Compass Mechanism Research Articles

The Effect of Spin Relaxation on Magnetic Compass Sensitivity in ErCry4a.

This study explores the impact of thermal motion on the magnetic compass mechanism in migratory birds, focusing on the radical pair mechanism within cryptochrome photoreceptors. The coherence of radical pairs, crucial for magnetic field inference, is curbed by spin relaxation induced by intra-protein motion. Molecular dynamics simulations, density-functional-theory-based calculations, and spin dynamics calculations were employed, utilizing Bloch-Redfield-Wangsness (BRW) relaxation theory, to investigate compass sensitivity. Previous research hypothesized that European robin's cryptochrome 4a (ErCry4a) optimized intra-protein motion to minimize spin relaxation, enhancing magnetic sensing compared to the plant Arabidopsis thaliana's cryptochrome 1 (AtCry1). Different correlation times of the nuclear hyperfine coupling constants in AtCry1 and ErCry4a were indeed found, leading to distinct radical pair recombination yields in the two species, with ErCry4a showing optimized sensitivity. However, this optimization is likely negligible in realistic spin systems with numerous nuclear spins. Beyond insights in magnetic sensing, the study presents a detailed method employing molecular dynamics simulations to assess for spin relaxation effects on chemical reactions with realistically modelled protein motion, relevant for studying radical pair reactions at finite temperature.

Stay the course: maintenance of consistent orientation by commuting penguins both underwater and at the water surface

Many marine vertebrates traverse more than hundreds of kilometres of the ocean. To efficiently achieve such long-distance movements, the ability to maintain orientation in a three-dimensional space is essential; however, it remains unevaluated in most species. In this study, we examined the bearing distributions of penguins undertaking long-distance foraging trips and compared their bearing consistency between underwater and at the water surface, as well as between night and day, to quantify their orientation ability. The subject species, king penguins, Aptenodytes patagonicus, from Possession Island, Crozet archipelago (46°25′S, 51°45′E; January to March 2011), showed high bearing consistency both during dives and at the water surface whilst commuting towards/from their main foraging area, the Antarctic polar front. Their bearing consistency was particularly high during and after shallow dives, irrespective of the time of day. Meanwhile, their bearings tended to vary during and after deep dives, particularly in the middle of the trip, probably owing to underwater foraging movements. However, the overall directions of deep dives during the commuting phases were similar to those of shallow dives and post-dive periods at the water surface. These findings indicate that king penguins employ compass mechanism(s) that are equivalently reliable both underwater and at the water surface, at any time of the day. This orientation ability appears to enable them to achieve long-distance trips under strong temporal constraints. Further studies on the fine-scale bearing distributions of other diving vertebrates are needed to better understand movement strategies in marine environments.

Simulating geomagnetic bird navigation using novel high-resolution geomagnetic data

Birds rely on precise navigational mechanisms, especially for long-distance migrations. One debated mechanism is their use of the geomagnetic field. It is unclear if and how different species of birds are using intensity or inclination (or both) for navigation. Previous geomagnetic modelling research is based on static geomagnetic data despite a temporally and spatially varying geomagnetic field. Animals supposedly have a high sensitivity to those changes of the geomagnetic field. In order to understand how birds respond in real-time to its temporal variation, we need to use accurate geomagnetic information linked to the position of the bird through co-location in space and time.We developed a data-driven approach to simulate geomagnetic migratory strategies, using, for the first time, accurate contemporaneous geomagnetic data obtained from Swarm satellites of the European Space Agency. We created biased correlated random walk models which were based on both GPS data from greater white-fronted geese (Anser albifrons) during fall migration between north-west Russia and central Europe and contemporaneous satellite geomagnetic data. Different strategies of geomagnetic navigation associated with different geomagnetic values were translated into probability surfaces, built from geomagnetic data, and included into the random walk models. To evaluate which strategy was most likely, we compared the measured GPS trajectories to the simulated trajectories using different trajectory similarity measurements. We propose this as an approach to track many bird species for future comparative studies.We found that navigational strategies in these geese using magnetic intensity were closer to the observed data than those using inclination. This was the case in 80% of the best models and is an indication that it should be more beneficial for these geese to use intensity over inclination. Additionally, our results supported results from a previous study, that navigation based on taxis and compass mechanisms were more similar to the observed data than other mechanisms. We therefore suggest that these geese may use a combination of these strategies for navigation at a broad-scale. Overall, it seems likely that for successful navigation to the target location more than one mechanism is necessary; indicating a multifactorial navigation mechanism of these migratory geese in the study area. The satellite geomagnetic data are available at a higher temporal resolution and the use significantly improved the fit of the modelled simulations in comparison to the modelled geomagnetic data. Therefore, using annotated geomagnetic data could greatly improve the modelling of animal geomagnetic navigation in future research.

