Seasonal Changes In Photoperiod Research Articles

Assessing the impacts of genetic defects on starch metabolism in Arabidopsis plants using the carbon homeostasis model.

Starch serves as an important carbon storage mechanism for many plant species, facilitating their adaptation to the cyclic variations in the light environment, including day-night cycles as well as seasonal changes in photoperiod. By dynamically adjusting starch accumulation and degradation rates, plants maintain carbon homeostasis, enabling continuous growth under fluctuating environmental conditions. To understand dynamic nature of starch metabolism at the molecular level, it is necessary to integrate empirical knowledge from genetic defects in specific regulatory pathways into the dynamical system of starch metabolism. To achieve this, we evaluated the impact of genetic defects in the circadian clock, sugar sensing and starch degradation pathways using the carbon homeostasis model that encompasses the interplay between these pathways. Through the collection of starch metabolism data from 10 Arabidopsis mutants, we effectively fitted the experimental data to the model. The system-level assessment revealed that genetic defects in both circadian clock components and sugar sensing pathway hindered the appropriate adjustment of the starch degradation rate, particularly under long-day conditions. These findings not only confirmed the previous empirical findings but also provide the novel insights into the role of each gene within the gene regulatory network on the emergence of carbon homeostasis.

Association of reproduction with seasonality in a subtropical viviparous fish, Jenynsia tucumana (Cyprinodontiformes: Anablepidae)

For fishes in temperate environments, the timing of seasonal reproduction has been correlated with changes in photoperiod and temperature. In tropical environments, seasonal hydrological patterns have been found to be drivers of the onset of reproduction. Despite these established relationships, data on reproductive seasonality for viviparous fish are limited. Here, we investigate aspects of reproduction in the viviparous fish Jenynsia tucumana Aguilera & Mirande, 2005 over the course of 12 months in the Salí River basin (Tucumán, Argentina), which is characterized by dry, short winters, and long, tropical summers. Size and reproductive data were collected each month. We found J. tucumana displayed marked sexual dimorphism in size, with females having higher length and weight when compared to males. Larger females have higher fecundities compared to smaller females. The breeding season corresponds with seasonal changes in photoperiod, air temperature, and rainfall, but ends with the arrival of heavy rainfall later in the season. Interestingly, J. tucumana produce and mature oocytes year-round, unlike congeneric species. This may be an adaptive strategy imposed by the irregular flooding of subtropical mountainous river stream habitats, which maintain high productivity well into early autumn.

Seasonal Changes in Photoperiod: Effects on Growth and Redox Signaling Patterns in Atlantic Salmon Postsmolts.

Farmed Atlantic salmon reared under natural seasonal changes in sea-cages had an elevated consumption of antioxidants during spring. It is, however, unclear if this response was caused by the increase in day length, temperature, or both. The present study examined redox processes in Atlantic salmon that were reared in indoor tanks at constant temperature (9 °C) under a simulated natural photoperiod. The experiment lasted for 6 months, from vernal to autumnal equinoxes, with the associated increase and subsequent decrease in day length. We found that intracellular antioxidants were depleted, and there was an increase in malondialdehyde (MDA) levels in the liver and muscle of Atlantic salmon with increasing day length. Antioxidant enzyme activity in liver and muscle and their related gene profiles was also affected, with a distinct upregulation of genes involved in maintaining redox homeostasis, such as peroxiredoxins in the brain in April. This study also revealed a nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response in muscle and liver, suggesting that fish integrate environmental signals through redox signaling pathways. Furthermore, growth and expression profiles implicated in growth hormone (GH) signaling and cell cycle regulation coincided with stress patterns. The results demonstrate that a change in photoperiod without the concomitant increase in temperature is sufficient to stimulate growth and change the tissue oxidative state in Atlantic salmon during spring and early summer. These findings provide new insights into redox regulation mechanisms underlying the response to the changing photoperiod, and highlight a link between oxidative status and physiological function.

