Shifts In Photoperiod Research Articles

Differentiation in life cycle of sympatric populations of two forms of Hyphantria moth in central Missouri

AbstractWing patterns of Hyphantria adult male moths collected in central Missouri were examined throughout the breeding season. Three major peaks of adult flight were observed: the first peak consisted mainly of adults with spotted wings, while the second and third peaks consisted of immaculate adults. Black‐headed larvae appeared in the field following the first major peak of moth flight, and red‐headed larvae appeared in the field following the second peak. Sympatric red‐headed and black‐headed forms were collected in the field and subsequently reared on an artificial diet under conditions of 16 h light : 8 h dark (LD 16:8) at 25°C. The larval period of the black‐headed form was shorter than the red‐headed, whereas the pupal period of the black‐headed form was longer than the red‐headed. Pupal development is retarded in some individuals at high temperatures in the black‐headed form. Photoperiodic response curves for pupal diapause were different between the two forms. The critical photoperiod for pupal diapause was 15 h 10 min in the red‐headed form, which was longer than that for the black‐headed form (14 h 40 min). The two forms responded to shifts in photoperiod differently. These developmental responses temporally separate the two forms in the field; the red‐headed and black‐headed forms represent a set of adaptations favoring univoltinism and bivoltinism, respectively. Red‐headed larvae fed mainly at night, while the black‐headed larvae fed without a clear day–night rhythm. Nocturnal feeding in the red‐headed form is adaptive to protection against predation, but fails to fully utilize heat units and thus to produce a second generation.

Reproductive performance of gilts and sows in temperate versus subarctic and arctic zones of Norway

The reproductive performance of gilts and sows from two regions in Norway was investigated in a retrospective analysis of data from the litter recording system. In the Northern region (North; between 65°N and 71°N), there are extreme shifts in natural photoperiod between winter and summer. In the Southern region (South; between 59°N and 60°30′N), photoperiodic changes are less dramatic. Gilts were 8 days older at first mating or insemination in the North than in the South ( P<0.01). A significantly lower proportion of sows in the North were mated or inseminated within 5 days post-weaning than in the South, a difference present both among primiparous and multiparous sows ( P<0.01). Overall farrowing rate in the North was lower than in the South, but litter size (total number born) among those pigs that farrowed was larger. After correction for year, month, breed and age at first service, there were still lower odds of farrowing for gilts in North than in South. Neither for primiparous nor multiparous sows were regional differences in farrowing probability significant when year, month, breed and weaning to service interval were included in the model. Gilts and primiparous sows had a lower probability of farrowing following insemination during summer or autumn months, but service month was not significantly related to the farrowing probability of multiparous sows. For gilts, litter size was positively related to age at first service. For sows, litter size was lowest at weaning to service intervals between 6 and 10 days. Total numbers of piglets born per litter were estimated to be 0.36, 0.38 and 0.55 larger in the North than in the South (differences in least square means; gilts, primiparous sows and multiparous sows, respectively) ( P<0.01). Litter size was lower after service during natural long photoperiod than during the rest of the year.

Photoperiod, Reproduction, and Immunity in Select Strains of Inbred Mice

The purpose of this study was to determine whether decreased day lengths affect reproduction or the immune system in inbred mice. Irrespective of a nocturnal pineal melatonin rise, the signal for day length information, body and testis weights were the same in various strains 8 weeks after transfer from long to short days (16 to 8 h of light/day) compared to mice that remained in long days. Serum testosterone was unaffected by the photoperiod shift. The second goal was to determine whether the shift from long to short days influenced lymphocyte populations in spleen or blood, as well as innate and cell-mediated immune cell functions in C3H/HeN mice, an inbred strain with a robust melatonin rhythm. By flow cytometry, a stable percentage and number of B cells, T cells, and natural killer cells were identified in spleen from mice in both long and short days during the day and night. This complement of immunophenotypes in spleen suggests that equivalent functional capabilities persist in secondary lymphoid tissue of mice irrespective of day length. This was supported by findings that cytolytic activity by splenic natural killer cells (innate immunity) and antigen-induced T cell-dependent B cell antibody production (adaptive immunity) were similar in mice in long and short days. In blood, cell numbers but not helper T cell subset percentages (i.e., naive, memory, cytotoxic, or activated) were augmented in mice in short compared to long days, a consequence of increased circulating B cells. Day length differences in certain immunophenotypes in circulation may forecast photoperiod-mediated alterations in responsiveness to pathogens that are associated with a change in season. At night, the reduced proportion of cytotoxic T cells (long and short days), as well as increases in the percentage of activated T cells (long days), B cells (short days), and NK cell activity (long and short days) relative to daytime, suggests that surveillance and function by select immunophenotypes may adapt to circadian transitions even in highly inbred species. Thus, inbred mice retain capabilities for photoperiod to influence trait-specific aspects of immune cell but not reproductive function.

