In chronobiology, the circannual cycle is characterized by biological processes and behaviors recurring on an approximate annual basis, spanning a period of about one year. This term is particularly relevant in the analysis of seasonal environmental changes and their influence on the physiology, behavior, and life cycles of organisms. Adaptations observed in response to these circannual rhythms include fur color transformation, molting, migration, breeding, fattening[1] and hibernation, all of which are inherently driven and synchronized with external environmental changes.[2][3]
The regulation of these cycles is linked to internal biological clocks, akin to the circadian rhythm, which respond to external cues such as variations in temperature, daylight length (photoperiod),[1] and food availability. Such environmental signals enable organisms to anticipate seasonal variations and adjust their behaviors and physiological states, thereby optimizing evolutionary fitness and reproductive success.[3]
Circannual rhythms are evident in a range of organisms, including birds, mammals, fish, and insects, facilitating their adaptation to the cyclical nature of their habitats. Circannual cycles can be defined by three primary characteristics: ersistence in the absence of apparent time cues, the capacity for phase shifting, and stability against temperature fluctuations.[3] Classified as an infradian rhythm, it occurs less frequently than a circadian rhythm. This cycle was first discovered by Ebo Gwinner and Canadian biologist Ted Pengelley.[3][4]
Derived from Latin, the term circannual combines circa, meaning approximately, with annual, referring to a period of one year.
Examples
In one study performed by Eberhard Gwinner, two species of birds were born in a controlled environment without ever being exposed to external stimuli. They were presented with a fixed Photoperiod of 10 hours of light and 14 hours of darkness each day. The birds were exposed to these conditions for eight years and consistently molted at the same time as they would have in the wild, indicating that this physiological cycle is innate rather than governed environmentally.[4]
Researchers Ted Pengelley and Ken Fisher studied the circannual clock in the golden-mantled ground squirrel. They exposed the squirrels to twelve hours of light and 12 hours of darkness and at a constant temperature for three years. Despite this constant cycle, they continued to hibernate once a year with each episode preceded by an increase in body weight and food consumption. During the first year, the squirrels began hibernation in late October. They started hibernating in mid August and early April respectively for the following two years, displaying a circannual rhythm with a period of about 10 months.[5]
An annual rhythm has been observed in humans diagnosed with obsessive compulsive tic disorder (OCTD). The study focused on observing the patients’ seasonal patterns and how the cycle of seasons affected their behaviors. They observed that there was a statistically significant annual rhythm in patients with OC symptoms but not in patients with tic symptoms. As a result of the study, the researchers concluded that treatments for this disorder can be implemented following an observation of the patient’s cycle and annual rhythm that they follow.[6]
Gwinner observed the willow warbler (Phylloscopus trochilus) which is a bird species that migrates seasonally to tropical and southern Africa. They follow an annual cycle of migration starting in September and ending in mid-November for the winter and then migrate back between March and May. The willow warblers follow this cycle to maximize reproduction in the spring/summer as well as increasing available resources in the fall/winter. Gwinner observed that even through a lack of environmental cues for migration, the willow warblers followed precise schedules attributed to their circannual rhythm. The willow warblers would consistently molt between January and February, they would have gonadal growth initiate in the winter and continue on their migration back for the spring, and they would begin a fattening process precisely at the same time year after year for their spring migrations.[7]
A classic example in insects is the varied carpet beetle. In a study performed by T. Nisimura and H. Numata in 2003, the seasonal timing and synchrony of pupation in the Varied Carpet Beetle (Anthrenus verbasci) was determined by studying how natural patterns in photoperiod and temperature affected it.[8] The authors first fostered larvae under various constant photoperiods at a constant temperature of 20°C to determine if there was a critical duration of the photophase that affected the phase of circannual rhythm. Secondly, they examined if a decrease in temperature caused a phase-shift in the circannual rhythm. Third, they fostered larvae under a natural photoperiod at a constant temperature of 20°C and compared it to a group under natural photoperiod and temperature. Lastly, to clarify the significance of the circannual control of the A. verbasci life cycle, larvae were reared under natural photoperiod and temperature from the various times of the year.[8] The results showed that the critical day-length was between 13 and 14 hours of light, that a decrease in temperature of 5°C did not affect the phase-shift, that larvae under controlled light but fluctuating temperatures experienced a delay in pupation compared to natural light and natural temperatures and that spring in Japan was the best time of the year for synchronous pupation which slowed as spring turned to summer.[8]