Reduced Plasticity in Coupling Strength in the Aging SCN Clock as Revealed by Kuramoto Modeling.

The mammalian circadian clock is located in the suprachiasmatic nucleus (SCN) and consists of a network of coupled neurons, which are entrained to the environmental light-dark cycle. The phase coherence of the neurons is plastic and driven by the duration of daylight. With aging, the capacity to behaviorally adapt to seasonal changes in photoperiod reduces. The mechanisms underlying photoperiodic adaptation are largely unknown, but are important to unravel for the development of novel interventions to improve the quality of life of the elderly. We analyzed the phase coherence of single-cell PERIOD2::LUCIFERASE (PER2::LUC) expression rhythms in the SCN of young and old mice entrained to either long or short photoperiod. The phase coherence was used as input to a 2-community noisy Kuramoto model to estimate the coupling strength between and within neuronal subpopulations. The model revealed a correlation between coupling strength and photoperiod-induced changes in the phase relationship among neurons, suggesting a functional link. We found that the SCN of young mice adapts in coupling strength over a large range, with weak coupling in long photoperiod (LP) and strong coupling in short photoperiod (SP). In aged mice, we also found weak coupling in LP, but a reduced capacity to reach strong coupling in SP. The inability to respond with an increase in coupling strength suggests that manipulation of photoperiod is not a suitable strategy to enhance clock function with aging. We conclude that the inability of aged mice to reach strong coupling contributes to deficits in behavioral adaptation to seasonal changes in photoperiod.

A correlation between seasonally changing photoperiod, whole body lipid, and condition factor in juvenile spring Chinook salmon (Oncorhynchus tshawytscha).

The regulation of lipid stores is a central process for the physiology and ecology of fishes. Seasonal variation in lipid stores has been directly linked to survival of fishes across periods of food deprivation. We assessed whether a seasonally changing photoperiod was correlated to seasonal changes in energetic status to help better understand these important processes. Groups of first feeding Chinook salmon fry were introduced to a seasonal photoperiod cycle, but the point of entrance into the seasonal cycle varied from near the winter solstice (December), to either side of the spring equinox (February & May). Temperature and feeding rate were similar for all treatments. Subsequently, condition factor and whole body lipid content were assessed through a seasonal progression. Throughout most of the experiment, length and weight did not differ between the different photoperiod treatments, however whole body lipid and Fulton's condition factor did. Furthermore, changes in both whole body lipid and Fulton's condition factor in all treatment groups followed a similar seasonal pattern that was inversely related to day length (highest K and lipid levels found during days with the least light). These results suggest that regardless of age or size, there is a correlation between seasonal changes in photoperiod and changes in body composition in juvenile Chinook salmonids.

Serine protease inhibitors LmSPN2 and LmSPN3 co-regulate embryonic diapause in Locusta migratoria manilensis (Meyen) via the Toll pathway

Female adults of the migratory locust, Locusta migratoria manilensis (Meyen), can sense seasonal photoperiod changes, which induces embryonic diapause as a key strategy to overwinter. Serine protease inhibitor genes (SPNs) were thought to play key roles during diapause, while few SPNs were functionally characterized. LmSPN2 was one of those genes differentially expressed between diapause and non-diapause eggs; however, its biological function remained to be explored. So, we conducted RNAi knockdown of LmSPN2, resulting in a significant decrease of the egg diapause rate by 29.7%. Using yeast two-hybrid assays, co-immunoprecipitation, and pull-down methods, we found an interaction between LmSPN2 and LmSPN3, which was proved to be mediated by a glutamate (E331) binding site of LmSPN2. RNAi knockdown of LmSPN3 resulted in a significant increase in diapause rate by 14.6%, indicating an inverse function of LmSPN2 and LmSPN3 on diapause regulation. Double knockdown of two SPN genes resulted in a 26.4% reduction in diapause rate, indicating that LmSPN2 was the dominant regulatory signal. Moreover, we found four Toll pathway genes (easter, spätzle, pelle, and dorsal) upregulated significantly after the knockdown of LmSPN2 while downregulated after the knockdown of LmSPN3. Therefore, we speculate that two SPNs regulate diapause through the Toll pathway. Our results indicated that LmSPN2 positively regulates locust egg entry into diapause, while LmSPN3 is a negative regulator of embryonic commitment to diapause. Their interaction is mediated by the binding site of E331 and influences egg diapause through the Toll pathway. This mechanistic understanding of diapause regulation expands our understanding of insect developmental regulation and provides functional targets for developing locust management strategies.

