Artificial Photoperiod Research Articles

Pineal denervation by cervical sympathetic ganglionectomy suppresses the role of photoperiod on pregnancy or pseudopregnancy, body weight and moulting periods in the mink (Mustela vison).

In mink, termination of the delayed implantation period, following reactivation of the corpora lutea, and onset of the spring moult are associated with a rise in prolactin secretion triggered by increasing daylength, while decreasing daylength induces the autumn moult. To establish whether suppression of the function of the pineal rendered the mink unresponsive to daylength changes, the superior cervical ganglion was removed bilaterally 2-4 weeks before mating. Intact and operated females were then left outdoors or were put under a lighting regime of either 15 h light:9 h darkness (15L:9D) or 8L:16D. In July, at the end of the spring moult, the 15L:9D lighting regime was changed to one of 8L:16D. Under artificial photoperiods ganglionectomy suppressed the stimulatory role of long days and the inhibitory role of short days on prolactin secretion, and consequently on progesterone secretion and spring moult. Neither was the autumn moult, induced early in intact females by the change to a short photoperiod, advanced in ganglionectomized females, showing that the latter were unresponsive to the artificial modification of the photoperiod. However, in animals kept outdoors, prolactin and progesterone secretion and spring moult were not changed by ganglionectomy. Increase in body weight and autumn moult were only slightly delayed by the operation suggesting that other environmental factors had replaced the synchronizing effect of the daylength changes. Alternatively the desynchronization between intact females responsive to photoperiodism and those rendered unresponsive may be too slow to be observed soon after ganglionectomy.

Evidence that the onset of the breeding season in the ewe may be independent of decreasing plasma prolactin concentrations.

Ten ewes of each of two breeds, Dorset Horn (long breeding season) and Welsh Mountain (short breeding season), were given subcutaneous oestradiol-17 beta implants and then ovariectomized. Another 10 ewes of each breed were left intact. On 3 May 1982, all the ewes were housed in an artificial photoperiod of 16L:8D. After 4 weeks, half of the ewes of each breed and physiological state were abruptly exposed to a short-day (8L:16D) photoperiod while the others remained in long days (16L:8D). The time of onset of the breeding season was significantly (P less than 0.05) advanced in ewes switched to short days (12 August +/- 10 days) compared to those maintained in long days (4 September +/- 14 days). Dorset Horn ewes began to cycle (20 July +/- 7 days) significantly (P less than 0.001) earlier than Welsh Mountain ewes (19 September +/- 6 days). Disparities in the time of onset of cyclic activity in ewes of different breeds and daylength groups were echoed in disparities in the time at which plasma LH and FSH concentrations rose in oestrogen-implanted, ovariectomized ewes of the same light treatment group. Prolactin concentrations showed an immediate decrease in ewes switched to short days, but remained elevated in long-day ewes. Since the breeding season started in the presence of high prolactin concentrations in long-day ewes, it seems unlikely that prolactin is an important factor determining the timing of the onset of cyclic activity.

FSH secretion in pinealectomized rams subjected to artificial photoperiods.

Eight mature Romney rams which had been pinealectomized and another eight sham-operated rams were allocated equally to one of two contrasting lighting regimes. They were housed indoors with the temperature held constant, offered a constant diet and plasma samples were collected each week for 9 months. Changes in plasma FSH in pinealectomized and sham-operated rams were similar when the rams were subjected to normal seasonal changes in photoperiod, with lower FSH levels recorded under increasing daily photoperiods than during the phase of decreasing (stimulatory) photoperiods. In contrast a reversed pattern of changes in lighting advanced the increase of plasma levels of FSH in the case of sham-operated rams, because the period of decreased daily photoperiods occurred earlier in this situation. In this case, however, pinealectomized rams did not behave like the control animals, but had raised plasma FSH levels at the same time as rams on the normal lighting regime. These results demonstrate that the pineal-mediated effects of photoperiod on reproduction in sheep directly involve FSH secretion and that seasonal cyclic changes in FSH secretion persist even after pinealectomy.

Interactions of temperature, size and photoperiod on growth and smoltification of chinook salmon ( Oncorhynchus tshawytscha)

Underyearling fall chinook salmon ( Oncorhynchus tshawytscha) were reared at two temperatures (9 and 15°C) and three photoperiods simulating winter (WIN), spring—summer (SS), and natural (NAT) conditions. The two artificial photoperiods were adjusted according to fish size so that an equinoctial photoperiod was synchronized with a hypothesized optimum size range for smolting (8–14 cm fork length). Fish exposed to a winter (WIN) photoperiod had the slowest growth rate. Fish under the SS photoperiod at both temperatures and under the WIN photoperiod at 9°C displayed hypoosmoregulatory capability near the equinoctial daylength. Thyroxine concentrations in fish reared under a natural photoperiod remained at basal levels during the period of early saltwater adaptiveness and throughout the remainder of the experiment. Thyroxine titers showed significant increases under all experimental photoperiod—temperature combinations near the equinoctial daylength with the exception of the 15°C/SS treatment.

