Annual Rhythm Research Articles

Clocks at a snail pace: biological rhythms in terrestrial gastropods.

Biological rhythms are ubiquitous across the tree of life. Organisms must allocate their activities into moments of the day and of the season that will increase their probability of surviving and reproducing, which is done in the form of daily and annual rhythms. So far, the vast majority of studies on biological rhythms have focused on classical laboratory model species. Still, the use of non-model species is gaining traction, as part of an effort to achieve a more holistic understanding of clock/calendar mechanisms in the "real world" but this requires species that can be studied in both the lab and in nature. Terrestrial gastropods, i.e., land snails and slugs, have the potential to be exciting models for the study of biological rhythms in nature. Therefore, we provide a review of the research on biological rhythms in terrestrial gastropods, with a focus on ecology and evolution. We present the state of the art in the field while giving a historical perspective of the studies, exploring each of the main lineages of terrestrial gastropods. We also point out some interesting directions that future studies could take to fill some of the more urgent gaps in current knowledge. We hope that our contribution will renew interest in this area and spark novel projects.

Diel and annual rhythms of tropical stem size changes in the Mayombe forest, Congo Basin

Diel and annual rhythms of tropical stem size changes in the Mayombe forest, Congo Basin

Determination of Rhythmicity and Gestational Stage-Related Distribution of Blood Plasma Melatonin Concentrations in Donkey Mares.

The aim of this study is to obtain a more complete picture of blood plasma melatonin concentrations in the donkey mares. To this purpose, sampling and statistical processing were carried out in such a way that allowed the researchers to establish the annual and daily rhythms. Based on human observations, according to the hypothesis of the authors, the blood plasma melatonin concentration of pregnant individuals rises during the late gestational period, before parturition. To confirm this, the melatonin concentrations of pregnant and non-pregnant jennies were monitored and compared. In regard to the circannual rhythm, the significantly lowest midnight melatonin value (27.67 pg mL-1) was typical for the summer solstice. Under consideration of circadian changes, a significantly strongest melatonin production (45.16 pg mL-1) was observed on the night of the winter solstice (p < 0.001). Considering gestational age, the blood plasma melatonin concentration (around 38 pg mL-1) does not change as gestation progresses (p = 0.136). The results obtained in this studied population of the domestic ass usefully expand the little knowledge previously gathered about the development of the blood plasma melatonin concentrations of this species.

Analysis of Water Temperature Variations in the Yangtze River’s Upper and Middle Reaches in the Context of Cascade Hydropower Development

The establishment and operation of cascade reservoirs in the mainstream of the upper and middle reaches of the Yangtze River have changed the river’s thermal regimes. This study analyzed the correlation between water temperature and its influencing factors and employed various evaluation indexes—including ∆T (the temperature-increasing index, °C/100 km), IEC (the extreme fluctuation index), IBD (the baseline deviation index), and IPO (the phase offset time index). The aim was to uncover the variation characteristics and influencing factors of water temperature and quantify the impact of cascade reservoir construction on annual and seasonal water temperature rhythms. Our findings show that the construction and operation of cascade reservoirs weaken the synchronization of water temperature and air temperature downstream. The construction and operation of cascade reservoirs in the middle and lower reaches of the Jinsha River led to obvious homogenization, baseline deviation, and lagging effects on water temperature downstream, which intensified with the increase in storage capacity. These effects were more pronounced in colder months compared to warmer months. Additionally, the influence of tributaries and water–air heat exchange on these effects is alleviated to different degrees. These results are significant for assessing river ecological health in the context of cascade hydropower development.

Revealing the profound influence of diapause on gene expression: Insights from the annual transcriptome of the copepod Calanus finmarchicus.