Circannual and circadian rhythms can be influenced by metabolism which is primarily influenced from natural external environmental factors such as daily weather and seasons. Location adaptations are needed to survive in extreme environmental changes.[9] These rhythms are influenced by variable environmental cues, and in some species are influenced by internal cues. In a study conducted by Catalina Reyes, the authors took a further look into how red-eared sliders showed circadian and circannual rhythms in metabolism, and if metabolic rates overall influenced the circadian and circannual cues. These rhythms were studied over one year, and displayed evidence of endogenous circadian and circannual rhythms in metabolism.[9] The understanding was that in order for these rhythms to be expressed, environmental cues influenced these thermo and phyto cycles eliciting circadian and circannual rhythms of the red-eared sliders. The sensitivity to these environmental influences reflect adaptations to migration patterns that could serve as further insight to the cost-and-benefit of transportation and risk of predation.[9]
Environmental external factors are the key drivers into influencing circannual and circadian rhythms. Although they may all differ depending on species, they all are influenced by factors like weather and seasonality. At temperate latitudes, circannual rhythms align with the day lengths, and in mammals, the hormone melatonin is reactive to the proportional length of evenings.[10] Authors that collaborated on this study focused on the circannual alignment of, (Rangifer tarandus tarandus), better known as arctic reindeer. They are known to limit production of a rhythmic melatonin signal when exposed to prolonged periods of midwinter darkness and midsummer light.[10] Areas in temperate regions are known to have prolonged periods of light and darkness, for instance, like in Alaska. They concluded that rhythmical melatonin secretion is a psychological response to the orientation of the sun in early winter months and the delay of circannual programme during the following autumnal months.[10]
Biological advantages
Generating biological rhythms internally helps organisms anticipate important changes in the environment before they occur, thus providing the organisms with time to prepare and survive.[4] For example, some plants have a very strict time frame in regards to blooming and preparing for spring. If they begin their preparations too early or too late they risk not being pollinated, competing with different species, or other factors that might affect their survival rate. Having a circannual cycle may keep them from making this mistake if a particular geographic region experiences a false spring, where the weather becomes exceptionally warm early for a short period of time before returning to winter temperatures.
Similarly, bird plumage and mammal fur change with the approach of winter, and is triggered by the shortening photoperiod of autumn.[11] The circannual cycle can also be useful for animals that Migrate or Hibernate. Many animals' reproductive organs change in response to changes in photoperiod. Male gonads will grow during the onset of spring to promote reproduction among the species. These enlarged gonads would be nearly impossible to keep year round and would be inefficient for the species. Many female animals will only produce eggs during certain times of the year.[5]
Interaction with changing climate
Changing climate may unravel ecosystems in which different organisms use different internal calendars. Warming temperatures may lead to earlier blooms of flora in spring. For instance, one study performed by Menzel et al., analyzed 125,000 phenological records of 542 plant species in 21 European countries from 1971 to 2000 and found that 78% of all plants studied advanced in flowering, leafing, and fruiting while only three percent were significantly delayed. They determined that the average advance of spring and summer was 2.5 days per decade in Europe.[12] Meanwhile, fauna may breed or migrate based on the length of day, and thus might arrive too late for critical food supplies they co-evolved with.
For example, the Parus major closely times the hatching of their chicks to the emergence of the protein-rich winter moth caterpillar, which in turn hatches to meet the budding of oaks.[5] These birds are a single-brood bird, meaning they breed once a year with about nine chicks per brood. If the birds and caterpillars and buds all emerge at the right time, the caterpillars eat the new oak leaves and their population increases dramatically, and this hopefully will coincide with the arrival of the new chicks, allowing them to eat. But if plants, insects, and birds respond differently to the advance of spring or other phenology changes, the relationship may be altered.
