Circadian clocks are responsible for scheduling many behavioral and physiological processes to occur at the most appropriate time of day. The resulting daily rhythms also synchronize (entrain) to external environmental cues, known as zeitgebers. This phenomenon of entrainment enables organisms to anticipate daily changes in environmental conditions such as sunrise/sunset, temperature variations, availability of prey, etc. Given the critical nature of entrainment to survival, it is no surprise that the mechanism is conserved across taxa. The misalignment of the intrinsic clock with the external environment results in a plethora of negative consequences, made apparent by studies involving shift work and jet lag. The focus of the present study is to investigate the chronobiology of Larinioides cornutus (Araneidae), a nocturnal orb-weaving spider, with an emphasis on its entrainment to light:dark cycles. Because spiders have received scarce attention with respect to their chronobiology, it is instructive to compare the properties of spider circadian systems with those of the more established circadian model systems, such as Drosophilaand Murines. We found that both lights-off and lights-on are equally influential zeitgeber cues for (determines the phasing of) both activity onset and offset. Locomotor activity typically begins within a half hour after nightfall, continues throughout the night, and ceases just prior to dawn. Phase shifting experiments show that these spiders can re-entrain within 2 days to a light/dark cycle shifted by 6 hours, and within 3 days when shifted by 12 hours. These rates of re-entrainment occur at an extremely accelerated rate compared to mammals, which readjust to a time shift at a rate of around 1 day/ 1 hour of phase shift. In other words, spiders have a minimal jet-lag response. This suggests an increased level of plasticity in the spider circadian clock that has yet to be observed in other organisms. Typical of circadian rhythms in nearly all organisms, activity also persisted (free-runs) under constant conditions. However, in constant darkness (DD), a drastic change in periodicity was revealed in 66% of individuals, from 23.4 to 25.2. This particular phenomenon is rare and likely indicates the possible interaction of multiple oscillators. Further evidence to support this interpretation is the consistent periods of the rhythm displayed before and after the change. In contrast, under constant light (LL) conditions, 65% of spiders were arrhythmic, with 4 individuals ceasing activity completely. Significant periods detected in LL were normally distributed over an unusually broad range, from 16.7 to 34.9 hours, suggesting a high sensitivity to light. Because of the unusual rates of re-entrainment to light/dark cycles, the spontaneous changes in free-running period under DD, and arrhythmicity in LL, we propose that spiders are valuable comparative model organism for elucidating fundamental mechanisms of circadian clocks.

Circadian rhythms are nearly ubiquitous and are responsible for timing biological processes and allowing for anticipation of regular changes in the environment. The internal clocks of most organisms have a period very close to 24 hours with little variation. Spiders, however, do not seem to follow this pattern. Both the fastest (18 hours) and slowest (29 hours) naturally-occurring clocks are found in spiders, and variation within a species can be orders of magnitude larger than that of previously studied animals. Circadian rhythms are assumed to be adaptive, yet little is known about their heritability in arthropods. Heritability is defined as the amount of phenotypic variation that can be attributed to genetic variation passed down from parent to offspring. Phenotype can be influenced by many complex factors including environmental effects, dominance of genetic sequences, and gene interactions. Because of these influences, the phenotypic characteristics of an individual can vary greatly, and it is often difficult to precisely identify what is truly heritable. Using spiders as a model system, we can exploit the extreme variation in circadian rhythms to investigate the potential contribution from heritability. Strong heritability would suggest that wide variation in circadian rhythms likely reflects high genetic variability in the species. Alternatively, the environment may have a greater contribution in this variation relative to the effects of heritability. To test this, we chose Parasteatoda tepidariorum, a common cobweb spider with a relatively short circadian period of 21.7 hours and intraspecific variation of more than 4 hours. To estimate the heritability of circadian rhythm, adult females were gathered with accompanying egg cases, and juveniles were raised from those cases. Six fundamental parameters of circadian rhythms were measured from the locomotor activity of adults and juveniles. Of those six, only one parameter differed between adults and juveniles: the onset of locomotor activity during the first five days when light cycles were present (Mann-Whitney U= 1814, p= 0.04). When all six circadian parameters were compared by regression of adults to respective offspring, none showed significant correlation. This indicates that variation in circadian rhythms was likely not caused by parental genetics, and that environmental factors, such as artificial light at night, may be the source of the extreme circadian rhythms seen in spiders. Another possible cause for this variation may be the presence of weak molecular circadian oscillators that are more sensitive to environmental factors than those in most other circadian systems.

