5 research outputs found
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
Measurement of Ion Currents through Porous Membranes with Scanning Ion Conductance Microscopy
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 (PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub>, PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>, and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub>, where the subscripts represent the polymerization
degree of each block; <i>f</i><sub>PAEFc</sub> = 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 PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> thin films but not on the surfaces
of PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> 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<sup>+</sup>/Fc)
regardless of <i>f</i><sub>PAEFc</sub> and film thickness.
For PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>, thicker films afforded
larger faradaic peak currents and exhibited diffusion-controlled voltammograms
at faster sweep rates. PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> produced voltammograms less influenced by solvent-induced
swelling than PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub>, reflecting the improved morphological stability of PAEFc microdomains
by redox-inert PS frameworks. In contrast, PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> films yielded similar faradaic peak
currents regardless of film thickness and exhibited voltammograms
indicative of surface-confined species. These observations suggest
that PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub> films contain continuous
PAEFc microdomains extending from the electrode to the surface, in
contrast to the PS<sub>154</sub>-<i>b</i>-PAEFc<sub>12</sub> 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<sup>–11</sup> cm<sup>2</sup>/s) for PS<sub>154</sub>-<i>b</i>-PAEFc<sub>51</sub> and PS<sub>154</sub>-<i>b</i>-PAEFc<sub>26</sub>. 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