Seasonal changes in photoperiod and temperature lead to changes in cuticular hydrocarbon profiles and affect mating success in Drosophila suzukii

Seasonal plasticity in insects is often triggered by temperature and photoperiod changes. When climatic conditions become sub-optimal, insects might undergo reproductive diapause, a form of seasonal plasticity delaying the development of reproductive organs and activities. During the reproductive diapause, the cuticular hydrocarbon (CHC) profile, which covers the insect body surface, might also change to protect insects from desiccation and cold temperature. However, CHCs are often important cues and signals for mate recognition and changes in CHC composition might affect mate recognition. In the present study, we investigated the CHC profile composition and the mating success of Drosophila suzukii in 1- and 5-day-old males and females of summer and winter morphs. CHC compositions differed with age and morphs. However, no significant differences were found between the sexes of the same age and morph. The results of the behavioral assays show that summer morph pairs start to mate earlier in their life, have a shorter mating duration, and have more offspring compared to winter morph pairs. We hypothesize that CHC profiles of winter morphs are adapted to survive winter conditions, potentially at the cost of reduced mate recognition cues.

Behavioral circatidal rhythms require Bmal1 in Parhyale hawaiensis

Organisms living in the intertidal zone are exposed to a particularly challenging environment. In addition to daily changes in light intensity and seasonal changes in photoperiod and weather patterns, they experience dramatic oscillations in environmental conditions due to the tides. To anticipate tides, and thus optimize their behavior and physiology, animals occupying intertidal ecological niches have acquired circatidal clocks. Although the existence of these clocks has long been known, their underlying molecular components have proven difficult to identify, in large part because of the lack of an intertidal model organism amenable to genetic manipulation. In particular, the relationship between the circatidal and circadian molecular clocks, and the possibility of shared genetic components, has been a long-standing question. Here, we introduce the genetically tractable crustacean Parhyale hawaiensis as a system for the study of circatidal rhythms. First, we show that P.hawaiensis exhibits robust 12.4-h rhythms of locomotion that can be entrained to an artificial tidal regimen and are temperature compensated. Using CRISPR-Cas9 genome editing, we then demonstrate that the core circadian clock gene Bmal1 is required for circatidal rhythms. Our results thus demonstrate that Bmal1 is a molecular link between circatidal and circadian clocks and establish P.hawaiensis as a powerful system to study the molecular mechanisms underlying circatidal rhythms and their entrainment.

Seasonal cues act through the circadian clock and pigment-dispersing factor to control EYES ABSENT and downstream physiological changes

Organisms adapt to seasonal changes in photoperiod and temperature to survive; however, the mechanisms by which these signals are integrated in the brain to alter seasonal biology are poorly understood. We previously reported that EYES ABSENT (EYA) shows higher levels in cold temperature or short photoperiod and promotes winter physiology in Drosophila. Nevertheless, how EYA senses seasonal cues is unclear. Pigment-dispersing factor (PDF) is a neuropeptide important for regulating circadian output rhythms. Interestingly, PDF has also been shown to regulate seasonality, suggesting that it may mediate the function of the circadian clock in modulating seasonal physiology. In this study, we investigated the role of EYA in mediating the function of PDF on seasonal biology. We observed that PDF abundance is lower on cold and short days as compared with warm and long days, contrary to what was previously observed for EYA. We observed that manipulating PDF signaling in eya+ fly brain neurons, where EYA and PDF receptor are co-expressed, modulates seasonal adaptations in daily activity rhythm and ovary development via EYA-dependent and EYA-independent mechanisms. At the molecular level, altering PDF signaling impacted EYA protein abundance. Specifically, we showed that protein kinase A (PKA), an effector of PDF signaling, phosphorylates EYA promoting its degradation, thus explaining the opposite responses of PDF and EYA abundance to changes in seasonal cues. In summary, our results support a model in which PDF signaling negatively modulates EYA levels to regulate seasonal physiology, linking the circadian clock to the modulation of seasonal adaptations.