The rôles of photoperiod and nutrition in the seasonal increases in growth and insulin-like growth factor-1 secretion in male red deer

AbstractYoung male red deer follow a seasonal growth pattern that can be shifted by altering the photoperiod they experience. An increase in photoperiod to 16 h of light per day (16L : 8D) during winter advances the onset of rapid growth and high food intake that normally commences in spring. These changes are associated with increased growth hormone (GH) and insulin-like growth factor-1 (IGF-1) secretion. The GH/IGF-1 axis is acutely sensitive to the level of nutrition and the relative rôles of photoperiod and nutrition in determining the spring IGF-1 rise is unknown. The present experiment set out to examine this by exposing two groups of deer (no. = 8 per group) to a photoperiod shift during their 1st year of life (16L : 8D from 2 June), designed to cause accelerated growth and increased food intake after approximately 7 weeks. However, after 6 weeks the food intake (pellets containing 11 MJ metabolizable energy and 160 g crude protein per kg dry matter (DM)) of one group (LDRES) was clamped, thereby preventing the intake component of the response. The intake of the other group (LDAL) remained ad libitum for a further 12 weeks until 6 October, when the experiment concluded.During the first 6 weeks of 16L : 8D, growth rate (118 (s.e. 15·4) g/day) and food intake (1·37 (s.e. 0·031) kg DM per head per day) did not differ between the groups. Food intake following the clamp in LDRES averaged 1·40 (s.e. 0·015) kg per head per day. The intake of LDAL increased 2 weeks after the clamp and thereafter was higher than LDRES (P &lt; 0·001). Food intake of LDAL averaged 2·13 (s.e. 0·051) kg during the nutritional clamp period. Growth rates increased in both groups during the first 3 weeks of the clamp, averaging 237 (s.e. 25·0) g/day, then growth slowed in LDRES and live weights diverged. Growth rates until the end of the experiment (147 (s.e.23·0) g/ day v. 299 (s.e. 12·5) g/day, P &lt; 0·001) and mean live weight over the last 5 weeks of the experiment were lower (P &lt; 0·05) in LDRES than LDAL, weights reaching 88·3 (s.e. 1·86) kg and 97·9 (s.e. 2·74) kg respectively on the final sampling date. Metatarsal bone length grew more in LDAL than in LDRES (3·1 v. 2·2 cm, s.e.d. = 0·23, P &lt; 0·01). Prior to the nutritional clamp, mean plasma prolactin and IGF-1 concentrations increased at 3 and 6 weeks after 16L : 8D respectively, in both groups. Prolactin concentrations were lower in LDRES than LDAL on two occasions, at weeks 3 and 7 after the onset of the nutritional clamp, and IGF-1 concentrations were lower in LDRES than LDAL (676 v. 872 ng/ml, s.e.d. = 73·8, P &lt; 0·05) over the last 7 weeks of sampling.In summary, a photoperiodically driven increase in IGF-1 occurred even when the usual associated increase in food intake was prevented. This indicates that the seasonal IGF-1 rise in red deer is not a consequence of the increased food intake, although the latter appears necessary to maintain elevated IGF-1 concentrations. The rise in IGF-1 may therefore be considered as a component of the photoperiodically entrained seasonal drive to grow, and the increase in food intake a response to satisfy the increased energy demand.

