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At least 37 records · Page 2Linked to original sources
PubMed2000

A long photoperiod overrides non-photoperiodic factors in blue tits' timing of reproduction.

Endocrinological studies have contributed considerably to the development of theory concerning the proximate aspects of the timing of reproduction. In non-domesticated, avian species, the relative importance of the photoperiodic and non-photoperiodic factors influencing later stages of the breeding cycle, such as the onset of egg laying, remains unclear because egg laying is difficult to obtain with captive populations and laboratory experiments of breeding are rarely carried out in the framework of long-term field studies. We set up a special experimental design such that captive Mediterranean blue tits (Parus caeruleus) can breed with success in large outdoor aviaries at similar latitudes and altitudes to their wild counterparts. Here we demonstrate experimentally that the non-photoperiodic factors responsible for large and consistent differences in the expression of natural breeding responses between three captive outdoor blue tit populations are ignored during long-day treatment. Based on these findings, an evolutionary explanation is provided for why the relative importance of the non-photoperiodic factors decreases with the progress of the season. The hypothesis can explain observed maladapted breeding dates in free-living populations and could possibly be used to increase the success of breeding programmes with some endangered, captive, non-domesticated, photoperiodic species.

Animals↗
PubMed2001

[Effect of photoperiod and temperature on fertility alteration of short photoperiod-low temperature induced male sterile rice].

Short photoperiod-low temperature induced male sterile rice is a new germplasm, whose fertility alteration characteristic is contrary to that of long photoperiod and high temperature induced male sterile rice. Compared with that of Yid1s sowed under natural conditions by stages, the fertility alteration of Yid1s was observed under simulated short photoperiod treatment. The results showed that the photoperiod-sensitive stage of Yid1s occurred from differentiation of rachis primordia (phase I) to secondary rachis-branch and spikelet primordia (phase III). The panicles induced by appropriate short daylight treatment at photoperiod-sensitive stage tended to be completely sterile under normal temperature, but the sterile effect was weakened under high temperature. The pollen fertility of Yid1s was reduced under high or low temperature. The temperature-sensitive stages of Yid1s based on the analysis of the effects of high and low temperature on fertility were basically identical, i.e., from pollen mother cell formation (phase V) to single nucleus (phase VII).

Fertility↗
PubMed1986

Comparative anatomy of the retino-hypothalamic tract in photoperiodic and non-photoperiodic rodents.

This study examined whether the nearly symmetrical input from each eye to each suprachiasmatic nucleus previously reported in Syrian hamsters (Mesocricetus auratus) is a universal feature of retino-hypothalamic projections in photoperiodic rodents. Intraocular injections of horseradish peroxidase (HRP) were used to trace the retino-hypothalamic tract in three species of photoperiodic rodents, Turkish hamster (Mesocricetus brandti), deer mouse (Peromyscus maniculatus bairdi) and white-footed mouse (Peromyscus leucopus), and in the non-photoperiodic house mouse (Mus musculus). The Turkish hamster displayed a pattern of retinal input to the suprachiasmatic nuclei (SCN) similar to that previously seen in the Syrian hamster. On the other hand, the two photoperiodic species of Peromyscus used in the study showed an asymmetrical distribution of retinal fibers with the heaviest input to each suprachiasmatic nucleus originating from the contralateral eye. This asymmetrical pattern was also evident in house mice and is similar to that previously seen in rats. Therefore, symmetrical retinal input to the SCN is not consistently related to photoperiodism in rodents.

Animals↗
PubMed1989

Reproductive refractoriness in the Welsh Mountain ewe induced by a short photoperiod can be overridden by exposure to a shorter photoperiod.

The objectives were to determine if relative lengths of photoperiods that induce reproductive cycles in ewes affect the length of the subsequent breeding season, if duration of the refractoriness that terminates breeding is affected by photoperiod length, and if the resulting refractoriness to an inductive photoperiod is absolute. Groups of Welsh Mountain ewes were exposed to either 12L:12D (n = 12) or 8L:16D (n = 6) photoperiods beginning at the summer solstice when daylengths reach a maximum of 17.5 h at Bristol, England. A control group (n = 10) was exposed to natural daylengths. Ovarian cycles in the controls, as judged by monitored plasma progesterone levels, commenced in early October, about 1 mo later (p less than 0.001 in both cases) than in sheep exposed to 12L:12D or 8L:16D. The advancement in cycle onset was similar under 12L:12D and 8L:16D (69 +/- 2 and 77 +/- 4 days after the summer solstice compared with 102 +/- 2 days in the controls). Duration of the breeding season (100 +/- 4 days) in ewes exposed to 12L:12D was significantly shorter (p less than 0.001 in both cases) than in ewes exposed to natural daylengths or 8L:16D (153 +/- 3 and 133 +/- 5 days, respectively). Approximately 70 days after the ending of ovulatory cycles in the 12L:12D group, half of the animals (n = 6) were transferred to 8L:16D. This treatment greatly (p less than 0.001) reduced the duration of anestrus and cycles began again 62 +/- 4 days after transfer to 8L:16D, or about 90 days earlier than in ewes (n = 6) remaining in 12L:12D.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Maternal transfer of photoperiodic information in Siberian hamsters. vi. effects of time-dependent 1-hr melatonin infusions in the mother on photoperiod-induced testicular development of her offspring.