Photoreception and transcriptomic response to light during early development of a teleost with a life cycle tightly controlled by seasonal changes in photoperiod.

Light cues vary along the axis of periodicity, intensity and spectrum and perception of light is dependent on the photoreceptive capacity encoded within the genome and the opsins expressed. A global approach was taken to analyze the photoreceptive capacity and the effect of differing light conditions on a developing teleost prior to first feeding. The transcriptomes of embryos and alevins of Atlantic salmon (Salmo salar) exposed to different light conditions were analyzed, including a developmental series and a circadian profile. The results showed that genes mediating nonvisual photoreception are present prior to hatching when the retina is poorly differentiated. The clock genes were expressed early, but the circadian profile showed that only two clock genes were significantly cycling before first feeding. Few genes were differentially expressed between day and night within a light condition; however, many genes were significantly different between light conditions, indicating that light environment has an impact on the transcriptome during early development. Comparing the transcriptome data from constant conditions to periodicity of white light or different colors revealed overrepresentation of genes related to photoreception, eye development, muscle contraction, degradation of metabolites and cell cycle among others, and in constant light, several clock genes were upregulated. In constant white light and periodicity of green light, genes associated with DNA replication, chromatin remodeling, cell division and DNA repair were downregulated. The study implies a direct influence of light conditions on the transcriptome profile at early developmental stages, by a complex photoreceptive system where few clock genes are cycling.

Effect of Natural Seasonal Changes in Photoperiod and Temperature on Immune Function in Striped Hamsters.

What environmental factors contribute to seasonal variation in immune function in striped hamsters (Cricetulus barabensis) remains unclear. How immune responses would respond to natural seasonal changes in photoperiod and temperature was investigated in the present study. Twenty-nine male and 30 female hamsters were randomly assigned to the winter, spring, summer, and autumn groups. Spleen mass was the highest in male hamsters during autumn, while it did not differ among seasons in females. Regardless of sex, bacteria killing activity (BKA) was the lowest in the spring, whereas phytohaemagglutinin (PHA) responses at 12 h, 24 h, and 48 h were all highest in the winter among the four seasons. Females had the lowest titers of immunoglobin (Ig)G5, 10, and 15 in winter, while they did not show seasonal variation in males. Compared with male hamsters, females had higher levels of IgG10 and IgG15 in the spring and autumn, but had lower BKA in autumn. Blood glucose was the lowest in the spring in both sexes. Males had higher leptin level in winter than in summer and autumn, while leptin level was higher in winter and spring than in autumn in females. Corticosterone level was higher in winter and summer than in spring and autumn in males, while it was higher in winter than in the other three seasons in females. Males had higher levels of leptin in winter, and corticosterone in summer, than females. In summary, distinct parts of the immune system respond differently to natural seasonal variations in photoperiod and temperature.

Combining photoperiod and thermal responses to predict phenological mismatch for introduced insects.

