Inherent Rhythm Research Articles

Circamensal Rhythms in Physical Performance

The eumenorrheic menstrual cycle represents a clear inherent biological rhythm that might interact with both physical performance, and/or the physiological response to performance. The predominant hormonal fluctuations throughout the cycle are in the ovarian steroids oestrogen and progesterone. Progesterone has both a thermogenic and ventilatory effect leading to a potential increase in minute ventilation and body temperature during exercise. Oestrogen has been linked to fluctuations in blood flow and heart rate via a vasodilatory mechanism, plus potential variation in muscle strength. If these hormones do indeed influence physical performance, or the physiological response to performance, female athletes might choose to manipulate the cycle through an endogenous hormonal mechanism. Furthermore, researchers utilizing a female population must control for these fluctuations in their research design.

A regional gradient of cardiac intrinsic rhythmicity depicted in embryonic cultured multiple hearts.

We used optical methods to examine the spatial gradient of intrinsic rhythmicity in early-stage multiple-heart chick embryos. The latter were induced experimentally in whole-embryo culture. The embryos were cut microsurgically through the tissue of the anterior intestinal portal at the 5- to early 7-somite developmental stage. Spontaneous electrical activity in 4 to 6 segmented hearts, during the 7- to 10-somite stages of development, were monitored simultaneously by means of multiple-site optical recordings of membrane potential activity, using a voltage-sensitive merocyanine-rhodanine dye (NK2761). Each segment of the heart exhibited its own inherent rhythmicity. In quadruple hearts, the order of the rhythmicity was often left-caudal segment>right-caudal segment>left-cephalic segment>right-cephalic segment; the heart rate in the left-caudal segment was often faster than that in the other segments. An atypical pattern of "bursting" rhythm was observed in the cephalic segments suggesting that, in these segments, the development of rhythmicity is relatively poor. These findings strongly emphasize the concept that, in the early phases of cardiogenesis, the formation of a regional gradient of pacemaker activity (i.e. a spatial gradient of intrinsic rhythmicity) results in the functional self-organization of the pacemaking area.

Free plasma magnesium following glucose loading in healthy humans

The recognized existence of a circadian pattern in extracellular magnesium balance might mirror either an inherent rhythm in the homeostasis of this ion or dietary factors. Since in vitro insulin enhances cellular magnesium uptake, the circadian rhythm in extracellular magnesium metabolism might be modulated at least in part by carbohydrate intake. To assess this hypothesis, the effects of oral glucose loading on plasma total and ionized magnesium were investigated in lean healthy humans with a negative family history for essential hypertension and diabetes mellitus. Plasma total and ionized magnesium was similar before glucose loading and 30, 60, 90, 180, and 210 min thereafter. It is therefore concluded that in healthy humans the circadian pattern of extracellular magnesium is not modulated by the metabolic and hormonal mechanisms that adjust the concentration of glucose.

The pineal organ as a component of the biological clock. Phylogenetic and ontogenetic considerations.

In conclusion, several trends are observed in regard to the phylogenetic development of the pineal organ, which are relevant for our understanding of the evolution of biological clock mechanisms. 1. The pineal organ of all vertebrates investigated thus far is capable of producing and releasing melatonin. Melatonin is rhythmically produced and released during darkness and, thus, represents an important neuroendocrine information on the ambient photoperiod. 2. The rhythmic production of melatonin is under control of endogenous oscillators and photoreceptor cells. In several nonmammalian species, these endogenous oscillators and photoreceptors are located within the pineal organ itself. In some avian species, the inherent rhythmicity of the pineal organ appears to be influenced by pacemakers located in other parts of the central nervous system. Their information may be transmitted to the pineal organ via the sympathetic innervation. This innervation develops progressively in the course of phylogeny. In mammals certain pinealocytes express proteins which are specific of retinal and pineal photoreceptors, but these proteins are obviously not involved in photoreception and phototransduction. The mammalian pineal organ lacks not only functioning photoreceptors, but also endogenous oscillators. The photoreceptor cells involved in regulation of the melatonin biosynthesis are located in the retina; the major endogenous oscillator is the suprachiasmatic nucleus (SCN) of the hypothalamus. Information from the retina and the SCN is transmitted to the mammalian pineal organ via a complex neuronal chain, whose last member is the sympathetic innervation originating from the superior cervical ganglion. This innervation is mandatory to maintain the rhythm of the melatonin biosynthesis in the mammalian pineal organ. Interestingly, the effects of noradrenaline, the major neurotransmitter in the sympathetic nerve fibers, displays opposite effects on the melatonin biosynthesis in birds and mammals: it stimulates the melatonin biosynthesis in the mammalian pineal organ, but inhibits the melatonin formation in the chicken. This conversion occurs at the level of the adrenoreceptors. 3. The intrapineal nerve cells giving rise to pinealofugal neuronal projections are reduced in the course of phylogeny. Nevertheless, direct neuronlike connections appear to exist between the pineal organ and the central nervous system of mammals. These projections originate from a population of pinealocytes. Whether such projections are involved in biological clock mechanisms remains an issue not yet resolved. The ontogenetic data reviewed support the notion that, in lower vertebrates, melatonin biosynthesis is primarily controlled by intrapineal photoreceptors, whereas, in mammals, it depends on retinal photoreceptors and the sympathetic innervation of the pineal.(ABSTRACT TRUNCATED AT 400 WORDS)

