Day Length In Spring Research Articles

Photoperiodic dependent regulation of photosynthesis in the polar diatom Fragilariopsis cylindrus

Introduction: Polar microalgae are exposed to dramatic seasonal changes in light availability, from continuous summer days to winter nights with rapid changes of the daylength in spring and fall. Under this challenging light climate, large diatoms spring blooms occur at the bottom sea-ice and underneath the icepack, accounting for a significant proportion of the annual marine primary production in the Arctic Ocean. The on-going earlier melt down of the snow and ice covers result in a stronger light penetration and consequent increase in irradiance at the bottom of the sea ice leading to earlier seasonal sea-ice diatom blooms under shorter daylengths. Therefore, elucidating the response of polar diatoms to different photoperiods will help to better understand the consequences of the changing arctic climate on their photosynthetic productivity.Methods: In this study, we characterized the response of F. cylindrus, a model polar diatom, across five different photoperiods with similar light and temperature conditions (30 μmol photons m-2 s-1 and 0°C respectively).Results: We report different photoacclimative strategies under shorter and longer daylengths, with the special case of prolonged darkness (mimicking winter polar night). We also observed a repeated daily regulation of the photochemistry and photoprotection parameters when cells were exposed to a light:darkness alternation, despite the constant and optimal light intensity during the light periods.Discussion: Our results highlight the ability of F. cylindrus to grow efficiently under a wide range of daylengths, finely adjusting the balance between photochemistry and photoprotection to make the best use of the available light, supporting sustained production and growth despite low light and temperature.

Seasonal weight changes in laboratory ferrets.

Ferrets (Mustela putorius furo) are a valuable animal model used in biomedical research. Like many animals, ferrets undergo significant variation in body weight seasonally, affected by photoperiod, and these variations complicate the use weight as an indicator of health status. To overcome this requires a better understanding of these seasonal weight changes. We provide a normative weight data set for the female ferret accounting for seasonal changes, and also investigate the effect of fluid regulation on weight change. Female ferrets (n = 39) underwent behavioural testing from May 2017 to August 2019 and were weighed daily, while housed in an animal care facility with controlled light exposure. In the winter (October to March), animals experienced 10 hours of light and 14 hours of dark, while in summer (March to October), this contingency was reversed. Individual animals varied in their body weight from approximately 700 to 1200 g. However, weights fluctuated with light cycle, with animals losing weight in summer, and gaining weight in winter such that they fluctuated between approximately 80% and 120% of their long-term average. Ferrets were weighed as part of their health assessment while experiencing water regulation for behavioural training. Water regulation superimposed additional weight changes on these seasonal fluctuations, with weight loss during the 5-day water regulation period being greater in summer than winter. Analysing the data with a Generalised Linear Model confirmed that the percentage decrease in weight per week was relatively constant throughout the summer months, while the percentage increase in body weight per week in winter decreased through the season. Finally, we noted that the timing of oestrus was reliably triggered by the increase in day length in spring. These data establish a normative benchmark for seasonal weight variation in female ferrets that can be incorporated into the health assessment of an animal’s condition.

Effects of a long-day light programme on the motility and membrane integrity of cooled-stored and cyropreserved semen in Shetland pony stallions

Increasing day length in spring stimulates reproductive functions in horses. In this study, we have analysed the effect of artificial long days on the quality of cooled-stored and cryopreserved semen in Shetland stallions. Stallions of the treatment group (AL, n=8) were exposed to 16h light and 8h darkness from 15th December to 20th March while control stallions (CON, n=7) were kept under natural photoperiod. Semen was collected once weekly and processed for cooled-storage and cryopreservation once per month. Total and progressive motility and percentage of membrane intact spermatozoa were analysed at 24, 48 and 72h of cooled-storage and after freezing-thawing, respectively. Total and progressive motility and membrane integrity decreased during cooled-storage for 72h in each month and both groups (p<0.001). All these parameters were lower in CON versus AL stallions (p<0.05) and the decrease was more pronounced in group CON (storage time x group p<0.05). Differences between groups decreased throughout the observation period from January (p<0.05 between groups) to July (e.g. total motility after 72h of cooled-storage in January for group AL 80±3 and group CON 49±12%, respective values in July, 83±2 and 72±6%). Neither total and progressive motility nor percentage of membrane-intact and morphologically defect spermatozoa in frozen–thawed semen differed between groups and months. In conclusion, motility of cooled-stored semen was reduced in January and increased in stallions kept under a long day light programme for at least 30 days.

