Correlation between torpor frequency and capacity for non-shivering thermogenesis in the Siberian hamster (Phodopus sungorus)

We investigated the correlation between torpor frequency and capacity for non-shivering thermogenesis (NST) in Siberian hamsters (Phodopus sungorus) during 25 weeks of acclimation to cold and short days. We hypothesized that torpor use is conditioned on the development of brown adipose tissue (BAT) capacity for NST. We found that (1) the degree of noradrenaline (NA)-induced hyperthermia was positively correlated with torpor frequency and its length and depth, and (2) the maximum response to NA occurred at the time of day when hamsters naturally arouse from torpor. The present study quantifies the correlation between torpor frequency and NST capacity and we suggest that a well-developed NST capacity is a prerequisite for the occurrence of torpor.     

Magnetic compass orientation by larval Drosophila melanogaster

We report evidence for magnetic compass orientation by larval Drosophila melanogaster. Groups of larvae were exposed from the time of hatching to directional ultraviolet (365 nm) light emanating from one of four magnetic directions. Larvae were then tested individually on a circular agar plate under diffuse light in one of four magnetic field alignments. The larvae exhibited magnetic compass orientation in a direction opposite that of the light source in training. Evidence for a well-developed magnetic compass in a larval insect that moves over distances of at most a few tens of centimeters has important implications for understanding the adaptive significance of orientation mechanisms like the magnetic compass. Moreover, the development of an assay for studying magnetic compass orientation in larval D. melanogaster will make it possible to use a wide range of molecular genetic techniques to investigate the neurophysiological, biophysical, and molecular mechanisms underlying the magnetic compass.     

Orientation to shorelines by the supratidal amphipod Talorchestia longicornis: Wavelength specific behavior during sun compass orientation

If released in water or on sand the supratidal amphipod Talorchestia longicornis Say amphipods moves in the onshore direction. The present study was designed to determine whether this species uses the sun as a cue for orientation and if so, which visual pigment in the compound eyes is involved. When tested in an apparatus with a view of only the sun and sky amphipods were disoriented when the sun was obscured by clouds. However, when the sun was visible, they oriented in the onshore direction of their home beach in both water and air during both the morning and afternoon. Resetting the time of their circadian rhythm in activity with either an altered light:dark or diel temperature cycle also reset the chronometric mechanism associated with sun compass. orientation. T. longicornis has two visual pigments with absorption maxima near 420 nm and 520 nm. Only the 420 nm pigment is used for sun compass orientation, which may be an adaptation for increasing the contrast between the sun and background scattered skylight or for detecting the radiance distribution of skylight. Irradiating the 520 nm absorbing pigment alone induced positive phototaxis to the sun but not onshore orientation. Thus, T. longicornis shows wavelength specific behavior by using only one of its visual pigments for sun compass orientation.     

Metabolic and thermoregulatory responses to heat and cold in the Djungarian hamster,Phodopus sungorus

Summary Djungarian hamsters,Phodopus sungorus (31.1 g body weight) were exposed to ambient temperatures (T _a ) between –35°C and +34°C. They tolerated severe cold stress but were less able to withstand heat. At –35° CT _a , normal body temperature was maintained for several hours. Thereby maximum thermal insulation was calculated at 1.1 g·°C/mW, which is only slightly higher than expected from the hamsters body size. High levels of heat production (60 to 90 m W/g) were maintained for several hours, suggesting that well developed means of heat production are the main reason for cold tolerance of the Djungarian hamster.     

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.     

Involvement of the sun and the magnetic compass of domestic fowl in its spatial orientation

