Sun Compass Research Articles

A magnetic compass aids monarch butterfly migration.

Convincing evidence that migrant monarch butterflies (Danaus plexippus) use a magnetic compass to aid their fall migration has been lacking from the spectacular navigational capabilities of this species. Here we use flight simulator studies to show that migrants indeed possess an inclination magnetic compass to help direct their flight equatorward in the fall. The use of this inclination compass is light-dependent utilizing ultraviolet-A/blue light between 380 and 420 nm. Notably, the significance of light <420 nm for inclination compass function was not considered in previous monarch studies. The antennae are important for the inclination compass because they appear to contain light-sensitive magnetosensors. For migratory monarchs, the inclination compass may serve as an important orientation mechanism when directional daylight cues are unavailable and may also augment time-compensated sun compass orientation for appropriate directionality throughout the migration.

How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment.

Vikings routinely crossed the North Atlantic without a magnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagas mentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a 'twilight board', which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about ±4° when the artificially occluded Sun had elevation angles between +10° and -8° relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago.

Coastal talitrids and connectivity between beaches: A behavioural test

Beach-hoppers and sandhoppers in the family Talitridae are strongly linked to the supralittoral environment. They are semi-terrestrial animals and because they are direct developers there is potentially no mobility between populations on adjacent beaches. In the case of coastlines fragmented by natural or artificial structures, the assumed lack of inter-connectivity between beaches may represent a severe threat for the resident populations: in case of impacts, they might not be able to recover and the habitat might not be re-colonised. Unless we consider another possible scenario: the potential connectivity of populations via water currents, from individuals swashed accidentally into the sea. We therefore tested two different species, the sandhopper Notorchestia quadrimana and the beach-hopper Platorchestia smithi for features relevant to dispersal and connectivity among beaches: 1) survival in sea-water; 2) orientation (baseline and scototaxis) in sea-water and; 3) behaviour in a current. Talitrid populations were sampled from a sheltered beach and an exposed beach along the New South Wales coast. On the sheltered beach both species were found, co-occurring within the same distance from the shoreline. On the exposed beach only P. smithi was found, in a dune slack far away from the shoreline. All individuals tested survived 96h in immersion, and when subjected to a current they were clinging on the edge of the flume apparatus for most of the duration of the test. Differences emerged when comparing orientation, with the sharpest precision towards a dark pattern (positive scototaxis) in P. smithi from the sheltered beach and bimodal orientation (partly scototactic and partly sun compass) in N. quadrimana. The behavioural differences observed are likely developed as risk-related: sandhoppers burrow in the substrate and are less exposed to occasional swash, while beach-hoppers living in cast wrack displayed the ability of swimming quickly towards a floating object, increasing the likelihood of being passively carried from one beach to another. Different ecological groups such “sandhoppers” and “beach-hoppers” showed different behavioural patterns. The consideration of behavioural answers to swash risk highlighted the possibility of the connectivity of talitrid populations across fragmented beaches.

Polarized Light Sensitivity and Orientation in Coral Reef Fish Post-Larvae

Recent studies of the larvae of coral-reef fishes reveal that these tiny vertebrates possess remarkable swimming capabilities, as well as the ability to orient to olfactory, auditory, and visual cues. While navigation according to reef-generated chemicals and sounds can significantly affect dispersal, the effect is limited to the vicinity of the reef. Effective long-distance navigation requires at least one other capacity–the ability to maintain a bearing using, for example, a sun compass. Directional information in the sun’s position can take the form of polarized-light related cues (i.e., e-vector orientation and percent polarization) and/or non-polarized-light related cues (i.e., the direct image of the sun, and the brightness and spectral gradients). We examined the response to both types of cues using commercially-reared post-larvae of the spine-cheeked anemonefish Premnas biaculeatus. Initial optomotor trials indicated that the post-larval stages are sensitive to linearly polarized light. Swimming directionality was then tested using a Drifting In-Situ Chamber (DISC), which allowed us to examine the response of the post-larvae to natural variation in light conditions and to manipulated levels of light polarization. Under natural light conditions, 28 of 29 post-larvae showed significant directional swimming (Rayleigh’s test p<0.05, R = 0.74±0.23), but to no particular direction. Swimming directionality was positively affected by sky clarity (absence of clouds and haze), which explained 38% of the observed variation. Moreover, post-larvae swimming under fully polarized light exhibited a distinct behavior of tracking the polarization axis, as it rotated along with the DISC. This behavior was not observed under partially-polarized illumination. We view these findings as an indication for the use of sun-related cues, and polarized light signal in specific, by orienting coral-reef fish larvae.