As another example, studies of the Pied Flycatcher (ficedula hypoleuca) have shown that their spring migration timing is triggered by an internal circannual clock that is fine tuned to day length.[5] These particular birds overwinter in dry tropical forest in Western Africa and breed in temperate forests in Europe, over 4,500km away. From 1980-2000, temperatures at the time of arrival and the start of breeding have warmed significantly. They have advanced their mean laying date by ten days, but have not advanced the spring arrival on their breeding grounds because their migration behavior is triggered by photoperiod rather than temperature.[11]
In short, even if each individual species can easily live with elevated temperatures, disruptions of phenology timing at ecosystem level may still imperil them.[5]
Challenges for scientific study
One reason for the paucity of research on circannual cycles is the duration of required efforts. The ratio of the period length of a circannual cycle to the length of the productive life of a scientist makes this branch of chronobiology difficult.[5] It takes an entire year to get a time series which makes it difficult to see how these cycles adjust over the years. To put this into perspective, a two-week experiment for a circadian biologist would take fourteen years for a circannual researcher, in order to achieve the same level of data robustness for the conclusions.
Related Topics
Circadian Rhythm - If circadian rhythm enables animals to prepare physiologically and behaviorally for certain predictable daily changes in the environment, might not some animals possess a circannual rhythm that runs on an approximately 365 cycle? A circannual clock mechanism could be similar to the circadian master clock, with an environment-independent timer capable of generating a circannual rhythm in conjunction with a mechanism that keeps the clock entertained to local conditions.[13]
Nocturnality is when animals are active during the night, and inactive during the day. This adaptation allows for animals to avoid predators that may not have this adaptability, as well as having availability to resources that are otherwise not harvested by non-nocturnal animals. Some animals that are nocturnal have disadvantages in animal sensory systems, such as bats, they have poor vision and use other adaptations such as echolocation, something a non-nocturnal animal would not have.
Photoperiodism is the ability of plants and animals to use the length of day or night, resulting in the modification of their activities.[14] A response from an organism to the length in daylight and time that allows for adaptations to seasonal variations and environmental changes. It orchestrates seasonal growth, development, reproduction, migration, and dormancy that affect survivorship and reproductive success.[14] Changes in photoperiod over days and seasons created the opportunity for the development of internal clocks and eventually create circadian and circannual rhythms.[3] Photoperiod can affect the circannual rhythms of animals if changed significantly.[3]
Related Research Articles
A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος, and biology, which pertains to the study, or science, of life. The related terms chronomics and chronome have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology, particularly where comparison of cycles between organisms is required.
Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time a hibernator spends at low body temperature, lasting days to weeks, or it can refer to a period of low body temperature and metabolism lasting less than 24 hours, as in "daily torpor".
Biological rhythms are repetitive biological processes. Some types of biological rhythms have been described as biological clocks. They can range in frequency from microseconds to less than one repetitive event per decade. Biological rhythms are studied by chronobiology. In the biochemical context biological rhythms are called biochemical oscillations.
The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is the principal circadian pacemaker in mammals, responsible for generating circadian rhythms. Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body and entrain to the environment. The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.
Photoperiodism is the physiological reaction of organisms to the length of light or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. They are classified under three groups according to the photoperiods: short-day plants, long-day plants, and day-neutral plants.
The varied carpet beetle is a 3 mm-long beetle belonging to the family Dermestidae. They are a common species, often considered a pest of domestic houses and, particularly, natural history museums, where the larvae may damage natural fibers and can damage carpets, furniture, clothing, and insect collections. A. verbasci was also the first insect to be shown to have an annual behavioral rhythm and to date remains a classic example of circannual cycles in animals.
Chronometry or Horology is the science of the measurement of time, or timekeeping. Chronometry provides a standard of measurement for time, and therefore serves as a significant reference for many and various fields of science.