Annual rhythms are observed in living organisms with numerous ecological implications. In the zooplanktonic copepod Calanus finmarchicus, such rhythms are crucial regarding its phenology, body lipid accumulation, and global carbon storage. Climate change drives annual biological rhythms out of phase with the prevailing environmental conditions with yet unknown but potentially catastrophic consequences. However, the molecular dynamics underlying phenology are still poorly described. In a rhythmic analysis of C. finmarchicus annual gene expression, results reveal that more than 90% of the transcriptome shows significant annual rhythms, with abrupt and dramatic upheaval between the active and diapause life cycle states. This work explores the implication of the circadian clock in the annual timing, which may control epigenetic mechanisms to profoundly modulate gene expression in response to calendar time. Results also suggest an increased light sensitivity during diapause that would ensure the photoperiodic entrainment of the endogenous annual clock.

Annual rhythm in immune functions of blood leucocytes in an ophidian, Natrix piscator

Annual variations in animal’s physiological functions are an essential strategy to deal with seasonal challenges which also vary according to the time of year. Information regarding annual adaptations in the immune-competence to cope with seasonal stressors in reptiles is scarce. The present research plan was designed to analyze the presence of circannual immune rhythms in defense responses of the leucocytes in an ophidian, Natrix piscator. Peripheral blood leucocytes were obtained, counted, and superoxide anion production, neutrophil phagocytosis, and nitrite release were tested to assess the innate immune functions. Peripheral blood lymphocytes were separated by centrifugation (utilizing density gradient) and the cell proliferation was measured. The Cosinor rhythmometry disclosed the presence of significant annual rhythms in the number of leucocytes, superoxide anion production, nitric oxide production, and proliferation of stimulated lymphocytes. The authors found that respiratory burst activity and proliferative responses of lymphocytes were crucial immune responses that showed the annual rhythm. It was summarized that the immune function of the N. piscator is a labile attribute that makes the animal competent to cope with the seasonal stressor by adjustment in the potency of response.

Chronobiology of Viscum album L.: a time series of daily metabolomic fingerprints spanning 27years.

Introduction: European mistletoe (Viscum album L.) has been gaining increasing interest in the field of oncology as a clinically relevant adjunctive treatment in many forms of cancer. In the field of phytopharmacology, harvesting time is pivotal. In the last century, a form of metabolomic fingerprinting based on pattern formation was proposed as a way to determine optimal harvesting times to ensure high quality of mistletoe as raw material for pharmaceutical use. In order to further evaluate the information obtained with this metabolomic fingerprinting method, we analysed a large time series of previously undigitised daily mistletoe chromatograms dating back to the 1950s. Methods: These chromatograms were scanned and evaluated using computerized image analysis, resulting in 12 descriptors for each individual chromatogram. We performed a statistical analysis of the data obtained, investigating statistical distributions, cross-correlations and time self-correlations. Results: The analysed dataset spanning about 27years, contains 19,037 evaluable chromatograms in daily resolution. Based on the distribution and cross-correlation analyses, the 12 descriptors could be clustered into six independent groups describing different aspects of the chromatograms. One descriptor was found to mirror the annual rhythm being well correlated with temperature and a phase shift of 10days. The time self-correlation analysis showed that most other descriptors had a characteristic self-correlation of ∼50days, which points to further infradian rhythms (i.e., more than 24h). Discussion: To our knowledge, this dataset is the largest of its type. The combination of this form of metabolomic fingerprinting with the proposed computer analysis seems to be a promising tool to characterise biological variations of mistletoe. Additional research is underway to further analyse the different rhythms present in this dataset.