Autumn migratory orientation and route choice in early and late dunlins Calidris alpina captured at a stopover site in Alaska.

ABSTRACTWe investigated the migratory orientation of early and late captured dunlins, Calidris alpina, by recording their migratory activity in circular orientation cages during autumn at a staging site in southwest Alaska and performed route simulations to the wintering areas. Two races of dunlins breeding in Alaska have different wintering grounds in North America (Pacific Northwest), and East Asia. Dunlins caught early in autumn (presumably Calidris alpina pacifica) oriented towards their wintering areas (east-southeast; ESE) supporting the idea that they migrate nonstop over the Gulf of Alaska to the Pacific Northwest. We found no difference in orientation between adult and juveniles, nor between fat and lean birds or under clear and overcast skies demonstrating that age, energetic status and cloud cover did not affect the dunlins’ migratory orientation. Later in autumn, we recorded orientation responses towards south-southwest suggesting arrival of the northern subspecies Calidris alpina arcticola at our site. Route simulations revealed multiple compass mechanisms were compatible with the initial direction of early dunlins wintering in the Pacific Northwest, and for late dunlins migrating to East Asia. Future high-resolution tracking would reveal routes, stopover use including local movements and possible course shifts during migration from Alaska to wintering sites on both sides of the north Pacific Ocean.

The role of the antennae in the compass-based orientation of the equatorial sandhopper Talorchestia martensii Weber (Crustacea Amphipoda)

The equatorial sandhopper Talorchestia martensii uses the sun, the moon and the natural magnetic field as orienting compass references. In some arthropod species, the antennae are important for time compensated solar orientation. Therefore, we evaluated the role of antennae in solar, lunar and magnetic compass orientation in T. martensii. We released intact and antennaeless individuals in a Plexiglas bowl in the dark, and under the sun or moon, with and without the horizontal component of the magnetic field and recorded their orientation. For the tests under the moon, sandhoppers were released in conditions of modest azimuthal speed (10–15°/hr) and high azimuthal speed (≈ 59°/hr) of the moon. No significant difference in the orienting behaviour between antennaeless and intact individuals was observed. Therefore, the antennae do not seem to be involved in the sun or moon compass mechanisms of T. martensii. The photopositive responses showed by individuals released under high azimuthal speed of the moon and with the horizontal component of the magnetic field zeroed, indicate that the moon is probably not used as a chronometric compass reference in this species because of the variations in its azimuthal speed. This suggests a mechanism of photomenotaxis and therefore, a difference from sandhoppers from temperate latitudes that use a moon compass.

