well as a primary communication modality. The weakly electric fish Eigenmannia virescens generates constant, quasi-sinusoidal electric organ discharges (EODs) at a frequency of 200-600Hz. The EOD signals are produced by the summed action potentials of electrocytes - the electrically excitable cells of the electric organ (EO). Electric signals with stronger intensity bring adaptive advantages such as better resolution for electrolocation and higher efficacy of elctrocommunication, but also require larger energetic investments. Two signal features, EOD amplitude (EODa) and EOD frequency (EODf), are likely the primary determinants of the energetic costs of the EOD. Previous studies have verified the positive relationship between EODf and signal metabolic costs via both electrocyte model estimations at the cellular level and whole-animal respirometry measurements at the organismal level. Experimental evidence from behavioral studies of electric fish under energetic stress also suggest a correlation between EODa and signal energetic demands. I estimated and examined the combined roles of energetic limitations and sensory effectiveness on signal modulation in E. virescens via numerical simulations and behavioral experiments. Computational simulations of single electrocytes revealed a strong positive relationship between EODf and signaling costs, but no clear relationship between EODa and signaling costs. In subsequent behavioral experiments, I hypothesized that an increase in EODa or EODf would be offset by a compensatory decrease in the other. However, I did not observe clear tradeoffs between EODa and EODf. Future studies of the relationship between EODa, EODf, and signal energetics are needed to more fully investigate the causes and mechanisms through which animals regulate their communication signals and balance the costs and benefits associated with signaling.