A wide variety of organisms use the regular seasonal changes in photoperiod as a cue to align their life cycles with favorable conditions. Yet the phenological consequences of photoperiodism for organisms exposed to new climates are often overlooked. We present a conceptual approach and phenology model that maps voltinism (generations per year) and the degree of phenological mismatch that can arise when organisms with a short-day diapause response are introduced to new regions or are otherwise exposed to new climates. Our degree-day-based model combines continent-wide spatialized daily climate data, calculated date-specific and latitude-specific day lengths, and experimentally determined developmental responses to both photoperiod and temperature. Using the case of the knotweed psyllid Aphalara itadori, a new biological control agent being introduced from Japan to North America and Europe to control an invasive weed, we show how incorporating a short-day diapause response will result in geographic patterns of attempted voltinism that are strikingly different from the potential number of generations based on degree-days alone. The difference between the attempted and potential generations represents a quantitative measure of phenological mismatch between diapause timing and the end of the growing season. We conclude that insects moved from lower to higher latitudes (or to cooler climates) will tend to diapause too late, potentially resulting in high mortality from inclement weather, and those moved from higher to lower latitude (to warmer climates) may be prone to diapausing too early, therefore not fully exploiting the growing season and/or suffering from insufficient reserves for the longer duration in diapause. Mapped output reveals a central region with good phenology match that shifts north or south depending on the geographic source of the insect and its corresponding critical photoperiod for diapause. These results have direct relevance for efforts to establish populations of classical biocontrol agents. More generally, our approach and model could be applied to a wide variety of photoperiod- and temperature-sensitive organisms that are exposed to changes in climate, including resident and invasive agricultural pests and species of conservation concern.

Pituitary Hormones mRNA Abundance in the Mediterranean Sea Bass Dicentrarchus labrax: Seasonal Rhythms, Effects of Melatonin and Water Salinity.

In fish, most hormonal productions of the pituitary gland display daily and/or seasonal rhythmic patterns under control by upstream regulators, including internal biological clocks. The pineal hormone melatonin, one main output of the clocks, acts at different levels of the neuroendocrine axis. Melatonin rhythmic production is synchronized mainly by photoperiod and temperature. Here we aimed at better understanding the role melatonin plays in regulating the pituitary hormonal productions in a species of scientific and economical interest, the euryhaline European sea bass Dicentrarchus labrax. We investigated the seasonal variations in mRNA abundance of pituitary hormones in two groups of fish raised one in sea water (SW fish), and one in brackish water (BW fish). The mRNA abundance of three melatonin receptors was also studied in the SW fish. Finally, we investigated the in vitro effects of melatonin or analogs on the mRNA abundance of pituitary hormones at two times of the year and after adaptation to different salinities. We found that (1) the reproductive hormones displayed similar mRNA seasonal profiles regardless of the fish origin, while (2) the other hormones exhibited different patterns in the SW vs. the BW fish. (3) The melatonin receptors mRNA abundance displayed seasonal variations in the SW fish. (4) Melatonin affected mRNA abundance of most of the pituitary hormones in vitro; (5) the responses to melatonin depended on its concentration, the month investigated and the salinity at which the fish were previously adapted. Our results suggest that the productions of the pituitary are a response to multiple factors from internal and external origin including melatonin. The variety of the responses described might reflect a high plasticity of the pituitary in a fish that faces multiple external conditions along its life characterized by marked daily and seasonal changes in photoperiod, temperature and salinity.

Field study reveals morphological and neuroendocrine correlates of seasonal breeding in female water voles, Arvicola terrestris

Seasonally breeding mammals display timely physiological switches between reproductive activity and sexual rest, which ensure synchronisation of births at the most favourable time of the year. These switches correlate with seasonal changes along the hypothalamo-pituitary–gonadal axis, but they are primarily orchestrated at the hypothalamic level through environmental control of KISS1-dependent GnRH release. Our field study shows that births of fossorial water voles, Arvicola terrestris, are concentrated between March and October, which indicates the existence of an annual reproductive cycle in this species. Monthly field monitoring for over a year further reveals dramatic seasonal changes in the morphology of the ovary, uterus and lateral scent glands, which correlate with the reproductive status. Finally, we demonstrate seasonal variation in kisspeptin expression within the hypothalamic arcuate nucleus. Altogether, this study demonstrates a marked rhythm of seasonal breeding in the water vole and we speculate that this is governed by seasonal changes in photoperiod.