Desensitization of Superfused Isolated Ovine Anterior Pituitary Cells to Human Corticotropin‐Releasing Factor

Abstract We have employed an in vitro system to study the time-course of beta-endorphin (beta-EP) immunoreactivity release from anterior pituitary cells stimulated with corticotropin-releasing factor (CRF) and whether exposure to CRF desensitizes the cells to subsequent stimulation. Ovine anterior pituitaries were enzymatically disrupted into single cells, mixed with Siegel P2 and superfused in mini-columns with carbogen-gassed medium at 37 degrees C. Superfusate fractions were collected at 5-min intervals and beta-EP immunoreactivity in the eluate was measured by radioimmunoassay. Peaks of beta-EP release that rose significantly above baseline noise were detected using the PULSAR algorithm. Unstimulated cell columns did not display any spontaneous peaks of beta-EP discharge detectable by PULSAR whereas peaks were identified in the output of columns exposed to 1 nM CRF for 100 min. beta-EP release increased after 10 min of stimulation and maximum stimulated output was achieved after 20 min of continuous CRF exposure. Between 20 and 60 min of CRF stimulation the rate of beta-EP release declined progressively but stabilized in the last 40 min of the exposure at a level significantly above controls for baseline secretion. Peak duration did not depend on the inclusion of calcium in the superfusion medium while peak amplitude and area were significantly reduced when cells were denied extracellular calcium. Following a 100-min exposure to 1 nM CRF, pituitary cell columns were given a 30-min rest period then restimulated with either 1 nM CRF or 50 mM KCI for 20 min. The columns given prior exposure to CRF did not mount a response (detectable by PULSAR) to a subsequent dose of 1 nM CRF whereas PULSAR detected a clear response in all members of a control group that had not received prior CRF challenge. Both CRF exposed and control columns responded to 50 mM KCI although the response was significantly attenuated in the cells that had received prior CRF treatment. These results indicate that unstimulated superfused isolated ovine anterior pituitary cells do not possess an inherent rhythmicity of beta-EP release that can be detected by the PULSAR algorithm while treatment of the cells with CRF results in detectable discharge. The rapid response of beta-EP discharge to CRF treatment suggests the presence of intracellular beta-EP stores available for rapid mobilization. Continuous exposure to 1 nM CRF can tonically amplify corticotrope output for the duration of its presence in the environment of the corticotrope, but the maximum rate of release cannot be maintained. An inrush of extracellular calcium is not essential for the corticotrope to mount a detectable response to continuous CRF exposure but the release of a maximum amount of beta-EP relies on calcium entry. Long-term treatment with CRF prevents the corticotrope releasing a detectable peak of beta-EP on subsequent CRF stimulation and therefore CRF exposure leaves a lasting impression on the physiological machinery of the corticotrope. The attenuation of responsiveness to 50 mM KCI after long-term CRF treatment indicates that depletion of beta-EP stores may play a part in corticotrope desensitization although a reduction in CRF receptor number and an alteration in the intracellular mechanisms controlling beta-EP release may also be a factor.

Age-related variation in circadian rhythms of mitosis in the adrenal cortex of the male rat.

