Hdc^JK910 mutants, like wild type flies, show arrhythmic behavior in constant dim white light conditions.

Hdc^JK910/Hdc^JK910 flies show defects in the visual alert response assay (around 80% of mutants are non-responsive to a moving object and most of the remainder show delayed alert responses, with a small minority displaying a brief pause), and show severe defects in both the optomotor and phototaxis responses.

Hdc^JK910 mutants exhibit normal light-dependent temperature preference. Similarly to wild-type, they prefer higher temperature in the light than in the dark.

Photoreceptor terminals in Hdc^JK910 mutants exhibit a reduced number of synaptic vesicles. The density of these synaptic vesicles is approximately 27% of wild-type.

Hdc^JK910 flies do not exhibit ON and OFF transients in ERG recordings of the laminar LMC neurons at the onset and end of light stimulation.

Approximately 60% of Hdc^JK910 mutants show no visual alert response (to a moving block, than in wild-type freezes fly movement). Approximately 25% exhibit a delayed response, and a brief-pause response is observed in 15% of flies.

Hdc^JK910 mutant photoreceptors form the correct number of synapses per presynaptic terminal independently of cartridge composition.

The temperature preference profile of Hdc^JK910 homozygous adults is abnormal. There is a broader spread of temperature preferences with a significantly with fewer flies choosing the wild-type majority preference of 24-25'C. Locomotor activity levels in these animals appear to be normal. However, when placed at 40'C, these flies are rendered unconscious at a significantly faster rate than wild-type and their recovery from a 10 minute 40'C heat shock is significantly slower than wild-type.

Hdc^JK910 homozygotes have a significantly increased death rate after 6 days at 4'C compared to wild-type.

Immediately after lights-off, both the wild-type and Hdc^JK910 mutant electroretinograms start a sharp recovery, but soon the mutant lags behind to wild-type. This phenotype is much diminished after a 0.2-second pulse of light compared to a 3-second pulse. Indeed, in the majority of cases, the individual mutant flies that display slow termination kinetics after a long pulse have a faster repolarization after a short pulse.

Hdc^JK910 flies exhibit abnormal phototaxis.

Electroretinograms (ERGs) of homozygous flies show no on- or off-transients. The ERG is essentially recovered in these flies after histamine feeding or expression of Hdc^hs.P. Homozygous flies exhibit abnormal behaviour in the "Buridan's paradigm" assay, showing disoriented random walks. This behaviour is partially rescued by histamine feeding. The scratch or escape response of homozygous flies to stimulation of the posterior scutellar macrochaeta or surface of the eye is reduced to approximately 10-15%. The response is restored to approximately 60% by histamine feeding. Response in a grooming assay is reduced compared to wild-type, but is partially rescued by histamine feeding.

The lobula plate is smaller than in wild-type flies. Hdc^JK910 flies kept in constant darkness have a smaller lamina volume than Hdc^JK910 flies kept in constant light, as is also seen for wild-type flies.

On/off transients of ERG are missing.