Anatomical and ultrastructural analysis of the posterior optic tubercle in the locust Schistocerca gregaria

Locusts, like other insects, partly rely on a sun compass mechanism for spatial orientation during seasonal migrations. To serve as a useful guiding cue throughout the day, however, the sun's apparent movement has to be accounted for. In locusts, a neural pathway from the accessory medulla, the circadian pacemaker, via the posterior optic tubercle, to the protocerebral bridge, part of the internal sky compass, has been proposed to mediate the required time compensation. Toward a better understanding of neural connectivities within the posterior optic tubercle, we investigated this neuropil using light and electron microscopy. Based on vesicle content, four types of synaptic profile were distinguished within the posterior optic tubercle. Immunogold labeling showed that pigment-dispersing hormone immunoreactive neurons from the accessory medulla, containing large dense-core vesicles, have presynaptic terminals in the posterior optic tubercle. Ultrastructural examination of two Neurobiotin-injected tangential neurons of the protocerebral bridge revealed that these neurons are postsynaptic in the posterior optic tubercle. Our data, therefore, support a role of the posterior optic tubercles in mediating circadian input to the insect sky compass.

A red knot as a black swan: how a single bird shows navigational abilities during repeat crossings of the Greenland Icecap

Despite the wealth of studies on seasonal movements of birds between southern nonbreeding locations and High Arctic breeding locations, the key mechanisms of navigation during these migrations remain elusive. A flight along the shortest possible route between pairs of points on a sphere (‘orthodrome’) requires a bird to be able to assess its current location in relation to its migration goal and to make continuous adjustment of heading to reach that goal. Alternatively, birds may navigate along a vector with a fixed orientation (‘loxodrome’) based on magnetic and/or celestial compass mechanisms. Compass navigation is considered especially challenging for summer migrations in Polar regions, as continuous daylight and complexity in the geomagnetic field may complicate the use of both celestial and magnetic compasses here. We examine the possible use of orientation mechanisms during migratory flights across the Greenland Icecap. Using a novel 2 g solar‐powered satellite transmitter, we documented the flight paths travelled by a female red knotCalidris canutus islandicaduring two northward and two southward migrations. The geometry of the paths suggests that red knots can migrate across the Greenland Icecap along the shortest‐, orthodrome‐like, path instead of the previously suggested loxodrome path. This particular bird's ability to return to locations visited in a previous year, together with its sudden course changes (which would be appropriate responses to ambient wind fields), suggest a map sense that enables red knots to determine location, so that they can tailor their route depending on local conditions.

Searching for magnetic compass mechanism in pigeon retinal photoreceptors.

Migratory birds can detect the direction of the Earth’s magnetic field using the magnetic compass sense. However, the sensory basis of the magnetic compass still remains a puzzle. A large body of indirect evidence suggests that magnetic compass in birds is localized in the retina. To confirm this point, an evidence of visual signals modulation by magnetic field (MF) should be obtained. In a previous study we showed that MF inclination impacts the amplitude of ex vivo electroretinogram (ERG) recorded from isolated pigeon retina. Here we present the results of an analysis of putative MF effect on one component of ERG, the photoreceptor’s response, isolated from the total ERG by adding sodium aspartate and barium chloride to the perfusion solution. Photoresponses were recorded from isolated retinae of domestic pigeons Columba livia. The retinal samples were placed in MF that was modulated by three pairs of orthogonal Helmholtz coils. Light stimuli (blue and red) were applied under two inclinations of MF, 0° and 90°. In all the experiments, preparations from two parts of retina were used, red field (with dominant red-sensitive cones) and yellow field (with relatively uniform distribution of cone color types). In contrast to the whole retinal ERG, we did not observe any effect of MF inclination on either amplitude or kinetics of pharmacologically isolated photoreceptor responses to blue or red half-saturating flashes. A possible explanations of these results could be that magnetic compass sense is localized in retinal cells other than photoreceptors, or that photoreceptors do participate in magnetoreception, but require some processing of compass information in other retinal layers, so that only whole retina signal can reflect the response to changing MF.

Atlantic Haddock (Melanogrammus aeglefinus) Larvae Have a Magnetic Compass that Guides Their Orientation.