Following the sun: a mathematical analysis of the tracks of clock-shifted homing pigeons.

We analysed the tracks of clock-shifted pigeons from six releases to determine how they cope with the conflict between their sun compass and other navigational cues. Time-lag embedding was used to calculate the short-term correlation dimension, a parameter that reflects the complexity of the navigational system, and with it, the number of factors involved. Initially, while pigeons were still at the release site, the short-term correlation dimension was low; it increased as the birds left the site, indicating that the birds were now actively navigating. Clock-shifted pigeons showed more scatter than the control birds, and their short-term correlation dimension became significantly smaller than that of the controls, remaining lower until the experimental birds reached their loft. This difference was small, but consistent, and suggests a different rating and ranking of the navigational cues. Clock-shifted pigeons do not seem to simply ignore the information from their manipulated sun compass altogether, but appear to merely downgrade it in favour of other cues, like their magnetic compass. This is supported by the observation that the final part of the tracks still showed a small deviation in the expected direction, indicating an effect of clock-shifting until the end of the homing flight.

Interactions of the polarization and the sun compass in path integration of desert ants

Desert ants, Cataglyphis fortis, perform large-scale foraging trips in their featureless habitat using path integration as their main navigation tool. To determine their walking direction they use primarily celestial cues, the sky's polarization pattern and the sun position. To examine the relative importance of these two celestial cues, we performed cue conflict experiments. We manipulated the polarization pattern experienced by the ants during their outbound foraging excursions, reducing it to a single electric field (e-)vector direction with a linear polarization filter. The simultaneous view of the sun created situations in which the directional information of the sun and the polarization compass disagreed. The heading directions of the homebound runs recorded on a test field with full view of the natural sky demonstrate that none of both compasses completely dominated over the other. Rather the ants seemed to compute an intermediate homing direction to which both compass systems contributed roughly equally. Direct sunlight and polarized light are detected in different regions of the ant's compound eye, suggesting two separate pathways for obtaining directional information. In the experimental paradigm applied here, these two pathways seem to feed into the path integrator with similar weights.

Circadian clock and sun compass orientation in hatchlings of the turtle Eretmochelys imbricata at Sisal, Yucatán, México

The sun compass orientation implies a circadian clock and the sun’s azimuth in order to establish a direction. This behavior has been observed in a diversity of invertebrate and vertebrate species including reptiles. Shifting an organism’s internal clock by a given period of time (via alterations in photoperiod) helps to demonstrate the presence of a sun compass and circadian clock mechanisms. This study aims to test whether a sun compass orientation mechanism exists in hatchlings of the hawksbill turtle Eretmochelys imbricata at the shore of Sisal, Yucatán, México. In order to mask the magnetic sensitivity, turtles were observed with and without a neodymium magnet attached to their carapaces. One group of animals was held in regular LD, while another group was maintained for three days in a 6- h-delayed LD. Observations were made by photographs in an open circular arena near the shore. Results obtained from these observations indicate that hatchlings exposed to a 6- h-delayed LD show a difference in angular direction of near 60° and that magnets do not change such difference. Swimming activity recorded during the first four days after hatching indicates an organized crepuscular rhythm. The implications of multiple orientation mechanisms in these species and conservation efforts are discussed.

MAGNETS AND PIGEON ORIENTATION

SUMMARY Two experiments of KEETON (1971), which aimed at verifying the effect of magnetic stimuli perceived during flight on the orientation of homing pigeons, had left some open questions, in particular the very small effect on homing performance, even when there was a considerable disturbance of initial orientation. These experiments were repeated using more rigorous methods. Adult pigeons equipped with bar magnets showed a complete initial disorientation when released under overcast skies. However, contrary to the findings reported by KEETON, the same magnets had no effect when the releases were performed in sunny conditions, even when 3-month-old inexperienced pigeons were used. Homing performance was not influenced in an appreciable way, even though, in three out of four experiments carried out when the sun was not visible, the total cloud cover extended over a wide area and lasted for a long time so excluding the use of the sun compass for the greater part of the homing flights.