Using a metaphase arrest technique, mitotic activity was quantified in the adrenal cortex over a 24-h period in 14-day-old male Sprague-Dawley rats before functional rhythmicity of the hypothalamic pituitary-adrenal (HPA) axis is established, and after its onset, in 6- to 7-week-old rats. At all times, proliferative activity was greater in the younger animals, as previously reported. A significant circadian rhythm was identified in both groups, but the timing of the peak differed, lying between 17.00 and 21.00 h at 14 days and 11.00 and 15.00 h at 6-7 weeks. These results raise the possibility that functional rhythmicity of the HPA axis may alter an inherent proliferative rhythm.

Conventions in the Documentary Recording of Dance: Research Needs

Many creative people have produced films using dance as the main or secondary subject matter. The past decade has brought such major studio productions as The Turning Point (Ross, 1977), Nijinsky (Ross, 1980), Saturday Night Fever (Badham, 1977), Flash Dance (Lyne, 1983), Staying Alive (Stallone, 1983), Breakin' I & II (Silberg 1984), and Dirty Dancing (Ardolino, 1987), and independent films like In a Rehearsal Room (Hahn, 1975), Dune Dance (Brown, 1981), and Space City (Brentano and Horn, 1980), as well as much of the rock-video genre. The directors and/or choreographers of these films have produced dances for the camera that often could not, or at least did not, exist except on the television or movie screen. Angles chosen to frame shots and the rhythm of editing used to determine pace were selected for the cinematic value they produced. They expressed either the creative impulses of the filmmaker, those of the choreographer interpreted by the filmmaker through an active collaboration, or (only rarely) those of the choreographer as filmmaker. In these cases the techniques unique to film and video have been used to create dance events for the screen.But what of dance works that have been choreographed to be seen on the proscenium stage? It is, perhaps, even more challenging, if not as apparently creative, to try to preserve on film or tape the composition and pattern and inherent rhythm of such choreography; that is, to bring a faithful translation of the choreographer's vision to the audience in front of the screen. Dance film that strives to provide the same aesthetic result as that of the staged choreography is a demanding art form in its own right; it draws upon all our understanding of the principles of documentary film and of visual perception. What makes this such a difficult task? Why is it so hard to maintain the energy, the excitement, and the aesthetic values of the performance when presenting the content of the prescribed space and the specific time of the real world, on the screen? The reason may be that we do not yet fully understand the interactions that occur between that objectively limited space of the world and the subjectively defined space produced by the camera.

Temperature rhythms in native Alaskan and Caucasian children

The oral temperatures of native Eskimo and Caucasian school children between 10 and 13 years of age were measured at four times of day and once at night on four consecutive days during the Spring and Fall. There were significant differences across the daily measures indicating circadian entrainment. There were no differences between the native and Caucasian groups indicating that earlier reports of less well defined circadian rhythms in adult native Eskimos were not due to inherent rhythm limitations in native Eskimos.

Relationships between body weight and body measurements of reindeer

Genus Rangifer populates the northernmost habitat of the Cervidae and shows alterations in body weight, skeletal growth rate and nutritional state with the marked seasonal changes in its environmental conditions. Body weight and measurements have long been the standard criteria for evaluation of growth in domestic animals. Body weight has been also used most by workers to describe growth and body size in reindeer and caribou. The numerical values of the weight to length ratios of skeletal bones are not so much expressions of growth rates, but rather of the growth patterns of these bones. Body measurements and ratios are useful taxonomic criteria and are used in Rangifer systematics. The results indicate that body ratios, such as shoulder height/foreleg length and shoulder height/back length are independent of body size and thus primarily of genetic origin (Nieminen & Helle 1980). The objective of this study was to measure the apparent ageand sex-related growth and the seasonal changes in body weight and body measurement in semidomesticated reindeer. During different seasons in 1969 85 the body weight was measured in Kaamanen experimental station and in different herding cooperatives from 2932 reindeer females ranging from birth to 14 years of age and from 1037 males ranging from birth to 10 years of age. General physical development was measured after the first 4 months of life by chest circumference and back length taken from 1490 females and 510 males. The mean birth-weight of female calves was 5.0 kg. Male calves weighed 0.3 kg more. After the first 6 months of life, body weight of reindeer calves followed alternating periods of positive and negative growth. The body weight increased until the age of about 3.5 years in females and until the age of 5 7 years in males. In winter both young and adult females lost between 13 and 19% of their prime autumn weight. However, the percentage of prime autumn weight lost by males in winter increased from about 10% the first year to 33% at maturity. The fluctuations of body weight are largely attributed to the seasonal depostition and mobilization of fat reserves. Growth of reindeer ceased in winter because of either an inherent physiological rhythm or a decline in nutritive value of the diet, or both. The body weight of female reindeer was highly correlated with the back length (r=0.809) and chest circumference (r=0.860). Similar relationships were also found for male reindeer (r= 0.892 and 0.872, respectively). However, the best relationships were noted between the body weight and the joint measure (back length + chest circumference) in female (r=0.877) and male reindeer (r=0.941). Similar relationships have been shown for domestic species. There were some differences in relationships between the body weight and the joint measure in young and over 3-year-old females and males. Differences were also found in these relationships during autumn and winter.