Genomics insights into flowering and floral pattern formation: regional duplication and seasonal pattern of gene expression in Camellia

BackgroundThe formation and domestication of ornamental traits are influenced by various aspects, such as the recognition of esthetic values and cultural traditions. Camellia japonica is widely appreciated and domesticated around the world mainly due to its rich variations in ornamental traits. Ornamental camellias have a diverse range of resources, including different bud variations from Camellia spp. as well as inter- and intra- specific hybridization. Despite research on the formation of ornamental traits, a basic understanding of their genetics and genomics is still lacking.ResultsHere, we report the chromosomal-level reference genome of C. japonica through combining multiple DNA-sequencing technologies and obtain a high-density genetic linkage map of 4255 markers by sequencing 98 interspecific F1 hybrids between C. japonica and C. chekiangoleosa. We identify two whole-genome duplication events in C. japonica: one is a shared ancient γ event, and the other is revealed to be specific to genus Camellia. Based on the micro-collinearity analysis, we find large-scale segmental duplication of chromosome 8, resulting to two copies of the AGAMOUS loci, which may play a key role in the domestication of floral shapes. To explore the regulatory mechanisms of seasonal flowering, we have analyzed year-round gene expression patterns of C. japonica and C. azalea—a sister plant of continuous flowering that has been widely used for cross breeding. Through comparative analyses of gene co-expression networks and annual gene expression patterns, we show that annual expression rhythms of some important regulators of seasonal growth and development, including GIGANTEA and CONSTANS of the photoperiod pathway, have been disrupted in C. azalea. Furthermore, we reveal that the distinctive expression patterns of FLOWERING LOCUS T can be correlated with the seasonal activities of flowering and flushing. We demonstrate that the regulatory module involved in GIGANTEA, CONSTANS, and FLOWERING LOCUS T is central to achieve seasonality.ConclusionsThrough the genomic and comparative genomics characterizations of ornamental Camellia spp., we propose that duplication of chromosomal segments as well as the establishment of gene expression patterns has played a key role in the formation of ornamental traits (e.g., flower shape, flowering time). This work provides a valuable genomic platform for understanding the molecular basis of ornamental traits.

The Annual Rhythms in Sleep, Sedentary Behavior, and Physical Activity of Australian Adults: A Prospective Cohort Study.

Sleep, sedentary behavior, and physical activity have fundamental impacts on health and well-being. Little is known about how these behaviors vary across the year. To investigate how movement-related behaviors change across days of the week and seasons, and describe movement patterns across a full year and around specific temporal events. This cohort study included 368 adults (mean age = 40.2 years [SD = 5.9]) who wore Fitbit activity trackers for 12 months to collect minute-by-minute data on sleep, sedentary behavior, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA). Data were analyzed descriptively, as well as through multilevel mixed-effects linear regression to explore associations with specific temporal cycles (day-of-the-week, season) and events. Movement patterns varied significantly by day-of-the-week and season, as well as during annual events like Christmas-New Year and daylight saving time (DST) transitions. For example, sleep was longer on weekends (+32 min/day), during autumn and winter relative to summer (+4 and +11 min/day), and over Christmas-New Year (+24 min/day). Sedentary behavior was longer on weekdays, during winter, after Christmas-New Year, and after DST ended (+45, +7, +12, and +8 min/day, respectively). LPA was shorter in autumn, winter, and during and after Christmas-New Year (-6, -15, -17, and -31 min/day, respectively). Finally, there was less MVPA on weekdays and during winter (-5 min/day and -2 min/day, respectively). Across the year, there were notable variations in movement behaviors. Identifying high-risk periods for unfavorable behavior changes may inform time-targeted interventions and health messaging.

Thirteen-year monitoring reveals that Mekong giant catfish (Pangasianodon gigas) has an annual feeding rhythm and a prolonged fasting period

Thirteen-year monitoring reveals that Mekong giant catfish (Pangasianodon gigas) has an annual feeding rhythm and a prolonged fasting period

Intra-annual stable isotopes in the tree rings of Hymenaea courbaril as a proxy for hydroclimate variations in southern Amazonia

