Biophysical properties of photoreceptors in Corixa punctata facilitate diurnal life-style.
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.
Department of Physics, Division of Biophysics, University of Oulu, P.O. Box 3000, 90014 Oulun Yliopisto, Finland. Electronic address: roman.frolov@oulu.fi.
Roman V
RV
Frolov
D000818:Animals; D059001:Aquatic Organisms / Q000502:physiology*; D005075:Biological Evolution; D055592:Biophysical Phenomena / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology; D007313:Insecta / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
Insect vision; Ion channels; Neural information processing; Visual ecology