Refractoriness to Inhibitory Day Lengths Initiates the Breeding Season of the Suffolk Ewe 1

Recent evidence indicates that the breeding season of the Suffolk ewe ends because of loss of response to a day length that was previously inductive. This condition of photorefractoriness could potentially also initiate reproduction, as is the case in several long-day breeding rodents. In this study we determined if ewes enter their breeding season because they become refractory to the long ambient photoperiods of late summer. On the summer solstice, 3 groups of ovariectomized ewes (n = 6) bearing s.c. Silastic implants of estradiol (OVX + E) were placed in different day length treatments: 1) natural photoperiod; 2) artificial photoperiod, stimulating natural day lengths; or 3) artificial photoperiod equivalent to that of the summer solstice (16.25L). Entry into the breeding season is associated with a striking (greater than 30-fold) increase in circulating levels of luteinizing hormone (LH). Timing of the onset of the breeding season was not delayed in ewes maintained on the summer solstice photoperiod; LH levels rose simultaneously in all groups. We conclude that ewes normally begin breeding not because they are actively driven to do so by decreasing or short days, but because they become refractory to prevailing long days. Because the pattern of circulating melatonin, which is known to transduce the photoperiodic message, remained entirely appropriate to day length, we believe that the mechanism responsible for photorefractoriness resides in the postpineal processing of the melatonin signal.

Alternate photoperiods time puberty in the female lamb.

In the spring-born lamb, puberty, the onset of repetitive ovarian cycles, occurs between 25 and 35 weeks of age during the decreasing day length of autumn. This study was conducted to determine the photoperiod conditions required for puberty. Several artificial photoperiod treatments were used, beginning from birth or soon after. Continuous exposure to long days or to short days delayed the first normal luteal cycle beyond 1 yr of age. Similarly, a single block of 4 or 10 weeks of long days at early ages, from either 3-7 or 3-13 weeks of age (afterwards under short days), produced only a few consecutive cycles within the first year after birth. However, exposure to blocks of long days at later ages resulted in the onset of cycles during the normal pubertal period. Lambs that experienced a 10-week block of long days (12-22 weeks of age; otherwise under short days) began reproductive cycles at 34 weeks of age. Reduction of the single block of long days to 5 weeks (17-22 weeks of age) or 1 week (week 22 of age) also resulted in the onset of normal luteal cycles within the normal age range for puberty. The results indicate that a sequence of long days followed by short days is required to initiate and sustain ovulatory cycles at the normal age in the lamb. Moreover, the age when long days are experienced is important, with later exposure to long days being more effective in producing consecutive cycles than early exposure to long days. These findings raise the possibility that the spring-born lamb uses a portion of the long days of summer to time the onset of puberty during the short day lengths of autumn.

Photoperiodic regulation of thyroid responsiveness to TSH in Fundulus heteroclitus.

Treatment of the killifish, Fundulus heteroclitus, with ovine thyrotropin (oTSH) produced elevations in serum thyroxin (T4) that varied seasonally with a strong inverse correlation to environmental photoperiod (P less than 0.001). At 20 degrees C, oTSH (0.2 IU) increased serum T4 to levels ranging from 1.5 micrograms/100 ml in midsummer to 7.5 micrograms/100 ml in midwinter despite relatively stable resting levels throughout the two years of study. Similar rates of clearance of T4 in summer and winter suggest that an alteration in thyroid response to oTSH accounts for this change. The serum T4 response to oTSH is both photoperiod- and temperature-dependent. In laboratory studies, fish exposed to a short artificial photoperiod (LD 8:16) for one month responded to oTSH with T4 levels about twice as high as those in fish exposed to long days (LD 14:10). On the other hand the T4 response to oTSH was sharply reduced at 5 degrees C from that seen at 20 degrees C. This suggests that, in nature, seasonal changes in photoperiod and temperature have opposite effects on thyroidal responsiveness to TSH. Overall, the annual variation in the T4 response to oTSH appears to be driven by photoperiod, inasmuch as the alterations preceded major temperature changes in the wild and can be shown to occur at constant temperature in captivity. Photoperiodic induction of changes in thyroid sensitivity may aid in the maintenance of basal T4 levels under changing thermal conditions.