Model analysis of temperature impact on the Norway spruce provenance specific bud burst and associated risk of frost damage

The annual growth cycle of boreal trees is synchronized with seasonal changes in photoperiod and temperature. A warmer climate can lead to an earlier bud burst and increased risk of frost damage caused by temperature backlashes. In this study we analysed site- and provenance specific responses to interannual variation in temperature, using data from 18 Swedish and East-European provenances of Norway spruce (Picea abies), grown in three different sites in southern Sweden. The temperature sum requirements for bud burst, estimated from the provenance trials, were correlated with the provenance specific place of origin, in terms of latitudinal and longitudinal gradients. Frost damage had a significant effect on tree height development. Earlier timing of bud burst was linked to a higher risk of frost damage, with one of the sites being more prone to spring frost than the other two. The estimated provenance specific temperature sum requirements for bud burst were used to parametrize a temperature sum model of bud burst timing, which was then used together with the ensemble of gridded climate model data (RCP8.5) to assess the climate change impact on bud burst and associated risk of frost damage. In this respect, the simulated timing of bud burst and occurrence of frost events for the periods 2021–2050 and 2071–2100 were compared with 1989–2018. In response to a warmer climate, the total number of frost events in southern Sweden will decrease, while the number of frost events after bud burst will increase due to earlier bud burst timing. The provenance specific assessments of frost risk under climate change can be used for a selection of seed sources in Swedish forestry. In terms of selecting suitable provenances, knowledge on local climate conditions is of importance, as the gridded climate data may differ from local temperature conditions. A comparison with temperature logger data from ten different sites indicated that the gridded temperature data were a good proxy for the daily mean temperatures, but the gridded daily minimum temperatures tended to underestimate the local risk of frost events, in particular at the measurements 0.5 m above ground representing the height of newly established seedlings.

The Role of Manipulating Photoperiod and Temperature in Oocyte Development of the Polychaete Hediste diversicolor (O.F. Müller, 1976)

Three different experiments were conducted to examine the oocyte development of the polychaete Hediste diversicolor in response to changing photoperiod and temperature at three different periods of oogenesis. In experiment I, worms collected during summer were reared under constant or decreasing photoperiod and temperatures to test the combined effects of the summer–autumn photoperiod and temperature transition on oogenesis. The result showed females collected during summer showed the highest oocyte growth when exposed to constant temperatures combined with decreasing photoperiod and decreasing temperature combined with constant photoperiod. In experiment II, worms collected in late autumn were under mimicked or shortened seasonal changes in photoperiod to evaluate the effect of accelerated change on oocyte growth. The result showed worms had 1.5 times faster oocyte growth rates when exposed to accelerated rate of change in photoperiod (2.5 times faster). In experiment III, worms collected in spring were exposed to different temperature regimes to examine the effect of raising temperature on the synchronization of oocyte growth and maturation. The results showed worms collected in spring showed increased temperatures will increase oocyte maturation synchronicity. It was concluded temperature and photoperiod transition can increase the oocyte development.

Central and peripheral actions of melatonin on reproduction in seasonal and continuous breeding mammals

