Interaction of Photoperiod,Grouping and Isolation in Female Reproduction of Lymnaea stagnalis

Summary

A study was made of the effects of the photoperiod on female reproductive activities in grouped and isolated specimens of the hermaphrodite freshwater snail Lymnaea stagnalis. Isolation of snails rapidly increased (< 3 days) egg production. The effect was long-lasting, and was probably caused by deprivation of copulation. Changes of photoperiod had similar effects in isolated and grouped snails. Compared to the effects of isolation, the photoperiodic effects were relatively slow in appearing (> 14 days). In comparison with a medium day (MD) (12 hr light/12 hr dark), a long day (LD; 16 hr light/8 hr dark) stimulated egg production whereas a short day (SD) (8 hr light/16 hr dark) lowered egg production. The LD effects were clearer in grouped than in isolated snails, but SD effects were clearer in isolated than in grouped snails. It is argued that the effects of grouping, isolation and photoperiod on egg production are mediated by the neuroendocrine system. It is suggested that the photoperiod plays an important role in the control of the egg laying season. Mating is probably important in the control of fecundity in relation to population density.     

Role of photoperiod in reproductive maturation and peripubertal hormone concentrations in male collared lemmings (Dicrostonyx groenlandicus).

Onset of sexual maturation was determined in weanling male collared lemmings exposed to one of three experimental regimens of different photoperiods before and after weaning. Animals gestated in photoperiods of either 16 h light:8 h dark or 8 h light:16 h dark. Those from 16 h light:8 h dark were transferred at 19 days of age to either 20 h light:4 h dark or 8 h light:16 h dark; those gestated under 8 h light: 16 h dark remained in that photoperiod throughout the experiment. After exposure for 15, 20, 25 or 30 days to the postweaning photoperiod, animals were killed and the following parameters assessed: body weight, testes weight, seminal vesicle weight, the presence or absence of epididymal spermatozoa and serum concentrations of prolactin, testosterone and corticosterone. All parameters except serum testosterone were significantly influenced by photoperiod. Animals housed under 8 h light:16 h dark had significantly greater body weights than those housed under 20 h light:4 h dark, a response that differs from that reported for other arvicoline rodents. The group gestated on 16 h light:8 h dark and transferred on day 19 to 8 h light:16 h dark had lower testes and seminal vesicle weights than the other two groups, and mature spermatozoa in the epididymides appeared 5 days later than in the 20 h light:4 h dark group. Serum prolactin was largely undetectable in animals from both 8 h light:16 h dark groups, but all males housed in 20 h light:4 h dark had 2.0-15.0 ng prolactin ml-1. Concentration of serum corticosterone was higher in animals weaned into long photoperiod, and decreased with age. These data indicate that weanling male D. groenlandicus are reproductively photoresponsive, but use a decrease in photoperiod, not static short-photoperiod exposure, to alter the rate of development. Prolactin was largely undetectable in animals exposed to short photoperiod, indicating that high concentrations of this hormone are not important for maturation. Low prolactin concentrations in animals in short photoperiods may mediate the annual moult to white pelage. The short-photoperiod-mediated decrease in corticosterone may play a role in seasonal changes in body weight and composition.     

Pubertal growth of the medial amygdala delayed by short photoperiods in the Siberian hamster, Phodopus sungorus

We investigated whether puberty influences the morphology of the medial nucleus of the amygdala (MeA) by comparing Siberian hamsters (Phodopus sungorus) that had been raised from birth in either long day (LD; 16:8 h light:dark) or short day (SD; 8:16) photoperiods. Hamsters were sacrificed at 42-49 days of age, at which point all LD hamsters were reproductively mature, as evidenced by adult-like testes weights (mean: 657 mg). In contrast, the testes weights of the SD hamsters were low (mean: 31 mg), indicating that the SD photoperiod had delayed puberty. The regional volume and mean soma size of the four MeA subnuclei was estimated bilaterally by stereological procedures. In the posterior dorsal and ventral MeA subnuclei, regional volume was 22-25% larger, and mean soma size 18% larger, in LD males than SD males. Unbiased cell counts in the posterior dorsal MeA showed that LD and SD hamsters have equivalent neuron numbers. In the anterior MeA subnuclei, regional volumes and soma sizes from LD and SD hamsters were equivalent. Additionally, the regional volume of the posteroventral subnucleus was larger in the right hemisphere than the left, but this laterality did not respond to photoperiod manipulation. These results suggest that the extant neurons within the posterior MeA, a steroid-sensitive nucleus implicated in socio-sexual behavior, grow in response to the elevated levels of circulating androgen accompanying puberty, and that photoperiodic regulation of puberty affects morphological maturation of this nucleus.     

