Correspondence Between Visual Spectral Sensitivity and Bioluminescence Emission in Click Beetles (Coleoptera: Elateridae)

Abstract

Abstract: : Purpose: The existence of spectral correspondence between the characteristics of visual receptors and the species’ bioluminescence emission was investigated in four species of click beetles. Methods: Electroretinograms elicited by colored stimuli were recorded from the corneal surface of the eye and visual spectral sensitivity functions were determined by the criterion amplitude method. Absorbance of photopigments and screening pigments was determined by in situ microspectrophotometry. In vivo bioluminescence emission spectra of the dorsal and the ventral lanterns in both the male and the female of the species were recorded on a Fluorolog Spectrofluorometer. Results: In situ microspectrophotometry reveals the presence of P540 rhodopsin that interconverts with M488 metarhodopsin in Pyrophorus species. A species–specific yellow screening pigment that absorbs broadly in the blue region of the spectrum is located in the ventral sector of the compound eyes. The electroretinographic visual spectral sensitivity [S()] functions for dark–adapted compound eyes obtained in click beetles show a broad peak in the green with a shoulder in the near–UV. Green/red chromatic adaptation differentially affected visual sensitivity such that sensitivity in the long wavelengths (green and red) was markedly reduced, thereby isolating high sensitivity in the near–UV. Spectral correspondence exists between the sensitivity peaks in the green for Fulgeochlizus bruchii (_max 540 nm), Pyrearinus termitilluminans (_max 540 nm), Pyrophorus punctatissimus (_max 545 nm), and P. divergens (_max 560 nm), and species BL: (_max 539 nm, 527 nm), (_max 542 nm, 540nm), (_max 542 nm, 540 nm), (_max 557 nm, 558 nm) emitted from the ventral lanterns in both the male and the female click beetles respectively. Conclusions: A spectral sensitivity model generated using different optical densities (O. D. from 0.6 to 2) of the screening pigment overlaid on P540 rhodopsin in the ventral retina shows spectral tuning between visual receptors and the range of species yellow–green BL spectra from the ventral abdominal lanterns among Pyrophorus. Hence optimization for the detection of BL optical signals has occurred among click beetles.

Keywords: photoreceptors • electrophysiology: non-clinical • photoreceptors: visual performance