Phylogenetic comparative analysis of electric communication signals in ghost knifefishes (Gymnotiformes: Apteronotidae)

Electrocommunication signals in electric fish are diverse, easily recorded and have well-characterized neural control. Two signal features, the frequency and waveform of the electric organ discharge (EOD), vary widely across species. Modulations of the EOD (i.e. chirps and gradual frequency rises) also function as active communication signals during social interactions, but they have been studied in relatively few species. We compared the electrocommunication signals of 13 species in the largest gymnotiform family, Apteronotidae. Playback stimuli were used to elicit chirps and rises. We analyzed EOD frequency and waveform and the production and structure of chirps and rises. Species diversity in these signals was characterized with discriminant function analyses, and correlations between signal parameters were tested with phylogenetic comparative methods. Signals varied markedly across species and even between congeners and populations of the same species. Chirps and EODs were particularly evolutionarily labile, whereas rises differed little across species. Although all chirp parameters contributed to species differences in these signals, chirp amplitude modulation, frequency modulation (FM) and duration were particularly diverse. Within this diversity, however, interspecific correlations between chirp parameters suggest that mechanistic trade-offs may shape some aspects of signal evolution. In particular, a consistent trade-off between FM and EOD amplitude during chirps is likely to have influenced the evolution of chirp structure. These patterns suggest that functional or mechanistic linkages between signal parameters (e.g. the inability of electromotor neurons increase their firing rates without a loss of synchrony or amplitude of action potentials) constrain the evolution of signal structure

Phylogenetic comparative analysis of electric communication signals in ghost knifefishes (Gymnotiformes: Apteronotidae)

Electrocommunication signals in electric fish are diverse, easily recorded and have well-characterized neural control. Two signal features, the frequency and waveform of the electric organ discharge (EOD), vary widely across species. Modulations of the EOD (i.e. chirps and gradual frequency rises) also function as active communication signals during social interactions, but they have been studied in relatively few species. We compared the electrocommunication signals of 13 species in the largest gymnotiform family, Apteronotidae. Playback stimuli were used to elicit chirps and rises. We analyzed EOD frequency and waveform and the production and structure of chirps and rises. Species diversity in these signals was characterized with discriminant function analyses, and correlations between signal parameters were tested with phylogenetic comparative methods. Signals varied markedly across species and even between congeners and populations of the same species. Chirps and EODs were particularly evolutionarily labile, whereas rises differed little across species. Although all chirp parameters contributed to species differences in these signals, chirp amplitude modulation, frequency modulation (FM) and duration were particularly diverse. Within this diversity, however, interspecific correlations between chirp parameters suggest that mechanistic trade-offs may shape some aspects of signal evolution. In particular, a consistent trade-off between FM and EOD amplitude during chirps is likely to have influenced the evolution of chirp structure. These patterns suggest that functional or mechanistic linkages between signal parameters (e.g. the inability of electromotor neurons increase their firing rates without a loss of synchrony or amplitude of action potentials) constrain the evolution of signal structure

Electron Propagation within Redox-Active Microdomains in Thin Films of Ferrocene-Containing Diblock Copolymers

This paper reports the electrochemical behavior of redox-active microdomains in thin films of ferrocene-containing diblock copolymers, polystyrene-<i>block</i>-poly­(2-(acryl­oyloxy)­ethyl ferrocene­carboxylate) (PS-<i>b</i>-PAEFc). PS-<i>b</i>-PAEFc with different PAEFc volume fractions (PS₁₅₄-<i>b</i>-PAEFc₅₁, PS₁₅₄-<i>b</i>-PAEFc₂₆, and PS₁₅₄-<i>b</i>-PAEFc₁₂, where the subscripts represent the polymerization degree of each block; <i>f</i>_PAEFc = 0.47, 0.30, and 0.17, respectively) was synthesized by sequential atom transfer radical polymerization. PS-<i>b</i>-PAEFc films of controlled thicknesses (20–160 nm) were prepared on gold substrates via spin-coating and characterized by ellipsometry. Microdomains were observed via atomic force microscopy on the surfaces of PS₁₅₄-<i>b</i>-PAEFc₅₁ and PS₁₅₄-<i>b</i>-PAEFc₂₆ thin films but not on the surfaces of PS₁₅₄-<i>b</i>-PAEFc₁₂ thin films. Electrochemical behavior of films was assessed by cyclic voltammetry and chronocoulometry in acetonitrile solution. The redox potential of ferrocene moieties was similar (ca. + 0.29 V vs Fc⁺/Fc) regardless of <i>f</i>_PAEFc and film thickness. For PS₁₅₄-<i>b</i>-PAEFc₅₁ and PS₁₅₄-<i>b</i>-PAEFc₂₆, thicker films afforded larger faradaic peak currents and exhibited diffusion-controlled voltammograms at faster sweep rates. PS₁₅₄-<i>b</i>-PAEFc₂₆ produced voltammograms less influenced by solvent-induced swelling than PS₁₅₄-<i>b</i>-PAEFc₅₁, reflecting the improved morphological stability of PAEFc microdomains by redox-inert PS frameworks. In contrast, PS₁₅₄-<i>b</i>-PAEFc₁₂ films yielded similar faradaic peak currents regardless of film thickness and exhibited voltammograms indicative of surface-confined species. These observations suggest that PS₁₅₄-<i>b</i>-PAEFc₅₁ and PS₁₅₄-<i>b</i>-PAEFc₂₆ films contain continuous PAEFc microdomains extending from the electrode to the surface, in contrast to the PS₁₅₄-<i>b</i>-PAEFc₁₂ films which contain isolated PAEFc microdomains buried within the PS matrix. Electron propagation took place only through PAEFc microdomains that could electrically communicate with the underlying electrode. Apparent diffusion coefficients within PAEFc microdomains were similar (≈ 2 × 10^–11 cm²/s) for PS₁₅₄-<i>b</i>-PAEFc₅₁ and PS₁₅₄-<i>b</i>-PAEFc₂₆. The relatively low efficiency in electron propagation was attributable to ineffective electron self-exchange reaction within the PAEFc microdomains and/or limited counterion migration through the acetonitrile-swollen microdomains. These results provide guidance in design of redox-active metalloblock copolymers for various applications, which include electrocatalysis, electrochemical mediation in enzyme sensors, and redox-controlled molecular deposition