Co-adaptation of electric organ discharges and chirps in South American ghost knifefishes (Apteronotidae)

Abstract

Animal communication signals that simultaneously share the same sensory channel are likely to coevolve to maximize the transmission of each signal component. Weakly electric fish continuously produce a weakly electric field that functions in communication. Fish modulate the electric organ discharge (EOD) on short timescales to produce context-specific signals called chirps. EODs and chirps are simultaneously detected by electroreceptors and processed in the electrosensory system. We analyzed these signals, first to explore whether EOD waveform is encoded in the signal received by electroreceptors and then to examine how EODs and chirps interact to influence conspicuousness. Our findings show that gross discrimination of sinusoidal from complex EOD waveforms is feasible for all species, but fine discrimination of waveform may be possible only for species with waveforms of intermediate complexity. The degree of chirp frequency modulation and chirp relative decay strongly influenced chirp conspicuousness, but other chirp parameters were less influential. The frequency difference between the interacting EODs also strongly impacted chirp conspicuousness. Finally, we developed a method for creating hybrid chirp/EOD combinations to independently analyze the impact of chirp species, EOD species, and EOD difference frequency on chirp conspicuousness. All three components and their interactions strongly influenced chirp conspicuousness, which suggests that evolutionary changes in parameters of either chirps or EODs are likely to influence chirp detection. Examining other environmental factors such as noise created by fish movement and species-typical patterns of sociality may enrich our understanding of how interacting EODs affect the detection and discrimination of chirps across species.

Evolution of electric communication signals in the South American ghost knifefishes (Gymnotiformes: Apteronotidae): A phylogenetic comparative study using a sequence-based phylogeny

“…Petzold et al (2016), found that the conspicuousness of chirps of different species was affected by parameters of both EODs and chirps. We hypothesized that EOD waveform and chirp parameters (FM and duration) might have co-evolved with each other to optimize the detection and/or discrimination of conspecific chirps.…”

“…We tested two additional hypothesized relationships based on recent findings that EOD waveform influences the conspicuousness of chirps (Petzold et al, 2016). Specifically, we asked whether EOD waveform complexity (F2-F1) was associated with chirp FM or chirp duration to test the hypothesis that EOD waveform complexity co-evolves with chirp parameters to maximize their conspicuousness.…”

Tracking activity patterns of a multispecies community of gymnotiform weakly electric fish in their neotropical habitat without tagging

“…Whereas rises seem to be highly conserved between species, chirps and EOD waveforms appear to be evolutionarily labile (Turner et al, 2007), and thus chirps are potential additional cues for species identification (Fugère and Krahe, 2010). The different types of chirps and EOD waveforms result in various degrees of conspicuousness of the resulting signals (Petzold et al, 2016) that may translate into discriminability by the electrosensory system. Chirps have also been suggested to aid disambiguation of the sign of high-frequency beats (Walz et al, 2014).…”

Behavioral and Neural Aspects of the Spatial Processing of Conspecifics in the Electrosensory System

“…Identity can be determined from the EOD pattern (Fig 2a): depending on the species, EOD frequency, shape or pulse pattern can be used to identify conspecifics from individuals of another species (Zupanc, Sîrbulescu, Nichols, & Ilies, 2006) or even differentiate amongst conspecifics (Zakon, Oestreich, Tallarovic, & Triefenbach, 2002). In wave type species, the EOD frequency (and possibly shape; Kolodziejski, Sanford, & Smith, 2007;Petzold, Marsat, & Smith, 2016) is perceived indirectly.…”