We tested in Siberian hamsters the nature of the maternal signal that relays photoperiodic information to the developing fetuses. As previous investigations have identified maternal hormonal and circadian components in this process, the specific goal of this presentation is to determine quality of the signal that connotes daylength when it is imparted to the fetus. Does the function of the signal received by the fetus best support the coincidence or duration hypotheses of photoperiodic induction? Pregnant hamsters received 1 or 8 hr melatonin or vehicle infusions everyday. Juveniles of intact mothers gestated on 16 hr of light per day (16L) experienced maximal suppression of testicular development when reared on 14L. However, when intact mothers gestated on 10L received a 1-hr melatonin infusion daily at 20:00-21:00 hr, their young responded to 14L with greatly accelerated testicular development. In the absence of the maternal pineal gland (and, therefore, the maternal melatonin signal), the effects of maternal melatonin infusions were reversed. Here, only the juveniles of 16L-gestated females infused at 20:00-21:00 hr daily responded to 14L with enhanced testicular development. All other groups showed the same extent of gonadal development, independent of the time or type of infusion their mothers received. Testicular development on 14L of all juveniles from pinealectomized mothers gestated on 10L was of the same magnitude, regardless of the type and time of infusion their mothers received during pregnancy. The results suggest that the maternal signal transferred to the fetuses during gestation consists not only of the daily melatonin signal, but also some circadian-based component that greatly affects the effect of the former. The timing, and not the duration, of the maternal melatonin signal with respect to the animals' (mother and fetus) circadian day is of crucial importance in the transfer of photoperiodic information from mother to fetus.

Animals↗
PubMed1995

Influence of prenatal photoperiod on postnatal plasma concentrations of progesterone and prolactin in female red deer (Cervus elaphus) reared in constant equatorial photoperiod.

Prenatal photoperiod influences postnatal prolactin secretion and the timing of reproductive development in male red deer reared from birth in a constant equatorial photoperiod (12:12 light:dark). The present trial investigated whether a similar phenomenon occurs in female red deer. Female deer whose mothers had been exposed for the last 14 weeks of gestation to long (group L, 18:6 light:dark) or short day length (group S, 6:18 light:dark) were kept from birth in constant equatorial day length with food available ad libitum. Both groups showed similar live-weight gain to 90-100 weeks of age. Blood samples taken once or twice weekly were analyzed for progesterone and prolactin. Progesterone concentrations indicated that there was no difference between the groups in the timing of the first incidence of ovarian (luteal) activity, which occurred at a normal or late age for natural puberty (67 weeks or older). Only one individual per group exhibited normal repeated luteal cyclicity since there was a high incidence of irregular or abnormal luteal function. Plasma prolactin concentrations at birth were higher in group L than group S (P < 0.001). Thereafter, although the mean and peak values did not differ significantly between the groups, there was a significant difference in the pattern of secretion; deer in group L showed significant clustering of prolactin peaks (P < 0.01) at a mean age of 48 weeks, whereas deer in group S showed a random distribution of peaks. Therefore, for female red deer raised in constant equatorial photoperiod, prenatal long day lengths did not advance timing of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Photoperiodic effects in the Djungarian hamster: one minute of light during darktime mimics influence of long photoperiods on testicular recrudescence, body weight and pelage colour.

In male Djungarian hamsters (Phodopus sungorus) short photoperiods (L/D 8/16) with additional 1- or 5-min light-pulses 8 h after light-off were as effective as long photoperiods (L/D 16/8) in stimulating testicular recrudescence, increase in body weight and moult into summer pelage. The results are discussed with regard to the hypothesis that the pattern of melatonin release from the pineal gland is important in mediating photoperiodic effects in mammals.

Animals↗
PubMed1967

Time measurement in insect photoperiodism: reversal of a photoperiod effect by chilling.

Spectacular reversals of the photoperiodic control of diapause are obtained if females of Nasonia vitripennis are chilled for 4 hours in certain lightdark cycles. Experiments in which chilling is combined with short light breaks (night interruptions) show that the first peak of diapause inhibition moves in response to the chilling. This result provides an explanation for the photoperiodic reversal; it is also circumstantial evidence for the participation of circadian rhythms in photoperiodism.

Animals↗
PubMed1980

Sexual maturation of boars and growth of swine exposed to extended photoperiod during decreasing natural photoperiod.

