Almost all organisms have approximately a 24-hour circadian rhythm that enables them to anticipate their environment’s daily rhythmicity. Anticipation increases their likelihood of success in foraging, reproduction, predation, and other life events. Therefore, a disruption of their endogenous clock results in detrimental physiological consequences that significantly impact organisms’ fitness. Surprisingly, we have found numerous spider species with free-running periods that deviate greatly from 24 hours. Free-running period (FRP) is a standard measurement of the period of an organism’s circadian rhythm found by measuring periodicity of behaviors or physiology under constant conditions (e.g., constant darkness and temperature). So far, these extreme spider FRPs have only been observed in the superfamily Araneoidea, but we have only limited sampling of species outside this clade. Therefore, we want to fill this data gap of non-araneoid spiders to deepen our understanding of the evolution of circadian clocks in spiders. Also, we will observe if significant deviation from 24 hours and wide variation in FRP are common to all spider species or are only characteristics of araneoid spiders. Here, we describe the FRPs of four non-araneoid spider species belonging to the RTA clade: Schizocosa avida, Phidippus audax, Agelenopsis pennsylvanica, and Mecaphesa celer. We detected significant free runs (mean + SD) at p<0.001 using Lomb-Scargle periodograms in three out of the four species: S. avida (23.84 ± 1.03 h); P. audax (22.67 ± 0.36 h); and A. pennsylvanica (23.97 ± 0.32 h). However, M. celer was found to be arrhythmic under constant conditions. These findings of near 24-hour FRPs with low deviation among the RTA species, along with previous data, strongly suggest that extreme FRPs are confined to the Araneoidea clade. Thus, we have phylogenetically localized a major evolutionary change in the circadian system of spiders occurring in the Araneoidea clade, approximately 170 million years ago.
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:asrf-1852 |
| Date | 07 April 2022 |
| Creators | Shepherd, Alexandria E, Jones, Thomas C, Moore, Darrell |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Source | Appalachian Student Research Forum & Jay S. Boland Undergraduate Research Symposium |
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