Visual learning in a photoreceptor degeneration mutant ofDrosophila melanogaster

Populations ofDrosophila melanogaster wildtype (strain CS) and of the photoreceptor mutantrdgB with functionally inactivated retinula cells R1–6 could be conditioned to avoid different intensities of a 406 nm light, which had been paired with aversive stimulation (shaking). Thus general visual learning ability is not impaired by therdgB mutation implying that conditionable intensity discrimination can be mediated by retinal receptors R7 and R8. Although therdgB mutant shows no conditionable intensity discrimination below an intensity threshold of 0.015 W·m−2, both the wildtype and the mutant could be conditioned to discriminate intensity differences as small as 0.5 log units at higher intensities (Fig. 4 and 5). Experiments in which two spectrally different stimuli (399 nm and 512 nm) are employed, show that conditioning effects for therdgB mutant and also for the wildtype are dependent on the given combinations of intensitiy values (Fig. 6). These experiments are in accordance with the expectation that the wildtype discriminates both wavelengths and intensities. ForrdgB flies no positive evidence for the existence of colour discrimination could be found (Fig. 7 and 8, Table 2).