SummaryAtlantic haddock (Melanogrammus aeglefinus) is a commercially important species of gadoid fish. In the North Sea, their main spawning areas are located close to the northern continental slope. Eggs and larvae drift with the current across the North Sea. However, fish larvae of many taxa can orient at sea using multiple external cues, including the Earth's magnetic field. In this work, we investigated whether haddock larvae passively drift or orient using the Earth's magnetic field. We observed the behavior of 59 and 102 haddock larvae swimming in a behavioral chamber deployed in the Norwegian North Sea and in a magnetic laboratory, respectively. In both in situ and laboratory settings, where the magnetic field direction was modified, haddock larvae significantly oriented toward the northwest. We conclude that haddock larvae orientation at sea is guided by a magnetic compass mechanism. These results have implications for retention and dispersal of pelagic haddock larvae.

Evidence for a southward autumn migration of nocturnal noctuid moths in central Europe.

Insect migrations are spectacular natural events and resemble a remarkable relocation of biomass between two locations in space. Unlike the well-known migrations of daytime flying butterflies, such as the painted lady (Vanessa cardui) or the monarch butterfly (Danaus plexippus), much less widely known are the migrations of nocturnal moths. These migrations - typically involving billions of moths from different taxa - have recently attracted considerable scientific attention. Nocturnal moth migrations have traditionally been investigated by light trapping and by observations in the wild, but in recent times a considerable improvement in our understanding of this phenomenon has come from studying insect orientation behaviour, using vertical-looking radar. In order to establish a new model organism to study compass mechanisms in migratory moths, we tethered each of two species of central European Noctuid moths in a flight simulator to study their flight bearings: the red underwing (Catocala nupta) and the large yellow underwing (Noctua pronuba). Both species had significantly oriented flight bearings under an unobscured view of the clear night sky and in the Earth's natural magnetic field. Red underwings oriented south-southeast, while large yellow underwings oriented southwest, both suggesting a southerly autumn migration towards the Mediterranean. Interestingly, large yellow underwings became disoriented on humid (foggy) nights while red underwings remained oriented. We found no evidence in either species for a time-independent sky compass mechanism as previously suggested for the large yellow underwing.

Use of sun compass orientation during natal dispersal in Blanding’s turtles: in situ field experiments with clock-shifting and disruption of magnetoreception

When hatchling freshwater turtles emerge from nests and first experience environmental stimuli, they primarily use visual cues to disperse toward nearby open horizons or far dark horizons. Within hours, hatchling Blanding’s turtles (Emydoidea blandingii) develop compass mechanisms to maintain their headings when the initial dispersal targets become invisible. We captured hatchling Blanding’s turtles during dispersal in natural habitat, attached a magnetic or non-magnet disk to each turtle, translocated them into an arena in a visually uniform field of corn, and measured their compass orientation (heading). Hatchlings from the magnet and no-magnet groups were evenly divided into two environmental chambers (6-h clock-shift or non-clock-shift) to create four experimental treatments. After 5 to 11 days hatchlings were re-released in the arena. If hatchlings used a time-compensated sun compass, then clock-shifting would cause a ~90° change in heading. If they used a geomagnetic compass, disruption of magnetoreception would cause wandering. If both compasses were used simultaneously or sequentially, we predicted a range of outcomes. All four treatment groups dispersed directionally during both trials, maintaining their prior headings in natural habitat except for the clock-shift treatment which changed heading ~90° as predicted. The ability of hatchlings to maintain prior headings despite the disruption of geomagnetism supports the absence, inactivity, or disregard of a geomagnetic compass. Only a time-compensated sun compass coupled with an internal clock was necessary and sufficient for hatchlings to maintain compass headings during natal dispersal when relocated from natural prairie habitat to a monoculture habitat with a relatively uniform visual horizon. Individuals moving long distances (e.g., migrating birds or dispersing salamanders) often maintain their movement headings using compass orientation (i.e., a geomagnetic or time-compensated sun compass). When hatchling freshwater turtles emerge from underground terrestrial nests they initiate dispersal in search of wetlands primarily based on visual horizon cues. Because such cues often become obscured by uneven terrain or dense vegetation and because straight-line travel is more efficient and less risky, hatchlings soon develop a mechanism of compass orientation to maintain their dispersal headings. We disrupted their ability to use magnetoreception by attaching magnets to their shells, manipulated their sense of time-of-day with clock-shifting, and then monitored their dispersal in a visually uniform field of mature corn. Our results demonstrated that a sun compass was necessary and sufficient for hatchlings with dispersal experience to maintain their dispersal headings when natural environmental cues were not visible.

