http://link.springer.com/content/pdf/10.1007/978-3-642-67868-4_4.pdf

Spatial Vision in Arthropods

Practically no other invertebrate has been used so extensively for the investigation of the visual system as the fly, particularly the genera Musca, Calliphora and Drosophila. The reasons are manifold: The fly’s visual system represents an intermediate grade of complexity at which sophisticated neural analysis is performed, but the underlying hardware is relatively simple. Not only are there far fewer neurones than in, for example, the vertebrate CNS, but the neurones are also organized into very precise repeating units (retinotopic columns). Thanks to extensive anatomical studies the neuroanatomical pathways, down to the level of single cells, are probably better known than in any other neuropil of comparable complexity (reviews: Strausfeld 1976; Strausfeld and Nassel 1981). The fly is also very amenable to behavioural experiments, and extensive quantitative data are available for a variety of visually guided behaviour (Reichardt and Poggio 1976; Poggio and Reichardt 1976; Heisenberg and Buchner 1977; reviews: Buchner 1984; Wehrhahm 1984).

Functional Organization of the Fly Retina

The visual world offers a variety of information that enables animals to orient themselves to their surroundings. One specific feature of the visual information is the wavelength difference of light emittedfrom light sources or reflectedfrom objects. Under natural conditions, a general difference in the spectral composition of light is based upon the fact that light coming directly from light sources, e.g., the sun, sky, and moon, is characterized by its relatively high content of short wavelength ( 450nm) (Figs. 1). The physical basis of these differences is the preferential absorption by pigment molecules, which—in contrast to atoms and small molecules—have resonances above 300 nm and shift the bulk of the reflected light into the green and orange region of the spectrum. In water, the wavelength range is compressed in the long-wavelength part of the spectrum due to water’s high absorption of red and infrared light (Fig. 1). But in water, too, direct light is relatively richer in shortwave light. Neglecting the finer differences in the spectral content of light, this general distinction between direct and reflected light could be the cue that allows an animal to differentiate such basically different habitats as open spaces, shadowed areas, spaces rich in food, hiding places, etc.

Spectral Sensitivity and Color Vision in Invertebrates

http://www.gatsby.ucl.ac.uk/~beierh/neuro_jc/reiser_dickinson_07.pdf

A modular display system for insect behavioral neuroscience.

“I come to the discussion of a remarkable optical phenomenon the unravelling of which has caused me a good deal of worry.” In this way Sigmund Exner (1891, p. 162) begins the chapter on pseudopupils in his invaluable monograph “Die Physiologie der facettirten Augen von Krebsen und Insecten”. His worry has proved worthwhile because his recognition that pseudopupils are optical revelations of the interior of compound eyes has been of longlasting and immense importance. The aims of this chapter are to show that pseudopupil phenomena provide a direct and deep insight, both figuratively and literally, into compound-eye structure and function, and also to indicate possible paths for future research.

Pseudopupils of Compound Eyes

Low vitamin A rearing decreases sensitivity and eliminates the ultraviolet but not the blue sensitivity maximum in R1-6 inDrosophila, Calliphora andMusca (Figs. 2–4). Spectral adaptation functions for control and vitamin A deprived flies yielded derived stable metarhodopsin absorption spectra from spectral sensitivity. Metarhodopsin has a long wavelength maximum and also has an ultraviolet maximum especially in the normal vitamin A condition (Figs. 2–4). M-potentials (fast early-receptor-like potentials) were obtained (Fig. 1) from all three genera in normal vitamin A rearing and were used for spectral adaptation studies (Figs. 2–3); the latter data are approximate inverses of sensitivity based spectral adaptation data. Thus, sensitivity must reflect proportion of rhodopsin, with metarhodopsin being inert in receptor potential generation. Vitamin A effects on spectral functions were further investigated inDrosophila. Ultraviolet (370 nm) and visible (470 nm) sensitivities varied approximately linearly with dietary vitamin A dose (Fig. 5); 370 nm sensitivity decreased more than 470 nm sensitivity at lower doses. Increasing adaptation intensities of 370 and 470 nm caused parallel decreases in spectral sensitivity assayed at 370 and 470 nm in normal vitamin A flies (Fig. 6); the adapting intensities were sufficient to convert photopigment. These and previous results suggest that the two R1-6 spectral peaks are ultimately mediated by one rhodopsin. R1-6 rhabdomeres were structurally similar in high and low vitamin A flies but emitted a long wavelength fluorescence to ultraviolet excitation in high vitamin A flies only (Fig. 7). These results suggest some form of energy transfer; i.e., a carotenoid may capture ultraviolet quanta and transfer energy to rhodopsin via inductive resonance. Spectral adaptation data are consistent with a calculated high rhabdomeric optical density of ECL=0.26 (i.e., 45% of incident light is absorbed) derived from presently available data onDrosophila. Calculations show electro-retinographic sensitivity to be extremely high, perhaps measurable at less than one absorbed quantum per rhabdomere.

Sensitivity and photopigments of R1-6, a two-peaked photoreceptor, inDrosophila, Calliphora andMusca

Chromatic adaptation and receptor-deficient mutants have been used to systematically eliminate specific receptor function to provide the first complete spectral sensitivity and photopigment characteristic data of all three receptor types (R1-6, R7 and R8) in Drosophila compound eyes. Different fly genera have different adaptation responses which allow characterization of photopigment spectra. Drosophila mutants with anomalous excitation also reveal mechanisms coupling photopigment activation with receptor excitation.

Austina M. Ivanyshyn

Papers

Sensitivity and photopigments of R1-6, a two-peaked photoreceptor, inDrosophila, Calliphora andMusca

Spectral sensitivities and photopigments in adaptation of fly visual receptors.