A comparison of the response to induced exercise in red- and white-blooded Antarctic fishes

The physiological responses to forced exercise were studied in yellowbelly and marbled rockcod (Notothenia coriiceps and N. rossii), and the haemoglobinless icefish (Chaenocephalus aceratus), from blood samples obtained via indwelling catheters. The maximal exertion tolerable by N. coriiceps was 3–5 min, although N. rossii was not fully exhausted by this effort, and it proved difficult to elicit sustained maximal activity in C. aceratus. Arterial O₂ tension reflected the relative degree of exhaustion, showing a significant fall in the case of N. coriiceps, little change in N. rossii, and even a rise in C. aceratus as a result of hyperventilation. Such changes in the red-blooded species were not caused by altered O₂ carrying capacity, as there was no change in haematocrit. In Notothenia spp. the decrease in arterial pH was better correlated with a rise in arterial CO₂ tension than with blood lactate concentration, which is reflected in a modest net metabolic acid load. In contrast, the icefish showed an attenuated hypercapnia and a more pronounced lactacidosis, but an insignificant net metabolic acid load. Disturbance in ionoregulation following exercise was limited to an elevated [Cl⁻] in Notothenia, while circulating catecholamine levels remained unusually low in all specimens. The response to stress appears to reflect lifestyle and/or endemic speciation, rather than specific adaptations to the stenothermal environment. Accepted: 9 August 1996     

Neural correlates of habituation of the proleg withdrawal reflex in larvae of the hawk moth, Manduca sexta

The larval proleg withdrawal reflex of the hawk moth, Manduca sexta, exhibits robust habituation. This reflex is evoked by deflecting one or more mechanosensory planta hairs on a proleg tip. We examined neural correlates of habituation in an isolated proleg preparation consisting of one proleg and its segmental ganglion. Repeated deflection of a single planta hair caused a significant decrease in the number of action potentials evoked in the proleg motor nerve (which carries the axons of proleg retractor motor neurons). Significant response decrement was seen for interstimulus intervals of 10 s, 60 s and 5 min. Response decrement failed to occur in the absence of repetitive stimulation, the decremented response recovered spontaneously following a rest, and electrical stimulation of a body wall nerve facilitated the decremented response (a neural correlate of dishabituation). Adaptation of sensory neuron responses occurred during repeated hair deflections. However, when adaptation was eliminated by direct electrical stimulation of sensory neurons, the response in the proleg motor nerve still decreased significantly. Muscle recordings indicated that the response of an identified proleg retractor motor neuron decreased significantly during habituation training. Thus, habituation of the proleg withdrawal reflex includes a central component that is apparent at the level of a single motor neuron. Accepted: 20 December 1996     

Oxygen consumption in the foraging honeybee depends on the reward rate at the food source

Oxygen consumption of the honeybee Apis mellifera ligustica was measured as a function of the flow rate supply of sucrose solution at an automatic feeder located inside a respirometric chamber. Trained bees freely entered the respirometric chamber and collected the sucrose solution supplied. The mean value of the O₂ consumption rate per visit increased with the sucrose flow rate, and for a given flow rate, with increasing locomotor activity. However, when no locomotor activity was displayed, O₂ consumption also increased with increasing nectar flow rate. Crop load attained at the end of the visit showed a positive relationship with the nectar flow rate; however, for a given flow rate, O₂ consumption showed either no correlation or a negative one with the final crop load attained. It is concluded that the energy expenditure of the foraging bee is controlled by a motivational drive whose intensity depends on the reward rate at the food source. Accepted: 30 July 1996     

The impact of vertebrate and invertebrate predators on a stream benthic community