BREEDING CONDITION OF MALE RED BISHOPS UNDER ARTIFICIAL PHOTOPERIODS

Summary Craig, A. J. F. K. 1985. Breeding condition of male Red Bishops under artificial photoperiods. Ostrich 56: 74–78. Testis development, as indicated by bill colour changes, and moult were followed over two years in nine birds kept under constant conditions of 14 h light:10 h dark. All birds maintained at least partial nuptial dumage throughout this period, but most continued normal cycles of wing moult. The testes continued to show cycles of enlargement and regression.

The influence of artificial and natural short photoperiods on male syrian hamsters: Reproductive effects

The influence of artificial and natural short photoperiods on male syrian hamsters: Reproductive effects

Effets du chimiostérilisant ornitrol sur le développement testiculaire du Carouge à épaulettes traité en captivité

Male red-winged blackbirds were kept in captivity and fed cracked corn containing 0.1% ornitrol for a period of 10 days in order to determine the optimal timing of this treatment during gonad growth. Treatments were administered before and during testis growth under conditions of natural photoperiod and under conditions of artificial photoperiod that stimulate testis development (18 h light: 6 h dark). In both experiments we observed a great deal of individual variation in the response to treatments. In the first trial, treatments applied both before and during testes growth inhibited their development. In the second trial, the same trend was observed, but differences were not significant. This treatment will have maximum efficiency in a natural environment and be profitable as a method of control only if the reproductive state of male redwings is determined with precision.[Journal translation]

The effect of a ?permanent? clock-shift on the orientation of experienced homing pigeons

A group of experienced homing pigeons vas subjected to a 6 h slow shift of their internal clock and kept under these conditions for more than 2 months. During the overlap time between the natural and artificial photoperiods they were released for training flights to familiarize them with an area while living in a “permanent shift”.

Regulation of maturation and spawning of an abalone, Haliotis (Gastropoda) by external environmental factors

Gonadal maturation of Haliotis discus hannai is proportional to the effective accumulative temperature (EAT), in accordance with the following formula: Y n= ∑ i=l n (T i−θ) where Y n = EAT in degree-days, t i = temperature to which the animals are exposed daily (°C), and θ = the biological minimum for gonadal growth, which is 7.6°C in H. discus hannai. The progress of gonadal maturation may be divided into three states: immature (0–500 degree-days), mature (500–1500 degree-days), and fully mature (after 1500 degree-days). This system agrees with qualitative observations of the progress of maturation confirmed by artificial induction of spawning, where EAT 0 is the beginning of conditioning started during the recovery stage of the reproductive cycle of this species in the winter. Temperature appears to be the major external environmental factor which regulates the breeding cycle of this mollusc, because the artificially produced spawning period (after 1500 degree-days) corresponds well with the natural breeding season in terms of EAT. Adequate nutritional levels of over 5% feeding rate (weight wet food ingested/body weight) are necessary for application of this relationship of EAT uniformly to experimental populations. Gravid adults are obtainable throughout the year by temperature control based on EAT. Spawning is induced by a stimulus produced by the UV irradiation of seawater. The release of gametes can be set for any desired time of day by artificial photoperiod (12L-12D) conditioning of the mollusc in advance.

Effects of pinealectomy on the hormonal response to artificial photoperiod in white-tailed deer