Effects of Decreasing Thermophotoperiod on the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Eastern subterranean termite, Reticulitermes flavipes (Kollar), workers were exposed to decreasing temperatures and a shift in photoperiod to simulate conditions that are encountered during the fall in eastern Nebraska. Mean water and fat content in termites exposed to a decreasing thermophotoperiod did not differ significantly from controls or laboratory colony termites. Survival was higher for termites subjected to a decreasing thermophotoperiod than for controls. This could be attributed to acclimation to low temperatures or a delayed mortality due to lowered metabolic activity at low temperature. Previously reported data on soil temperatures taken in Lincoln, NE, at a depth of 91.4 cm showed that the temperature rarely went below 0°C. Our results, observations from previous reports of R. flavipes found at depths >100 cm during the winter, and previously determined lower lethal temperatures and supercooling points suggest that successfully overwintering R. flavipes colonies retreat to soil depths where freezing temperatures are not encountered.

Circadian Locomotor Rhythms in Mice with Targeted Disruption of the Gene for the Carbon Monoxide Synthesizing Enzyme, Heme Oxygenase-2

Carbon monoxide (CO), generated in neurons by the enzyme heme oxygenase-2 (HO2), is postulated to be a gaseous signaling molecule in the mammalian brain. Because of the recent evidence suggesting an important role of another endogenously produced gas, nitric oxide (NO), in entrainment of circadian rhythms in mammals, we hypothesized that CO may also be involved in regulating these rhythms. Consistent with this idea, others have found a circadian rhythm of heme turnover and CO synthesis can be induced by bright light. Furthermore, HO2 is co-localized with guanylyl cyclase, the putative target of CO, throughout the brain, with high amounts of staining in the suprachiasmatic nucleus (SCN) of the hypothalamus. The goal of the present study was to evaluate the role of CO in photic entrainment in wild-type and HO2 deficient mice. HO2–/– mice did not display any abnormalities in circadian rhythmicity. Entrainment to a light–dark cycle, the ability to phase delay locomotor activity after a four hour phase shift in photoperiod, and the period of the free running rhythm (t) were similar between HO2–/– and wild-type mice. Taken together, these data suggest that CO does not play a major role in regulating circadian activity rhythms in mice.

Seasonal regulation of prolactin secretion in hypophyseal stalk transected beef calves.

Seasonal regulation of prolactin secretion was investigated in crossbred beef heifer calves. Calves were randomly assigned to hypophyseal stalk transection (HST, n = 6) or sham-operation control (SOC, n = 6) groups and fitted 1 day before surgery with an indwelling external jugular catheter. Prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), thyroxine (T4), and tri-iodothyronine (T3) in peripheral serum were measured by radioimmunoassay in samples obtained before and after HST or SOC. During the first 8 days after HST, PRL concentrations remained significantly greater than SOC, but then decreased in both HST and SOC calves to 4 +/- 2 (+/- SE) and 10 +/- 3 ng/ml, respectively (P < 0.001). PRL remained low in both HST and SOC groups for three months after surgery. By four months, HST calves had lower basal PRL (5 +/- 1 ng/ml) than observed in SOC (40 +/- 4 ng/ml), and seasonal changes in PRL blood concentration also were attenuated by HST. Although HST reduced PRL secretion, it did not abolish the effect of seasonal changes (P < 0.01); circulating PRL concentration increased six-fold by shifts in photoperiod and temperature from winter to summer in these stalk-transected calves. The SOC group had higher serum GH during the winter (3.8 +/- 0.8) than in July (1.3 +/- 0.03 ng/ml). The HST group had the opposite profile of GH concentration, however, with concentrations being higher during May through July. Thyroid stimulating hormone secretion was partly sustained after stalk transection possibly by negative feedback of reduced circulating thyroxine and tri-iodothyronine. These results in both hypophyseal stalk-transected and sham-operated beef calves maintained in a natural environment strongly suggest that hypothalamic regulation of PRL secretion by adenohypophyseal cells is extremely sensitive to seasonal changes throughout the year. Additionally, immediately after HST, PRL blood concentration remains significantly greater than in SOC calves but eventually decreases to low blood concentration in HST calves, and unlike that seen after HST in primates. Regardless, basal PRL serum concentration responds to seasonal changes, but a less distinct change in basal GH serum concentration in HST calves than seen in the SOC calves.

Photoperiod shift effects on yield characteristics of rice.

