Circadian rhythms are often tightly confined around a mean of 24 hours with little variation in traditional model organisms in the absence of environmental time cues. Some spider species fall well outside this normal range with mean periods of 18 hours and variation around these means of 6 hours or more. This extreme variation in circadian rhythm is not well-understood and is the focus of the current study. Using Parasteatoda tepidariorum as a model organism, we investigated whether variation in eight circadian parameters could be explained by genetic variability, environmental conditions, or an endogenous feature of the circadian system of P. tepidariorum. No significant correlation was found between mother spiders and their offspring for all circadian parameters, nor was a significant difference found among groups exposed to different environmental conditions. We conclude that circadian variation seen in P. tepidariorum is likely a result of an innate circadian feature such as relaxed selection for a precise, 24-hour circadian rhythm.

We examined the circadian rhythms of locomotor activity in three spider species in the Family Theridiidae under light–dark cycles and constant darkness. Contrary to previous findings in other organisms, we found exceptionally high variability in endogenous circadian period both within and among species. Many individuals exhibited circadian periods much lower (19–22 h) or much higher (26–30 h) than the archetypal circadian period. These results suggest relaxed selection on circadian period as well as an ability to succeed in nature despite a lack of circadian resonance with the 24-h daily cycle. Although displaying similar entrainment waveforms under light–dark cycles, there were remarkable differences among the three species with respect to levels of apparent masking and dispersion of activity under constant dark conditions. These behavioral differences suggest an aspect of chronotype adapted to the particular ecologies of the different species.

Whereas circadian rhythms in humans and many other organisms are closely linked to the solar day and even slight deviations could cause significant health problems, several spider species thrive despite extremely shortened or extended circadian clocks. These naturally occurring clocks influence a variety of behaviors, which may help spiders maintain a precarious balance between their conflicting roles as predator and prey. The southern black widow, Latrodectus mactans, is primarily nocturnal in its locomotor activity, but this activity appears only loosely regulated by its circadian clock. This study attempts to determine how internal circadian oscillators affect other aspects of black widow behavior, since preliminary data suggest that they also possess potentially irregular circadian patterns. The behavioral patterns of twenty female black widows were recorded over a span of several weeks. Approximately 3,400 hours of footage in standard (12-hour light-dark cycles) and constant conditions (complete darkness) were analyzed and specific behaviors were recorded using the software BORIS. This study focused on three specific sets of behavior: foraging versus retreat patterns, general activity levels throughout a 24-hr period, and waste disposal. Predation stimuli were also introduced during each cycle set to determine how the widows’ responses were affected by their internal circadian oscillators. Free-run behaviors (behavior no longer entrained to the standard 24hr cycle) observed during the dark-dark cycles differed from the behavior observed during light-dark cycles in both frequency and duration of actions, particularly those related to foraging or web work. Likewise, certain behaviors and prey avoidance techniques observed during light-cycle periods were not observed during constant conditions. This experiment examines several previously unstudied black widow behaviors for generating a better understanding on how they act in natural conditions and to determine how their actions may be influenced by their highly unusual circadian rhythms. Ultimately, this experiment will contribute to a larger, ongoing study investigating circadian-controlled behaviors and rhythms in 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.

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Coastal meadows are important habitats for many animals, but the habitats are threatened by changes in land use such as abandonment of grazing. On the Swedish East coast, many coastal meadows can be found and they are highly influenced by the brackish marine environment which supports large populations of spiders. Spiders are the most abundant carnivorous arthropods on coasts of Uppland, and it is known that spider communities are closely associated with the vegetation. This study aims to investigate the spider communities in coastal meadows in Uppland and Sörmland, Sweden, and spiders were collected with pitfall traps and vacuum suction sampling. The meadows are under varying management either grazed by cattle, abandoned or has never been managed, and this is expected to influence the vegetation structure. The vegetation was on average higher in the abandoned sites, but the coefficient of variation in height was similar. The Lycosid community was not influenced by the vegetation structure, but was extremely abundant. Mean height of the vegetation had a positive influence on species richness, and a higher number of species were found in the abandoned and grazed meadows compared to the non-managed meadows, in the analysis of the vacuum sampled community. The communities were distinctly different in meadows under different management, and this was influenced by the height of the vegetation. Management of costal meadows is therefore also important for conserving diverse communities of spiders, but clearly some spiders prefer the less species rich un-managed habitats, so consideration should be taken to this.