Use of a magnetic compass for Y-axis orientation in premetamorphic newts (Triturus boscai)

Experiments were carried out to investigate whether premetamorphic larvae of Boscas newt (Triturus boscai) are capable of using the geomagnetic field for Y-axis orientation (i.e., orientation toward and away from shore). Larvae were trained outdoor in two different training configurations, using one training tank aligned along the magnetic north–south axis, with shore facing north, and another training tank positioned with its length along the east–west axis, with shore located west. After training, premetamorphic newts were tested in an outdoor circular arena surrounded by a pair of orthogonally aligned cube-surface coils used to alter the alignment of the Earths magnetic field. Each newt was tested only once, in one of four magnetic field alignments: ambient magnetic field (i.e., magnetic north at North), and three altered fields (magnetic north rotated to East, West, South). Distributions of magnetic bearings from tested larvae indicated that they oriented bimodally along the magnetic direction of the trained Y-axis. These findings demonstrate that T. boscai larvae are sensitive to the geomagnetic field and can use it for orienting along a learned Y-axis. This study is the first to provide evidence of Y-axis orientation, accomplished by a magnetic compass, in larval urodeles.     

Toxicity of cypermethrin: hsp70 as a biomarker of response in transgenic Drosophila

Heat shock protein induction is often associated with a cellular response to a harmful environment or to adverse life conditions. The main aims of our study were (1) to evaluate the cytotoxic potential of cypermethrin; and (2) to investigate the suitability of stress-induced heat shock protein Hsp70 as a biomarker for environmental pollutants in transgenic Drosophila melanogaster (Hsp70-lacZ)Bg⁹. Different concentrations of cypermethrin (0.002, 0.2, 0.5 and 50.0 p.p.m.) were mixed with food. Third instar larvae of transgenic Drosophila melanogaster were allowed to feed on these mixtures for different time intervals (2, 4, 6, 12, 24 and 48h). Following feeding, hsp70 induction and tissue damage were evaluated. In the highest concentration treatment group (50 p.p.m.), 100% larval mortality was recorded after 12 h exposure. Hsp70 was found to be induced even at the lowest concentration (0.002 p.p.m.) of the insecticide, while tissue damage was observed in the larvae exposed for 48 h. While an insignificant decline in hsp70 expression was observed in the larvae exposed to cypermethrin at a dietary concentration of 0.002 p.p.m. after 48 h compared with those exposed for 24 h, in the next two higher concentrations of the toxicant, a similar but significant decline in hsp70 expression was evident in the exposed larvae after 48 h. The present study reveals the cytotoxic potential of cypermethrin and further proposes that hsp70 induction in transgenic Drosophila melanogaster could be used as a sensitive biomarker in risk assessment.     

Short-term hardening effects on survival of acute and chronic cold exposure by Drosophila melanogaster larvae

We quantified the variation and plasticity in cold tolerance among four larval stages of four laboratory strains of Drosophila melanogaster in response to both acute (<2 h of cold exposure) and chronic (7 h of cold exposure) cold exposure. We observed significant differences in basal cold tolerance between the strains and among larval stages. Early larval instars were generally more tolerant of acute cold exposures than third-instar larvae. However, wandering larvae were more tolerant of chronic cold exposures than the other stages. Early stages also displayed a more pronounced rapid cold-hardening response than the later stages. Heat pre-treatment did not confer a significant increase in cold tolerance to any of the strains at any stage, pointing to different mechanisms being involved in resolving heat- and cold-elicited damage. However, when heat pre-treatment was combined with rapid cold-hardening as sequential pre-treatments, both positive (heat first) and negative (heat second) effects on cold tolerance were observed. We discuss possible mechanisms underlying cold-hardening and the effects of acute and chronic cold exposures.     

Orientation and navigation in Amphibia

Aquatic and terrestrial amphibians integrate acoustic, magnetic, mechanical, olfactory and visual directional information into a redundant-multisensory orientation system. The sensory information is processed to accomplish homing following active or passive displacement by either path integration, beaconing, pilotage, compass orientation or true navigation. There is evidence for two independent compass systems, a time-compensated compass based on celestial cues and a light-dependent magnetic inclination compass. Beaconing along acoustic or olfactory gradients emanating from the home site, as well as pilotage along fixed visual landmarks also form an important part in the behaviour of many species. True navigation has been shown in only one species, the aquatic salamander Notophthalmus viridescens. Evidence on the nature of the navigational map obtained so far is compatible with the magnetic map hypothesis.     