The hydrology of Amazonia is changing due to climate and land-use changes, especially in the southern region, which has warmed and dried faster than other tropical regions. Yet there are no long-term hydrological records to put these changes in a historical perspective. Here we investigate the use of tree-ring carbon (δ13C) and oxygen isotopes (δ18O) to assess the seasonal variation in climate for the southern Amazonia basin. We analysed the intra-annual variation of δ13C and δ18O in 10 segments of each tree ring from 2013 to 2017 from individuals of Hymenaea courbaril, a long-lived and widespread neotropical tree species. We find strong seasonal patterns of tree-ring δ13C supporting previous observations of annual growth rhythms for this species. The intra-annual variation in δ18O shows that the lowest values generally occur just after the middle point of ring formation, corresponding to the peak rainy season. We find strong correlations between the δ18O in the middle of the growth ring and vapour pressure deficit (r = 0.92, P = 0.02) and precipitation (r = −0.93, P = 0.02). We further find associations between the oxygen isotopic series and the discharge of the Araguaia basin’s main rivers during the rainy period. Our results show that these δ18O records are sensitive to fluctuations in rainfall and humidity, and thus to river discharge in the region. Longer reconstructions of based on tree-ring δ18O of Hymenaea courbaril could provide a novel proxy to assess past hydrological changes.

Variation in photoperiod response corresponds to differences in circadian light sensitivity in northern and southern Nasonia vitripennis lines

The circadian clock times physiological and behavioural processes and resets on a daily basis to synchronize with the environment. The involvement of the circadian clock in photoperiodic time measurement synchronising annual rhythms is still under debate and different models have been proposed explaining their integration. Insects overcome unfavourable conditions in diapause, a form of dormancy. A latitudinal cline in diapause induction in the parasitoid wasp Nasonia vitripennis as well as a difference in circadian light sensitivity between north and south provide us with additional evidence that the circadian system of Nasonia is involved in photoperiodic time measurement and that latitude-specific seasonality drives adaptive evolution in photoperiodism partly through adaptation responses in the circadian system. We tested diapause induction in a range of T-cycles and photoperiods and found diapause induction in short photoperiods in all T-cycles in the northern line but in the southern line, diapause only occurred in T-cycles close to 24 h. Due to a lower light sensitivity in the southern line, a wider distribution of phase angles of entrainment can be expected at a specific T-cycle duration, while the range of entrainment will decrease. Taking these oscillator properties into account, our data can be explained by an external coincidence model involving a single oscillator with a light-sensitive phase that drives annual timing of diapause in Nasonia vitripennis.

Genome-wide identification of late embryogenesis abundant protein family and their key regulatory network in Pinus tabuliformis cold acclimation.

Cold acclimation is a crucial biological process that enables conifers to overwinter safely. The late embryogenesis abundant (LEA) protein family plays a pivotal role in enhancing freezing tolerance during this process. Despite its importance, the identification, molecular functions and regulatory networks of the LEA protein family have not been extensively studied in conifers or gymnosperms. Pinus tabuliformis, a conifer with high ecological and economic values and with high-quality genome sequence, is an ideal candidate for such studies. Here, a total of 104 LEA genes were identified from P. tabuliformis, and we renamed them according to their subfamily group: PtLEA1-PtLEA92 (group LEA1-LEA6), PtSMP1-PtSMP6 (group seed maturation protein) and PtDHN1-PtDHN6 (group Dehydrin). While the sequence structure of P. tabuliformis LEA genes are conserved, their physicochemical properties exhibit unique characteristics within different subfamily groupings. Notably, the abundance of low-temperature responsive elements in PtLEA genes was observed. Using annual rhythm and temperature gradient transcriptome data, PtLEA22 was identified as a key gene that responds to low-temperature induction while conforming to the annual cycle of cold acclimation. Overexpression of PtLEA22 enhanced Arabidopsis freezing tolerance. Furthermore, several transcription factors potentially co-expressed with PtLEA22 were validated using yeast one-hybrid and dual-luciferase assays, revealing that PtDREB1 could directly bind PtLEA22 promoter to positively regulate its expression. These findings reveal the genome-wide characterization of P. tabuliformis LEA genes and their importance in the cold acclimation, while providing a theoretical basis for studying the molecular mechanisms of cold acclimation in conifers.