I assessed the impact of both vertebrate and invertebrate predators on a lotic benthic community in a 1-month-long experiment, using enclosures containing cobble/gravel bottoms, with large-mesh netting that allowed invertebrates to drift freely. Brown trout (Salmo trutta) and leeches (Erpobdella octoculata) were used as predators and four treatments were tested: a predator-free control, leeches only, trout only, and leeches and trout together. A density of 26.7 leeches/m² (20 leeches/enclosure) and 1.3 trout/m² (one trout per enclosure) was stocked into the enclosures. The total biomass of invertebrate prey was significantly lower in the trout and trout plus leech treatments than in the leech and control treatments, which were due to strong negative effects of trout on Gammarus. On the individual prey taxon level, both trout and leeches affected the abundance of Asellus , Baetis and Ephemerella, whereas the abundance of Gammarus was only affected by trout, and the abundance of Orthocladiinae and Limnephilidae was only affected by leeches. In the treatment with trout and leeches together, the abundance of Ephemerella and Baetis was higher than when trout or leeches were alone, which was probably due to predator interactions. Leeches and trout had no effects on prey immigration but did affect per capita emigration rates. Both trout and leeches indirectly increased periphyton biomass in enclosures, probably due to their strong effects on grazers. Both trout and leeches were size-selective predators, with trout selecting large prey, and leeches selecting small prey. Size-selective predation by trout and leeches affected the size structure of five commonly consumed prey taxa. Trout produced prey populations of small sizes owing to consumption of large prey as well as increased emigration out of enclosures by these large prey. Leech predation produced prey assemblages of larger size owing to consumption and increased emigration of small prey. These results suggest that in lotic habits, predatory invertebrates can be as strong interactors as vertebrate predators. Received: 23 June 1997 / Accepted: 4 May 1998     

Adaptive reconfiguration of a reflex circuit during different motor programmes in the locust

The cuticle strain which develops in the hindleg tibiae when a locust prepares to kick, or when the tibia thrusts against an obstacle, is detected by two campaniform sensilla, which reflexly excite the fast extensor tibiae motoneuron, some of the flexor tibiae motoneurons and nonspiking interneurons. The reflex excitation is adaptive for the extensor motoneuron during both co-activation and thrusting, but is only adaptive for the flexor motoneurons during co-activation, and is maladaptive during thrusting. We show that the femoral chordotonal organ, which monitors tibial position, controls the efficacy of the strain feedback. The campaniform sensilla-induced depolarization in the extensor motoneuron is about twice as large when the tendon is in mid position (reflecting a tibial-femoral angle of 90°) than when fully stretched (reflecting tibial flexion), while in the flexors the reverse is true. The amplitudes of excitatory postsynaptic potentials evoked by single campaniform sensilla spikes, are, however, not affected. Our data suggests that the chordotonal organ modulates the gain of the strain feedback onto the motoneurons by exciting interneuronal circuits whose output sums with the former. Thrusting typically occurs with the tibia partially extended, therefore the actions of the chordotonal organ support the production of a maximal thrusting force. Accepted: 27 December 1996     

Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis

By caching acorns, jays serve as important dispersal agents for oak (Quercus) species. Yet little is known about which acorn characteristics affect selection by jays. In the traditional model of jay/oak symbiosis, large, brown, ripe acorns free of invertebrate parasites (e.g., Curculio acorn weevils) are selected by jays. Recently, it has been suggested that a tri-trophic relationship between oaks, jays, and weevils may have evolved to counter the negative dietary effects of acorn tannins. Under the tri-trophic model, jays would preferentially select acorns containing weevil larvae. We tested the assumptions that (1) acorns containing curculionid larvae exist in sufficient quantities to support jay populations and (2) jays can detect, and preferentially select, acorns containing weevil larvae, and investigated the cues by which jays select acorns. Captive Mexican jays (Aphelocomaultramarina) were presented Emory oak (Quercusemoryi) acorns in aviary feeding trials. Large, dense, viable acorns free of curculionid larvae were preferentially selected. Contrary to results of previous research, color did not affect selection. Acorn viability increased and curculionid larval occupancy decreased in adjacent savannas and isolated stands relative to existing oak woodland, perhaps favoring oak recruitment into adjacent lower-elevation grasslands. Our results compel us to reject the tri-trophic model for this system, and are consistent with the traditional jay/oak symbiosis model. Relatively long-distance dispersal of viable acorns favors Emory oak replacement, and spatial patterns of acorn viability and curculionid parasitism suggest expansion of Emory oak into adjacent low-elevation semi-arid grasslands. Received: 29 February 1996 / Accepted: 26 September 1996     

