Seasonal Changes In Photoperiod Research Articles

The effects of reversal of seasonal changes in photoperiod on the growth and food consumption of cod, Gadus morhua L.

The effect of reversing the natural seasonal change in photoperiod on the feeding and growth of juvenile cod, Gadus morhua. was investigated in two experiments. In an experiment conducted in spring no photoperiod effects on overall growth and food consumption were observed; however, tissue analysis at the end of the experiment showed that treatment groups differed significantly in their muscle water content. A repeat experiment conducted in early winter similarly failed to reveal an effect of photoperiod reversal on overall growth and feeding, although a very marked decline in growth rate was observed for all fish. The decline in growth rate observed in the second experiment cannot be accounted for by any changes in experimental procedure and is interpreted as possible evidence for an endogenous circa‐annual rhythm in growth rate.

Reproductive ecology of an obligately fissiparous population of the sea star Stephanasterias albula Stimpson

A population of the fissiparous sea star Stephanasterias albula (Stimpson) was studied at North Lubec, Maine, U.S.A. This population consisted of a dense (up to 40/m 2 localized group of roughly 5500 small ( R, the length of longest arm from disc center to arm tip, nearly always <18 mm) contagiously distributed individuals. Very small individuals ( R<3 mm) were totally absent suggesting that larval recruitment had not occurred recently. Fission is a seasonal phenomenon that takes place most frequently in the spring and summer. Incidence of fission appears to be correlated with seasonal changes in photoperiod. Rates of regeneration following fission are sufficient to allow individuals of S. albula to split once every 1 or 2 yr. Examination of 1-μm plastic sections from even the largest specimens revealed no trace of a differentiated reproductive system and of associated aboral haemal and coelomic rings, strong evidence that S. albula is obligately fissiparous. The ecological and developmental consequences of this finding are considered.

Seasonal changes of heart weight and erythrocytes in the Djungarian hamster, Phodopus sungorus

1. 1. Djungarian dwarf hamsters ( Phodopus sungorus) show an annual cycle in weight-specific metabolic rate with a high level during winter. 2. 2. These seasonal changes in oxygen demand are met by hematological adjustments, primarily based on an increased number of erythrocytes, but a decreased erythrocyte volume during winter. 3. 3. Subsequently, the diffusion area for blood gas exchange is increased during this time of high metabolic capabilities. 4. 4. Blood oxygen capacity (hemoglobin, 2,3-diphosphoglycerate (2,3-DPG) does not change with the season. 5. 5. However, seasonal changes in heart weight suggest changes in cardiac output, causing an increased blood flow per unit tissue weight during winter. 6. 6. This increase in circulatory efficiency, as well as changes in erythrocyte surface, are primarily controlled by photoperiod, since it occurred in hamsters living indoors at thermoneutrality but subjected to seasonal changes in photoperiod to the same extent as in hamsters living outdoors.

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.

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.

Seasonal adaptation of brown adipose tissue in the Djungarian Hamster.

The composition and oxidative capacity of brown adipose tissue (BAT) were investigated in Djungarian hamsters kept under natural photoperiod, either indoors at neutral Ta (23 degrees C) or under outdoor conditions. BAT comprises up to 5% of the body weight in summer/indoor hamsters, with lipid representing 86% of the total tissue mass. Tissue mass and thermogenic capacity are inversely related during seasonal adaptation: 30% decrease of total DNA, accompanied by extensive lipid depletion, reduces the amount of BAT by almost 60% during acclimatization from summer/indoor to winter/outdoor conditions. Mitochondrial protein in BAT is increased by a factor of 2.6 concomitantly, and by a factor of 4 when related to body weight (body weight reduction 36%). Cytochrome oxidase activity in different brown fat deposits varies by up to 150% in summer/indoor hamsters; depending on the fat pad, the enzyme activity is increased 200%-700% during adaptation to winter/outdoor conditions. Natural photoperiod is decisive in determining the seasonal adaptation of DNA content in BAT and of body weight. Short photoperiod alone may lead to depletion of lipid content of BAT and thus decrease the tissue mass practically to the lowest seasonal level, even though both parameters may be also influenced by Ta. One third of the maximum adaptive increase of tissue mitochondria may be attributed to seasonal changes in photoperiod and up to two thirds to Ta. Photoperiod establishes a fixed fundament of slow-reacting functional adaptation of BAT, whereas the effect of decreased Ta depends on the rate and duration of cold influence.

Seasonal LH profile in ovariectomized cattle

Two experiments were conducted to examine seasonal changes in circulating LH concentrations in ovariectomized heifers. In experiment 1, four Holstein heifers were ovariectomized in April 1977 during middiestrus. Blood samples were collected daily for 30 days surrounding each equinox and solstice for one year to examine changes in plasma LH levels at the time of seasonal photoperiod changes. The LH concentrations were highest during the winter solstice period and lowest during the summer solstice period. In addition, samples taken at two-week intervals indicated a distinct LH profile with maximal LH concentrations during November–April and minimal concentrations during May–October. In experiment 2, eight Holstein heifers were ovariectomized in June–July, 1979 and given an estradiol or a control implant in October. A distinct LH profile for the interval extending from January, 1980 to February, 1981 was found in the heifers that were not treated with estradiol. Concentrations were maximal during December–April and minimal during May–November. The LH profile followed a similar pattern in the estradiol-treated heifers; however, the overall profile was at a higher level. These data indicate that underlying seasonal reproductive mechanisms are present in cattle even though the species ovulates and breeds throughout the year.