Daily changes in concentrations of prolactin in serum of prepubertal bulls exposed to short- or long-day photoperiods

Early temporal changes in concentrations of prolactin (PRL) in serum after a sudden change in photoperiod and daily responsiveness to PRL-releasing and inhibiting factors were investigated in prepubertal Holstein bull calves exposed to different photoperiods. In calves switched from 8-hr light: 16-hr dark to 16-hr light:8-hr dark, there was no observable change in the daily pattern of serum concentrations of PRL after 1, 2, or 4 days. On the other hand, in animals switched from 16-hr light:8-hr dark to 8-hr light:16-hr dark, there was a consistent increase in serum PRL from 33.4 ng/ml on Day 0 to maximum values of 57.3, 62.7, and 78.9 ng/ml between 14 and 18 hr after onset of light on Days 1, 2, and 4, respectively. Thus, absence of light allowed expression of a daily rhythm in serum concentrations of PRL that persisted for at least 4 days after the photoperiod switch. There were no differences in L-dopa inhibition of PRL release in animals exposed to 16-hr light:8-hr dark at 3 or 15 hr after onset of light. However, thyrotropin-releasing hormone-induced release of PRL was greater 3 hr after onset of light (11 hr after onset of dark) compared with release at 9, 15, and 21 hr after onset of light in animals exposed to 16-hr light:8-hr dark, but not in bulls exposed to 8-hr light:16-hr dark. The results provide evidence that the cue for the putative photosensitive period of PRL secretion in cattle may be more closely associated with onset of dark, not onset of light.     

Effect of photoperiod on growth and feed conversion of juvenile wild carp, Cyprinus carpio

Because of the effect of photoperiod on physiological and biochemical processes in fish, this study aimed to evaluate the effect of manipulated photoperiod on growth, feed conversion and survival of wild carp, Cyprinus carpio. Fish received six photoperiod regimes (light:dark cycle) including: natural photoperiod (control), 24L:0D, 16L:8D, 12L:12D, 8L:16D and 0L:24D by the three replications. Regulated photoperiods as a 16L:8D or 12L:12D light/dark cycle significantly improved growth rate and food conversion ratio of wild carp.     

Photoperiod regulates dietary preferences and energy metabolism in young developing Fischer 344 rats but not in same-age Wistar rats

The effects of photoperiod on dietary preference were examined using young growing Fischer 344 and Wistar rats, which are seasonal and nonseasonal breeders, respectively. Rats were provided a low-fat, high-carbohydrate diet (LFD: 66/10/24% energy as carbohydrate/fat/protein) and high-fat, low-carbohydrate diet (HFD: 21/55/24% energy as carbohydrate/fat/protein) simultaneously under long- (LD: 16 h light/day) and short-day (SD: 8 h light/day) conditions for 3 wk. Fischer 344 rats preferred the LFD to the HFD under the LD condition, whereas preference for both diets was equivalent under the SD condition. Consequently, their body weight and total energy intake exhibited 11-15 and 10-13% increases, respectively, under the LD condition. Calculation of energy intake from macronutrients revealed that rats under the LD condition consumed 20-24 and 9-13% higher energy of carbohydrates and proteins, respectively, than those under the SD condition. In contrast, Wistar rats preferred the LFD to the HFD irrespective of photoperiod and exhibited no photoperiodic changes in any parameters examined. Next, Fischer 344 rats were provided either the LFD or HFD for 3 wk under LD or SD conditions. Calorie intake was 10% higher in the rats fed the LFD than those fed the HFD under SD condition. However, rats under LD condition exhibited 5-10, 14, and 64% increases in body weight, epididymal fat mass, and plasma leptin levels, respectively, compared with those under the SD condition irrespective of dietary composition. In conclusion, photoperiod regulates feeding and energy metabolism in young growing Fischer 344 rats via the interactions with dietary macronutrient composition.     

Photoperiod influences endogenous indoleamines in cultured green alga Dunaliella bardawil

Effect of light intensity and photoperiod on growth, indoleamines and carotenoid production was studied in unicellular green algae D. bardawil. Maximum biomass and carotenoid contents were found when cultures were grown in light (intensity of 2.0 Klux) at a photoperiod of 16/8h light and dark cycle. There was a profound influence of tested photoperiod conditions of light:dark viz. 8:16, 10:14, and 12:12 hr, continuous light on indoleamines (SER and MEL) production as estimated by HPLC and confirmed by mass spectral data obtained from LC-MS-ESI studies. Serotonin level increased from 908 to 1765 pg/g fresh wt with increase in light duration and melatonin level increased from 267 to 584 pg/g fresh wt during increase in dark phase. Carotenoids production was high in continuous light than other tested conditions.     