The association between 24-hour activity, sedentary and sleep compositions and mental health in Australian adults: a cross-sectional study

BackgroundPhysical activity, sedentary behaviour, and sleep are key components to health and well-being. Compositional data analysis of activity data overcomes the limitations of traditional statistical approaches and comprehensively assesses the association of all activities throughout a 24-hour day. Few studies have used compositional analysis to explore associations between movement behaviours and mental health. This study examined the association between 24-hour activity compositions and mental health in middle-aged Australian adults.MethodsThis study used cross-sectional data from participants (n = 322; mean age 40.4 years; 58.1% female; 47.8% university degree; 84.8% partnered) in the longitudinal Annual Rhythms in Adults’ lifestyle and health study (Adelaide, Australia). Activity composition (sleep, sedentary behaviour, light physical activity, and moderate-to-vigorous physical activity) was derived using 24-hour Fitbit accelerometry from the first month of participation (December). Mental health outcomes (depression, anxiety, and stress) were obtained from the Depression Anxiety Stress Scale 21-item short-form (DASS-21). The associations between activity composition (conveyed as isometric log ratios) and DASS-21 scores were examined using compositional multi-level linear regression models with a random intercept for clustering of individuals within families. Using the compositional time reallocation model, expected differences in mental health were examined for hypothetical time reallocations between individual activities.ResultsFavourable associations were observed when time (15 min) was reallocated to light physical activity from sleep (depression: -0.31 [95% CI=-0.57: -0.06]; anxiety: -0.20 [95% CI=-0.37: -0.03] and from sedentary behaviour (depression: -0.29 [95% CI=-0.46: -0.13]; anxiety: -0.14 [95% CI=-0.25: -0.03]; stress: -0.16 [95% CI=-0.31: -0.01]). Detrimental associations were observed when time was reallocated away from light physical activity to sleep (depression: 0.32 [95% CI = 0.07: 0.58]; anxiety: 0.20 [95% CI = 0.03: 0.37]) and to sedentary behaviour (depression: 0.30 [95% CI = 0.13: 0.48); anxiety: 0.15 [95% CI = 0.03: 0.26]; stress: 0.17 [95% CI = 0.01: 0.32]). There were no associations when time was allocated to or from moderate-to-vigorous physical activity.ConclusionThe way adults spend their time across a 24-hour day is associated with their mental health. Spending more time in light physical activity appears favourable if this time is taken from sleep and sedentary behaviour. These findings provide support for “move more, sit less” public health messages.Trial registrationThis study was prospectively registered on the Australian New Zealand Clinical Trial Registry (Trial ID: ACTRN12619001430123) on the 16/10/2019.

Seasonal Immune Rhythms of head kidney and spleen cells in the freshwater Teleost, Channa punctatus

Annual rhythms in immune function are the reflection of a crucial physiological strategy to deal with environmental stressors. The fish are pivotal animal models to study the annual rhythm and to understand the evolution of the vertebrate biological system. The current research was planned to assess the annual changes in the innate immune functions of immune cells in a teleost, Channa punctatus. Head kidney and splenic macrophage phagocytosis, superoxide generation, and nitrite release were evaluated to assess innate immunity. Cell-mediated immunity was measured through head kidney and splenic lymphocyte proliferation in presence of mitogens. The superoxide anion generation by the cells of head kidney and spleen was maximum in October. A bimodal pattern in nitrite production was observed with the first peak in November and the second in March. Cosinor analysis revealed a statistically significant annual rhythm in nitrite production. Similarly, phagocytosis and lymphocyte proliferation also showed statistically significant annual rhythms. It was concluded that animals maintain an optimum immune response in seasonally changing environments. Elevated immunity during certain times of the year might assist animals deal with seasonal environmental stressors. Further research may be focused upon measuring survival rate and reproductive success after season induced elevated immunity.