Littermate pairs of crossbred boars, barrows and gilts were used to study the effects of an artificially extended photoperiod during decreasing daylength on puberty in boars and on weight gain and feed efficiency. Libido scores of the boars exposed to the extended photoperiod were higher (P < .01) than those of controls at 24 and 26 weeks of age. At 26 weeks of age, semen had been collected from 74% of the boars on supplemental light but from only 26% of the controls. Lighting treatment did not affect semen quality. The number of ejaculates previously collected did affect semen quality. Motility and total sperm per ejaculate increased with increasing ejaculate number, while the percentage of abnormalities appeared to decrease. A second group of boars was delayed in the development of mating behavior, perhaps because of inadvertent consumption of Gibberella zeae-infected corn. The extended photoperiod did not exert a beneficial effect on weight gain or feed efficiency of boars, barrows or gilts.

Animals↗
PubMed1988

Significance of growing photoperiod and light stimulation at various ages for Leghorn pullets subjected to regular or ahemeral photoperiods.

Leghorn pullets were cage reared to 15 or 19 wk of age in environmentally controlled rooms that provided either 8 h or 14 h of light per day. In Experiment 1, birds were moved to laying cages at 15 wk of age and subjected to either 14 h light (L): 10 h (D) dark or ahemeral 14L:14D photoperiods. Feed intake, egg weight, shell quality, and egg production were monitored to 67 wk of age. In Experiment 2, pullets were moved at 19 wk of age and subjected to 14L:10D or 17L:7D light programs. Production parameters were measured as previously described. No significant (P greater than 0.5) interactions were observed between rearing and laying photoperiods, suggesting that increase in the length of photoperiod around time of maturity is not essential for adequate performance. In Experiment 1, ahemeral lighting resulting in reduced egg production, whereas egg shell quality and egg weight were improved (P less than .05). In both experiments, the 14-h rearing program resulted in improved egg size together with improved eggshell quality (P less than .05). Whereas increased egg size may relate to body weight, no explanation is apparent for the consistent pattern with respect to shell quality. In Experiment 2, poorer shell quality was observed with 17 vs. 14 h light per day. It is concluded that light stimulation at maturity has little effect on overall egg production. Improved shell quality observed with birds reared under 14 h light vs. those reared under 8 h per day may relate to a less rapid attainment of peak egg production.

Aging↗
PubMed1997

Evidence that the circadian system mediates photoperiodic nonresponsiveness in Siberian hamsters: the effect of running wheel access on photoperiodic responsiveness.

Juvenile male Siberian hamsters from a line of hamsters selected for nonresponsiveness to short photoperiod (PNRj) and animals from the general colony (UNS) were separated at weaning into two groups. Group 1 males were moved into short days (10 h light:14 h dark [10L:14D]) with free access to running wheels (RW). Group 2 animals were the male siblings of Group 1 hamsters; they were moved at the same time into the same room, but were housed in cages without access to RW. Group 2 hamsters only had access to RW for the final week of short-day exposure (Week 8). Animals were blood sampled at the time of sacrifice for analysis of serum prolactin (PRL) and follicle-stimulating hormone (FSH) concentrations. At sacrifice, paired testis weights were obtained and pelage color was scored. Animals from the UNS line showed the expected declines in testis weight, body weight, and serum concentrations of both PRL and FSH, regardless of the presence or absence of RW. These animals also exhibited a high proportion of individuals molting to winter-type pelage. By contrast, a marked difference was noted between siblings from the PNRj line depending on whether RW access was provided at the time of weaning. Animals with access to RW exhibited identical responses to those of the UNS responder animals, whereas PNRj animals without access to RW showed no adjustments to short days (i.e., testis regression, pelage molt, expansion of alpha). In a second experiment, PNRj and UNS males were placed in constant darkness (DD), with or without RW access. The results of this experiment indicated that PNRj animals respond to DD regardless of the presence or absence of RW. In DD, PNRj hamsters also exhibited significantly longer free-running period lengths (taus) than did UNS hamsters; all the PNRj hamsters had taus > 24 h, whereas none of the UNS hamsters had a tau > 24 h. These results indicate that PNRj hamsters retain the proper neural pathways for responding to short day lengths and establish a role for locomotor activity feedback in modulating the circadian system and, subsequently, photoperiodic responsiveness in PNRj hamsters.

Activity Cycles↗
PubMed2004

Photoperiodic regulation of type 2 deiodinase gene in Djungarian hamster: possible homologies between avian and mammalian photoperiodic regulation of reproduction.