Use of a light-dependent magnetic compass for y-axis orientation in European common frog (Rana temporaria) tadpoles

We provide evidence for the use of a magnetic compass for y-axis orientation (i.e., orientation along the shore-deep water axis) by tadpoles of the European common frog (Rana temporaria). Furthermore, our study provides evidence for a wavelength-dependent effect of light on magnetic compass orientation in amphibians. Tadpoles trained and then tested under full-spectrum light displayed magnetic compass orientation that coincided with the trained shore-deep water axes of their training tanks. Conversely, tadpoles trained under long-wavelength (≥500 nm) light and tested under full-spectrum light, and tadpoles trained under full-spectrum light and tested under long-wavelength (≥500 nm) light, exhibited a 90° shift in magnetic compass orientation relative to the trained y-axis direction. Our results are consistent with earlier studies showing that the observed 90° shift in the direction of magnetic compass orientation under long-wavelength (≥500 nm) light is due to a direct effect of light on the underlying magnetoreception mechanism. These findings also show that wavelength-dependent effects of light do not compromise the function of the magnetic compass under a wide range of natural lighting conditions, presumably due to a large asymmetry in the relatively sensitivity of antagonistic short- and long-wavelength inputs to the light-dependent magnetic compass.     

Developmental studies on Drosophila melanogaster glutathione s-transferase and its induction by oxadiazolone

Glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene was detected in various developmental stages of Drosophila melanogaster. The specific activity of the enzyme was 110, 35, 25 and 15 nmol/min/mg protein in crude extracts prepared from eggs, larvae, pupae and adult stages respectively. The enzymes from larval, pupal and adult stages were purified and compared. Incorporation of the widely used herbicide oxadiazolone at concentrations of 375 and 563 part/million into the culture media caused 4- and 2.5-fold increase in the enzyme activity in pupal and adult stages respectively.     

How Nemo finds home: the neuroecology of dispersal and of population connectivity in larvae of marine fishes

Nearly all demersal teleost marine fishes have pelagic larval stages lasting from several days to several weeks, during which time they are subject to dispersal. Fish larvae have considerable swimming abilities, and swim in an oriented manner in the sea. Thus, they can influence their dispersal and thereby, the connectivity of their populations. However, the sensory cues marine fish larvae use for orientation in the pelagic environment remain unclear. We review current understanding of these cues and how sensory abilities of larvae develop and are used to achieve orientation with particular emphasis on coral-reef fishes. The use of sound is best understood; it travels well underwater with little attenuation, and is current-independent but location-dependent, so species that primarily utilize sound for orientation will have location-dependent orientation. Larvae of many species and families can hear over a range of ~100-1000 Hz, and can distinguish among sounds. They can localize sources of sounds, but the means by which they do so is unclear. Larvae can hear during much of their pelagic larval phase, and ontogenetically, hearing sensitivity, and frequency range improve dramatically. Species differ in sensitivity to sound and in the rate of improvement in hearing during ontogeny. Due to large differences among-species within families, no significant differences in hearing sensitivity among families have been identified. Thus, distances over which larvae can detect a given sound vary among species and greatly increase ontogenetically. Olfactory cues are current-dependent and location-dependent, so species that primarily utilize olfactory cues will have location-dependent orientation, but must be able to swim upstream to locate sources of odor. Larvae can detect odors (e.g., predators, conspecifics), during most of their pelagic phase, and at least on small scales, can localize sources of odors in shallow water, although whether they can do this in pelagic environments is unknown. Little is known of the ontogeny of olfactory ability or the range over which larvae can localize sources of odors. Imprinting on an odor has been shown in one species of reef-fish. Celestial cues are current- and location-independent, so species that primarily utilize them will have location-independent orientation that can apply over broad scales. Use of sun compass or polarized light for orientation by fish larvae is implied by some behaviors, but has not been proven. Use of neither magnetic fields nor direction of waves for orientation has been shown in marine fish larvae. We highlight research priorities in this area.     

Light-dependent orientation responses in animals can be explained by a model of compass cue integration

The magnetic compass sense of animals is currently thought to be based on light-dependent processes like the proposed radical pair mechanism. In accordance, many animals show orientation responses that depend on light. However, the orientation responses depend on the wavelength and irradiance of monochromatic light in rather complex ways that cannot be explained directly by the radical pair mechanism. Here, a radically different model is presented that can explain a vast majority of the complex observed light-dependent responses. The model put forward an integration process consisting of simple lateral inhibition between a normal functioning, light-independent magnetic compass (e.g. magnetite based) and a vision based skylight color gradient compass that misperceives compass cues in monochromatic light. Integration of the misperceived color compass cue and the normal magnetic compass not only explains most of the categorically different light-dependent orientation responses, but also shows a surprisingly good fit to how well the animals are oriented (r-values) under light of different wavelength and irradiance. The model parsimoniously suggests the existence of a single magnetic sense in birds (probably based on magnetic crystals).     