The effect of a thiamin derivative on exercise performance

The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD), on oxygen uptake (˙VO₂), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over design with a 10-day washout between trials, 14 subjects ingested either 1 g · day⁻¹ of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer for the determination of ˙VO_2submax, ˙VO_2peak, lactate concentration ([La⁻ ]), lactate threshold (Th_La) and heart rate ( f _c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with repeated measures was used to determine significant differences between trials. There were no significant differences detected between trials for serial measures of ˙VO_2submax, [La⁻] or f _c. Likewise, ˙VO_2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min⁻¹, P = 0.83], Th_La [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min⁻¹, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation does not influence high-intensity exercise performance. Accepted: 19 December 1996     

Multiple excitatory receptor types on individual olfactory neurons: implications for coding of mixtures in the spiny lobster

The aim of our paper was to investigate whether single olfactory receptor neurons (ORNs) of the spiny lobster Panulirus argus functionally express more than one type of receptor, examine the consequences of this on coding of mixtures, and compare principles of odorant mixture coding by spiny lobsters with that by the channel catfish, which has been studied extensively using the same experimental and analytical procedures (Caprio et al. 1989; Kang and Caprio 1991). We examined responses of individual taurine-sensitive ORNs to binary mixtures of excitatory compounds, either competitive agonists (taurine, β-alanine, hypotaurine) or non-competitive agonists (taurine, l-glutamate, ammonium chloride, adenosine-5′-monophosphate). Responses to mixtures were compared to two indices: mixture discrimination index (MDI) and independent component index (ICI). Binary mixtures of competitive agonists had MDI values close to 1.0, as expected for competitors. Mixtures of non-competitive agonists had ICI values averaging 0.83, indicating the effects of the components are not independent. We conclude that individual olfactory cells of spiny lobsters can express more than one type of receptor mediating excitation, one of which typically has a much higher density or affinity, and that spiny lobster and catfish olfactory cells encode mixtures of two excitatory agonists using similar rules. Accepted: 20 December 1996     

Effects of plant hybridization on herbivore-parasitoid interactions

We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hybrid and parental willow plants in the field and in a common garden experiment. P. salicifoliella survival differed significantly among three willow taxa in the field in 1994 but not in the field in 1995 or in the common garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in their survival. In the field in 1995, host feeding predation varied significant among taxa. The theory of tritrophic interactions predicts that plant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation in survival and eulophid parasitism was also found among genotypes within taxa in the field in both years and in the common garden experiment. The common garden results show that genetic differences in plants affect the herbivore-parasitoid interaction. Variation among years in the patterns of survival and causes of mortality among field plants suggest that genotype by environment interactions may be important. Received: 1 March 1996 / Accepted: 4 November 1996     

Cold hardiness in Entomobrya nivalis (Collembola, Entomobryidae): annual cycle of polyols and antifreeze proteins, and antifreeze triggering by temperature and photoperiod