Maternal dominance of intergeneric hybridization between Lycoris and Clivia

Distant hybridization can expand genetic variations and is widely applied in plant breeding. Lycoris has high economic value, but the ornamental period is short. To prolong the florescence and leaf period of Lycoris, intergeneric hybridization between Lycoris and Clivia was conducted. The offspring bloomed 7–8 years after sowing. The characteristics of the offspring were observed from three dimensions: annual growth rhythm, morphological feature, and foliage anatomy structure. The hybrids were similar to the maternal plants (L. haywardii) with some variation, but did not show any paternal (C. nobilis) characteristics. The hybrid was identified by molecular marker, only a few paternal bands were amplified. The intergeneric hybrid exhibited absolute unilateral parent dominance that was few reported. This study offers innovative insight into the characteristics of distant hybrids.

Shoot Phenology as a Driver or Modulator of Stem Diameter Growth and Wood Properties, with Special Reference to Pinus radiata

Seasonal phenology is expressed in the annual rhythms of growth and quiescence, which may range from being sharply defined to weakly quantitative. These rhythms, both vegetative and reproductive, are a key aspect of a plant’s survival strategy. They enable the plant to both survive seasonal stresses and take advantage of favourable conditions, while making pollination efficient through synchronised flowering. Maturation in woody perennials causes some ontogenetic modulation of seasonal phenology. Shoot phenology is driven by various environmental cues, notably temperatures and daylength, with shoot extremities often being prime receptors. The phenology of shoot extremities is in turn seen as a strong driver of cambial activity, which itself is an aspect of shoot phenology and the basis of stem diameter growth. The aspects of cambial activity reflecting hoot–tip phenology primarily involve the timing of xylem formation and the anatomical and physical properties of xylem cells. The actual amount of diameter growth, however, is governed much more by other factors, notably the growth potential of the species, the space for the tree to grow in, and how favourable local conditions are for growth. Somehow, all tree species allocate resources to shoot extension and diameter growth to represent viable adaptive strategies, although there is no identified role of phenology per se in such allocation. Among species, Pinus radiata is extremely important commercially, largely through a high growth potential that reflects distinctive phenology. Much research on the species provides a basis for linking its phenology and shoot–tip architecture to seasonal timing of diameter growth and fine details of within-ring variation in xylem cell properties. This provides a baseline for comparison with many other tree species, conifers and hardwoods. Selected examples are considered to illustrate the range of adaptive strategies. Regulation of diameter growth and internal variation in wood properties reflects the response to competitive pressures. Modifying the regulation to optimise wood production and quality poses a great challenge for future domestication.

How do 24-h movement behaviours change during and after vacation? A cohort study

BackgroundFor adults, vacations represent a break from daily responsibilities of work – offering the opportunity to re-distribute time between sleep, sedentary behaviour, light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) across the 24-h day. To date, there has been minimal research into how activity behaviour patterns change on vacation, and whether any changes linger after the vacation. This study examined how daily movement behaviours change from before, to during and after vacations, and whether these varied based on the type of vacation and vacation duration.MethodsData collected during the Annual Rhythms In Adults’ lifestyle and health (ARIA) study were used. 308 adults (mean age 40.4 years, SD 5.6) wore Fitbit Charge 3 fitness trackers 24 h a day for 13 months. Minute-by-minute movement behaviour data were aggregated into daily totals. Multi-level mixed-effects linear regressions were used to compare movement behaviours during and post-vacation (4 weeks) to pre-vacation levels (14 days), and to examine the associations with vacation type and duration.ResultsParticipants took an average of 2.6 (SD = 1.7) vacations of 12 (SD = 14) days’ (N = 9778 days) duration. The most common vacation type was outdoor recreation (35%) followed by family/social events (31%), rest (17%) and non-leisure (17%).Daily sleep, LPA and MVPA all increased (+ 21 min [95% CI = 19,24] p < 0.001, + 3 min [95% CI = 0.4,5] p < 0.02, and + 5 min [95% CI = 3,6] p < 0.001 respectively) and sedentary behaviour decreased (-29 min [95% CI = -32,-25] p < 0.001) during vacation. Post-vacation, sleep remained elevated for two weeks; MVPA returned to pre-vacation levels; and LPA and sedentary behaviour over-corrected, with LPA significantly lower for 4 weeks, and sedentary behaviour significantly higher for one week. The largest changes were seen for “rest” and “outdoor” vacations. The magnitude of changes was smallest for short vacations (< 3 days).ConclusionsVacations are associated with favourable changes in daily movement behaviours. These data provide preliminary evidence of the health benefits of vacations.Trial registrationThe study was prospectively registered on the Australian New Zealand Clinical Trial Registry (Trial ID: ACTRN12619001430123).

