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

Clk^Jrk mutant flies show circadian-dependent activation of apoptosis in the head at an earlier age than do wild-type flies.

Sleep bout duration and total daily sleep are significantly reduced compared to controls in mutant flies, while there is no compensatory increase in sleep bout number. Sleep latency is significantly increased.

1 day memory retention is normal after spaced training in an olfactory conditioning assay.

Triglyceride levels in Clk^Jrk mutants are similar to wild-type.

Mutant flies show no rhythmic locomotor activity under free-running conditions (after entrainment in light-dark cycles or temperature cycles).

44% of heterozygous flies are arrhythmic under constant darkness conditions.

100% of Clk^Z3-0084/Clk^Jrk flies are arrhythmic under constant darkness conditions.

Clk^Jrk mutants consume similar amounts of food, regardless of the circadian period (i.e. light or dark) after 3 days of entrainment to LD and then transference to DD for 2 days before the assay.

Clk^Jrk flies display rhythmic feeding patterns in LD, indicating that the feeding rhythm is under the control of an internal clock, but can also be driven by light.

Clk^Jrk mutants do not display phenotypes related to either survival time under starvation conditions or glycogen storage. Total food consumption is also unchanged in these mutants compared to controls.

Clk^Jrk has no effect on experience-dependent responses in sleep need.

Clk^Jrk mutant larvae are highly sensitive to light (shown in light avoidance assays), even at low intensities (150 lux).

Mutant flies are arrhythmic for locomotor activity under constant light conditions at a constant temperature of 25[o]C, but become rhythmic immediately after being exposed to a temperature cycle of 12 hours at 25[o]C and 12 hours at 30[o]C. The locomotor activity is rather dispersed over 24 hours with slightly higher activity during the thermophase. The locomotor activity rhythm of the mutant flies differs from that of wild-type flies, in that neither anticipatory activity nor transients after a transfer to temperature cycles is observed.

There is no significant increase in the time spent copulating by pairs of Clk^Jrk homozygous flies compared to wild-type pairs.

Long term memory of courtship conditioning (reduction in time spent in courtship behaviour 5 days after a 7 hour conditioning) is normal in Clk^Jrk homozygous males.

Heterozygotes exhibit a locomotor rhythmicity of ~24.67 hours. Homozygotes are arrhythmic. Clk^Jrk/Clk^ar animals are arrhythmic.

Clk^Jrk mutant females mated to Clk^Jrk mutant males lay significantly less eggs and produce significantly less progeny than wild-type flies. The percentage of unfertilised eggs from this mating is not significantly greater than for wild-type.

Clk^Jrk flies are often arrhythmic; only one third of these mutants are rhythmic in LD and over half are completely arrhythmic in DD.

The startle response to lights-on normally seen in the locomotor activity rhythms of wild-type flies exposed to 12 hour light:12 hour dark ( 12:12LD ) conditions is not seen in Clk^Jrk flies. The flies are preferentially nocturnal. Under constant darkness conditions, Clk^Jrk flies show roughly equal amounts of locomotor activity during the subjective day and night.

Mutant females show a more prominent sleep rebound after sleep deprivation (in constant darkness) than wild-type flies; they recover 100% of lost sleep within 12 hours (wild-type flies recover 30-40% of lost sleep within 12 hours). Exposure of mutant females to heat before 12 hours of sleep deprivation reduces homeostatic drive (sleep rebound).

In wild-type larvae, dorsally projecting axonal processes arising from the s-LN_v cells terminate near the calyx of the dorsal brain mushroom body. These projections are absent in Clk^Jrk brains. The projections from the l-LN_v cells are also aberrant. Approximately half of mutant brains have abnormal projections; in others one or two axons in this region projected farther and irregularly toward a dorsal or median region of the brain. None of these projections are similar to then more dorsal-reaching projections in the brains of wild-type adults.

Homozygotes show completely arrhythmic locomotor behaviour in constant darkness. 47% of heterozygotes are arrhythmic under constant darkness, and those flies that do show rhythmic locomotor behaviour in these conditions have a slightly longer period than wild-type controls. Only 64% of heterozygotes and 14% of homozygotes show measurable rhythmic locomotor behaviour under 12 hour light:12 hour dark conditions. Like wild-type flies, some homozygotes react to the lights-on transition, but they fail to react to the lights-off transition. Homozygotes are also arrhythmic with respect to adult emergence.