Do sandhoppers use the skylight polarization as a compass cue?

Investigations carried out in the 1950s on the use of polarized light by sandhoppers as a compass reference did not reach convincing results. Therefore, polarized light compass orientation in the sandhopper Talitrus saltator seems to be a traditional attribute more than a solid demonstration. Our tests carried out under artificial and natural conditions of illumination using different polarizing and neutral density (grey) filters demonstrated that T. saltator perceives polarized light; however, it does not use the skylight polarized light as a cue for menotactic orientation. However, since the sky spectral and luminance gradients were not completely eliminated in our tests, a possible influence of these two celestial factors of orientation could still be present. Therefore, we conclude that this species, in this experimental paradigm at least, does not use a polarized light compass mechanism, despite a very good sun compass system of orientation.

Sun Compass Orientation Helps Coral Reef Fish Larvae Return to Their Natal Reef

Reef fish sustain populations on isolated reefs and show genetic diversity between nearby reefs even though larvae of many species are swept away from the natal site during pelagic dispersal. Retention or recruitment to natal reefs requires orientation capabilities that enable larvae to find their way. Although olfactory and acoustically based orientation has been implicated in homing when larvae are in the reef’s vicinity, it is still unclear how they cope with greater distances. Here we show evidence for a sun compass mechanism that can bring the larvae to the vicinity of their natal reef. In a circular arena, pre-settlement larvae and early settlers (<24 hours) of the cardinal fish, Ostorhinchus doederleini, showed a strong SSE directional swimming response, which most likely has evolved to compensate for the locally prevailing large scale NNW current drift. When fish were clock-shifted 6 hours, they changed their orientation by ca. 180° as predicted by the tropical sun curve at One Tree Island, i.e. they used a time-compensated sun compass. Furthermore, the fish oriented most consistently at times of the day when the sun azimuth is easy to determine. Microsatellite markers showed that the larvae that had just arrived at One Tree Island genetically belonged to either the local reef population or to Fitzroy Reef located 12 kilometers to the SSE. The use of a sun compass adds a missing long-distance link to the hierarchy of other sensory abilities that can direct larvae to the region of origin, including their natal reef. Predominant local recruitment, in turn, can contribute to genetic isolation and potential speciation.

Y-axis orientation in the South American freshwater snail species Chilina patagonica (Gastropoda: Chilinidae)

Y-axis orientation, a movement perpendicular to the shore or coastline, enables aquatic animals to stay in a preferred zone in generally unstable habitats. Such behaviour is a widespread phenomenon in many freshwater and intertidal animal taxa. In the present study, an arena approach was used to test the orientation response of pulmonate freshwater snails. Using this experimental design, Y-axis orientation was shown for the first time in a freshwater snail species, the riverine Chilina patagonica. Some cues, potentially mediating Y-axis orientation, appeared to play no role in the shown orientation behaviour, such as chemical, gravity and humidity cues or a sun compass. Magnetic cues, however, could not be excluded. Since no significant differences in orientation were detected between different size classes in C. patagonica, orientation behaviour may not vary substantially throughout the snail's life history. In contrast to C. patagonica, no consistent orientation response was seen in the related lacustrine species Chilina llanquihuensis. The adaptation of C. patagonica to exhibit orientation along the Y-axis may be driven by the avoidance of high velocities in deeper water.

Coldness Triggers Northward Flight in Remigrant Monarch Butterflies

Each fall, eastern North American monarch butterflies (Danaus plexippus) migrate from their northern range to their overwintering grounds in central Mexico. Fall migrants are in reproductive diapause, and they use a time-compensated sun compass to navigate during the long journey south. Eye-sensed directional cues from the daylight sky (e.g., the horizontal or azimuthal position of the sun) are integrated in the sun compass in the midbrain central complex region. Sun compass output is time compensated by circadian clocks in the antennae so that fall migrants can maintain a fixed flight direction south. In the spring, the same migrants remigrate northward to the southern United States to initiate the northern leg of the migration cycle. Here we show that spring remigrants also use an antenna-dependent time-compensated sun compass to direct their northward flight. Remarkably, fall migrants prematurely exposed to overwintering-like coldness reverse their flight orientation to the north. The temperature microenvironment at the overwintering site is essential for successful completion of the migration cycle, because without cold exposure, aged migrants continue to orient south. Our discovery that coldness triggers the northward flight direction in spring remigrants solves one of the long-standing mysteries of the monarch migration.