In the Swiss Prealps Entomobrya nivalis hibernates in an inactive state, hidden under bark flakes on spruce. For freeze avoidance it relies on thermal hysteresis proteins (THPs) and polyols (mainly ribitol, with small amounts arabitol and threitol). Polyols are present only during the inactive state, THPs additionally protect during the transition phase in spring and autumn, when animals are still active but frosts may occur. Peak values were recorded in February/March for THPs (3.5 °C hysteresis between melting and freezing point) and for polyols (26 μg mg⁻¹ FW; hemolymph osmolality 680 mosmol l⁻¹). E. nivalis is able to control its hemolymph osmolality independently of body water content. Mean osmolality in summer was 350– 440 mosmol l⁻¹, in winter it was elevated to 650 mosmol l⁻¹, due to a synthesis mainly of ribitol. Body water content varied between 1.8 and 3.3 mg H₂O mg⁻¹ DW, depending on humidity conditions. Experiments on triggering of antifreeze synthesis showed the action of temperature and photoperiod as cues, but there was also evidence for an endogenous rhythm. No clear correlation between antifreeze concentration and supercooling ability could be established, suggesting that gut content or other parameters also play an inportant role. Accepted: 18 November 1995     

An Aspergillus nidulans nuclear protein, AnCP, involved in enhancement of Taka-amylase A gene expression, binds to the CCAAT-containing taaG2 , amdS , and gatA promoters

Using AnCP (Aspergillus nidulans CCAAT-binding protein) as a CCAAT-specific binding factor model, the possibility that one factor is able to recognize CCAAT sequences in several different genes in A.␣nidulans was examined. DNase I protection analysis showed that AnCP specifically bound to CCAAT sequence-containing regions comprising 21 to 36 bp of the taa, amdS and gatA genes. Furthermore, replacement of the CCAAT sequence with CGTAA was found to abolish the binding of AnCP and to have an inhibitory effect on taa promoter activity. This clearly demonstrates a positive function of the CCAAT element. However, amylase was induced by starch and repressed by glucose in a CCAAT-box disruptant, as in wild-type cells. Received: 28 June 1996 / Accepted: 7 October 1996     

Physiological characterization of antennular flicking reflexes in the crayfish

The cellular substrates of antennular flicking behavior in the crayfish Procambarus clarkii were investigated. Flicking involves fast downward movements of the external filament of each biramous antennule (1st antenna), and is mediated by phasic contractions of a short muscle, the external filament depressor. Phasic contractions of the external filament depressor depend upon stereotyped impulse bursts in a single motorneuron (P1). These bursts have a characteristic impulse frequency profile that is consistent upon successive occurrences. The temporal characteristics of the impulse burst suggest that the central depolarizations generating each burst may be similar to driver potentials described for motor neurons in crustacean cardiac ganglia. Responses of the external filament to odorants have a long latency and are characterized by repetitive bursts and tonic activity in some external filament depressor fibers. Tonic activity in a slowly contracting muscle, the antennular depressor muscle, is also evoked by chemical stimulation. Flicking is consistently evoked only by mechanical or hydrodynamic stimulation of the cephalothorax, antennae and antennules. The sensitivity and short latency of the hydrodynamic antennule-generated flick reflex is consistent with the sensitivity of rapidly conducting, hydrodynamically activated mechanoreceptor neurons in both antennular filaments. I propose that antennular flicking, which has been shown to enhance the dynamic response characteristics of olfactory receptor neurons on the external antennular filament, has evolved as a response to the turbulence associated with fluid movement, within which chaotic odorant concentration fronts may be imbedded. Accepted: 23 October 1996     

Invasive capacity of Tamarix ramosissima in a Mojave Desert floodplain: the role of drought

