Entrainment of eclosion rhythm in Drosophila melanogaster populations reared for more than 700 generations in constant light environment

In this paper, we report the results of our extensive study on eclosion rhythm of four independent populations of Drosophila melanogaster that were reared in constant light (LL) environment of the laboratory for more than 700 generations. The eclosion rhythm of these flies was assayed under LL, constant darkness (DD) and three periodic light-dark (LD) cycles (T20, T24, and T28). The percentage of vials from each population that exhibited circadian rhythm of eclosion in DD and in LL (intensity of approximately 100 lux) was about 90% and 18%, respectively. The mean free-running period (τ) of eclosion rhythm in DD was 22.85 ± 0.87 h (mean ± SD). Eclosion rhythm of these flies entrained to all the three periodic LD cycles, and the phase relationship (ψ) of the peak of eclosion with respect to “lights-on” of the LD cycle was significantly different in the three periodic light regimes (T20, T24, and T28). The results thus clearly demonstrate that these flies have preserved the ability to exhibit circadian rhythm of eclosion and the ability to entrain to a wide range of periodic LD cycles even after being in an aperiodic environment for several hundred generations. This suggests that circadian clocks may have intrinsic adaptive value accrued perhaps from coordinating internal metabolic cycles in constant conditions, and that the entrainment mechanisms of circadian clocks are possibly an integral part of the clockwork.     

Activity rhythm of Drosophila kept in complete darkness for 1300 generations

Locomotor activity rhythms of dark stock flies of Drosophila melanogaster kept in complete darkness for 700 to 1340 generations were examined. The stock was established by the late Prof. S. Mori in November 1954 to investigate long-term effects of darkness on organisms. The activity of flies was recorded under three types of light conditions: DD after LD12:12, and DD after exposure to a 3.5 h (P3) or 7.5 h (P7) light pulse. In all of these conditions, the experimental dark flies exhibited clear circadian rhythms similar to those of control light flies. We compare our results with those of various studies on troglobites.     

Relationship between a metabolic rhythm and emergence rhythm in Drosophila melanogaster

Oxygen consumption and lactic acid dehydrogenase (LDH) activity were determined for Drosophila melanogaster pupae and pharate adults exposed to 12 : 12 or 1 : 23 light-dark (LD) regime. Bimodal circadian fluctuations of oxygen consumption were found in pupae and pharate adults exposed to either LD regime and organisms appeared to demonstrate an anticipatory change in oxygen consumption associated with change in illumination. The oxygen-consumption trend for the entire period spent in the puparium showed a high at the time of emergence, but the diurnal rhythm showed a low at the time of emergence suggesting that emergence occurs at a low in the diurnal cycle. Emergence maximum showed a 3 hr lead over the oxygen-consumption maximum. Changing the LD regime produced similar changes in the phasing of both oxygen consumption and emergence rhythms. LDH activity did not demonstrate a detectable circadian rhythm but did show a steady decrease during pupal and pharate adult development.     

Altitudinal variation in the circadian rhythm of oviposition in Drosophila ananassae

The effect of altitude on four basic properties of the pacemaker controlling the circadian rhythm of oviposition in two strains of Drosophila ananassae was determined. The high altitude (HA) strain from Badrinath (5123 m above sea level) had a low amplitude peak in the forenoon while the low altitude (LA) strain from Firozpur (179 m a.s.l.) had a high amplitude peak after the lights-off of LD 12:12 cycles. Free running periods in continuous darkness were about 22.6 and 27.4 h in the HA and LA strains, respectively. The light pulse phase response curve (PRC) for the HA strain showed a low amplitude and a dead zone of 8h; the ratio for the advance to delay region (A/D) was less than 1, while the PRC for the LA strain had a high amplitude, which was devoid of a dead zone and showed a ratio of A/D > 1. The magnitude of the delay phase shifts at CT 18 evoked by light pulses of 1 h duration, but varying light intensity was significantly different in the HA and LA strain, which suggests that the photic sensitivity of the clock photoreceptors mediating the phase shifts had been affected by the altitude.     

