Comparing the Rates of Circadian Re-Entrainment Between Araneoid and Non-Araneoid Spiders

Circadian rhythms are a roughly 24-hour endogenous process that allows organisms to anticipate regular changes in their environment. These rhythms are present in almost all living eukaryotes and regulate important physiological process such as sleep-wake cycles, metabolic changes, hormone release, and activity patterns. In nature, organisms reset their internal clocks to synchronize daily with Earth’s solar day. The inability to synchronize with the environment has shown to result in fitness costs. Spider species within the superfamily Araneoidea have been found to exhibit extreme circadian periods up to five hours different than the 24-hour day, with little evidence of such extremes occurring outside of this superfamily. Studies have also shown that araneoid spiders can undergo large phase shifts without exhibiting any evidence of fitness costs such as reduced survivorship. Araenoid species can re-synchronize their internal clocks to large phase shifts, up to 10 hours daily. The rate of re-synchronization also appears to be accelerated in araneoid species. This indicates a functional difference between the circadian clocks of araneoid species and non-araneoid species. To further investigate differences between the circadian systems of araneoid and non-araneoid spiders, we are conducting a series of phase-shift experiments. Rates of re-entrainment to a six-hour phase shift were compared between an araneoid species (Metazygia wittfeldae) and a non-araneoid species (Pholcus manueli). We hypothesized that the non-araneoid spiders would require a longer amount of time to re-entrain. Results to date are ambiguous. M. wittfeldae, as expected can re-entrain to a six-hour shift within two days. For comparison, such re-entrainment would take a mammal about six days. An interruption in the experimental protocol prevents us from drawing robust conclusions in P. manueli. However, the data suggest that this species may have two circadian oscillators, one which re-entrains to a phase shift rapidly, and one which is highly resistant to re-entrainment