Circadian rhythms and the induction of flowering in the long-day grass Lolium temulentum L.

Plants of Lolium temulentum L. strain Ceres were grown in 8-h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8-h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24-h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty-fourth hour. Full flowering was also induced by one 8-h SD beginning 4 or 28 h after the start of a 40-h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so-called ‘displaced short day’ (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 μmol m⁻² s⁻¹, a 4-h light exposure beginning 4 h after the start of a 40-h dark period was sufficient to induce 100% flowering. The flower-inducing effect of a single 8-h DSD was also assessed during a 64-h dark period. Results revealed two maxima at a 20-h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum.     

Cue hierarchies and testicular development: is food a more potent stimulus than day length in an opportunistic breeder (Taeniopygia g. guttata)?

Opportunistic breeders inhabit areas with unpredictable changes in environmental conditions. In such places favorable breeding conditions can occur during any time of year, and one prediction is that individuals should attend to photoperiod less than to more immediate cues to time reproduction. This study tests whether zebra finches utilize photoperiod independently of other proximate cues, specifically food availability. We transferred semi-domesticated male Lesser Sundas zebra finches (Taeniopygia guttata guttata) from 8 h light, 16 h dark per day (8L:16D) with ad libitum food availability to 20L:4D with ad libitum food (LD ad lib group) or food restriction (LD restricted group). A third group remained on 8L:16D with ad libitum food availability (SD ad lib group). Testis volume in LD ad lib males increased and was larger than other groups within 30 and 60 days of photostimulation. By contrast, LD restricted males and SD ad lib males did not exhibit significant gonadal growth. However, both LD groups increased mass irrespective of food availability. Surprisingly, at the end of the experiment the SD ad lib group sang the most undirected song. Our data demonstrate that long days alone are not sufficient to drive reproductive development in this opportunistically breeding species. Rather, it appears that reproductive development is stimulated by extended feeding times or increased food abundance during long days, and not by changes in day length per se. These data lend support to the proposition that photoperiod acts as a supplementary cue or permissive factor in this system, and thus represents the possibility of a reversal in the hierarchy of cue sensitivity.     

Sustained reproductive responses in Djungarian hamsters (Phodopus sungorus) exposed to a single long day

Male and female Djungarian hamsters maintained from birth in a short photoperiod (8 h light per day; 8L:16D) showed substantial testicular and uterine growth in response to a single long photoperiod or a 15-min light pulse that interrupted the 16-h dark period at 18 days of age. These light regimens resulted in heavier testes and uteri at 30 and 35 days of age when compared with those of control animals. Similar results were obtained in hamsters maintained from birth to Day 18 in a long photoperiod (16L:8D), given a single longer day (20L:4D) or constant light on Day 18 and then transferred to a short photoperiod (8L:16D) on Day 19. At 35 days of age animals that received extended light treatment on Day 18 had significantly more developed reproductive structures than did control hamsters. The marked effects of brief light treatment in producing long-term changes in the reproductive axis provide a convenient mammalian model system in which to study neuroendocrine events that underlie photoperiodism.     

Perinatal photoperiod organizes adult immune responses in Siberian hamsters (Phodopus sungorus)

Individuals of many nontropical rodent species display reproductive, immunological, and somatic responses to day length. In general, short day (SD) lengths inhibit reproduction and enhance immune function in the laboratory when all other conditions are held constant. Most studies to date have focused on seasonal variation in immune function in adulthood. However, perinatal photoperiods also communicate critical day length information and serve to establish a developmental trajectory appropriate for the time of year. Nontropical rodents born early in the breeding season undergo rapid reproductive development, presumably to promote mating success during their first reproductive season. Rodents born late in the breeding season suspend somatic growth and puberty until the following vernal breeding season. We tested the hypothesis that perinatal day lengths have similar enduring effects on the immune system of rodents. Siberian hamsters (Phodopus sungorus) were maintained prenatally and until weaning (21 days) in either SDs (8 h light:16 h dark) or long days (LD) (16 h light:8 h dark), then they were weaned into either the opposite photoperiod or maintained in their natal photoperiod, forming four groups (LD-LD, LD-SD, SD-LD, and SD-SD). After 8-wk in these conditions, cell-mediated immune activity was compared among groups. SD-SD hamsters of both sexes enhanced immune function relative to all other groups. The reproductive effects of perinatal photoperiod were not evident by the end of the experiment; circulating testosterone and cortisol sampled at the end of the experiment reflected the postweaning, but not the perinatal photoperiod. This experiment demonstrates long-lasting organizational effects of perinatal photoperiod on the rodent immune system and indicates that photoperiod-induced changes in the immune system are dissociable from changes in the reproductive system.     