Regulation of annual weight cycles in reindeer and other cervids

Seasonal changes in weight, food intake and metabolic rate are characteristic of reindeer and other northern ungulates. This article reviews relationships between endocrine and weight cycles in reindeer and other cervids, and the effect of manipulations with endocrine cycles upon the weight cycle. It appears that the secretions of most endocrine glands change throughout the year, either as a result of nutritional changes or of an inherent seasonal rhythm. It is suggested that the weight and metabolic cycles are secondary to an appetite cycle that is hormonally regulated. The hormonal control may include several hormones: sex steroids, thyroid hormones, and prolactin.

Sympathetic regulation of chicken pineal rhythms

Adult hens were chronically cannulated and held in light-dark (LD) 12:12 h lighthing regimes or in constant darkness (DD). Periodic blood sampling for 5–9 days revealed circadian rhythms in plasma melatonin titres. Superior cervical ganglionectomy (SCG-X) performed 1 week after hatching had little or no effect on these rhythms in LD, but unlike normals. SCG-X birds did not sustain persistent rhythms in DD. In SCG-X birds, norepinephrine (NE) infusion for 12 h of each 24 h in DD significantly reduced plasma melatonin titres during the infusion and re-established a rhythm. After each experiment, hens were killed, their pineals were removed and assayed by HPLC-EC for NE. dopamine (DA). serotonin (5-HT) and 5-hydroxy-3-indole-acetic acid (5-HIAA). SCG-X resulted in a 90% depletion of pineal NE: DA content was reduced to undetectable levels. Pineal 5-HT and 5-HIAA were also reduced by SCG-X. The chicken pineal contains circadian oscillators which persist in vitro 8.19.29. The results reported here suggest that noradrenergic fibres from the SCG regulate the pineal's inherent rhythmicity. NE normally released from sympathetic terminals during the bird's day may synchronize oscillators within the pineal by inhibiting melatonin synthesis.

Evidence for an inherent rhythm in pulsatile LH release in ovariectomized cows

Luteinizing hormone levels were measured in blood samples collected at 5 minute (min) intervals for 3 hours (hr) during the a.m. and p.m. of 3 consecutive days from long-term ovariectomized cows. Levels of LH fluctuated in a pulsatile manner in all animals. During the pulses, LH levels increased rapidly (2.5 to 6.0 ng/ml). Following the rapid increase, a more gradual exponential decline was observed. The interval between pulses was consistent both within and between days of blood sample collection within cows. From the results we suggest that each cow may have an inherent consistent rhythmic pattern of LH release in the absence of an ovarian source of hormones.

The effects of ryanodine, acetylcholine and epinephrine on electrical and mechanical activity in an insect heart

1. 1. Ryanodine, an alkaloid used as an insecticide, has been shown to depress contraction while leaving excitation unaffected in mammalian hearts, an effect presumed to result from uncoupling of the transverse tubular system (TTS) from the sarcoplasmic reticulum (SR). 2. 2. The heart of the adult moth Hyalophora cecropia, a tissue known to have septate junctions between the TTS and SR and a Ca 2+ -spike generating sarcolemma was used to further test this hypothesis. 3. 3. We first report the basic characteristics of the contractile response and demonstrate a negative force-frequency effect, a diminished calcium current ( I Ca 2+ ) in the presence of acetylcholine and an enhanced I Ca 2+ with epinephrine. 4. 4. Ryanodine 10 −8M added to this preparation slowed the inherent rhythm (interval 0.6–4 sec), depolarized the cells by 10–14 mV, reduced action-potential amplitude (from 66 to 52 mV), prolonged the plateau (from 80 to 280 msec), and decreased d V/d t from 4 to 2.8 V/sec. 5. 5. The magnitude of peak tension was not affected, but the time to peak tension was increased from 160 to 200 msec and the relaxation time was prolonged from 200 to 480 msec. 6. 6. The refractory period was increased, thereby preventing the heart from following increased rates of pacing by externally applied stimuli. 7. 7. We conclude that ryanodine interferes first with the sarcolemmal Ca 2+-delivery system and then the SR calcium-sequestration system.