Edible yield must be maximized for each crop species selected for inclusion in the Controlled Ecological Life-Support System (CELSS) proposed by NASA to support long-term manned space missions. In a greenhouse study aimed at increasing biomass partitioning to rice (Oryza sativa L.) grain, plants of the high yielding semi-dwarf rice cultivar Ai-Nan-Tsao were started in pots under 8-h photoperiods at a density of 212 plants m-2. After different periods of time under 8-h photoperiods, pots were switched to continuous light for the remainder of the cropping cycle. Continuous light did not delay time to first panicle emergence (60 d) or time to harvest (83 d). There was a positive correlation between the length of continuous light treatments and nongrain biomass. Grain yield (1.6 +/- 0.2 g plant-1) did not increase in continuous light. Yield-efficiency rate (grain weight per length of cropping cycle, canopy volume, and weight of nongrain shoot biomass) was used to compare treatments. Small Ai-Nan-Tsao rice canopies grown under 8-h photoperiods were more efficient producers of grain than canopies grown under continuous light for a portion of the rice cropping cycle.

Effect of anterior hypothalamic area lesions on photoperiod-induced shifts in reproductive activity of the ewe.

The areas of the brain involved in photoperiodic control of reproduction are not well defined. The objective of this study was to determine whether anterior hypothalamic area (AHA) lesions in the ewe affected the responses of the reproductive system to shifts in the length of the daily photoperiod and development of photorefractoriness to a constant short day photoperiod. Eleven intact ewes received bilateral radiofrequency lesions of the AHA (AHAX), and five received sham lesions (sham). The ewes then were placed in photochambers and exposed alternately to two approximately 90-day periods of long [16 h of light, 8 h of darkness (16L:8D)] and short (10L:14D) days and then to 10L:14D for an additional 165 days. Blood samples were collected twice weekly to monitor plasma profiles of progesterone, PRL, and total T4, and during the second 16L:8D photoperiod, hourly for one 24-h period to assess melatonin release. Lesions increased (P < 0.001) the interval between the start of long days and cessation of estrous cycles during both long day periods, but did not affect the interval between the start of short days and the onset of estrous cycles for either the first (P = 0.08) or second (P > 0.10) short day period. Consequently, the durations of both anestrous periods were shorter (P < 0.001) for AHAX than for sham ewes. AHA lesions did not affect (P > 0.10) diurnal patterns of melatonin release. No effects (P > 0.10) of lesions were evident on plasma patterns of PRL or total T4 for any short or long day photoperiod. Development of photorefractoriness to constant short days either did not occur or was markedly delayed in five of nine AHAX (P < 0.01) ewes, whereas the other four AHAX ewes became refractory at a time similar (P > 0.10) to that in sham ewes. Responses to inhibitory long day photoperiods and constant short days were highly (P < 0.05) correlated (r = 0.74) and appeared dependent upon the extent of the AHA lesion. These results suggest that AHA lesions disrupt neuronal pathways mediating the effects of shifts in photoperiod on reproductive activity and development of photorefractoriness to constant short days. Our results suggest that the effects of AHA lesions are confined to the termination of reproductive activity, and that different neural pathways participate in photostimulation vs. photosuppression or photorefractoriness.

Circadian activity rhythms in colonies of ‘blind’ Molerats,Cryptomys damarensis(Bathyergidae)

Various activity rhythms (general, feeding, and toilet) were measured under controlled laboratory conditions in two colonies of the Damara molerai Cryptomys damarensis, for 140 consecutive days (following a 30 day test period) under various photoperiod regimes (16:8 LD, 12:12 LD, and constant dark DD). As a general rule, all activities showed a significant diurnal rhythm with a period of 24 h under LD photoperiods. However, under a 16 : 8 LD photoperiod a very prominent activity component during the first part of the subjective night was observed, especially following a shift in photoperiod. The molerats responded rapidly to LD phase shifts. In constant dark, all activities had free-running periods of τ = 24,1-24,2 h, thus indicating that light can synchronize and entrain endogenous circadian rhythms in these molerats.

Importance of retinal photoreceptors to the photoperiodic control of seasonal breeding in the ewe.