DISAPPEARING HOMING PIGEON MYSTERY SOLVED

Homing pigeons are usually remarkably efficient navigators; however, on rare occasions, things go drastically wrong. So, when Jon Hagstrum of the US Geological Survey (USGS) read in his local newspaper about two races during which pigeons had been lost in 1998, he was reminded of a lecture by Bill Keeton that he had heard years before as an undergraduate at Cornell University. Keeton had been studying how birds successfully navigated from distant and unfamiliar release sites. However, the birds almost always had problems selecting the correct bearing home when released from three local sites. According to Keeton, pigeons released at Castor Hill and the town of Weedsport consistently took the same wrong turn when they departed. Meanwhile, birds that were released from Jersey Hill tended to head off in random directions, but with one exception: all of the birds that departed from the hill on 13 August 1969 returned home successfully, having taken the correct bearing. Explaining that Keeton had already ruled out the possibility of a disturbance in the local magnetic field, Hagstrum recalls, ‘Bill asked if we geologists had an idea what might be going on at these sites.’Several years after Keeton’s lecture, Hagstrum came up with a possible solution to the problem when he read that pigeons can hear incredibly low frequency ‘infrasound’. Explaining that infrasound – which can be generated by minute vibrations of the planet surface caused by waves deep in the ocean – travels for thousands of kilometres, Hagstrum wondered whether homing pigeons are listening for the distinctive low-frequency rumble of their loft area to find their bearing home. In which case, birds that could not hear the infrasound signal, because the release site was shielded from it in some way, could not get their bearing and would get lost. Hagstrum decided to investigate the meteorological conditions on the days of unsuccessful releases to find out if there was something in the air that could explain the pigeons’ disorientation (p. 687).Fortunately, Hagstrum had access to accurate temperature, wind direction and speed measurements taken at local weather stations on the days of the releases so that he could reconstruct the atmospheric conditions. Having successfully installed a complex acoustics program – HARPA – with the help of USGS computer scientist Larry Baker to reconstruct the atmospheric conditions, Hagstrum then calculated how infrasound travelled from the loft through the atmosphere, refracting through layers in the air and bouncing off the ground, to find out if Jersey Hill was shaded from the loft’s infrasound homing beacon and how the signal from the loft was channelled by the wind and local terrain to Castor Hill and Weedsport.Amazingly, on all of the days when the birds vanished from Jersey Hill, Hagstrum could see that the loft’s infrasonic signal was guided away from the ground and high into the atmosphere: the birds could not pick it up. However, on 13 August 1969, the atmospheric conditions were perfect and this time the infrasonic signal was guided directly to the Jersey Hill site. And when he calculated the paths that the loft’s infrasonic signal travelled to Castor Hill and Weedsport they also explained why the birds consistently took the wrong bearing. The terrain and winds had diverted the infrasound so that it approached the release site from the wrong direction, sending the birds off on the wrong bearing.Explaining that the birds must use the loft’s infrasonic homing beacon to get their bearing before setting the direction for their return flight according to their sun compass, Hagstrum says, ‘I am a bit surprised that after 36 years I finally answered Bill Keeton’s question to the Cornell Geology Department’, adding that he is particularly pleased that he was able to use Keeton’s own data to solve the mystery.

The depth of the honeybee's backup sun-compass systems

Honeybees have at least three compass mechanisms: a magnetic compass; a celestial or sun compass, based on the daily rotation of the sun and sun-linked skylight patterns; and a backup celestial compass based on a memory of the sun's movements over time in relation to the landscape. The interactions of these compass systems have yet to be fully elucidated, but the celestial compass is primary in most contexts, the magnetic compass is a backup in certain contexts, and the bees' memory of the sun's course in relation to the landscape is a backup system for cloudy days. Here we ask whether bees have any further compass systems, for example a memory of the sun's movements over time in relation to the magnetic field. To test this, we challenged bees to locate the sun when their known celestial compass systems were unavailable, that is, under overcast skies in unfamiliar landscapes. We measured the bees' knowledge of the sun's location by observing their waggle dances, by which foragers indicate the directions toward food sources in relation to the sun's compass bearing. We found that bees have no celestial compass systems beyond those already known: under overcast skies in unfamiliar landscapes, bees attempt to use their landscape-based backup system to locate the sun, matching the landscapes or skylines at the test sites with those at their natal sites as best they can, even if the matches are poor and yield weak or inconsistent orientation.