Underyearling masu salmon were reared under a 8L:16D photoperiod for approximately 3 months, and subsequently transferred to 8L, 10L, 11L, 12L, 13L, 14L or 16L photoperiod in October, in order to determine the suitable photoperiod for induction of smolting (Experiment 1). Smolt was judged by the external appearance of fish, i.e., silvery body color, black margin on the dorsal and caudal fins, and slim body shape. As early as 1 month following this transfer, smolts appeared in the 16L group. After 2 months, the 13L group had the highest frequency of smolts. After 3 months, most smolts were found in the 11L group and presmolts appeared even under constant short daylength (8L:16D). Overall, the largest number of smolts appeared in the group transferred from 8L:16D to 13L:11D. Underyearling fish reared under natural photoperiod were also transferred to 11L, 12L, 13L, 14L, 15L or 16L photoperiod in October (Experiment 2). Only a few smolts appeared during this experiment.In order to determine a suitable short daylength for pretreatment prior to the transfer to long daylength, underyearling masu salmon were reared under 6L, 7L, 8L, 9L, 10L, 11L, 12L and 13L photoperiods for approximately 5 months, and subsequently transferred to a 13L:11D photoperiod in October (Experiment 3). One month after the transfer, a small number of smolts appeared in only the group transferred from 6L. After 2 months, a large number of smolts appeared in the groups transferred from 10L and downward. After 3 months, a small number of smolts newly appeared in the groups transferred from 12L and 11L. A few smolts appeared in the group under constant 13L after 6 months. Finally, effects of increasing daylength on the secretion of growth hormone (GH), thyroxine (T4) and triidothyronine (T3) were investigated (Experiment 4). Seven days after transfer from short (8L:16D) to long (13L:11D) daylength, plasma GH levels were significantly higher than those in the control group under constant 8L. Plasma GH levels tended to increase gradually in both groups throughout the experiment. Plasma T4 and T3 levels were not affected by increasing daylength. These results indicate that it is necessary to rear fish under short daylength for a sufficient period of time before daylength can be changed to long-day for purposes of artificial induction of smolting, and the larger the difference in daylength after changing photoperiod to long daylength, the earlier smolts appear. Furthermore, an increase in daylength may stimulate the transient secretion of GH, which may participate in the process of smolting.

Effect of Artificial Photoperiod on Eating Behavior and Other Behavioral Observations of Dairy Cows

Twenty-eight cows were assigned randomly to a daily photoperiod of 18h light and 6h darkness or to continuous light and were observed 1 day each month from December 1981 to February 1982. Lighting regimen did not affect eating behavior or milk production. Overall means of total eating time, number of eating bouts, and average time eating per bout on the 3 observation days were 270 to 280min, 10 to 12 times, and 24 to 27min. Eating behavior and milk production were not significantly correlated. Eating patterns were similar in both groups and across observation days. Peaks of eating activity occurred before sunset, bracketing the evening milking and after the offering of fresh feed in the morning. Approximately 80% of total eating activity occurred between 0900 and 2100h in both groups. Cows had a clear preference for entry into the right or left side of the milking parlor, and entry order was repeatable. Milking order and milk production were not correlated. In one group, location of free stalls did not influence utilization; but in the other group, centrally located stalls were utilized more than stalls at either end of the alley. About 40% of cows had individual free stall preferences.

The influence of artificial photoperiod on the growth, appetite and reproductive status of male red deer and sheep

Young male red deer and Suffolk X (Finn X Dorset) sheep were kept on an artificial photoperiod such that two cycles of daylength occurred during one calendar year. They were penned separately, fed to appetite, weighed weekly and measured tri-weekly. Both species showed two cycles of intake, growth and gonadal activity in response to the daylength when only one would have been shown on natural photoperiod, although in the sheep these cycles were of lower amplitude than in the deer. The deer grew two sets of antlers during the study. A lag of some 3–4 months occurred between an event such as peak food intake and the time it would have been expected to occur relative to the daylength cycle. It is considered that although daylength controls these cycles, there is an endogenous rhythm which photoperiod cannot completely suppress.

Increases in volume, fluid content, and lens weight of eyes following systemic administration of melatonin.

Melatonin's effects were studied in male golden hamsters (Mesocricetus auratus) distributed among five surgical groups (nonoperated, sham-pinealectomized, sham-pinealectomized plus black plastic shielding of the pineal region, pinealectomized, and pinealectomized plus black plastic shielding of the pineal region) and three injection groups (vehicle only, 25 micrograms melatonin, and 2,500 micrograms melatonin). Injections (s.c.) were daily for 28 d at L11 to L11.75 in a (light:dark) L:D 14:10 artificial photoperiod. Animals (N = 112) were killed and dissected on the day after the last injection (at 55-65 d of age). None of the surgical procedures affected weights of eyes or their parts, nor did they influence the effects of administered melatonin on the eyes. Melatonin caused an increase in absolute and relative eye weight and an increase in fluid content of intraocular space. The magnitudes of these effects were positively related to melatonin dose. These same eyes had a progressively lower weight of nonlenticular tissues with low to high doses of melatonin, probably in relation to greater fluid content, and suspected increase in intraocular pressure. Lens wet and dry weights were significantly greater in animals receiving melatonin, but only at the high dose. These actions of melatonin are likely to be direct and are shown to not require the presence of the pineal. Experiments of other designs are suggested in order to determine whether the effects of the low, near physiological, dose of melatonin represent physiological actions of endogenous melatonin, synthesized and released within the eye. However, effects of large doses of melatonin on the eye are still noteworthy in relation to interpretation of experiments employing such dosages, and of disease states involving changes in intraocular pressure.