Two experiments were performed to determine whether the eyes are necessary for photoperiodic control of reproduction in ewes. In the first, intact and estradiol-treated ovariectomized (OVX + E) ewes were housed in each of 2 photoperiod-controlled rooms with a vasectomized ram and subjected to 90-day alternations between long and short days. Prior to blinding, long days initiated anestrus in intact ewes and a suppression of serum luteinizing hormone (LH) levels in OVX + E ewes; short days caused onset of estrous cycles and an increase in LH levels in the intact and OVX + E ewes, respectively. After 1.5 years of such photoperiodic control, all ewes were blinded by bilateral orbital enucleation. Photoperiodic control was lost following blinding, but circannual alternations between cyclicity and anestrus or high and low LH levels, were maintained in most ewes for the remaining 2.5 years of the study. In one group of OVX + E ewes, serum LH levels remained synchronized to the 90-day shifts in photoperiod for about 1 year after blinding. Once the sighted ram was removed from the room, however, the 90-day rhythm in LH disappeared and a circannual pattern of LH became evident, suggesting that blind ewes may receive photoperiodic information from a sighted ram. This possibility was supported by the results of the second experiment in which 12 additional OVX + E ewes were blinded and exposed to 90 long days and 90 short days in the absence of a sighted ram. In these ewes, serum LH levels were not controlled by the changes in photoperiod. These results are consistent with the following conclusions: 1) the eyes are necessary for perception of photoperiod in the ewe and 2) ewes have an endogenous circannual rhythm of reproduction and/or they can be controlled by other environmental signals in the absence of photoperiodic input. Further, the results lead to the hypothesis that blind ewes can receive photoperiodic information indirectly from a sighted ram.

The induction of sexual reproduction in Daphnia magna: genetic differences between arctic and temperate populations

Even when provided with abundant food and grown in isolation, Daphnia magna from arctic Canada responds to declining photoperiods by producing male and then ephippial offspring. In contrast, clones of English origin do not alter their reproductive behaviour when exposed to photoperiod shifts. Hybrid clones show an intermediate response in terms of ephippial egg production, but a variable response in male production. The results indicate that variation exists at gene loci controlling sexual behaviour in local populations as well as between distant populations. The significance of this variation is discussed in relation to the environmental heterogeneity encountered by D. magna over its extensive range.

The effect of photoperiod on temperature selection in the European green lizard, Lacerta viridis.

Voluntary body temperature selection of unrestrained Lacerta viridis revealed consistant photoperiod entrained diel patterns. Each daily cycle was characterized by an elevation in body temperature (T b) to a high level plateau which declined at the onset of scotophase to a low level; both of which were maintained within narrow ranges.Under natural photoperiod in fall, lizards responded to shorter days by sinking low level T b's and expanding the duration of these low levels until no rhythmicity was shown. Subsequent exposure to long day, LD 16:8, induced self-arousal and a slightly altered diel T b selection with significantly higher T b's being chosen at both the elevated and lower daily levels. Changes in the relations of diel T b selection due to shift in photoperiod, suggest that photoperiod acts as a seasonal indicator for thermal adaptation.

Control of behavioral circadian rhythms for nesting and wheel running in mice

In Experiment 1 a circadian rhythm for nest-building behavior is demonstrated in 10 males from a genetically heterogeneous stock of Mus musculus. In Experiment 2, this circadian rhythm in nesting and that for wheel running activity were monitored simultaneously in an additional sample of five males from the same stock. Under a 16:8 LD photoperiod, mice displayed a 24-hr periodicity for both behaviors but a phase difference in peak behavioral intensities of approximately two and one-half hours. After ten days of exposure to constant light both rhythms persisted, but with no detectable difference in phase. The altered phase relationship under constant light suggests a difference in control of the circadian periodicities of these two behaviors. In Experiment 3, 5 additional males were subjected to a 10-hr shift in photoperiod to further examine control of these rhythms as well as those in food and water consumption. All four circadian rhythms re-entrained within four days. Thus, their entrainment mechanisms are functionally similar in spite of the differences in control suggested in Experiment 2.

Photoperiodic acclimation and circadian variations in tolerance of juvenile rainbow trout (Salmo gairdneri) to zinc.