Overexpression of suppressor of cytokine signaling 3 in the arcuate nucleus of juvenile Phodopus sungorus alters seasonal body weight changes

The profound seasonal cycle in body weight exhibited by the Djungarian hamster (Phodopus sungorus) is associated with the development of hypothalamic leptin resistance during long day photoperiod (LD, 16:8 h light dark cycle), when body weight is elevated relative to short day photoperiod (SD, 8:16 h light dark cycle). We previously have shown that this seasonal change in physiology is associated with higher levels of mRNA for the potent inhibitor of leptin signaling, suppressor of cytokine signaling-3 (SOCS3), in the arcuate nucleus (ARC) of LD hamsters relative to hamsters in SD. The alteration in SOCS3 gene expression preceded the body weight change suggesting that SOCS3 might be the molecular switch of seasonal body weight changes. To functionally characterize the role of SOCS3 in seasonal body weight regulation, we injected SOCS3 expressing recombinant adeno-associated virus type-2 (rAAV2-SOCS3) constructs into the ARC of leptin sensitive SD hamsters immediately after weaning. Hamsters that received rAAV2 expressing enhanced green fluorescent protein (rAAV2-EGFP) served as controls. ARC-directed SOCS3 overexpression led to a significant increase in body weight over a period of 12 weeks without fully restoring the LD phenotype. This increase was partially due to elevated brown and white adipose tissue mass. Gene expression of pro-opiomelanocortin was increased while thyroid hormone converting enzyme DIO3 mRNA levels were reduced in SD hamsters with SOCS3 overexpression. In conclusion, our data suggest that ARC-directed SOCS3 overexpression partially overcomes the profound seasonal body weight cycle exhibited by the hamster which is associated with altered pro-opiomelanocortin and DIO3 gene expression.     

温度与光周期对白头鹎体质量、能量收支和消化道形态的影响

温度与光周期是环境季节性变化的最直接表现因子及时间变化指示标志,对动物的形态、生理及行为产生重要的影响.本文以白头鹎为研究对象,探讨了不同温度与光周期对其体质量、能量收支和消化道形态的影响,分析了能量收支与消化道形态特征的关系.将28只白头鹎(12雄16雌)分为4组:暖温长光组(30℃,16 L8 D;3雄4雌)、暖温短光组(30 ℃,8 L16 D;3雄4雌)、低温长光组(10 ℃,16 L8 D;3雄4雌)和低温短光组(10 ℃,8 L16 D;3雄4雌).结果表明: 低温与短光照可促进白头鹎的体质量、摄入能及同化能明显增加,同时温度与光周期的交互作用对白头鹎的摄入能及同化能影响显著.低温条件下,胃、小肠、直肠及总消化道的湿质量及干质量明显增加.残差分析表明,小肠与总消化道的长度及干质量与摄入能和同化能显著相关.表明低温与短光照下白头鹎通过增加体质量、能量摄入和改变消化道形态来应对严酷的环境条件.     

Combined effects of photoperiod and feeding frequency on survival and growth of juvenile cuttlefish Sepia officinalis L. in experimental rearing

The combined effects of photoperiod and feeding frequency on survival and growth of juvenile cuttlefish has been studied in experimental rearing. During juvenile cuttlefish growth, survival and growth rate were low when the photoperiod was short (8 h of light and 16 h of dark). Increased frequency of diet did not stimulate the appetite of animals reared in normal or long photoperiod (16 h of light and 8 h of dark). However, by studying the combined effects of photoperiod and feeding frequency, we have demonstrated that an increase in feeding frequency can enhance survival and growth in the group receiving the shortest period of light per day. Temperature is an important factor in the regulation of the incubation period of eggs and of growth after hatching, but it also appears in this investigation that the combined effect of photoperiod and feeding frequency must be considered during growth of juvenile cuttlefish.     

Short photoperiod influences energy intake and serum leptin level in Brandt's voles (Microtus brandtii)

Photoperiod cues play important roles in the regulation of seasonal variations in body mass (BM) and energy balance for many small mammals. The present study was designed to examine the effects of photoperiod acclimation on BM, energy intake, and serum leptin levels in Brandt's voles (Microtus (Lasiopodomys) brandtii). After 4 weeks of acclimation to either long (LD; light:dark, 16:8) or short (SD; 8:16) photoperiod, SD voles had lower BM, body fat mass, and dry mass of liver and kidneys, but higher digestible energy intake in comparison to LD voles. SD voles also showed a lower level of serum leptin than did LD voles. Furthermore, the level of serum leptin was correlated positively with body fat mass and negatively with gross energy intake. Together, these data suggest that Brandt's voles employ a strategy of minimizing body growth, increasing energy intake, and mobilizing fat deposition in response to cues associated with short photoperiod. Furthermore, leptin seems to be involved in the regulation of BM and energy balance mediated by photoperiod.     