Seasonal Variations of Steroid Hormones and Triiodothyronine Concentrations in Migratory Northern Shovelers

Endogenous serum testosterone, estradiol, and triiodothyronine concentrations were measured in the northern shoveler (Anas clypeata, n = 20) during different stages of migratory condition at their wintering grounds to look at how these hormones may be linked to the development of migratory condition. These hormones were assayed by enzyme-linked immunosorbent assay (ELISA). The changes in hormones concentrations were parallel to each other and correspond to the increasing day lengths of spring. Furthermore, the northern shovelers showed a distinct seasonal cycle in serum concentrations of triiodothyronine, estradiol, and testosterone. It is suggested that these seasonal cycles in the northern shovelers are endogenously programmed and their entrainment to the environmental photoperiod ensures the occurrence of different physiological functions at temporally fixed time of the year. The results of this study offer a captive model of the seasonal changes in physiology and behavior that occur in the months preceding and including vernal migration of the northern shovelers.

Sleep fragmentation in mentally retarded people decreases with increasing daylength in spring

We studied the sleep–wake behavior of mentally retarded people from late winter to early summer at 60°N. During this time the daylength increased 8 h 51 min. The data were collected by observing the sleep–wake status of 293 subjects at 20-min intervals for five randomized 24h periods (=recording days). The intervals during which the individual recording days of the same order (1st, 2nd, etc.) were carried out, were called recording periods. Consequently, there were five recording periods, each containing 293 individual recording days. Even though there was overlap among the recording periods, the median daylength from one period to another increased approximately by 100 min. In the initial statistical analysis, the number of wake–sleep transitions was found to differ significantly among the five recording periods (Friedman test, p<0.001). The mean ranks in the Friedman test suggested that the number of wake–sleep transitions was highest during the 1st and lowest during the 5th recording period. In further statistical analyses using a program for mixed effects regression analysis (mixor 2.0) it was found that the increase in daylength during the study period was associated with a simultaneous decrease of approximately 0.5 wake–sleep transitions in the whole study population (p<0.001). The decrease in the number of wake–sleep transitions was significant only in the subgroups of subjects with a daylength change of more than 350 min between the 1st and 5th recording days (Wilcoxon tests, p<0.005). This suggests that after a marked prolongation of the natural photoperiod, the reduction in sleep episodes was more probable than after smaller changes in daylength. It is concluded that the sleep of mentally retarded people living in a rehabilitation center at a northern latitude is more fragmented in winter than in early summer and that the change is related probably to the simultaneous increase in the length of the natural photoperiod. The sleep quality of persons living in institutional settings might be improved by increasing the intensity and/or duration of daily artificial light exposure during the darker seasons.

Effects of photoperiod manipulation on development of seawater tolerance in Arctic charr

Effects of photoperiod manipulation on the development of seawater tolerance were studied in Arctic charr. Three groups of fish, previously reared under natural photoperiod and ambient water temperature conditions, were subjected to a constant short daylength, 4L:20D, from 21 December to 30 January, followed by exposure to either 4L:20D, continuous light (24L:0D) or simulated natural photoperiod (nLD). Temperature of the fresh water was held constant at 4°C until mid-May, after which it increased gradually to reach 8.5°C at the termination of the experiment on 2 July. All groups displayed improved seawater tolerance during the course of the study, assessed as changes in plasma chloride and osmolality concentrations following 72-h exposure to seawater (33–34‰). The tolerance to seawater was positively related to fork length within some sampling dates in all groups. Exposure to 24L:0D advanced the development of seawater tolerance by approximately 6 weeks, compared to the nLD group. Both groups displayed increases in gill Na +/K +-ATPase activity that coincided with the period of improved seawater tolerance. Seawater tolerance of the 4L:20D group was delayed by 6 weeks in comparison with that of the nLD group, but without any concomitant increase in gill Na +/K +-ATPase activity. The results corroborate previous findings, and suggest that the seasonal changes in seawater tolerance of Arctic charr are controlled by an endogenous, circannual timing mechanism that is entrainable by artificially extended daylengths in spring. Our data further suggest that development of seawater tolerance in Arctic charr may occur independently of changes in gill Na +/K +-ATPase activity.

Time measurement and the control of flowering in plants.