Influence of photoperiod and melatonin administration on growth and metamorphosis in Discoglossus pictus larvae

1. 1. The participation of an environmental factor such as photoperiod in the metamorphic development of Discoglossus pictus has been studied. 2. 2. Short photoperiods were more effective in accelerating the rate of growth and the stages of development of tadpoles than were long photoperiods. 3. 3. Daily melatonin injections to tadpoles during larval development showed different effects depending on the artificial photoperiod in which the tadpoles were maintained.

Evidence that the onset of seasonal anoestrus in the ewe may be independent of increasing prolactin concentrations and daylength.

Nine ewes of each of two breeds, Dorset Horn (long breeding season) and Welsh Mountain (short breeding season), were ovariectomized after insertion of subcutaneous implants containing oestradiol-17 beta. A further 9 ewes of each breed were left entire. All of the ewes were placed in an artificial photoperiod of 8L : 16D on 12 December 1980. After 5 weeks half of the ewes of each breed and physiological state were abruptly changed into a long-day photoperiod (16L :8D) while the rest remained in short days. The time of onset of seasonal anoestrus in entire animals was significantly advanced in ewes changed to long days, with the end of the breeding season coming at the normal time of year in ewes maintained in short days. These differences in oestrous cycle activity were reflected by differences in the time at which LH concentrations in ovariectomized, oestrogen-treated ewes on the two light treatments fell to basal values. Prolactin concentrations showed an immediate and sustained rise in ewes changed to long days, but remained low in ewes maintained in short days. Since the onset of seasonal anoestrus occurred in the absence of high levels of prolactin (in short-day ewes), it is concluded that prolactin is not the major vehicle by which seasonal changes in hypothalamic responsiveness to the negative feedback effects of oestradiol are produced. The results suggest that anoestrus may be due to photorefractoriness.

Response to experimental photoperiods by a migratory bunting, Emberiza melanocephala

Little is known about the effects of photoperiod on avian migrants that visit southeast Asia. In this paper, we report experiments performed on an emberizid finch, the Black‐headed Bunting Emberiza melanocephala, to investigate its photoperiodic responses under artificial photoperiods, and continuous light and darkness.Two series of experiments were performed with the photosensitive male birds. In the first series, different groups were exposed to seven different artificial photoperiods: 3L/21D, 6L/18D, 8L./16D, 11L/13D, 12L/12D, 15L/9D and 20L/4D, for 30 days. They were weighed and laparotomized at the beginning and end of the experiments. The birds responded to 12L/12D, 15L/9D and 20L/4D, but not to 3L/21D, 6L/18D, 8L/16D and 11L/13D. In the second series, photosensitive birds were placed under continuous light (LL) and dark (DD) conditions for 130 and 90 days. Periodic observations indicated that testicular growth and fattening followed by involution and fat‐depletion had resulted in birds under LL, indicating the onset of photorefractoriness, while DD had no effect either on gonads or fattening in the buntings.Our results demonstrate that light stimulation is a prerequisite to reproductive and metabolic activities (pre‐migratory and migratory changes, fattening and weight gain) in the Black‐headed Bunting, which has a photoperiodic threshold to these events at between 11 and 12 h daily photoperiods.

Plasma prolactin and gonadotrophins during gonadal development and the onset of photorefractoriness in male and female starlings (Sturnus vulgaris) on artificial photoperiods.

Previous studies have shown that an increase in prolactin secretion coincides with the beginning of the photorefractory phase in starlings (Sturnus vulgaris). To determine how closely this increase is associated with the onset of refractoriness, we kept starlings on photoperiods which would induce refractoriness at different rates. Four groups of males and females were transferred from 8h light:16h darkness (8L:16D) to either 18L:6D, 13L:11D, 11L:13D or 8L:16D. Weekly blood samples were assayed for LH, FSH and prolactin and the males were frequently laparotomized to determine testis volume. In males, both 18L and 13L induced marked increases in plasma gonadotrophin levels and rapid gonadal maturation. A photoperiod of 18L induced an earlier onset of refractoriness (2-4 weeks) than 13L (6 weeks). In both cases prolactin levels began to increase immediately before the onset of refractoriness. Males on 11L showed a slight increase in gonadotrophin levels and slow gonadal maturation. There was no increase in prolactin levels and these birds did not become refractory. Hormonal data from the females were similar to those from males. These results confirm that increased prolactin secretion is associated, in some way, with the onset of photorefractoriness in this species, although whether it is a cause or consequence of photorefractoriness, or simply of gonadal regression, remains unclear.