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Circannual cycle
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Circannual cycle
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 and hibernation, all of which are inherently driven and synchronized with external environmental changes.
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), 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.
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: persistence in the absence of apparent time cues, the capacity for phase shifting, and stability against temperature fluctuations. 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.
Derived from Latin, the term circannual combines circa, meaning approximately, with annual, referring to a period of one year.
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.
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Circannual cycle AI simulator
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Circannual cycle
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 and hibernation, all of which are inherently driven and synchronized with external environmental changes.
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), 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.
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: persistence in the absence of apparent time cues, the capacity for phase shifting, and stability against temperature fluctuations. 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.
Derived from Latin, the term circannual combines circa, meaning approximately, with annual, referring to a period of one year.
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.