A zeitgeber is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
Diurnality is a form of plant and animal behavior characterized by activity during daytime, with a period of sleeping or other inactivity at night. The common adjective used for daytime activity is "diurnal". The timing of activity by an animal depends on a variety of environmental factors such as the temperature, the ability to gather food by sight, the risk of predation, and the time of year. Diurnality is a cycle of activity within a 24-hour period; cyclic activities called circadian rhythms are endogenous cycles not dependent on external cues or environmental factors except for a zeitgeber. Animals active during twilight are crepuscular, those active during the night are nocturnal and animals active at sporadic times during both night and day are cathemeral.
In the study of chronobiology, entrainment occurs when rhythmic physiological or behavioral events match their period to that of an environmental oscillation. It is ultimately the interaction between circadian rhythms and the environment. A central example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by the Earth's rotation. Exposure to certain environmental stimuli will cue a phase shift, and abrupt change in the timing of the rhythm. Entrainment helps organisms maintain an adaptive phase relationship with the environment as well as prevent drifting of a free running rhythm. This stable phase relationship achieved is thought to be the main function of entrainment.
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
Jürgen Walther Ludwig Aschoff was a German physician, biologist and behavioral physiologist. Together with Erwin Bünning and Colin Pittendrigh, he is considered to be a co-founder of the field of chronobiology.
Serge Daan was a Dutch scientist, known for his significant contributions to the field of Chronobiology.
Colin Stephenson Pittendrigh was a British-born biologist who spent most of his adult life in the United States. Pittendrigh is regarded as the "father of the biological clock," and founded the modern field of chronobiology alongside Jürgen Aschoff and Erwin Bünning. He is known for his careful descriptions of the properties of the circadian clock in Drosophila and other species, and providing the first formal models of how circadian rhythms entrain (synchronize) to local light-dark cycles.
Ecological light pollution is the effect of artificial light on individual organisms and on the structure of ecosystems as a whole.
In the field of chronobiology, the dual circadian oscillator model refers to a model of entrainment initially proposed by Colin Pittendrigh and Serge Daan. The dual oscillator model suggests the presence of two coupled circadian oscillators: E (evening) and M (morning). The E oscillator is responsible for entraining the organism’s evening activity to dusk cues when the daylight fades, while the M oscillator is responsible for entraining the organism’s morning activity to dawn cues, when daylight increases. The E and M oscillators operate in an antiphase relationship. As the timing of the sun's position fluctuates over the course of the year, the oscillators' periods adjust accordingly. Other oscillators, including seasonal oscillators, have been found to work in conjunction with circadian oscillators in order to time different behaviors in organisms such as fruit flies.
Randy J. Nelson is an American neuroscientist who holds the Hazel Ruby McQuain Chair for Neurological Research and the founding chair of the Department of Neuroscience at the West Virginia University School of Medicine. Much of his research has focused on the contribution of circadian and seasonal rhythms on physiology and behavior.
Eberhard Gwinner was a German ornithologist and founding director of the Max-Planck Institute for ornithology. He specialized in the study of annual rhythms, their endocrine control, and biological clocks in birds.
Nicholas Mrosovsky was a Canadian zoologist known for his research in the fields of homeostasis, chronobiology, and sea turtle biology. He spent his whole professional career at the University of Toronto. His laboratory was notable for its seminal investigations of the influence of behavioural arousal on circadian rhythms. He was also the founder, in 1976, of Marine Turtle Newsletter. He received a Guggenheim Fellowship in 1973, and in 1993 he was elected a Fellow of the Royal Society of Canada.
1 2 3 4 5 6 Foster RG, Kreitzman L. Seasons of life: The biological rhythms that enable living things to thrive and survive 1-303.New Haven (Connecticut): Yale University Press.ISBN9780300115567. 2009.[pageneeded]
↑ Gwinner E (November 1977). "Circannual Rhythms in Bird Migration". Annual Review of Ecology and Systematics. 8 (1): 381–405. doi:10.1146/annurev.es.08.110177.002121.
1 2 3 Reyes C, Milsom WK (March 2010). "Circadian and circannual rhythms in the metabolism and ventilation of red-eared sliders (Trachemys scripta elegans)". Physiological and Biochemical Zoology. 83 (2): 283–98. doi:10.1086/597518. PMID19358691. S2CID8957676.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
