Is the white eye of insect eye-color mutants really white?

Abstract

1. Spectral sensitivity curves (SSCs) of (a) the whole eye and peripheral photoreceptors R1–6 were recorded in wild-type flies and chalky mutants of Calliphora, and (b) the whole eye of Drosophila, wild type and mutant white. Our spectrosensitometer provided good resolution and accuracy. 2. A vibrational fine structure of the SSC in the ultra-violet spectral range was clearly resolved in all the genotypes studied (Fig. 1). 3. In the visible spectral range, the SSCs of white-eyed mutants appeared to be significantly narrower than the absorption spectrum of the template visual pigments (Fig. 2). The bandwidth ratios (wild type: visual pigment: white-eyed mutant) were as follows: 111±10:102:95±4nm and 114±14:102:93±7 nm in Calliphora whole eye and cells R1–6, respectively; and 118±6:100:97±2 nm in the whole eye of Drosophila (Fig. 3). 4. Long-wave portions of SSCs in mutants showed a good fit with those of the absorption spectrum of visual pigments: P490 for the whole eye, P487 for receptors R1-6 of chalky mutants of Calliphora, and P478 for the whole eye of Drosophila. 5. The narrowing of the SSCs compared with the absorption spectrum of the template visual pigment is believed to be due to the presence of hypothetical blue-absorbing pigments in the eye media.