The psychoneuroendocrinology of the ovulatory cycle of woman: A review

This review has as its objective to show that the mammalian, specifically human, ovulatory cycle is subject to many influences which can alter its inherent rhythmicity. This cyclicity is, in essence, a displaying of a pattern that is endogenously driven but which is also subjected to, and subject to, exogenous influences that alter the basic endogenous rhythm. This literature review is in 2 sections. The first discusses 7 major aspects of the endogenous nature of the primate ovulatory cycle: 1) natural rhythmicity of the ovaries; 2) steroid production and control; 3) gonadotropin production and control; 4) prolactin production, effects, and control; 5) monoamine control of the gonadotropins; 6) autonomic innervation of ovarian tissue; and 7) metabolic influence on ovarian cyclicity. This section concludes with a summary of the endogenous aspects of the ovulatory rhythm. Secton 2 reviews 3 exogenous influences of fertility: 1) nutritional influences; 2) geophysical influences; and 3) childbearing and lactation influences on subsequent ovulation.

Pulsatile secretion of prolactin in the male rat after pimozide administration is not due to pulsatile inhibition of PIF secretion

Sequential blood samples were taken every 2 min from intact male rats implanted with a permanent indwelling right atrial cannula. The relationship between pimozide dose and prolactin secreation was established by administering graded doses of pimozide (30–3000 μg/kg) as a single bolus injection through the indwelling cannula. The maximum response of prolactin secretion was achieved with 300 μg/kg pimozide. Higher doses of pimozide did not raise further the circulating prolactin concentration suggesting that the receptors for the presumed prolactin inhibiting factor (PIF) were blocked completely at this dose. Marked pulsatile fluctuations in circulating prolactin concentration were observed after administration of pimozide, at all dosages, or of another ‘specific’ dopaminergic receptor blocking agent, d-butaclamol. Since we assume that PIF receptors are completely blocked by the higher doses of pimozide, we conclude that this pulsatile secretion of prolactin cannot be due to the inhibition of PIF secretion but may be due either to the stimulation of prolactin releasing factor (PRF) secretion, or to an inherent rhythmicity in the prolactin secreting cells.

Proprioceptive feedback dominates the central oscillator in the patterning of the flight motoneuron output inTipula (Diptera)

1. Action potentials were recorded from units of the indirect power flight muscles dvm1 and dlm of tethered flying crane flies (Tipula paludosa). The normal wingbeat frequencies of the animals were in the range of about 50 to 60 Hz. By mutilating or loading the wings the wingbeat frequencies could be adjusted to any values between 25 Hz and 160 Hz. 2. There is a strong tendency for the action potentials to be phase-locked with respect to the wingbeat period at all wingbeat frequencies up to about 120 Hz (Figs. 4, 5). This holds true in spite of the fact that the action potentials do not occur in every wingbeat period (Fig. 6). Thus, wingbeat synchronous afferences influence phasically (trigger) the production of spikes in the output systems. -The dvm1-units and the dlm-units fire at different phase bands within the wingbeat period. 3. If both wing nerve afferences are disrupted then in most cases only very short flights can be initiated. It can be concluded that these afferences are involved in the maintenance of flight. Prolonged flights can be elicited only exceptionally. In all cases, however, the tendency of the spikes to accumulate at small phase bands within the wingbeat cycle is drastically reduced (Fig. 8). Thus, wingbeat synchronous afferences travelling along the wing nerves contain important timing cues for the production of the neuromotor output. 4. In the absence of wing nerve afferences the motor output systems supplying the flight muscle units of the dvml and the dlm, respectively, fire with their own inherent rhythm; the occurrences of spikes in the dlm are strongly correlated with the occurrences of spikes in the dvm1 and vice versa (Figs. 11B, 12). This demonstrates the existence of a central nervous mechanism which is able to produce a rhythmic motor output autonomously. -Under physiological conditions, however, the endogenous rhythm is overridden by timing cues from wingbeat synchronous afferences. 5. The neural output driving the indirect flight muscles inTipula is compared with the neural output supplying the flight muscles in “higher” Diptera on the one hand and in locusts on the other. It is suggested that the tipulid flight motor system represents an early stage in the evolution of the highly specialized systems of the “higher” Diptera. -Some features of the flight motor in Diptera are summarized in a block diagram (Fig. 13).

