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

Summary

• 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.