Many plants are adapted to flower at particular times of year, to ensure optimal pollination and seed maturation. In these plants flowering is controlled by environmental signals that reflect the changing seasons, particularly daylength and temperature. The response to daylength varies, so that plants isolated at higher latitudes tend to flower in response to long daylengths of spring and summer, while plants from lower latitudes avoid the extreme heat of summer by responding to short days. Such responses require a mechanism for measuring time, and the circadian clock that regulates daily rhythms in behaviour also acts as the timer in the measurement of daylength. Plants from high latitudes often also show an extreme response to temperature called vernalisation in which flowering is repressed until the plant is exposed to winter temperatures for an extended time. Genetic approaches in Arabidopsis have identified a number of genes that control vernalisation and daylength responses. These genes are described and models presented for how daylength might regulate flowering by controlling their expression by the circadian clock. BioEssays 22:38-47, 2000.

Why does only Athalia Japonica enter summer diapause among three sympatric Athalia sawflies feeding on crucifers?

SummaryThis report assesses the primary factor for the evolution of summer diapause of the three species of sawfly, Athalia japonica, A. rosae and A. infumata that feed on cruciferous plants and coexist in the same area. A. japonica has two discrete spring and autumn generations, but A. rosae and A. infumata 5–6 generations. Only A. japonica enters summer diapause in response to the long daylengths in spring. Although these three sawflies usually feed on the same cultivated crucifers, they differ markedly in the utilization of wild crucifers. They oviposit only on young leaves. A. japonica mainly uses Cardamine plants which sprout in spring and autumn. A. rosae and A. infumata primarily use hosts with new leaves all the year round, i.e. cultivated crucifers and Rorippa indica, respectively. The thermal threshold for development is lower in A. japonica than in the other two species. The low heat tolerance of A. japonica is adapted only to cool shady habitats where Cardamine grows. Presumably, summer diapause of A. japonica is adaptation to the deterioration of the primary host plants rather than unfavorable climatic conditions. This interpretation is supported by the movement patterns of the three Athalia sawflies, alternative means to escape from deteriorated habitat conditions.

Endocrine and Testicular Changes Associated with Season, Artificial Photoperiod, And the Peri-Pubertal Period in Stallions

The seasonal reproductive cycle of stallions is characterized by an annual regression and recrudescence in testicular function and concentrations of LH, FSH, and testosterone in serum. Maximum reproductive capacity occurs during the increasing day lengths of spring and summer. The annual cycle in LH secretion may reflect a seasonally associated and photosensitive reduction and replenishment in pituitary content of LH. Similar to other seasonal breeders, it appears that stallions may possess an endogenous circannual rhythm in reproductive function that is subject to manipulation by altering the light:dark ratio, i.e., photoperiod. The application of a long-day photoperiod (16 hours light:8 hours dark) in December, following 20 weeks of short days (8 hours light:16 hours dark), was effective in hastening the seasonal sexual recrudescence of stallions but was not effective in prolonging the interval of heightened reproductive capacity. The infantile period in colts lasts approximately 32 weeks and is characterized by low gonadotropin concentrations and little gonadal activity. The start of the pre-pubertal period is marked by changes in the hypothalamic-pituitary axis which result in increased amounts of LH and FSH secretion between 32 and 40 weeks of age. Testosterone concentrations in serum exhibit a dramatic increase at 75 to 80 weeks of age, with puberty (defined as the age when the first ejaculate was obtained containing a minimum of 50 x 10(6) sperm with greater than or equal to 10% progressive motility) occurring at 83 weeks of age.

Photoperiodic Regulation of Gametogenesis in Sea Stars, with Evidence for an Annual Calendar Independent of Fixed Daylength

SYNOPSIS. Gametogenesis and gonadal growth in the west coast sea star Pisaster ochraceus normally begins in the fall and leads to large gonads full of gametes in the spring, when spawning occurs. The timing of gametogenesis can be shifted simply by maintaining the animals on a seasonally changing photoperiodic regime out of phase with ambient. When they are kept on a spring-summer photoperiodic regime during the fall and winter, gametogenesis proceeds 6 mo ahead of schedule in the following spring and summer. Gametogenesis can be shifted out of phase even when the eyespots are removed. Short daylengths that normally occur during the fall and winter are not required for gametogenesis to proceed, nor are even the long daylengths of spring and summer that precede the initiation of gametogenesis in the fall. The temporal program is insensitive to fixed daylengths (LD 15:9, 13:11, 12:12, 9:15) and appears to involve an endogenous calendar. Shifting the photoperiodic regime 6 mo out of phase also leads to a shift of the gametogenic temporal program in the sea stars Leptasterias sp. (a brooder) and Asterias vulgaris (from the New England coast), but not in the sea star Patiria miniata . Gametogenic timing also can be switched in the sea urchin Strongylocentrotus purpuratus but the mechanism of the photoperiodic response is fundamentally different; gametogenesis requires short daylengths; continues indefinitely under a repeated short day, fall-winter photoperiod regime, and apparently does not involve an endogenous calendar. As photoperiodic responses are investigated further in these and other marine invertebrates, the models developed primarily from studies on terrestrial organisms may need to be extensively modified or additional new models required.