Domestic chicks are able to find a food goal at different times of day, with the sun as the only consistent visual cue. This suggests that domestic chickens may use the sun as a time-compensated compass, rather than as a beacon. An alternative explanation is that the birds might use the earth's magnetic field. In this study, we investigated the role of the sun compass in a spatial orientation task using a clock-shift procedure. Furthermore, we investigated whether domestic chickens use magnetic compass information when tested under sunny conditions.Ten ISA Brown chicks were housed in outdoor pens. A separate test arena comprised an open-topped, opaque-sided, wooden octagonal maze. Eight goal boxes with food pots were attached one to each of the arena sides. A barrier inside each goal box prevented the birds from seeing the food pot before entering. After habituation, we tested in five daily 5-min trials whether chicks were able to find food in an systematically allocated goal direction. We controlled for the use of olfactory cues and intra-maze cues. No external landmarks were visible. All tests were done under sunny conditions. Circular statistics showed that nine chicks significantly oriented goalwards using the sun as the only consistent visual cue during directional testing. Next, these nine chicks were subjected to a clock-shift procedure to test for the role of sun-compass information. The chicks were housed indoors for 6 days on a light-schedule that was 6 h ahead of the natural light–dark schedule. After clock-shifting, the birds were tested again and all birds except one were disrupted in their goalward orientation. For the second experiment, six birds were re-trained and fitted with a tiny, powerful magnet on the head to disrupt their magnetic sense. The magnets did not affect the chicks’ goalward orientation.In conclusion, although the strongest prediction of the sun-compass hypothesis (significant re-orientation after clock-shifting) was neither confirmed nor refuted, our results suggest that domestic chicks use the sun as a compass rather than as a beacon. These findings suggest that hens housed indoors in large non-cage systems may experience difficulties in orientation if adequate alternative cues are unavailable. Further research should elucidate how hens kept in non-cage systems orient in space in relation to available resources.     

Nocturnal orientation by the Asian honey bee, Apis dorsata

Honey bees have been observed to forage and dance on moonlit nights, but it has never been established whether the moon serves as a reference in orienting nocturnally active bees. The present study, of the Asian honey bee Apis dorsata, suggests that although the moon's illumination is essential for nocturnal flight, the moon itself is ignored for orienting the dances. Rather, bees probably use the sun's position as a reference point for their dances, even though the sun is below the horizon. This ability may involve an extension of the mechanism that honey bees employ to find the sun on overcast days.     

The magnetic compass orientation of the burrows of the Damara mole-rat Cryptomys damarensis (Bathyergidae)

In response to reports claiming that part of the ability of mole-rats (Bathyergidae) to orientate with respect to the geomagnetic field involves orientation of their burrow systems in a southward direction, we measured the orientation of burrows of the Damara mole-rat, Cryptomys damarensis , in the Kalahari Desert. It was found that burrow orientation was not significantly different from that expected for a random distribution of compass orientations.     

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     

A visual pathway links brain structures active during magnetic compass orientation in migratory birds

The magnetic compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, "Cluster N", show high neuronal activity when night-migratory songbirds perform magnetic compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference compass direction of the geomagnetic field and that migratory birds "see" the reference compass direction provided by the geomagnetic field.     

Nepotistic alarm calling in the Siberian jay, Perisoreus infaustus

From a life history perspective, parents have an incentive to protect their reproductive investment, and so may provide care even after their offspring are independent. Such prolonged parental care could lead to postponed dispersal of the offspring and thereby facilitate the formation of kin groups. We tested whether alpha birds in Siberian jays protected their independent, retained offspring by giving alarm calls during simulated predator attacks. We compared the responses to predator attacks simulated by flying a hawk model over a dyad of birds on a feeder for dyads composed of an alpha bird and either a relative or a nonrelative. Alpha females were nepotistic in their alarm-calling behaviour, in that they called more frequently when accompanied by their retained offspring than by unrelated immigrants, but alpha males called indiscriminately. This difference in alarm calling could reflect dominance relationships in Siberian jay groups, because the presence of immigrants may be less costly to alpha males, but alpha females are more vulnerable to competition from immigrants. Alarm calls were usually given during escape, when both individuals in the dyad had left the feeding site. However, results of a playback experiment suggest that alarm calls conveyed information about danger and incited an immediate escape reaction. Our results indicate that alarm calling can be nepotistic, and that factors other than kinship influence alarm-calling behaviour. Nepotistic antipredator behaviours are benefits that offspring can gain only in their natal territory. Hence, in the absence of preferential treatment by their parents, offspring may be more likely to disperse and kin groups are prevented from forming.     

Penetration of zona-free hamster ova by Siberian tiger sperm

Sperm from the electroejaculate of captive Siberian tigers (Panthera tigris altaica) penetrated zona pellucida-free hamster ova in vitro, evidenced by a decondensation reaction. This assay, when used in conjunction with semen analysis, may be useful in assessing the fertility potential of males of this and other related felids. Such information is an important step in developing successful long-term management strategies for captive and wild populations of this severely endangered species.