Two different types of light-dependent responses to magnetic fields in birds

A model of magnetoreception proposes that the avian magnetic compass is based on a radical pair mechanism, with photon absorption leading to the formation of radical pairs. Analyzing the predicted light dependency by testing migratory birds under monochromatic lights, we found that the responses of birds change with increasing intensity. The analysis of the orientation of European robins under 502 nm turquoise light revealed two types of responses depending on light intensity: under a quantal flux of 8.10(15) quanta m(-2) s(-1), the birds showed normal migratory orientation in spring as well as in autumn, relying on their inclination compass. Under brighter light of 54.10(15) quanta m(-2) s(-1), however, they showed a "fixed" tendency toward north that did not undergo the seasonal change and proved to be based on magnetic polarity, not involving the inclination compass. When birds were exposed to a weak oscillating field, which specifically interferes with radical pair processes, the inclination compass response was disrupted, whereas the response to magnetic polarity remained unaffected. These findings indicate that the normal inclination compass used for migratory orientation is based on a radical-pair mechanism, whereas the fixed direction represents a novel type of light-dependent orientation based on a mechanism of a different nature.     

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 degrees 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 degrees 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 degrees CW. This result is being discussed as one of a few cases of 90 degrees shift reported to date, and as an argument corroborating the hypothesis of a close connection between photoreception and magnetoreception in insects.     

Chemical magnetoreception: bird cryptochrome 1a is excited by blue light and forms long-lived radical-pairs

Cryptochromes (Cry) have been suggested to form the basis of light-dependent magnetic compass orientation in birds. However, to function as magnetic compass sensors, the cryptochromes of migratory birds must possess a number of key biophysical characteristics. Most importantly, absorption of blue light must produce radical pairs with lifetimes longer than about a microsecond. Cryptochrome 1a (gwCry1a) and the photolyase-homology-region of Cry1 (gwCry1-PHR) from the migratory garden warbler were recombinantly expressed and purified from a baculovirus/Sf9 cell expression system. Transient absorption measurements show that these flavoproteins are indeed excited by light in the blue spectral range leading to the formation of radicals with millisecond lifetimes. These biophysical characteristics suggest that gwCry1a is ideally suited as a primary light-mediated, radical-pair-based magnetic compass receptor.     

Sun-Compass Orientation in Mediterranean Fish Larvae

Mortality is very high during the pelagic larval phase of fishes but the factors that determine recruitment success remain unclear and hard to predict. Because of their bipartite life history, larvae of coastal species have to head back to the shore at the end of their pelagic episode, to settle. These settlement-stage larvae are known to display strong sensory and motile abilities, but most work has been focused on tropical, insular environments and on the influence of coast-related cues on orientation. In this study we quantified the in situ orientation behavior of settlement-stage larvae in a temperate region, with a continuous coast and a dominant along-shore current, and inspected both coast-dependent and independent cues. We tested six species: one Pomacentridae, Chromis chromis, and five Sparidae, Boops boops, Diplodus annularis, Oblada melanura, Spicara smaris and Spondyliosoma cantharus. Over 85% of larvae were highly capable of keeping a bearing, which is comparable to the orientation abilities of tropical species. Sun-related cues influenced the precision of bearing-keeping at individual level. Three species, out of the four tested in sufficient numbers, oriented significantly relative to the sun position. These are the first in situ observations demonstrating the use of a sun compass for orientation by wild-caught settlement-stage larvae. This mechanism has potential for large-scale orientation of fish larvae globally.     