Ten grams and 13,000\xa0km on the wing \u2013 route choice in willow warblers Phylloscopus trochilus yakutensis migrating from Far East Russia to East Africa

BackgroundHigh-latitude bird migration has evolved after the last glaciation, in less than 10,000–15,000 years. Migrating songbirds rely on an endogenous migratory program, encoding timing, fueling, and routes, but it is still unknown which compass mechanism they use on migration. We used geolocators to track the migration of willow warblers (Phylloscopus trochilus yakutensis) from their eastern part of the range in Russia to wintering areas in sub-Saharan Africa. Our aim was to investigate if the autumn migration route can be explained by a simple compass mechanism, based on celestial or geomagnetic information, or whether migration is undertaken as a sequence of differential migratory paths possibly involving a map sense. We compared the recorded migratory routes for our tracked birds with simulated routes obtained from different compass mechanisms.ResultsThe three tracked males were very similar in the routes they took to their final wintering sites in southern Tanzania or northern Mozambique, in their use of stopover sites and in the overall timing of migration. None of the tested compass mechanisms could explain the birds’ routes to the first stopover area in southwest Asia or to the destination in Southeast Africa without modifications. Our compass mechanism simulations suggest that the simplest scenarios congruent with the observed routes are based on either an inclination or a sun compass, assuming two sequential steps.ConclusionsThe birds may follow a magnetoclinic route coinciding closely with the tracks by first moving west, i.e. closer to the goal, and thereafter follow a constant apparent angle of inclination to the stopover site. An alternative would be to use the sun compass, but with time-adjustments along the initial part of the migration to the first stopover, and thereafter depart along a new course to the winter destination. A combination of the two mechanisms cannot be ruled out, but needs to be confirmed in future studies.

Cue-conflict experiments between magnetic and visual cues in dunlin Calidris alpina and curlew sandpiper Calidris ferruginea

Despite our extensive knowledge on various aspects of their lives, there has been limited investigation into the hierarchical relationships among different compass systems in shorebirds. The aim of this study was to investigate the relationship between magnetic and celestial compasses in two species of shorebirds, the curlew sandpiper (Calidris ferruginea; pre-breeding migration) and the dunlin (Calidris alpina; post-breeding migration) using cue-conflict experiments. Birds were captured in a Mediterranean stopover site, after which their magnetic orientation was determined under simulated overcast conditions at sunset using modified Emlen funnels fitted with infrared video cameras. Birds that demonstrated a well-defined directional preference were then exposed over two sunsets to conflicting directional information between the local geomagnetic field and the ±90° shifted band of maximum polarisation. These individuals were tested again for magnetic orientation at sunset in the same conditions as previous test, to determine whether their directional choices had changed after the cue-conflict. Our results showed that individuals from both species did not recalibrate their magnetic compass from visual cues after the cue-conflict, even though at least dunlins did not appear to completely disregard the information derived from celestial cues. This study is one of the few experimental studies on the migratory orientation of Charadriiformes and on the hierarchical relationships between the different compasses used by these birds during their extensive migratory movements. Migrating birds are able to use different compass mechanisms based on geomagnetic or celestial cues, and it seems reasonable to hypothesise that birds calibrate their various compasses to maintain the correct direction especially when the directional information does not agree. The hierarchy among different compasses has been studied largely on night migrating passerines, but it is still poorly understood. We investigated the hierarchy among geomagnetic and celestial cues (band of maximum polarisation) in two species of Charadriiformes by means of cue-conflict experiments. Our result showed that the geomagnetic cues have a dominant role in the orientation mechanisms of the studied species, even though the information derived from celestial cues did not appear to be completely disregarded.

