Biophysical properties of photoreceptors in Corixa punctata facilitate diurnal life-style

Abstract

Measurement of evolutionary adaptations of a visual system to its visual and operational ecology requires comparison of visual function in different species with similar morphologies and visual ecologies, occupying the same habitats but displaying differences in visually-guided behavior. The goal here was to document the biophysical properties of photoreceptors in the lesser water boatman Corixa punctata, which shares many features with the previously studied aquatic predator water boatman backswimmer Notonecta glauca. However, unlike the backswimmer, which heavily relies on vision to catch its prey, Corixa is a detritivore. Using the patch-clamp method, I found that the average whole-cell capacitance of Corixa photoreceptors was 441±206 pF, higher than in any other insect studied so far, and that absolute sensitivity was positively correlated with capacitance (Spearman rank correlation coefficient, 0.73). Interestingly, both the sensitivity distribution median and variation in Corixa were similar to the corresponding values in the diurnal water strider Gerris lacustris and were substantially smaller than in the noctidial N. glauca or the nocturnal/crepuscular cockroach Periplaneta americana. Furthermore, capacitance was correlated with the amplitudes of light-induced (0.70) and delayed rectifier K(+) (0.46) currents, membrane corner frequency (0.68) and maximal information rate (IRmax, 0.74). No correlation was observed between capacitance and transient K(+) current. Average IRmax in Corixa was 36.0±21.3 bits s(-1), much higher than in G. lacustris but smaller than in N. glauca. These findings support the hypothesis that Corixa's retinal function is adapted to its diurnal life-style, which is also consistent with field observations.

Not flying blind: A comparative study of photoreceptor function in flying and non-flying cockroaches

“…However, when only the first 10 repeats were used, the average IR max was 33±12 bits s −1 , indicating a drastic decrease in information capacity for prolonged responses in moderately bright light (however, the residual noise level is 1.73 times higher when 10 repetitions are used for signal estimation instead of 30). Similar to several other species Frolov and Weckström, 2014;Frolov, 2015;Immonen et al, 2014a), a positive correlation was found between photoreceptor capacitance, a proxy for cell size, and maximal information rate.…”

“…To evaluate photoreceptor performance, two contrast-modulated light stimuli, a naturalistic and Gaussian white-noise, were used as described previously (Frolov, 2015). The white-noise stimulus was made of 30 repetitions of a 2 s Gaussian randomly modulated sequence preceded by an adapting 1 s steady light to accommodate the initial depolarizing transient.…”

“…The analysis of responses to white-noise stimulus was performed using Matlab 7.5 (MathWorks, Natick, MA, USA), first by averaging 30 repeats in the time domain to obtain the 2 s signal, and then subtracting the signal from each individual response to get noise traces, spectra of which were subsequently averaged. The signal-to-noise ratio (SNR) was calculated in the frequency domain and information rate (IR) was obtained according to the Shannon equation (Shannon, 1948), where f is frequency, S(f ) is the signal power and N(f ) is the noise power, within a frequency range from 0.5 to 50.0 Hz (Frolov, 2015). In the analysis of responses to the naturalistic stimulus, the SNR was obtained from the coherence function.…”

“…Ommatidia were dissociated and whole-cell recordings were performed as described previously (Frolov, 2015). In brief, an Axopatch 1D patch-clamp amplifier and pClamp software (Axon Instruments/Molecular Devices, CA, USA) were used for data acquisition.…”

Visual ecology and potassium conductances of insect photoreceptors

“…Part of the data presented in this study were obtained from previously published work on C. morosus , C. punctata (Frolov 2015), D. melanogaster (Krause et al 2008), G. lacustris , G. bimaculatus , N. glauca (Immonen et al 2014a), and P. americana (Immonen et al 2014b). Additional experiments were performed on P. xuthus, generously provided by Prof. Kentaro Arikawa (Sokendai, Hayama, Japan), G. integer, generously provided by Petri Niemelä (Munich, Germany), C. vicina, P. schultei, and G. portentosa, purchased from Blades Biological (Edenbridge, UK), and A. mellifera, E. lapponicus, and M. roeselii, which were caught locally in Oulu (Finland).…”