Electroretinograms of Cricket Compound Eyes Evoked by Ultraviolet, Visible, and Mid-infrared Irradiation

Abstract

Light-emitting diodes (LEDs) and a mid-infrared (IR) free-electron laser (FEL) at Nihon University, Laboratory for Electron Beam Research and Application (mid-IR LEBRA-FEL) were used as irradiation stimuli for compound eyes of arthropodan cricket (Gryllus bimaculatus, Insecta, Arthropoda). The LEDs covered ultraviolet and visible wavelength ranges from 365 to 680 nm, and the mid-IR FEL wavelengths were from 3 to 6 μm. The electrical signals from the compound eyes were detected as amplitude functions of electroretinograms (ERGs) with an electrophysiological technique using a cotton-wick electrode. The maximum sensitivities were at wavelengths of 388 nm for ultraviolet and 478 nm for visible light. These data support previous studies in which xenon or monochromatic light was used as the irradiation stimulus. To verify that the ERG signal depended solely on mid-IR irradiation, several kinds of filters, including glass plates, a long-pass filter, a band-pass filter, and silicon plates, were used. The maximum spectral sensitivity to mid-IR FEL of cricket compound eyes is probably at longer wavelengths than 6 μm; however, we did not examine longer wavelength regions owing to the wavelength limits of the LEBRA-FEL. However, the mid-IR response (ERGs) of the cricket compound eyes were not an anomaly but the second discovery of an animal's light perception of mid-IR. These results support the first discovery that we reported, revealing that the compound eyes of crayfish (Procambarus clarkii, Crustacea, Arthropoda) responded to mid-IR stimuli. We plan to use the mid-IR FEL at Kyoto University (wavelength regions: 3.4-28 μm) instead of LEBRA-FEL to examine the sensitivity to longer mid-IR wavelengths.