Combined archaeomagnetic and thermoluminescence study of a brick kiln excavated at Fontanetto Po (Vercelli, Northern Italy)

A combined archaeomagnetic and thermoluminescence study was carried out as part of a rescue archaeological excavation on a kiln discovered during the installation of methane gas pipelines beneath a rice field, along the southern border of Fontanetto Po village (Vercelli province, Italy). A total of 23 independent brick samples have been collected, oriented in situ with an inclinometer; the use of magnetic and sun compass was not possible due to the existence of metallic tubes beneath the kiln and a plastic cover above it. Standard archaeomagnetic procedures have been used for the determination of the archaeomagnetic inclination and absolute geomagnetic intensity. Stepwise thermal demagnetization shows a very stable characteristic remanent magnetization and the calculated mean inclination of the 23 samples is I = 65.3° with α95 = 2.4° and k = 156. Archaeointensity experiments have been performed using the classical Thellier method as modified by Coe, with regular partial thermoremanent magnetization (pTRM) checks. The cooling rate and remanence anisotropy effects upon thermoremanent magnetization (TRM) have been investigated in all the specimens. A total of 19 archaeointensity determinations (at specimen level) that correspond to linear NRM–TRM plots were used for the calculation of the site mean archaeointensity that is 46.4 ± 2.9 μT. Archaeomagnetic dating results show two possible dating intervals for the last 1000 years, calculated at 95% confidence interval: a first one from 1511 to 1614 AD, and a second one from 1768 to 1872 AD. Thermoluminescence (TL) study has been also performed on two brick samples from the kiln's internal wall, using conventional laboratory procedures. According to the thermoluminescence results the kiln's last usage lies between 1796 and 1914 AD. This age is in good agreement with the second dating interval obtained by the archaeomagnetic analysis. The combined archaeomagnetic and thermoluminescence results suggest that the last firing of the kiln could have occurred between the end of the 18th century and the beginning of 20th century.

Behaviour of Talitrus saltator (Crustacea: Amphipoda) on a rehabilitated sandy beach on the European Atlantic Coast (Portugal)

Environmental and human controls are widely accepted as the main structuring forces of the macrofauna communities on sandy beaches. A population of the talitrid amphipod Talitrus saltator (Montagu, 1808) was investigated on an exposed sandy beach on the Atlantic coast of Portugal (Leirosa beach) to estimate orientation capabilities and endogenous rhythms in conditions of recent changes in the landscape (artificial reconstruction of the foredune) and beach morphodynamics (stabilization against erosion from the sea). We tested sun orientation of talitrids on the beach and recorded their locomotor activity rhythms under constant conditions in the laboratory. The orientation data were analysed with circular statistics and multiple regression models adapted to angular distributions, to highlight the main factors and variables influencing the variation of orientation. The talitrids used the sun compass, visual cues (landscape and sun visibility) to orient and the precision of orientation varied according to the tidal regime (rising or ebbing tides). A well-defined free-running rhythm (circadian with in addition a bimodal rhythmicity, likely tidal) was highlighted in this population. This showed a stable behavioural adaptation on a beach that has experienced a process of artificial stabilization of the dune through nourishment actions over a decade. Monitoring the conditions of such dynamic environments and the resilience capacity of the inhabiting macroinfauna is a main challenge for sandy beach ecologists.

Anatomical basis of sun compass navigation II: The neuronal composition of the central complex of the monarch butterfly

