Martin Vácha

Magnetic orientation in the mealworm beetle Tenebrio and the effect of light.

SUMMARY There is evidence for both light-dependent and light-independent mechanisms of magnetoreception of terrestrial animals. One example of a light-independent mechanism frequently cited is the magnetic compass of the mealworm beetle (Tenebrio molitor). We found that magnetoreception of the mealworm beetle per se is a replicable phenomenon but that, in contrast to earlier findings, Tenebrio only exhibited consistent magnetic compass orientation when light was present. The problem of whether the loss of orientation is due to a light-dependent magnetoreception mechanism or is instead an effect of motivation change is discussed.

Laboratory behavioural assay of insect magnetoreception: magnetosensitivity of Periplaneta americana.

SUMMARY A relatively simple all-laboratory behavioural assay of insect magnetoreception has been developed. We found non-conditioned reactions of American cockroach to the periodical shifts of the geomagnetic field. The movement activity of animals individually placed into Petri dishes was scored as a number of body turns. Test groups were exposed to a 90-min interval with the horizontal component of the geomagnetic field periodically rotated by 60° back and forth with 5 min periodicity. The number of body turns was compared with the preceding and following intervals and with the corresponding interval of the control group kept in the natural field. We obtained a significant increase in activity when changes in field were applied. Interestingly, the period of increased activity did not coincide precisely with the 90 min stimulation interval. The onset of animal restlessness was delayed by tens of minutes and persisted correspondingly after the stimulation stopped. A respective evaluation criterion was suggested and verified. Owing to its simplicity and minimal manipulation of the insects, together with low demands on the memory and motivation state of animals, the approach potentially may be used as a laboratory diagnostic tool indicating magnetoreception in insect neurophysiology research.

Cryptochrome 2 mediates directional magnetoreception in cockroaches

Significance The photosensitive protein Cryptochrome (Cry) is involved in the detection of magnetic fields (MFs) in Drosophila. However, Cry-dependent responses to natural MF intensities and to the direction of the MF vector have not been demonstrated previously in any insect. Birds, monarch butterflies, and many other species perceive the direction of geomagnetic field (GMF) lines, but the involvement of Cry has not been rigorously proven using genetic tools. In this study, by combining behavioral and genetic approaches, we provide the first unambiguous evidence to our knowledge of a Cry-dependent sensitivity to the direction of GMF in two cockroach species. Furthermore, by eye-covering experiments and by immunolocalization of a crucial mammalian-type Cry2 under the retina, we clearly show that the eye is an indispensable organ for the directional GMF response. The ability to perceive geomagnetic fields (GMFs) represents a fascinating biological phenomenon. Studies on transgenic flies have provided evidence that photosensitive Cryptochromes (Cry) are involved in the response to magnetic fields (MFs). However, none of the studies tackled the problem of whether the Cry-dependent magnetosensitivity is coupled to the sole MF presence or to the direction of MF vector. In this study, we used gene silencing and a directional MF to show that mammalian-like Cry2 is necessary for a genuine directional response to periodic rotations of the GMF vector in two insect species. Longer wavelengths of light required higher photon fluxes for a detectable behavioral response, and a sharp detection border was present in the cyan/green spectral region. Both observations are consistent with involvement of the FADox, FAD•− and FADH– redox forms of flavin. The response was lost upon covering the eyes, demonstrating that the signal is perceived in the eye region. Immunohistochemical staining detected Cry2 in the hemispherical layer of laminal glia cells underneath the retina. Together, these findings identified the eye-localized Cry2 as an indispensable component and a likely photoreceptor of the directional GMF response. Our study is thus a clear step forward in deciphering the in vivo effects of GMF and supports the interaction of underlying mechanism with the visual system.

American cockroaches prefer four cardinal geomagnetic positions at rest.

A specific behavior based on the ability to perceive the magnetic field has been described in several species: when resting or grazing animals take up a position placing their main body axis parallel with the North-South or East-West geomagnetic axes, which is referred to as magnetic alignment. The adaptive significance of this behavior remains an enigma. No experiments have been made to date to demonstrate conclusively whether that orientation will adequately change in response to an experimental rotation of geomagnetic axes which is a key step to prove the use of exclusively magnetic cues for orientation. In our study, we identified a preference regarding the four cardinal magnetic axes, i.e. a quadrimodal alignment both in natural and in 60deg rotated fields. The study gives the original evidence that quadrimodal alignment is a type of animal behavior specifically related to the cardinal magnetic axes of the Earth.

Effect of light wavelength spectrum on magnetic compass orientation in Tenebrio molitor

In many animal species, geomagnetic compass sensitivity has been demonstrated to depend on spectral composition of light to which moving animals are exposed. Besides a loss of magnetic orientation, cases of a shift in the compass direction by 90° following a change in the colour of light have also been described. This hitherto unclear phenomenon can be explained either as a change in motivation or as a side effect of a light-dependent reception mechanism. Among the invertebrates, the 90° shift has only been described in Drosophila. In this paper, another evidence of the phenomenon is reported. Learned compass orientation in the Tenebrio molitor was tested. If animals were trained to remember the magnetic position of a source of shortwave UV light and then tested in a circular arena in diffuse light of the same wavelength, they oriented according to the learned magnetic direction. If, however, they were tested in blue-green light after UV light training, their magnetic orientation shifted by 90° CW. This result is being discussed as one of a few cases of 90° shift reported to date, and as an argument corroborating the hypothesis of a close connection between photoreception and magnetoreception in insects.