Latitude dependent arrhythmicity in the circadian oviposition rhythm of Drosophila ananassae

Latitude dependent arrhythmicity in the circadian rhythm of oviposition of Drosophila ananassae strains originating from 8.1°N to 32.7°N was studied by inbreeding them in cycles of 12 h of light at 20 lux and 12 h of darkness. The number of inbreeding generations required to initiate arrhythmicity in oviposition rhythm was dependent on the origin of latitude of the strain. The strains from the lower latitudes became arrhythmic after notably more numbers of generations than those from the higher latitudes. This might be attributed to the higher inherent degree of oviposition rhythmicity in the F₁ generation, and enhanced photic sensitivity of the circadian pacemaker mediating entrainment of oviposition rhythm of the strains from lower latitudes as compared to those from the higher latitudes.     

Persistence of orientation toward a temporarily invisible landmark in Drosophila melanogaster

In arena experiments with the walking fruit fly, we found a remarkable persistence of orientation toward a landmark that disappeared during the fly's approach. The directional stability achieved by `after-fixation' allows a fly to continue pursuit under natural conditions, where a selected target is frequently concealed by surrounding structures. The persistence of after-fixation was investigated in Buridan's paradigm, where a fly walks persistently back and forth between two inaccessible landmarks. Upon disappearance of a selected target, the flies maintained their intended course for more than 15 body lengths of approximately 2.5 mm in about 50% of the trials. About 13% even exceeded 75 body lengths. About 88% of the approaches clustered in equal portions around peaks at 2.4 s and 8.6 s. About 12% of the approaches persisted even longer. In contrast, a single peak at about 2.2 s is sufficient to describe the persistence of orientation in a random walk. The ability to pursue an invisible landmark is disturbed neither by a transient angular deviation from the course toward this landmark, when this target disappeared, nor by a distracting second landmark. Accordingly, after-fixation seems to require an internal representation of the direction toward the concealed target, and idiothetical course control to maintain this direction. Accepted: 19 September 1997     

Developmental plasticity of the locomotor activity rhythm of Drosophila melanogaster

We used four replicate outbred populations of Drosophila melanogaster to investigate whether the light regimes experienced during the pre-adult (larval and pupal) and early adult stages influence the free-running period (τ_DD) of the circadian locomotor activity rhythm of adult flies. In a series of two experiments four different populations of flies were raised from egg to eclosion in constant light (LL), in light/dark (LD) 12:12 h cycle, and in constant darkness (DD). In the first experiment the adult male and female flies were directly transferred into DD and their locomotor activity was monitored, while in the second experiment the locomotor activity of the emerging adult flies was first assayed in LD 12:12 h for 15 days and then in DD for another 15 days. The τ_DD of the locomotor activity rhythm of flies that were raised in all the three light regimes, LL, LD 12:12 h and in DD was significantly different from each other. The τ_DD of the locomotor activity rhythm of the flies, which were raised in DD during their pre-adult stages, was significantly shorter than that of flies that were raised as pre-adults in LL regime, which in turn was significantly shorter than that of flies raised in LD 12:12 h regime. This pattern was consistent across both the experiments. The results of our experiments serve to emphasise the fact that in order to draw meaningful inferences about circadian rhythm parameters in insects, adequate attention should be paid to control and specify the environment in which pre-adult rearing takes place. The pattern of pre-adult and early adult light regime effects that we see differs from that previously observed in studies of mutant strains of D. melanogaster, and therefore, also points to the potential importance of inter-strain differences in the response of circadian organisation to external influences.     

Temperature entrainment of the circadian cuticle deposition rhythm in Drosophila melanogaster