果蝇造血器官淋巴腺的研究进展

黑腹果蝇（Drosophila melanogaster）是生物学研究中重要的模式生物之一。果蝇造血过程主要发生于胚胎和幼虫阶段，淋巴腺作为幼虫阶段的主要造血器官，由髓质区（medullary zone，MZ）、皮质区（cortical zone，CZ）及后端信号中心区（posterior signal center，PSC）组成。淋巴腺在多种信号通路的调控下，能够维持血细胞的增殖和分化相对稳态，这对于果蝇的造血活动和正常生存均具有重要作用。综述了造血器官淋巴腺的形成过程及维持淋巴腺稳态的信号调节通路，以期为淋巴腺血细胞的详细分类和相应的功能研究奠定理论基础。     

The effect of yellow and blue light on magnetic compass orientation in European robins, Erithacus rubecula

To analyze the wavelength dependency of magnetic compass orientation, European robins were tested during spring migration under light of various wavelengths. Under 565-nm green light (control) the birds showed excellent orientation in their migratory direction; a 120° deflection of magnetic North resulted in a corresponding shift in the birds' directional tendencies, indicating the use of the magnetic compass. Under 443-nm blue light, the robins were likewise well oriented. Under 590-nm yellow, however, oriented behavior was no longer observed, although the activity was at the same level as under blue and green light. The spectral range where magnetic orientation is possible thus differs from the range of vision, the former showing parallels to that of rhodopsin absorption. The interpretation of the abrupt change in behavior observed between 565 green to 590 yellow is unclear. There is no simple relationship between magnetoreception and the known color receptors of birds. Accepted: 17 December 1998     

Uptake of juvenile hormone esterase by pericardial cells of Manduca sexta

Immunohistochemical studies were conducted to determine tissue(s) which might be involved in the uptake of juvenile hormone esterase (JHE) from larval hemolymph. Purified JHE expressed by a recombinant baculovirus carrying the JHE gene from Heliothis virescens was injected into the hemolymph of second stadium larvae of Manduca sexta. Immunoreactive material detected with specific antibodies against the natural JHE purified by affinity chromatography from the hemolymph of H. virescens was localized only in the dorsal regions of whole larval mounts. Further immunohistochemical studies of whole and dissected larvae at the light and electron microscopic level showed the specific localization of JHE in pericardial cells. Western blot analysis confirmed the localization of injected JHE in pericardial cells and also indicated some apparent degradation of the incorporated JHE. Similar results were obtained with the JHE from H. virescens injected into larvae of H. virescens. These results indicate that pericardial cells are involved in the uptake of injected JHE from insect hemolymph and its degradation.     

Bats use magnetite to detect the earth's magnetic field

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a "compass organelle" containing the iron oxide particles magnetite (Fe(3)O(4)). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic "Kalmijn-Blakemore" pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals.     

Entrainment Properties of the Locomotor Activity Rhythm of Drosophila melanogaster Under Different Photoperiodic Regimens

In this paper we report the results of an experiment to assess how closely repeated brief light pulses (LPs) mimic the effects of 12:12 h light/dark (LD) cycles (PPc). The locomotor activity rhythm of individual fruit flies from a laboratory population of Drosophila melanogaster was monitored under four different photoperiodic regimens, created using 12 h of light and 12 h of darkness or brief light pulses (LPs). The phase relationship (Ψ) and the stability (precision) of the locomotor activity rhythm during entrainment were estimated in order to compare the state of the circadian clocks under the four different photoperiodic regimens. The flies (n = 72) were subjected to four different LD cycles: (i) 12 h of light and 12 h of darkness (complete photoperiod, PPc); (ii) a single brief LP of 15 min duration presented close to the onset of activity (SLP-1); (iii) a single brief LP of 15 min duration administered close to the offset of activity (SLP-2); and (iv) two brief LPs administered 12 h apart (skeleton photoperiod, PPs). The locomotor activity rhythm of the flies was first monitored under constant darkness (DD) for about 10 days and then under the four different photoperiodic regimens for about 10 days, and finally in DD for the remainder of the experiment. The Ψ of the locomotor activity rhythm and its precision under PPc and PPs did not differ significantly, but they were significantly different from the SLP-1 and SLP-2 conditions. The results provide interesting insights into photoentrainment mechanisms of circadian clocks in D. melanogaster, and suggest that skeleton photoperiods, but not single brief LPs, mimic the actions of complete photoperiods.     

The Light and Magnetic Compass of the Weaver Ant,Oecophylla smaragdina (Hymenoptera: Formicidae)

Some of the foraging of the arboreal Australian weaver ant Oecophylla smaragdina takes place on the ground. Odor trails and compass orientation are used to return to the trunk of their nesting tree. Field experiments established directional responses to light and the natural magnetic field. The precision of the light compass orientation is much greater than that of the magnetic compass orientation: the respective average wrapped-around standard deviations (WSD) of directional choices towards home are WSD = ± 48° and WSD = ± 105°.