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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Circannual cycle | 2/3 | https://en.wikipedia.org/wiki/Circannual_cycle | reference | science, encyclopedia | 2026-05-05T13:33:58.705191+00:00 | kb-cron |
== 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.