Most organisms maintain a nearly 24-hour circadian rhythm which allows them to anticipate daily events in the Earth’s solar day. Circadian clocks can be regulated by external time cues such as light/dark (LD) cycles, allowing nocturnal organisms to synchronize their rhythms around dusk in a process known as entrainment. In the absence of external time cues, these rhythms persist, revealing the period of the organism’s internal clock. In nature, day-night cycles have gradual transitions at dawn and dusk, yet these transitions often are not reflected in laboratory studies. Most utilize instantaneous transitions from light to dark, including previous work on spider circadian behavior. To mimic natural conditions, the next logical step is to evaluate how a gradual, dusk transition affects activity patterns and entrainment in nocturnal spiders. Two spider species were used: Pholcus phalangioides and Metazygia wittfeldae. Three hypotheses were identified: 1) spider circadian behavior is unaffected by the type of dusk transition; 2) spider activity entrains to a proportional decrease in light intensity; and 3) spider activity entrains to a specific dimness threshold. Spiders were placed in activity monitors and exposed to 12:12 LD cycles with high (8934 lux) and low (2918 lux) light intensities. There were two groups within each light intensity: one with instantaneous, dusk transitions and one with linear 4-hour transitions. In all experiments, spiders were switched to constant darkness after 5 days of LD cycles to identify the phasing of the circadian clock. In P. phalangioides, there were no significant differences among onsets of activity for high and low light intensities with ramped transitions, nor high and low intensities with instantaneous transitions. The average onset of activity was 0.2 ± 0.1 hours after absolute darkness. For M. wittfeldae, onsets of activity were significantly earlier in ramped than instantaneous LD cycles. However, there was no observable difference in activity onset associated with absolute light intensity for either transition type. The average onset of activity for ramped transitions was 1.9 ± 0.5 hours before complete darkness, while the average onset for instantaneous transitions was 0.5 ± 0.1 hours after complete darkness. Pholcus phalangioides requires complete darkness before activity begins, supporting the hypotheses that either the activity onset is unaffected by the type of dusk transition or requires a very low threshold of light. However, M. wittfeldae began activity about 2 hours earlier or around when light decreases by 50%, supporting the hypothesis that this species entrains to a proportional decrease in light intensity. These activity patterns match their ecologies, as P. phalangioides typically sits and waits in a permanent web while the orbweaver M. wittfeldae begins building a new web during the dusk transition. Overall, these results suggest that ramping light cycles should be considered when circadian rhythms are evaluated in the lab.

Circadian rhythms are outputs of the internal clock that regulates the daily functions of almost all living organisms. Circadian rhythms are typically 24 hours because they are synchronized by external cues such as the natural light/dark cycles of the environment. When external cues are removed, the circadian rhythm “free-runs,” thus revealing the organism’s endogenous circadian period. Recent studies have found that the trashline orbweaving spiders Cyclosa turbinata and Allocyclosa bifurca have abnormally short circadian rhythms of approximately 19 and 18 hours, respectively. Trashline orbweavers construct a line of debris made of prey carcasses in the center of their web and then remain undetectable by being cryptic within their trashline. Despite similar circadian rhythms and web-building behaviors, recent genetic findings indicate that these species actually are not closely related. In fact, both genetic and morphological data now suggest A. bifurca is more closely related to Cyrtophora citricola, the Tropical Tent-web spider. This would suggest that trashline behavior and exceptionally short circadian clocks evolved independently in C. turbinataand A. bifurca. This study analyzed the circadian rhythm of C. citricola and compared it to the circadian rhythm of A. bifurca. If C. citricola has an abnormally short clock like A. bifurca, this would indicate that the evolution of the short clock preceded the divergence of these species’ lineages. However, if C. citricola has a more typical clock, this would suggest that the unusually short clock evolved in the A. bifurca lineage and may be more ecologically linked to the trashline behavior. Thirty-two female C. citricola were collected in Southern Florida and had their locomotor activity measured over four days of 12:12 light/dark cycles followed by complete darkness to determine their circadian free-running periods (FRP). Cyrtophora citricola was found to have a more typical FRP of 24.0 + 0.43 hours. Despite being closely related, C. citricola and A. bifurca differ significantly in their circadian rhythms, suggesting that short circadian rhythms may be ecologically linked with trashline behavior.

Circadian rhythms are the endogenous, roughly 24-hour rhythms that coordinate an organism's interaction with its cycling environment. The molecular mechanism underlying this physiological process is a cell-autonomous oscillator comprised of a complex regulatory network of interacting DNA, RNA and proteins that is surprisingly conserved across many different species. It is not a trivial task to understand how the positive and negative feedback loops interact to generate an oscillator capable of a) maintaining a 24-hour rhythm in constant conditions; b) entraining to external light and temperature signals; c) responding to pulses of light in a rather particular, predictable manner; and d) compensating itself so that the period is relatively constant over a large range of temperatures, even for mutations that affect the basal period of oscillation. Mathematical modeling is a useful tool for dealing with such complexity, because it gives us an object that can be quickly probed and tested in lieu of the experiment or actual biological system. If we do a good job designing the model, it will help us to understand the biology better by predicting the outcome of future experiments. The difficulty lies in properly designing a model, a task that is made even more difficult by an acute lack of quantitative data. Thankfully, our qualitative understanding of a particular phenomenon, i.e. the observed physiology of the cell, can often be directly related to certain mathematical structures. Bifurcation analysis gives us a glimpse of these structures, and we can use these glimpses to build our models with greater confidence. In this dissertation, I will discuss the particular problem of the circadian clock and describe a number of new methods and tools related to bifurcation analysis. These tools can effectively be applied during the modeling process to build detailed models of biological regulatory with greater ease. / Ph. D.