Photoperiod controls the induction,retention, and retrieval of antigen-specific immunological memory

Changes in day length affect several measures of immunity in seasonally breeding mammals. In Siberian hamsters (Phodopus sungorus), short day lengths suppress specific secondary antibody responses to the keyhole limpet hemocyanin (KLH) antigen and enhance cutaneous delayed-type hypersensitivity (DTH) responses to dinitrofluorobenzene (DNFB). These experiments tested whether day length affects secondary antibody and DTH responses by altering immune function solely during the interval after the initial exposure to each antigen, solely during the interval after the second exposure, or during both stages of the respective immune responses. Adult male Siberian hamsters were exposed to either a long (16 h light/day; LD) or a short (8 h light/day; SD) photoperiod for 7.5 wk before receiving an initial exposure to each antigen (KLH injection, cutaneous DNFB treatment; separate groups of animals for each antigen). A subset of LD hamsters was transferred to the SD photo-period, and a subset of SD hamsters was transferred to the LD photoperiod. Other hamsters remained in LD or SD. Eight weeks later, all hamsters were challenged with a second subcutaneous injection of KLH or a second application of DNFB to the ear, and immune responses were measured. Exposure to SD during the primary antibody response did not affect secondary IgG responses, but SD exposure during the secondary response significantly suppressed IgG production independent of day length during the initial KLH treatment. In contrast, exposure to SD during the DNFB challenge enhanced the ensuing DTH response, but this enhancement depended on the photoperiod prevailing during the initial exposure. Exposure to SD during the sensitization stage did not enhance DTH in hamsters subsequently exposed to LD. The data suggest that short photoperiods have enduring effects on immune responsiveness and on the establishment and retention of immunological memory.     

Effects of photoperiod reduction on rat circadian rhythms of BP, heart rate, and locomotor activity

The effects of a photoperiod reduction in the entrainment of circadian rhythms of systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and spontaneous locomotor activity (SLA) were determined in conscious Wistar rats by using radiotelemetry. Two groups of seven rats were maintained in a 12:12-h light-dark (12L/12D) photoperiod for 11 wk and then placed in a reduced photoperiod of 8:16-h light-dark (8L/16D) by advancing a 4-h darkness or by advancing and delaying a 2-h darkness for 6 wk. Finally, they were resynchronized to 12L/12D. Advancing a 4-h dark phase induced a 1-h advance of acrophase for SBP, DBP, and HR, but not for SLA. The percent rhythm, amplitude, and the 12-h mean values of all parameters were significantly decreased by the photoperiod reduction. When symmetrically advancing and delaying a 2-h dark phase, a 1 h 20 min delay of acrophases and a decrease in percent rhythms and amplitudes of SBP, DBP, HR, and SLA were observed. Only the 12-h mean values of HR and SLA were decreased. Our findings show that the cardiovascular parameters differ from SLA in phase-shift response to photoperiod reduction and that the adjustment of circadian rhythms to change from 12L/12D to 8L/16D photoperiod depends on the direction of the extension of the dark period.     

光照周期对叙利亚地鼠生长发育和繁殖的影响

对离乳雄性叙利亚地鼠（Ｍｅｓｏｃｒｉｃｅｔｕｓａｕｒａｔｕｓ）和雌性叙利亚地鼠各３０只分别给以长光照（１６Ｌ：８Ｄ）、中光照（１２Ｌ：１２Ｄ）和短光照（８Ｌ：１６Ｄ）三种光周期处理,研究光周期对叙利亚地鼠生长发育和繁殖的影响。１３周龄时,短光照处理组雄性地鼠的体重显著（Ｐ＜０．０５）高于长光照和中光照组的体重;雌性地鼠９周龄时长光照组的体重显著（Ｐ＜０．０１）高于另外两个处理组的体重,较高的日食量可能是长光照组具有较大体重的原因之一,雄性地鼠的睾丸、副睾和肾上腺重量及雌性地鼠的卵巢、子宫和肾上腺重量表现了随着光照时间的延长而递增的趋势。长光照条件有利于雌性地鼠的正常发情和繁殖。每天１６ｈ的光照对繁殖地鼠是比较适宜的。