Seasonal Adaptation: Geographic Photoperiod-Temperature Patterns Explain Genetic Variation in the Common Vole Tsh Receptor.

The vertebrate photoperiodic neuroendocrine system uses the photoperiod as a proxy to time the annual rhythms in reproduction. The thyrotropin receptor (TSHR) is a key protein in the mammalian seasonal reproduction pathway. Its abundance and function can tune sensitivity to the photoperiod. To investigate seasonal adaptation in mammals, the hinge region and the first part of the transmembrane domain of the Tshr gene were sequenced for 278 common vole (Microtus arvalis) specimens from 15 localities in Western Europe and 28 localities in Eastern Europe. Forty-nine single nucleotide polymorphisms (SNPs; twenty-two intronic and twenty-seven exonic) were found, with a weak or lack of correlation with pairwise geographical distance, latitude, longitude, and altitude. By applying a temperature threshold to the local photoperiod-temperature ellipsoid, we obtained a predicted critical photoperiod (pCPP) as a proxy for the spring onset of local primary food production (grass). The obtained pCPP explains the distribution of the genetic variation in Tshr in Western Europe through highly significant correlations with five intronic and seven exonic SNPs. The relationship between pCPP and SNPs was lacking in Eastern Europe. Thus, Tshr, which plays a pivotal role in the sensitivity of the mammalian photoperiodic neuroendocrine system, was targeted by natural selection in Western European vole populations, resulting in the optimized timing of seasonal reproduction.

Influence of circadian rhythms and seasonal and annual variations on acute myocardial infarction incidence

Background/Aim: Acute myocardial infarction (AMI) is a consequence of complete coronary artery occlusion. There is a considerable seasonal variation in the incidence of AMI. The aim of the study was to establish a circadian and seasonal pattern of AMI. Methods: A retrospective observational study was conducted, using the database of the Institute of Emergency Medical Service of the City of Novi Sad. The study included 982 patients, both male and female, diagnosed with AMI (I.21 - ICD-10 code) in the period between 15 March 2018 and 14 March 2022. Data were classified according to the time of the day, days of the week, quarters and months. Data were analysed by using descriptive statistical methods, Mann-Whitney U test, Chi-squared test and Fisher's exact test. Results: AMI most frequently occurred between 6 am and 2 pm (389; 39.6 %). A statistically significant incidence of AMI was calculated for the periods between 6 am and 2 pm (ch2 = 39.69; p &lt; 0.001) and between 2 pm and 10 pm (ch2 = 28.06; p &lt; 0.001). Most cases of AMI were noted on Monday (153; 15.6 %) and in January (93; 9.5 %). The highest incidence of AMI was in the period between 15 March 2021 and 14 March 2022 (304; 31.0 %), while the lowest incidence was noted between 15 March 2019 and 14 March 2020 (190; 19.3 %). Conclusion: Circadian, seasonal and annual rhythm may have a significant impact on the incidence of AMI. This fact can have an important role in the prevention, timely recognition and adequate treatment of acute coronary disease.