Under field conditions, especially for mammals that inhabit high latitudes, the regulation of seasonal breeding activity to ensure delivery of the young at the time most conducive to their survival is essential. This is most frequently accomplished by the annual reproductive cycle being linked to seasonal photoperiod changes which determine the nocturnal duration of the pineal melatonin signal. Mating can occur during any season that ensures spring/early summer delivery of the offspring. Thus, the season of mating is determined by the duration of pregnancy. The precise hormonal control of the annual cycle of reproduction by melatonin is accomplished at the level of the hypothalamo-pituitary axis which, in turn, determines the physiological state of the gonad and adnexa due to the regulation of pituitary gonadotrophin release. Many species are continuous rather than seasonal breeders. In these species, melatonin has a minor hormonal influence on the central regulation of reproduction but, nevertheless, its antioxidant functions at the level of the gonads support optimal reproductive physiology. Possibly like all cells, those in the ovary, e.g., granulosa cells and oocytes (less is known about melatonin synthesis by the testes or spermatogenic cells), synthesize melatonin which is used locally to combat free radicals and reactive nitrogen species which would otherwise cause oxidative/nitrosative stress to these critically important cells. Oxidative damage to the oocyte, zygote, blastocyst, etc., results in an abnormal fetus which is either sloughed or gives rise to an unhealthy offspring. The importance of the protection of the gametes (both oocytes and sperm) from oxidative molecular mutilation cannot be overstated. Fortunately, as a highly effective free radical scavenger and indirect antioxidant (by upregulating antioxidant enzyme), locally-produced melatonin is in the optimal location to protect the reproductive system from such damage.

Histological study of the thin skin of a migratory song bird

AbstractAvian skin is remarkably different from common mammalian and much less studied in comparison. In the absence of recent studies on clear histological structure of avian skin, we undertook this study to see the thin skin structure of migratory song bird red‐headed bunting (Emberiza bruniceps). The seasonal changes in photoperiod results in significant changes in the colour, texture, fat content and external plumage, and as of yet no reports exist on how it effects the structure of integument itself. As a primary report, we find that thin section of skin of the migratory buntings in breast region is very lightly attached to the underlying muscle tissue while supporting a major plumage transition. There exists an extensive network of blood vessels beneath the loosely attached skin raising a possibility of the role of blood to bring nutrients/factors for seasonal changes seen in the external features of these birds. Cresyl violet staining of skin also indicates the presence of nucleic acid in skin‐muscle pockets. Finally, we show the arrangement of small muscle pockets in such loosely attached skin which holds a repertoire of feathers. Our results provide the first histological view of a migratory avian species.

Insect photoperiodism: Seasonal development on a revolving planet

This review starts by comparing photoperiodic diapause with non-photoperiodic quiescence in four representative species, paying particular attention to overwintering in Drosophila melanogaster. In the second part it describes dormancy strategies of insects from the equator to the polar regions, addressing topics such as the role of the circadian system in photoperiodic time measurement, latitudinal clines in diapause-related traits, hourglass-like photoperiodic clocks based on dampening circadian oscillators, and the dormancy strategies of insects close to the equator or at high latitudes where seasonal changes in photoperiod are unreliable or absent.

EYES ABSENT and TIMELESS integrate photoperiodic and temperature cues to regulate seasonal physiology in Drosophila

Organisms possess photoperiodic timing mechanisms to detect variations in day length and temperature as the seasons progress. The nature of the molecular mechanisms interpreting and signaling these environmental changes to elicit downstream neuroendocrine and physiological responses are just starting to emerge. Here, we demonstrate that, in Drosophila melanogaster, EYES ABSENT (EYA) acts as a seasonal sensor by interpreting photoperiodic and temperature changes to trigger appropriate physiological responses. We observed that tissue-specific genetic manipulation of eya expression is sufficient to disrupt the ability of flies to sense seasonal cues, thereby altering the extent of female reproductive dormancy. Specifically, we observed that EYA proteins, which peak at night in short photoperiod and accumulate at higher levels in the cold, promote reproductive dormancy in female D. melanogaster Furthermore, we provide evidence indicating that the role of EYA in photoperiodism and temperature sensing is aided by the stabilizing action of the light-sensitive circadian clock protein TIMELESS (TIM). We postulate that increased stability and level of TIM at night under short photoperiod together with the production of cold-induced and light-insensitive TIM isoforms facilitate EYA accumulation in winter conditions. This is supported by our observations that tim null mutants exhibit reduced incidence of reproductive dormancy in simulated winter conditions, while flies overexpressing tim show an increased incidence of reproductive dormancy even in long photoperiod.