The cuticle deposition rhythm, which is observed in the apodeme of the furca in the thorax, is controlled by a peripheral circadian clock in the epidermal cells and entrained to light-dark (LD) cycles via CRYPTOCHROME (CRY) in Drosophila melanogaster. In the present study, we examined the effects of temperature (TC) cycles and the combination of LD and TC cycles on entrainment of the cuticle deposition rhythm. The rhythm was entrained to TC cycles, whose period was 28 h. In T = 21 and 24 h, the rhythm was entrained to TC cycles in some individuals. CRY is not necessary for temperature entrainment of the cuticle deposition rhythm because the rhythm in cry(b) (lacking functional CRY) was entrained to TC cycles. Temperature entrainment of the rhythm was achieved even when the thoraxes or furcae were cultured in vitro, suggesting that the mechanism for temperature entrainment is independent of the central clock in the brain and the site of the thermoreception resides in the epidermal cells. When LD and TC cycles with different periods were applied, the rhythm was entrained to LD cycles with a slight influence of TC cycles. Thus, the LD cycle is a stronger zeitgeber than the TC cycle. The variance of the number of the cuticle layers decreased in the flies kept under LD and TC cycles with the same period in which the thermophase coincided with the photophase. Therefore, we conclude that LD and TC cycles synergistically entrain the rhythm. Synergistic effects of LD and TC cycles on entrainment were also observed even when the thoraxes were cultured in vitro, suggesting that the light and temperature information is integrated within the peripheral circadian system.     

Latitudinal variation in oviposition rhythm of Drosophila ananassae strains originating from the equator to subtropics

Parameters of oviposition rhythm of Drosophila ananassae strains originating from the equator, 0°N to 22.29°N were variable and latitude dependent. Phase angle difference (Ψ), amplitude of rhythm (R) and the percent oviposition in photophase (POP) were determined in LD 12:12 cycles. Although the R did not vary, the Ψ and POP varied by ∼5 h and 60, respectively. Ψ was positively correlated while the POP was negatively correlated with latitude. Transfers from LD 12:12 cycles to constant darkness initiated free-running rhythms in all strains. Although the R did not vary, the τ varied by ∼3.5 h which was positively correlated with latitude.     

Setting the clock--by nature: circadian rhythm in the fruitfly Drosophila melanogaster

Nowadays humans mainly rely on external, unnatural clocks such as of cell phones and alarm clocks--driven by circuit boards and electricity. Nevertheless, our body is under the control of another timer firmly anchored in our genes. This evolutionary very old biological clock drives most of our physiology and behavior. The genes that control our internal clock are conserved among most living beings. One organism that shares this ancient clock mechanism with us humans is the fruitfly Drosophila melanogaster. Since it turned out that Drosophila is an excellent model, it is no surprise that its clock is very well and intensely investigated. In the following review we want to display an overview of the current understanding of Drosophila's circadian clock.     

The fate of several migrant genes in isolated populations of Drosophila melanogaster

Sepia-eyed flies carrying the slow electrophoretic variant of either Est-6 or Adh were introduced in low numbers and at infrequent intervals into populations of wildtype flies (+^se/+^se) that were also homozygous for the fast moving variant of either Est-6 (50 populations) or Adh (50 populations). After 24 generations, the frequency of the sepia alleles was approximately 25%, although there was considerable variation from population to population. The fate of the Est-6 slow allele corresponded closely to that of sepia (which is located ten map units distant), although one population retained the slow allozyme variant but rejected sepia. The Adh slow allele was also retained by many populations. A number of them retained Adh-S but not sepia, and vice versa; these loci are on different chromosomes. The advantage of sepia heterozygotes was estimated to be about twice that of wildtype homozygotes. The data suggest that the selective advantage resides not with the sepia locus itself, but with a nearby chromosomal region.Financial support for work reported here was supplied under grant number GM24850, National Institutes of Health.     

Reassessment of the effect of biological rhythm mutations on learning in Drosophila melanogaster

A link between learning deficits and circadian period-lengthening mutations in Drosophila melanogaster previously has been reported. Mutant long-period males performed poorly in two learning assays involving experience-dependent courtship inhibition. In one, normal males that have courted fertilized females subsequently show courtship inhibition with virgin females. In the other, normal males that have courted sexually immature males subsequently fail to court other immature males. Those results have been reassessed in an extended study of genetic variants involving the period gene. 1. Long-period perL1 males demonstrated poor conditioned courtship inhibition when exposed to fertilized females; they showed normal courtship conditioning when exposed to immature males. This could be due to a perL1-associated olfactory deficit with fertilized females, since perL1 males were unable to discriminate behaviorally between fertilized and virgin females. 2. Other long-period males, including perL2 males and transgenic perL1 males bearing a truncated form of the per+ gene, were conditioned normally by fertilized females. Thus, the courtship inhibition defect is specific to the perL1 mutant strain. 3. perL1 (and other per mutant) flies showed normal acquisition and retention of a classically conditioned olfactory avoidance response. 4. Results from a new conditioned courtship inhibition experiment are presented; males exposed to fertilized females during training showed further courtship inhibition during subsequent exposure to fertilized females. From the perspective of learning theory, this can be viewed as a savings experiment.     