Oscillations and cell development in Dictyostelium discoideum stimulated by folic acid pulses

Folic acid is known to be a chemoattractant of pre-aggregation cells of Dictyostelium discoideum. When supplied in pulses, folic acid induces biochemical oscillations and stimulates the development of pre-aggregation to aggregation-competent amoebae. The continuous supply of folic acid has no stimulatory effect. Folic-acid-induced oscillations are accompanied by periodic changes in the cyclic AMP concentration. Pulses of folic acid applied with rhythms between 7 and 11 min efficiently induce oscillations. In contrast, a rhythm of 2 min neither induces oscillations nor suppresses them. Cells start to oscillate with a rhythm of about 8 min. This inherent rhythm is independent of the inducing rhythm. Oscillating cells are less sensitive to folic acid than pre-oscillating ones. They respond only to high concentrations of folic acid which also interact with the oscillating system.

A Dynamic Approach to the Analysis of Daily Height Growth of Plants

A model for analysing the daily height increments of vascular plants is presented. Temperature plays a dual role in growth. It strongly affects the daily increments and it determines the rate of maturation. Therefore the concept of inherent growth rhythm had to be introduced into the model in order to obtain satisfactory agreement between computed and measured daily increments. The model which includes the effect of temperature and that of inherent growth rhythm was found to have quite a good predictive value when applied to independent material.

Seasonal profiles of plasma luteinizing hormone, testosterone and estradiol in the ram.

Plasma profiles of luteinizing hormone (LH), testosterone (T), and estradiol (E2) have been determined in five mature rams during the primary breeding season (September) and again when breeding activity was low (May). Blood samples collected every half h for 24 h during September or May showed that LH was released into the general circulation as distinct peaks. Although this secretory pattern was not the same for all rams and seasonal differences were noted in certain individuals, it is suggested that an inherent rhythm persists within each ram. With the exception of one ram in September, obvious T peaks were preceded by LH peaks greater than 2 ng/ml (LH-T interval less than 60 min). Season had no effect on the number and magnitude of LH peaks or on the mean concentrations; however, basal levels of LH were higher (P less than 0.01) in September than in May. Seasonal differences in peripheral T levels were more dramatic with mean, baseline, and peak concentrations elevated (p less than 0.01) during the fall. The number of T peaks, like those of LH, was not affected by season. Large variations in circulating levels of E2 made any possible relationship between this hormone and LH or T difficult to identify. Furthermore, a diurnal or seasonal rhythm could not be established for E2 in this study. It is concluded that seasonal differences occur in secretory patterns of LH and T and that a cause and effect relationship between these two hormones exists. Under conditions of this study, neither a consistent relationship between E2 and LH or T, nor a seasonal difference in mean E2 levels, was apparent.

Cuticular bands as age criteria in the sheep blowfly Lucilia cuprina (Wied.) (Diptera, Calliphoridae)

AbstractIn Lucilia cuprina (Wied.), cuticular bands are deposited most clearly on the mesothoracic post-phragmata, and up to ten such layers can be counted. The bands are deposited clearly only in response to fluctuating temperatures where the minimum temperature in a cycle falls below about 15·5°C. Growth bands are deposited whenever such a change in ambient temperature occurs and the deposition appears to show no inherent rhythmicity. The maximum width of the phragmata is more or less constant and the number of bands which can be distinguished depends upon how quickly the maximum width of the phragmata is reached. The rate of growth of the growth bands and their consequent width depends upon the maximum temperature experienced and the length of time the insect is maintained at that temperature in any cycle. Trials showed that the count of growth bands was an acceptable estimate of the actual age in days when temperatures rose 3·5°C or more above the threshold value of 15·5°C. With a greater temperature range, greater accuracy was achieved. The availability of protein food was shown to have little effect on the deposition of growth bands. A mean age in days was calculated for samples of field-caught flies of a uniformly young ovarian ‘age’ using the counts of growth bands and by working back in the temperature records from their sites of capture using the day-degrees method. Significant differences between the two estimates of age were taken to indicate the occurrence of developmental delays. These were attributable to shortages of protein food in the field and were associated with periods of drought. The method allows the demonstration that developmental delays have occurred but does not provide an accurate estimate of the duration of these delays. It does not permit the confident identification of delays imposed by shortages of oviposition sites.