Cattle on pastures do align along the North–South axis, but the alignment depends on herd density

Alignment is a spontaneous behavioral preference of particular body orientation that may be seen in various vertebrate or invertebrate taxa. Animals often optimize their positions according to diverse directional environmental factors such as wind, stream, slope, sun radiation, etc. Magnetic alignment represents the simplest directional response to the geomagnetic field and a growing body of evidence of animals aligning their body positions according to geomagnetic lines whether at rest or during feedings is accumulating. Recently, with the aid of Google Earth application, evidence of prevailing North–South (N–S) body orientation of cattle on pastures was published (Begall et al. PNAS 105:13451–13455, 2008; Burda et al. PNAS 106:5708–5713, 2009). Nonetheless, a subsequent study from a different laboratory did not confirm this phenomenon (Hert et al. J Comp Physiol A 197:677–682, 2011). The aim of our study was to enlarge the pool of independently gained data on this remarkable animal behavior. By satellite snapshots analysis and using blinded protocol we scored positions of 2,235 individuals in 74 herds. Our results are in line with the original findings of prevailing N–S orientation of grazing cattle. In addition, we found that mutual distances between individual animals within herds (herd density) affect their N–S preference—a new phenomenon giving some insight into biological significance of alignment.

Tenebrio beetles use magnetic inclination compass

Animals that guide directions of their locomotion or their migration routes by the lines of the geomagnetic field use either polarity or inclination compasses to determine the field polarity (the north or south direction). Distinguishing the two compass types is a guideline for estimation of the molecular principle of reception and has been achieved for a number of animal groups, with the exception of insects. A standard diagnostic method to distinguish a compass type is based on reversing the vertical component of the geomagnetic field, which leads to the opposite reactions of animals with two different compass types. In the present study, adults of the mealworm beetle Tenebrio molitor were tested by means of a two-step laboratory test of magnetoreception. Beetles that were initially trained to memorize the magnetic position of the light source preferred, during the subsequent test, this same direction, pursuant geomagnetic cues only. In the following step, the vertical component was reversed between the training and the test. The beetles significantly turned their preferred direction by 180°. Our results brought until then unknown original findings that insects, represented here by the T. molitor species, use—in contrast to another previously researched Arthropod, spiny lobster—the inclination compass.

The influence of a static, homogenous magnetic field (B=320 mT) on extracardiac pulsations of Tenebrio molitor pupae (Coleoptera: Tenebrionidae)

While investigating and describing interactions among living organisms and magnetic fields (MFs) it is imperative to lay great emphasis on independent reproducibility of published experimental results. Mutual confrontation of existing theoretical models with reliable data obtained under comparable conditions can aid gradual mapping of this hitherto badly organized and understood discipline of biology. The objective of our experiment, based on analysing extracardiac pulsations of the pupae of Tenebrio molitor under the influence of a MF, was to verify published data on allegedly accelerated development induced by a MF employing a different procedure. The obtained data are in agreement with a hypothesis of increased pupal metabolism during the period of MF activity. Furthermore, some dependence on the age of the pupae cannot be ruled out.

How do honeybees use their magnetic compass? Can they see the North?

While seeking food sources and routes back to their hive, bees make use of their advanced nervous and sensory capacities, which underlie a diverse behavioral repertoire. One of several honeybee senses that is both exceptional and intriguing is magnetoreception - the ability to perceive the omnipresent magnetic field (MF) of the Earth. The mechanism by which animals sense MFs has remained fascinating as well as elusive because of the intricacies involved, which makes it one of the grand challenges for neural and sensory biology. However, investigations in recent years have brought substantial progress to our understanding of how such magneto-receptor(s) may work. Some terrestrial animals (birds) are reported to be equipped even with a dual perception system: one based on diminutive magnetic particles - in line with the original model which has also always been hypothesized for bees - and the other one, as the more recent model describes, based on a sensitivity of some photochemical reactions to MF (radical-pair or chemical mechanism). The latter model postulates a close link to vision and supposes that the animals can see the position of the geomagnetic North as a visible pattern superimposed on the picture of the environment. In recent years, a growing body of evidence has shown that radical-pair magnetoreception might also be used by insects. It is realistic to expect that such evidence will inspire a re-examination and extension or confirmation of established views on the honeybee magnetic-compass mechanism. However, the problem of bee magnetoreception will not be solved at the moment that a receptor is discovered. On the contrary, the meaning of magnetoreception in insect life and its involvement in the orchestration of other senses is yet to be fully understood. The crucial question to be addressed in the near future is whether the compass abilities of the honeybee could suffer from radio frequency (RF) smog accompanying modern civilization and whether the fitness of this dominant pollinator might be affected by RF fields. The goal of this review is to provide an overview of the path that the behavioral research on honeybee magnetoreception has taken and to discuss it in the context of contemporary data obtained on other insects.

Tenebrio beetle pupae show a conditioned behavioural response to pulse rotations of a geomagnetic field

Abstract Pupae of holometabolous insects are not motionless and insensitive developmental stages. Their behavioural display is restricted to rotations or contractions of the abdomen in a range of movements from the clearly visible to the microscopic of the order of tenths of microns. Pupae react spontaneously and surprisingly sensitively to mechanical, light or sound stimuli. In the present study, reactions of yellow mealworm beetle (Tenebrio molitor, L.) pupae to a geomagnetic field rotation are examined. By means of a micromechanical recording technique, peaks of abdominal contractions are monitored before and after magnetic treatment and show that spontaneous behavioural reaction to a magnetic pulse is insignificant. Nevertheless, using negative reinforcement training, a conditioned magneto‐sensitive reaction is elicited. These surprising sensory and behavioural capacities of an insect pupa are discussed.