The intent of this study was to determine if circadian variations occur in the tolerance of juvenile rainbow trout (Salmo gairdneri) to an acutely lethal concentration of zinc. Further, the influence of photoperiodic acclimation on this tolerance was examined since seasonal or photoperiodic acclimation may alter hormonal rhythms and toxic responses at a particular time of day, thus complexing the potential variations in acute lethal or sublethal aquatic toxicity data. Although SPIELER et al. (1977) noted that differing acclimation photoperiods did not shift the diel rhythm of tolerance of a fish species to formalin, ZITKO and CARSON (1977) recently reported seasonal variations in acute tolerance to zinc of juvenile salmonid fish held under constant temperature but ambient photoperiod conditions; and TERPIN et al. (1976) found changes in critical thermal maxima of fish due to photoperiodic acclimation. In mammals, shifts in photoperiod are known to alter circadian patterns of drug tolerance.

Biological aspects of suicide: circadian disorganization.

Disturbances in the circadian rhythmicity of biological functions have been reported in various mental disorders. Four lines of research--hormonal, electroencephalographic, cerebral spinal fluid, and circadian rhythmicity--suggest possible changes in suicidal individuals. During a study investigating the effect of a photoperiod shift on circadian rhythms, 15 male, healthy, normal subjects were used. Following a 5-day baseline period a 12-hour photoperiod shift took place and was followed by 10 days of recovery period. Multiple parameters were monitored. Two weeks following completion of the study one subject suicided. The data were examined to determine whether the suicided subject differed, rhythmically, from other subjects. Summation dials describing phase changes and vector difference dials describing dynamic phase relationships of rhythm pairs showed that the rhythms of this subject were poorly synchronized internally during baseline. Total urinary output of all parameters was lower than all other subjects during baseline and more of his urinary parameters rephased incompletely during recovery. The results suggest that circadian asynchrony and an inability to respond effectively to a phase shift may characterize a presuicidal state. These results are discussed in terms of the four lines of research involving biological aspects of suicide and suggest some intriguing interactions.

Sun-Compass Orientation in the Meadow Vole, Microtus pennsylvanicus

Meadow voles (Microtus pennsylvanicus) utilized the sun for sun-compass orientation. Orientation was most predictable when food was utilized as a training goal. A delayed photoperiod shift altered orientation predictably in a clockwise direction. This orientation shift associated with the photoperiod change indicates an operative biological clock for sun-cued orientation. Also, females utilized this orientation mechanism predictably during homing studies; males responded nonpredictably. Reasons for this sexual difference are discussed.

Response of mice to repeated photoperiod shifts: susceptibility to stress and barbiturates.

Three inbred strains of mice selected for their spontaneous aggressive behavior and differential susceptibility to stress were exposed to a controlled environment where on an average of once every 4 days for 76 days and subsequently on an average of once every 2 days for an additional 55 days a 12L:12D photoperiod was reversed by 180 degrees. This procedure did not affect the growth of the mice and appeared to reduce fighting. However, plasma corticosterone concentrations in all three strains of mice were high, and their response to a 24-hr cold stress was no longer evident. The most pronounced effect of the altered photoperiod was on the barbiturate-induced sleeping time which showed a 40% reduction in all strains in spite of differential suceptibility to the drug among strains. It is concluded that repeated random phase shifting by varying the photoperiod is a stressful experience to which animals do not adapt and that the ability to respond to an additional stimulus or drugs may be greatly altered.

Physiological significance of the pineal during adaptation to shifts in photoperiod

Running activity was continuously recorded for about one year from individual adult female S 1 rats under controlled conditions. Characteristics of this activity were compared in matched pinealectomized, sham-operated, and unoperated siblings during and following 4 separate 12-hr shifts in photoperiod (ΔΦ = 12) with standard conditions = LD 12:12 (110–470:5–20). Time for entrainment was about 8 days in all groups but during the phase shifting of the animals' circadian running activity, that of the pinealectomized animals differed in shifting initially more quickly in starting time and activity midpoint, in having less increase post ΔΦ in activity phase length (α) and amount of activity (A), and in having a different distribution of activity per transient cycle. These results suggest that the mammalian pineal may be more closely related to general central homeostatic mechanisms than to specific service in transducing photoperiod information to peripheral response systems. However, the probable relevance of these results to the interpretation of variable and photodependent or environmentally dependent physiologic effects of pinealectomy is pointed out.