The molecular mechanisms responsible for seasonal time measurement have yet to be fully described. Recently, we used differential analysis to identify that the type 2 iodothyronine deiodinase (Dio2) gene is responsible for the photoperiodic response of gonads in Japanese quail. It was found that expression of Dio2 in the mediobasal hypothalamus is induced by light and that T(3) content in the mediobasal hypothalamus increased under long day conditions. In addition, we showed that intracerebroventricular infusion of T(3) mimics photoperiodically induced testicular growth. Because it is well known that thyroid hormone is also essential for the maintenance of the seasonal reproductive changes in a number of mammals, we examined expression of Dio2 in Djungarian hamsters and found expression in the ependymal cell layer lining the infralateral walls of the third ventricle and the cell-clear zone overlying the tuberoinfundibular sulcus. Signal intensity was high under long days and weak under short days. Although light pulse did not affect Dio2 expression, melatonin injections decreased Dio2 expression under long days. These results indicate that Dio2 may be involved in the regulation of seasonal reproduction in mammals in the same way as observed in birds.

Animals↗
PubMed1990

The effect of temperature on photoperiodic induction of diapause in insects and mites: a model for the photoperiodic "counter".

Existing models for the accumulation of photoperiodic information (the photoperiodic "counter") cannot explain satisfactorily the various effects of temperature on diapause induction in insects and mites, nor the observation that in several insect species the so-called "required day number" has a high degree of temperature compensation. In the model presented in this paper the effect of temperature has been incorporated in such a way that both the rate of increase of the "induction sum" (or "diapause titre") and the level of the "minimally required induction sum" (or "threshold level") are temperature dependent. The proposed model is in accordance with observed temperature effects, and gives an explanation for a temperature-compensated "required day number".

Animals↗
PubMed1991

Entrainment of Syrian hamsters to short photoperiod T-cycles does not reverse the inhibitory nature of feedback lighting on the photoperiodic response.

Experiments examining the photoperiodic effects of various light-dark cycles unexpectedly demonstrated that light during the subjective night is not necessarily photoinductive to the reproductive system of long day breeders. Feedback lighting (illumination in response to locomotor activity) and a high-frequency light-dark cycle with 1 minute (m) of light followed with 1 minute of dark (LD1m:1m) failed to maintain reproductive function in Syrian hamsters despite exposing the animal to 5-6 hours of light per cycle during the subjective night. In an effort to determine why feedback lighting and LD1m:1m do not maintain reproductive function, male Syrian hamsters were exposed to one of the following lighting conditions for ten weeks: a light-dark cycle with 14 hours of light followed by a 10 hour light-dark cycle of 1 minute of light followed by 1 minute of dark ¿LD14:10(1m:1m)¿; a cycle of a 14 hour light-dark cycle of 1 minute of light followed by 1 minute of dark, followed by 10 hours of dark ¿LD14(1m:1m):10)¿; a light-dark cycle of 2 hours of light and 21 hours of dark (LD2:21); a light-dark cycle of 2 hours of light and 22 hours of dark (LD2:22); LD2:21 in conjunction with feedback lighting (LD2:21/FB); LD2:22 in conjunction with feedback lighting (LD2:22/FB); constant dark (DD) or constant light (LL). All hamsters exposed to LD14(1m:1m):10 entrained. Only 7 of 12 hamsters exposed to LD14:10(1m:1m) entrained. This supports previous findings, which suggest that the circadian system has difficulty differentiating between LD1m:1m and LL. Exposure to LD2:22 and DD induced testicular regression, while LL, LD2:21 and LD14(1m:1m):10 maintained reproductive function, as expected. The addition of approximately 5 hours of nocturnal illumination by feedback lighting, however, not only failed to prevent reproductive regression in LD2:22, but attenuated the stimulatory nature of LD2:21. This suggests that feedback lighting is not only not stimulatory, but may be actively inhibitory. Perhaps this is due to a photoinhibitory effect of multitransitional nocturnal illumination. This hypothesis is supported by the finding that LD14:10(1m:1m) allows regression, while LD14(1m:1m):10 is stimulatory. These findings also imply that the state of the circadian system is instrumental in the reproductive system's interpretation of a light signal.

Activity Cycles↗
PubMed1982

Photoperiodism in quail: testicular growth and maintenance under skeleton photoperiods.

Testicular growth was induced in quail which were exposed to a skeleton photoperiod that included a pulse of light given during the dark period (night-interruption). The minimum duration of the pulse inducing testicular growth was 3.75 min per day. Longer pulses induced greater rates of growth, and of LH and FSH secretion; maximum rates occurred with a night-interruption of 60 min. Pulses even shorter than 3.75 min maintained testicular function in previously photostimulated quail. A night-interruption of 14s maintained full testicular size and hormone secretion in four out of six quail, and with 56s no regression whatsoever occurred. The rate of testicular growth was largely independent of the duration of the main light period used in the skeleton treatment. The light intensity within the night-interruption also affected the degree of testicular development and gonadotrophin secretion.

Animals↗