Circadian rhythms are ubiquitous among eukaryotic organisms and have evolved several times independently which strongly suggests that the presence of a biological clock is adaptive. A prevailing, though relatively untested, hypothesis is that having an internal clock allows organisms to anticipate daily changes in the environment and physiologically and/or behaviorally prepare for them. Locomotor activity is commonly interpreted as an indicator of neurological arousal, and, thus, is a useful indicator in studies of circadian rhythm. We have observed that some species of spiders exhibit a tight and predictable band of activity at a particular time of day, while in other species activity is more spread out through the day. Such patterns tend to continue, or are exaggerated, under conditions of constant darkness. We hypothesize that these predators with tight activity bands are ‘circadian specialists’ using their internal clocks to focus their attention in the narrow temporal window when prey are available to them. On the other hand, the species with broader activity bands are employing a ‘circadian generalist’ strategy, and are able to be more opportunistic with temporally unpredictable prey. Some support of this hypothesis comes from the observation that species that forage only at night tend to have tighter bands of locomotor activity than those species which forage continuously day and night. In this study we present a simulation model that supports this idea that a tight distribution of neurological alertness is advantageous when prey is predictable, but an evenly clumped distribution of alertness is favored when prey are unpredictable. We also tested the abilities of four nocturnal spider species to opportunistically respond to an unexpected period of darkness. Consistent with our hypothesis, we found that in the predicted circadian specialist species activity could not be elicited with unexpected darkness at any time of day, while the predicted circadian generalist showed activity in mid and late day. In two species intermediate on the specialist-generalist scale we only elicited activity in late day. This work represents a test of a novel hypothesis regarding the adaptiveness of circadian rhythms.

No description available.

Photoperiod manipulation is routinely used in the aquaculture industry with the aim to enhance growth by manipulating the timing of reproduction in several commercially important temperate fish species. However, there are clear gaps in our understanding of how photoperiod is perceived by the circadian axis and transmitted to the brain to alter reproduction. Furthermore, due to the wide range of environments inhabited by fish, it is unlikely that one single organization exists. It is therefore believed that comparative studies of temperate species “models” with tropical species such as the African catfish (Clarias gariepinus) that adapted to different environments characterized by weaker light signals can help in such an aim. A number of studies were therefore performed in this PhD project to expand our knowledge on circadian biology and environmental physiological effects in African catfish. The first aim was to characterize the circadian melatonin system in this species (chapter 3). Results clearly showed that the control of melatonin production by the pineal gland was very different in the African catfish as compared to temperate species such as salmon and trout. Indeed, melatonin production appeared to mainly depend on light stimuli perceived by the eyes as opposed to salmonids where light directly perceived by the pineal gland regulates its own melatonin production within photoreceptors. The main evidence was obtained in ophthalmectomised fish that were unable to synthesize and release melatonin into the blood circulation during the dark period. This was the first time that such a decentralized organisation, similar in a way to the mammalian system, was found in any teleost species. In vitro results also supported such findings as African catfish pineal glands in isolation were not able to normally produce melatonin at night as usually seen in all other fish species studied so far. This indirectly suggested that pineal gland photo-sensitivity might be different in this tropical species. Further studies were performed to better determine the amount of light that can be perceived by the African catfish pineal gland depending on light transmittance though the skull (where the pineal gland is located). Surprisingly, it appeared that catfish cranium act as a stronger light filter than in other species resulting in lower light irradiance of the pineal gland. This could explain, although it still needs to be further confirmed, why African catfish photic control of melatonin produced by the pineal would have evolved differently than in temperate species. The work then focused on better characterizing diel melatonin production and endogenous entrainment through exposure to continuous photic regimes (continuous light, LL or darkness, DD) (chapter 4). Daily melatonin profiles of fish exposed to 12L:12D photoperiod (routinely used in indoor systems) confirmed low melatonin production at day (<10 pg/ml) and increase at night (50 pg/ml) as reported in most vertebrate species studied to date. Interestingly, results also showed that melatonin production or suppression can anticipate the change from night to day with basal melatonin levels observed 45 mins prior to the switch on of the light. These observations clearly suggest the involvement of a clock-controlled system of melatonin secretion that is capable of anticipating the next photophase period. Furthermore, when constant light (LL) was applied, day/night melatonin rhythms were abolished as expected due to the constant photic inhibition of AANAT activity (e.g. one of the enzyme responsible for the conversion of serotonin into melatonin). However when fish were exposed to constant darkness (DD), a strong endogenous melatonin rhythm (maintained for at least 4 days and 18 days in catfish and Nile tilapia respectively) was found, demonstrating once again the presence of robust circadian oscillators in this species. The next aim of the doctoral project was then to investigate circadian behaviour of catfish through locomotor activity studies (Chapter 5). African catfish is again a very interesting “model” due to its reported nocturnal activity rhythmicity as compared to most other teleosts species. Locomotor activity is considered as a very useful tool to elucidate the mechanisms of circadian organization in both invertebrates and vertebrates circadian. Results first confirmed the nocturnal activity rhythms in the species. Furthermore, clear circadian endogenous rhythms were observed under constant light (LL) or darkness (DD) during several days before losing rhythmicity. Interestingly, the activity levels varied depending on the stocking density. Finally, the last aim of this project was to test the effects of a range of photoperiodic manipulations on growth performances, sexual development and reproductive performances in African catfish reared from eggs to puberty. Results did not show any differences at the early sages (up to 90 days post hatching) in growth performances nor mortality (high) between control 12L:12D and LL treatments. In contrast, during the juvenile-adult period (from 120 to 360 DPH), significant growth effects were observed, as previously reported in other catfish species, with fish under LL displaying lower growth rate, food consumption and feed conversion efficiency in comparison to most other treatments (12:12, LL, 6:6, 6:18, 12-LL and LL-12) especially 12l:12D. However, no major effects of the photoperiodic treatments were observed with all fish recruited into puberty and developing gonads although differences in the timing of gametogenesis could be observed, especially a delay (circa 2 months) in females exposed to short daylength (6L:18D and 6L:6D). As for egg quality, egg diameter was the only parameter to differ between treatments (slightly larger in egg batch from LL treated females). Overall, none of the photoperiodic regime suppressed maturation in African catfish as opposed to some temperate species. The work carried out during this PhD project clearly advanced our understanding of circadian rhythmicity, light perception and effects of photoperiod on physiology in a tropical species. Future studies are now required to further characterise the circadian system and link it to evolutionary trends within vertebrates.