Periodic hair shedding by a normal bitch

ABSTRACTOver several years, the mass of hair shed weekly by a normal Alsatian bitch varied cyclically. Base‐line values were less than 5 grams, while the maximum loss recorded was over 70 grams. Moults (and, by implication, the growth of new hairs which must have preceded them) were related to the bitch's oestrous cycle, always occurring shortly before or coincidentally with the onset of pro‐oestrus, even when megestrol acetate was administered to prevent ovulation or to re‐time the oestrous cycle. Fluctuating levels of ovarian hormones over‐rode any influence upon hair cycles of seasonal changes in photoperiod or temperature.

Seasonal control of energy requirements for thermoregulation in the djungarian hamster (Phodopus sungorus), living in natural photoperiod

Summary. Djungarian dwarf hamsters, Phodopus s. sungorus, were kept in natural photoperiodic conditions throughout the year, either inside at a constant Ta of 23 ~ or outside subjected to seasonally varying Ta. Comparisons were made between hamsters from both conditions to evaluate the significance of seasonal changes in photoperiod and/or Ta as environmental cues for seasonal acclimatization in Phodopus. Basal metabolic rate was lowest in July (1.68 ml/g.h) and highest in January (2.06 ml/g-h in Phodopus living outside), combined with a decrease in Tic from 26 ~ in July to 20 ~ in January. This was parallelled by seasonal changes in body weight (summer 42 g, winter 25 g), fur colouration, fur depth and the occurrence of short daily torpor. At Ta below thermoneutrality total energy requirements for thermoregulation in winter acclimatized Phodopus were found 36% lower than summer values (e.g. at 0 ~ T, in summer 1,160roW, in winter 760 mW), which were effected by a combined strategy of reducing body weight (19%) together with improvements of thermal insulation of the body surface (17%)i All seasonal changes were similar in Phodopus living inside or outside, suggesting that seasonal changes in photoperiod and not seasonal changes in Ta is the overriding controller for the environmental cueing of seasonality in energy requirements for thermoregulation.

Seasonality of endogenous circadian rhythms in a diurnal rodentAmmospermophilus leucurus and a nocturnal rodentDipodomys merriami

1. Circadian locomotor rhythms were measured continuously for 16 months in 27 animals which were exposed during most of this time to the natural daily cycle of illumination (ND) at 47°58′ N. Lat., and held at 19 °C. However, at two solstices (June and December) and two equinoxes (March and September) the animals were transferred to continuous illumination (LL) for one month, where two groups of each species were exposed to two different intensities of LL, and then returned to ND. 2. Circadian period (τ) was virtually constant throughout the year.Dipodomys merriami showed the positive correlation between τ and light intensity predicted by Aschoff's rule, but mean τ inAmmospermophilus leucurus was essentially unchanged over a wide range of light intensities. The theoretically predicted seasonal relationship between τ and phase relationship of activity to Zeitgeber signals (ψ) was not found. 3. The duration of activity (α) inA. leucurus was unusual in showing little seasonal change in ND, despite marked seasonal changes in photoperiod. Perhaps due to this relative constancy of α in ND (αND), the change of α upon transition into LL was generally not significant. There were also no significant differences between any of the four seasonal values of α in LL (αLL). InD. merriami αND generally paralleled seasonal changes in length of night, and change of α upon transition into LL was significant at all seasons. Mean αLL fell within a narrow range over the year, during which there were almost no significant season-to-season differences. 4. Neither species showed a marked seasonal cycle of body weight. However, body weight ofA. leucurus consistently increased upon each transfer from ND to LL. 5. MaleA. leucurus, investigated by external examination, showed an annual gonadal cycle with a peak in spring, whereas mostD. merriami developed and then maintained testicular maturity throughout the study. 6. The role of τ in seasonal homeostasis of the circadian system may lie in its availability as a constant reference signal. It cannot be directly responsible in these two species for stimulation of adaptive seasonal functions. However, complementary changes in either α orψ may interact with τ to promote some component of adaptive seasonal cyclic functions. The apparent endogenous circannual gonadal cycle ofA. leucurus could be either generated or entrained via such interactions, but the opportunistically responsive gonadal function ofD. merriami probably has relatively little relation to such circadian functions.

Natural daylengths regulate insect seasonality by two mechanisms.

FOR many animal species in temperate regions of the world, the photoperiod is the major environmental factor that reliably signals forthcoming seasonal changes. With the exception of studies dealing with several species of birds1,2, experiments generally have not shown what features of the natural photoperiod are used by animals to perceive calendar time. Not only have investigations of photoperiodicity usually used stationary photoperiods in the laboratory, but generally they have not taken into account the seasonal variations in the rate of change in the length of the day3; these changes are greatest at the time of the equinoxes and smallest at the time of the solstices. Our results demonstrate for the first time that insects have evolved at least two mechanisms based on seasonal changes in photoperiod to end diapause at the end of winter.

Letter: Photoperiodism and adaptive behaviour in a small mammal.

SEASONAL changes in photoperiod have wide-ranging effects on the biology of most temperate zone vertebrates1,2. Although photoperiodic responses have been extensively studied in birds3, research on photoperiodic effects in mammals has been confined largely to their influence on reproductive and pelage cycles4,5. Less well understood are the effects of seasonal differences in photoperiod on mammalian behaviour, although modification of behaviour is the principal means by which small mammals adjust to seasonal changes in their environment6. Furthermore, seasonal changes in photoperiod may be used as a cue by small mammals to alter behaviour before more critical changes in other environmental conditions, such as temperature. We describe here the effects of previous exposure to differences in both photoperiod and temperature on the expression of nesting, hoarding, daily activity, and food consumption in the white-footed mouse, Peromyscus leucopus.