Evidence for discrete solar and lunar orientation mechanisms in the beach amphipod, Talitrus saltator Montagu (Crustacea, Amphipoda)

Animals that use astronomical cues to orientate must make continuous adjustment to account for temporal changes in azimuth caused by Earth’s rotation. For example, the Monarch butterfly possesses a time-compensated sun compass dependent upon a circadian clock in the antennae. The amphipod Talitrus saltator possesses both a sun compass and a moon compass. We reasoned that the time-compensated compass mechanism that enables solar orientation of T. saltator is located in the antennae, as is the case for Monarch butterflies. We examined activity rhythms and orientation of sandhoppers with antennae surgically removed, or unilaterally occluded with black paint. Removing or painting the antennae did not affect daily activity rhythms or competence to orientate using the sun. However, when tested at night these animals were unable to orientate correctly to the moon. We subsequently measured circadian gene expression in the antennae and brain of T. saltator and show the clock genes period and cryptochrome 2 are rhythmically expressed in both tissues, reminiscent of other arthropods known to possess antennal clocks. Together, our behavioural and molecular data suggest that, T. saltator has anatomically discrete lunar and solar orientation apparatus; a sun compass, likely located in the brain and a moon compass in the antennae.

Assessing vector navigation in long-distance migrating birds

Birds migrating between distant locations regularly perform long continuous flights lasting several days. What compass mechanism they use is still a mystery. Here, we use a novel approach, applying an individual-based model, taking compass mechanisms based on celestial and geomagnetic information and wind into account simultaneously, to investigate what compass mechanism likely is used during long continuous flights and how wind drift or compensation affects the resulting tracks. We found that for the 6 cases of long continuous migration flights, the magnetoclinic route could best explain the route selection in all except one case compared with the alternative compass mechanisms. A flight strategy correcting for wind drift resulted most often in routes ending up closest to the predicted destinations. In only half of the cases could a time-compensated sun compass explain the migration routes observed with sufficient precision. Migration from Europe to the Siberian tundra was especially challenging to explain by one compass mechanism alone, suggesting a more complex navigation strategy. Our results speak in favor of a magnetic compass based on the angle of inclination used by birds during continuous long-distance migration flights, but also a capacity to detect and correct for drift caused by winds along the route.

The radical-pair mechanism as a paradigm for the emerging science of quantum biology

The radical-pair mechanism (RPM) was introduced in the 1960s to explain anomalously large EPR and NMR signals in chemical reactions of organic molecules. It has evolved to the cornerstone of spin chemistry, the study of the effect electron and nuclear spins have on chemical reactions, with the avian magnetic compass mechanism and the photosynthetic reaction center dynamics being prominent biophysical manifestations of such effects. In recent years the RPM was shown to be an ideal biological system where the conceptual tools of quantum-information science can be fruitfully applied. We will here review recent work making the case that RPM is indeed a major driving force of the emerging field of quantum biology.

Cues indicating location in pigeon navigation

Domesticated Rock Pigeons (Columba livia f. domestica) have been selected for returning home after being displaced. They appear to use many of the physical cue sources available in the natural environment for Map-and-Compass navigation. Two compass mechanisms that have been well documented in pigeons are a time-compensated sun compass and a magnetic inclination compass. Location-finding, or map, mechanisms have been more elusive. Visual landmarks, magnetic fields, odors, gravity and now also infrasound have been proposed as sources of information on location. Even in highly familiar locations, pigeons appear to neither use nor need landmarks and can even return to the loft while wearing frosted lenses. Direct and indirect evidence indicates magnetic field information influences pigeon navigation in ways that are consistent with magnetic map components. The role of odors is unclear; it might be motivational in nature rather than navigational. The influence of gravity must be further analyzed. Experiments with infrasound have been interpreted in the sense that they provide information on the home direction, but this hypothesis is inconsistent with the Map-and-Compass Model. All these factors appear to be components of a multifactorial system, with the pigeons being opportunistic, preferring those cues that prove most suitable in their home region. This has made understanding the roles of individual cues challenging.