The amount of sleep per day among new Cadets at West Point during Cadet Basic Training (CBT) was investigated. Sleep was measured using actigraphy. The results indicated that new Cadets slept an average of approximately 340 minutes or 5 hours, 40 minutes per night. The results were compared with survey data to determine whether or not reported sleep prior to arrival at West Point matched measured sleep at CBT. The findings indicate that the study population is sleep-deprived during CBT. Additionally, the results show that, on average, New Cadets receive 2 hours, 6 minutes less sleep per night during CBT than before their arrival at West Point. The findings also indicate that sleep achieved was not due to the various comparison factors: Gender, Race, Company, Age, Recruited Athlete, and Morningness/Eveningness preference.

ABSTRACT Seasonal affective disorder (SAD) is characterized by annual recurrence of clinical depression in the fall and winter months. The importance of SAD as a public health problem is underscored by its high prevalence (an estimated 5%) and by the large amount of time individuals with SAD are impaired (on average, 5 months each year). The specific cause of SAD remains unknown; however, researchers have identified possible chronobiological and psychological vulnerabilities to SAD. The study aimed to clarify psychological and chronobiological correlates of SAD in the first test of an integrative model of SAD. The project used a longitudinal design to test the respective contributions of the chronobiological and cognitive vulnerabilities on winter depression severity in 31 SAD patients and 33 never-depressed controls at sites in Burlington, VT and Pittsburgh, PA. The measures selected for the cognitive vulnerability were established measures of vulnerability to nonseasonal depression with empirical support for their relevance to SAD: brooding rumination, dysfunctional attitudes, cognitive reactivity to an induced sad mood, and season-specific cognitions. The chronobiological vulnerability was measured as Phase Angle Difference (PAD) and deviation from PAD of 6 hours. All measures were completed once in the summer, when the SAD patients were remitted, and once in the winter, when patients were clinically depressed. Patients were distinguished from controls on most cognitive vulnerability measures (brooding, as well as rumination, dysfunctional attitudes, and seasonal beliefs). SAD patients exhibited shorter PAD than controls, but did not exhibit greater deviation from PAD-6. Results provide further support for specific cognitive, but not chronobiological, vulnerabilities in prediction of SAD. Limitations of the current sample are discussed. Results hold implications for future SAD research bridging the chronobiological and psychological disciplines with the ultimate aim of improved understanding, assessment, treatment, and prevention of SAD.