An organism’s circadian clock exists as a self-regulating oscillator that can synchronize with its surroundings. This manifests as physiological and behavioral output which can anticipate changes in environment. These rhythms may even persist internally and are known to oscillate at a period (tau) of around 24 hours even in the absence of external cues. In the laboratory, such rhythmic output is known as a free-running period (FRP).
Given that circadian rhythms are distributed in a number of taxa as well as their tendency to oscillate along with the solar day, it has been suggested that they result from natural selection. The argument that tone’s clock is adaptive is based on how it is advantageous: the clock instills temporal order among physiological processes as well as enabling one to anticipate external cues. Losing that order in one’s clock has also been associated with a number of metabolic and neurological pathologies.
Along with adaptive significance, it has been surmised that an internal clock which synchronizes with one’s surrounding environment is beneficial to an individual. An organism whose free-running period closest matches the rhythmic output of its external environment will exhibit a higher relative fitness as compared to those whose periods deviate from 24 hours. This forms the basis of the ‘circadian resonance hypothesis’. Circadian resonance has been examined in a number of species, from Cyanobacteria to mammals. Collectively, experimental results have supported the rationale that an individual does best when its internal clock resonates with the 24 hour day.
The bowl and doily spider, Frontinella communis, not only has its own endogenous rhythm (free-running period), it exhibits an average free-running period of 28.26 hours, deviating from a usual period of ~24 hours. Keeping in mind the circadian resonance hypothesis, an internal clock with such an extreme deviation from the 24 hour day should prove detrimental to one’s overall health. Despite this, Frontinella communis not only has a long clock; among the species, their clocks also appear to be highly variable, FRPs ranging from ~24 to ~33 hours.
This study monitored locomotor activity of Frontinella communis to examine whether its free-running period, on average, remained the same throughout its active season (May-September). It was found that average free-running period in F. communis varied significantly over a five-month period. Average FRP appears to peak in June followed by a steady, linear decline as the season continues. A variety of organisms have been shown to exhibit seasonal responses that allow them to cope with environmental change. It is not known whether the change in Frontinella’s FRP is such an advantage or is merely coincidental.
Any free running period detected under the alpha level of 0.05 was not ruled significant. Along with the rise and fall of average FRPs, the presence of FRP deemed significant was found to decline as the season ended- 42% of individuals (n= 19) reported as arrhythmic. While age has been found to correlate with circadian desynchrony in other taxa (rats, humans), an association in Frontinella remains to be tested.
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:asrf-1477 |
| Date | 12 April 2019 |
| Creators | Crain, Shae, Jones, Thomas, Moore, Darrell, 2346742 |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Source | Appalachian Student Research Forum |
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