Photoactivation of cryptochromes from Drosophila melanogaster and Sylvia borin: insight into the chemical compass mechanism by computational investigation.

Although behavioral studies demonstrated light-induced magnetoreception in the insect Drosophila melanogaster, gaining insight into the possibility that a radical-pair mechanism accounts for the magnetic response of the cryptochrome (DmCry1) is complicated by a number of factors. In addition, the mechanism of magnetoreception for the cryptochrome from the garden warbler bird Sylvia borin (gwCry1a), which demonstrated a long-lived radical pair by transient optical absorption measurements, has also not been rationalized. To assess potential feasibility of a radical-pair mechanism in DmCry1 and gwCry1a, formed by excitation and electron transfer between a Trp-triad and flavin adenine dinucleotide (FAD), further separated by electron transfer within the triad, we applied a combination of theoretical methods, including homology modeling and molecular dynamics (MD) for structure refinement, high-level ab initio theory, and MD simulations using a polarizable force-field for prediction of pKa and the electron transfer rate. Calculated excitation energies, followed by electron transfer in model compounds of DmCry1 that assume proton transfer in conjunction with electron transfer from Trp (W420) to FAD and the predicted pKa for the proximate residue to FAD (Cys416), support a radical-pair mechanism. Furthermore, free-energy and reorganization energies for the Trp-triad in DmCry1 demonstrate facile electron transfer, explained by the local protein environment and exposure to solvent, which in turn enables a large enough distance separation for the radical-pair partners. Results for gwCry1a demonstrated the importance of accounting for relaxed excited-state geometries in validating the first stage of a radical-pair mechanism. This work provides insight into the so-called chemical compass mechanism to explain magnetic-field sensing in DmCry1 and gwCry1a, expanding on previous work on the cyrptochrome from the plant Arabidopsis thaliana (Solov'yov et al. J. Am. Chem. Soc. 2012, 134, 18046-18052. Solov'yov et al., Sci. Rep. 2014, 4, 1-8.).

Salt concentration and solar orientation in two supralittoral sandhoppers: Talitrus saltator (Montagu) and Talorchestia ugolinii Bellan Santini and Ruffo.

The influence of salt concentration in the seawater on solar orientation in Talitrus saltator and Talorchestia ugolinii was studied in a confined environment (transparent plexiglass bowls). Sodium and calcium concentrations strongly affect both sea-land orientation and the sun compass mechanism in T.saltator, whereas the behaviour of T. ugolinii is less influenced. The absence of Na(+) does not influence the sun compass mechanism, but causes an inversion in the mean direction of orientation in T. saltator. In T. ugolinii, there was no influence on the compass mechanism for solar orientation and no inversion in the directional choice. In the absence of Ca(2+), a photonegative tendency was observed for T saltator together with marked reduction in the capacity to go in any direction. However, the effect of Ca(2+) absence on the orientation capacity of T. saltator is reversible and the orientation capacity can be reduced in a few minutes. The different behaviour of the two species of sandhoppers is discussed.

Retrodictive derivation of the radical-ion-pair master equation and Monte Carlo simulation with single-molecule quantum trajectories.

Radical-ion-pair reactions, central in photosynthesis and the avian magnetic compass mechanism, have been recently shown to be a paradigm system for applying quantum information science in a biochemical setting. The fundamental quantum master equation describing radical-ion-pair reactions is still under debate. Here we use quantum retrodiction to formally refine the theory put forward in the paper by Kominis [I. K. Kominis, Phys. Rev. E 83, 056118 (2011)]. We also provide a rigorous analysis of the measure of singlet-triplet coherence required for deriving the radical-pair master equation. A Monte Carlo simulation with single-molecule quantum trajectories supports the self-consistency of our approach.