Persistence of predator-prey systems in an uncertain environment

Summary The time derivatives of prey and predator populations are assumed to satisfy a set of inequalities, instead of a precise differential equation, reflecting an uncertain environmental and/or lack of knowledge by the modeler. A system of differential equations is found whose solution gives the boundary of a persistent set, which is positive flow invariant for any system satisfying the inequalities. Conditions are given for the persistent set to be bounded away from both axes, which show that resonance effects cannot drive either predator or prey to extinction if that does not happen for an autonomous system satisfying the inequalities. In general predator-prey systems are more persistent when there is strong asymptotic stability, when there is correlation between prey and predator dynamics, when the effect of perturbations is density dependent, and are more persistent under perturbations of the prey than of the predator.     

Persistence time of loss-of-function mutations at nonessential loci affecting eye color in Drosophila melanogaster

Persistence time of a mutant allele, the expected number of generations before its elimination from the population, can be estimated as the ratio of the number of segregating mutations per individual over the mutation rate per generation. We screened two natural populations of Drosophila melanogaster for mutations causing clear-cut eye phenotypes and detected 25 mutant alleles, falling into 19 complementation groups, in 1164 haploid genomes, which implies 0.021 eye mutations/genome. The de novo haploid mutation rate for the same set of loci was estimated as 2 x 10(-4) in a 10-generation mutation-accumulation experiment. Thus, the average persistence time of all mutations causing clear-cut eye phenotypes is approximately 100 generations (95% confidence interval: 61-219). This estimate shows that the strength of selection against phenotypically drastic alleles of nonessential loci is close to that against recessive lethals. In both cases, deleterious alleles are apparently eliminated by selection against heterozygous individuals, which show no visible phenotypic differences from wild type.     

Effects of photophase and altitude on oviposition rhythm of the himalayan strains of Drosophila ananassae

The effects of varying photophase and altitude of origin on the phase angle difference (Ψ) of the circadian rhythm of oviposition during entrainment to light-dark (LD) cycles and the aftereffects of such photophases on the period of the free-running rhythm (τ) in constant darkness (DD) were evaluated in two Himalayan strains of Drosophila ananassae, the high-altitude (HA) strain from Badrinath (5,123 m above sea level=ASL) and the low-altitude (LA) strain from Firozpur (179 m ASL). The Ψ (i.e., the hours from lights-on of the LD cycle to oviposition median) of both strains was determined in LD cycles in which the photophase at 100 lux varied from 6 to 18 h/24 h. The HA strain was entrained by all LD cycles except the one with 6 h photophase in which it was weakly rhythmic, but the LA strain was entrained by only three LD cycles with photophases of 10, 12, and 14 h, but photophases of 6, 8, 16, and 18 h rendered it arrhythmic. Lights-off transition of LD cycles was the phase-determining signal for both strains as oviposition medians of the HA strain occurred∼6 h prior to lights-off, while those of the LA strain occurred∼1 h after lights-off. The Ψ of the HA strain increased from∼2 h in 8 h photophase to∼11 h in 18 h photophase, while that of the LA strain increased from∼11 h in 10 h photophase to∼15 h in 14 h photophase. The aftereffects of photophase of the prior entraining LD cycles on τ in DD were determined by transferring flies from LD cycles to DD. The τ of the HA strain increased from∼19 to∼25 h when transferred to DD from LD 8:16 and LD 18:6 cycles, respectively, whereas the τ of the LA strain increased from∼26 to∼28 h when transferred to DD from LD 10:14 and LD 14:10 cycles, respectively. Thus, these results demonstrate that the photophases of entraining LD cycles and the altitude of origin affected several parameters of entrainment and the period of the free-running rhythm of these strains.