Extraocular light perception in photoperiodic responses of the White-crowned sparrow (Zonotrichia leucophrys) and of the Golden-crowned sparrow (Z. atricapilla)

Testicular maturation, migratory restlessness (Zugunruhe) and fattening are induced in many species of birds by long day-lengths in Spring. We have tested the hypothesis that extraocular photoreceptors located in the brain are involved in mediating these photoperiodic responses in White-crowned sparrows (Zonotrichia leucophrys) and Golden-crowned sparrows (Z. atricapilla). Our approach consisted in reducing the amount of light penetrating to the brain with either black India ink injected under the skin of the head (Golden-crowned sparrows) or by covering the entire head (except eyes and beak) with a black collodion hood (White-crowned sparrows). Birds treated in these ways showed significantly less testicular growth, Zugunruhe and premigratory fattening when placed under a 16L-8D photoperiod than control birds which did not have their brains shielded from light. However, even when the bird brains were shielded from light and although light intensity was close to threshold level, some testicular growth, Zugunruhe and fattening did occur. We conclude that extraocular photoreceptors are involved in the control of the three photoperiodic responses studied, but that the eyes are possibly of significance as well.

Gonadal Responses of Brown-Headed Cowbirds to Long Daylength

Experimental work with several species has shown that the gonads of wild birds develop from sexual inactivity into breeding condition when the birds are kept on increased hours of daily light in the winter months before the natural breeding season. The effect of the long daily photoperiods on the experimental birds is thought to be similar to the gradual gonadal development in wild birds during the slowly increasing daylengths of spring. The birds of temperate regions have probably evolved the photoperiodic response rather than a response to other environmental conditions because of the greater predictive value of daylength in timing the breeding season (Farner, 1959, 1964). Energy is conserved by remaining in a sexually inactive condition until a few weeks before the breeding season. The breeding seasons of the birds are thought to be timed to the occurrence of abundant food for their young, and daylength in early spring provides a reliable source of information about the coming of spring. As the time of nesting of host species is determined by daylength, it is of interest to know whether the development of the gonads in spring in brood parasites is determined to the same degree by daylength. The Brown-headed Cowbird (Molothrus ater) was studied to compare the gonadal response of a brood parasite to long daylengths with the photoperiodic responses of nonparasitic species. In addition, the significance of the refractory period as a timing factor in the annual cycle of temperate-zone songbirds was evaluated by a comparison of the breeding seasons and the timing of the refractory period in four species of North American icterids.

Salinity Preference, Thyroid Activity and the Seaward Migration of Four Species of Pacific Salmon (Oncorhynchus)

In juvenile Pacific salmon the changes in salinity preference associated with seaward migration and thyroid activity were studied and used as criteria for the induction of the physiological condition required for migration (migration-disposition).Four species of Oncorhynchus (chum, pink, coho and sockeye) changed preference from fresh to salt water at the onset of seaward migration and maintained this preference throughout the migration season. At the end of this migration period coho and sockeye salmon changed preference from salt to fresh water if retained in fresh water, indicating a re-adaptation to this medium in which they may survive for several years. Chum and pink fry did not show this change in preference and usually died when retained in fresh water. They were apparently unable to re-adapt to this environment.The increasing day length in spring controls the time at which the change in preference from fresh to salt water takes place, and is thus involved in timing the induction of migration-disposition.The photoperiod seems to affect particularly the pituitary-thyroid system. Thyroid activity increases shortly before the onset of migration, remains high during the migration season, and decreases towards its end. The level of thyroid hormone in the blood influences salinity tolerance and preference and, thus, the induction of migration-disposition. Metamorphosis, osmotic "stress" and iodine content of the water may have some additional effect on thyroid activity, but are not the only factors responsible for thyroid hyperactivity during migration.Animals in which migration-disposition has been induced are thought to have become susceptible to appropriate external stimuli "releasing" migration.