AbstractEach fall, eastern North American monarch butterflies in their northern range undergo a long‐distance migration south to their overwintering grounds in Mexico. Migrants use a time‐compensated sun compass to determine directionality during the migration. This compass system uses information extracted from sun‐derived skylight cues that is compensated for time of day and ultimately transformed into the appropriate motor commands. The central complex (CX) is likely the site of the actual sun compass, because neurons in this brain region are tuned to specific skylight cues. To help illuminate the neural basis of sun compass navigation, we examined the neuronal composition of the CX and its associated brain regions. We generated a standardized version of the sun compass neuropils, providing reference volumes, as well as a common frame of reference for the registration of neuron morphologies. Volumetric comparisons between migratory and nonmigratory monarchs substantiated the proposed involvement of the CX and related brain areas in migratory behavior. Through registration of more than 55 neurons of 34 cell types, we were able to delineate the major input pathways to the CX, output pathways, and intrinsic neurons. Comparison of these neural elements with those of other species, especially the desert locust, revealed a surprising degree of conservation. From these interspecies data, we have established key components of a conserved core network of the CX, likely complemented by species‐specific neurons, which together may comprise the neural substrates underlying the computations performed by the CX. J. Comp. Neurol. 521:267–298, 2013. © 2012 Wiley Periodicals, Inc.

Anatomical basis of sun compass navigation II: The neuronal composition of the central complex of the monarch butterfly

Each fall, eastern North American monarch butterflies in their northern range undergo a long-distance migration south to their overwintering grounds in Mexico. Migrants use a time-compensated sun compass to determine directionality during the migration. This compass system uses information extracted from sun-derived skylight cues that is compensated for time of day and ultimately transformed into the appropriate motor commands. The central complex (CX) is likely the site of the actual sun compass, because neurons in this brain region are tuned to specific skylight cues. To help illuminate the neural basis of sun compass navigation, we examined the neuronal composition of the CX and its associated brain regions. We generated a standardized version of the sun compass neuropils, providing reference volumes, as well as a common frame of reference for the registration of neuron morphologies. Volumetric comparisons between migratory and nonmigratory monarchs substantiated the proposed involvement of the CX and related brain areas in migratory behavior. Through registration of more than 55 neurons of 34 cell types, we were able to delineate the major input pathways to the CX, output pathways, and intrinsic neurons. Comparison of these neural elements with those of other species, especially the desert locust, revealed a surprising degree of conservation. From these interspecies data, we have established key components of a conserved core network of the CX, likely complemented by species-specific neurons, which together may comprise the neural substrates underlying the computations performed by the CX.

The skylight gradient of luminance helps sandhoppers in sun and moon identification

To return to the ecologically optimal zone of the beach, the sandhopper Talitrus saltator (Montagu) maintains a constant sea-land direction based on the sun and moon compasses. In this study, we investigated the role of the skylight gradient of luminance in sun and moon identification under natural and artificial conditions of illumination. Clock-shifted (inverted) sandhoppers tested under the sun (during their subjective night) and under the full moon (during their subjective day) exhibit orientation in accordance with correct identification of the sun and the moon at night. Tested in artificial conditions of illumination at night without the artificial gradient of luminance, the artificial astronomical cue is identified as the moon even when the conditions of illumination allow sun compass orientation during the day. When the artificial gradient of luminance is added, the artificial astronomical cue is identified as the sun. The role of the sky gradient of luminance in sun and moon identification is discussed on the basis of present and past findings.

General anesthesia alters time perception by phase shifting the circadian clock

Following general anesthesia, people are often confused about the time of day and experience sleep disruption and fatigue. It has been hypothesized that these symptoms may be caused by general anesthesia affecting the circadian clock. The circadian clock is fundamental to our well-being because it regulates almost all aspects of our daily biochemistry, physiology, and behavior. Here, we investigated the effects of the most common general anesthetic, isoflurane, on time perception and the circadian clock using the honeybee (Apis mellifera) as a model. A 6-h daytime anesthetic systematically altered the time-compensated sun compass orientation of the bees, with a mean anticlockwise shift in vanishing bearing of 87° in the Southern Hemisphere and a clockwise shift in flight direction of 58° in the Northern Hemisphere. Using the same 6-h anesthetic treatment, time-trained bees showed a delay in the start of foraging of 3.3 h, and whole-hive locomotor-activity rhythms were delayed by an average of 4.3 h. We show that these effects are all attributable to a phase delay in the core molecular clockwork. mRNA oscillations of the central clock genes cryptochrome-m and period were delayed by 4.9 and 4.3 h, respectively. However, this effect is dependent on the time of day of administration, as is common for clock effects, and nighttime anesthesia did not shift the clock. Taken together, our results suggest that general anesthesia during the day causes a persistent and marked shift of the clock effectively inducing "jet lag" and causing impaired time perception. Managing this effect in humans is likely to help expedite postoperative recovery.