Tamarix ramosissima (Tamaricaceae) is a woody phreatophyte that has invaded thousands of hectares of floodplain habitat in the southwestern U.S. In this study, we examined the response of gas exchange and stem sap flow of Tamarix and three co-occurring native phreatophytes (Pluchea sericea (Asteraceae), Prosopis pubescens (Fabaceae) and Salix exigua (Salicaceae)) to drought conditions in an early successional floodplain community in the Mojave Desert of southern Nevada. In an analysis of a size/age series of each species across the whole floodplain (both mature and successional stands), stem growth rate was lowest for Tamarix. However, along the same successional chronosequence, Tamarix came to dominate the 50+ year old stands with dense thickets of high stem density. Xylem sap flow, when expressed on a sapwood area basis, was highest in Tamarix under early drought conditions, but comparable between the four species toward the end of the summer dry season. Multivariate analysis of the gas exchange data indicated that the four species differentiated based on water use under early drought conditions and separated based on plant water potential and leaf temperature (indices of drought effects) at the end of the summer dry season. This analysis suggests that the invasive Tamarix is the most drought tolerant of the four species, whereas Salix transpires the most water per unit leaf surface area and is the least tolerant of seasonal water stress. Therefore, Salix appears to be well adapted to early successional communities. However, as floodplains in this arid region become more desiccated with age, Tamarix assumes greater dominance due to its superior drought tolerance relative to native phreatophytes and its ability to produce high density stands and high leaf area. Received: 8 August 1996 / Accepted: 29 January 1997     

The expression of genes involved in parasitism by Trichoderma harzianum is triggered by a diffusible factor

The mycoparasite Trichoderma harzianum has been extensively used in the biocontrol of a wide range of phytopathogenic fungi. Hydrolytic enzymes secreted by the parasite have been directly implicated in the lysis of the host. Dual cultures of Trichoderma and a host, with and without contact, were used as means to study the mycoparasitic response in Trichoderma. Northern analysis showed high-level expression of genes encoding a proteinase (prb1) and an endochitinase (ech42) in dual cultures even if contact with the host was prevented by using cellophane membranes. Neither gene was induced during the interaction of Trichoderma with lectin-coated nylon fibres, which are known to induce hyphal coiling and appressorium formation. Thus, the signal involved in triggering the production of these hydrolytic enzymes by T. harzianum during the parasitic response is independent of the recognition mediated by this lectin-carbohydrate interaction. The results showed that induction of prb1 and ech42 is contact-independent, and a diffusible molecule produced by the host is the signal that triggers expression of both genes in vivo. Furthermore, a molecule that is resistant to heat and protease treatment, obtained from Rhizoctonia solani cell walls induces expression of both genes. Thus, this molecule is involved in the regulation of the expression of hydrolytic enzymes during mycoparasitism by T. harzianum. Received: 8 June 1998 / Accepted: 28 July 1998     

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii

Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause is positively correlated with latitude (r ² = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude, so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14 (T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying circadian pacemaker. Received: 22 July 1996 / Accepted: 30 September 1996     

The effect of light environment, leaf area, and stored carbohydrates on inflorescence production by a rain forest understory palm

Variation in flowering by long-lived plants may be correlated with current resource availability. If, however, there are trade-offs between current and future reproduction, or between reproduction and storage or growth, then understanding variation requires a whole-plant, longer-term perspective. Inflorescence production by Calyptrogyne ghiesbreghtiana Linden ex. H. Wendl., an understory palm, was studied over 3 years. Annual inflorescence production varied greatly and was correlated with variation in plant size and light environment. There was no trade-off between past inflorescence production and the frequency of future inflorescence production. On the contrary, individuals that produced more inflorescences than predicted from their size and light environment tended to continue to do so in subsequent years also. I manipulated the resource environment of a subset of plants by removal of leaves and/or reproductive spikes. Leaf removal suppressed inflorescence production for the following 2 years, but spike removal had no effect. One year after leaf removal stored reserves were, on average, back to pre-treatment levels. There was, however, a negative effect of recent inflorescence production on storage. Plants with higher levels of storage had higher inflorescence production in the next 75 days. In C. ghiesbreghtiana the resource cost of reproduction is apparent in short-term variation in stored reserves. In contrast, annual inflorescence production does not follow a trade-off pattern between successive years, but consistently reflects both plant size and the light environment. Received: 20 October 1996 / Accepted: 25 January 1997     

The effect of exercise and restraint on pectoral muscle metabolism in pigeons

The effect of various activity regimes on metabolism of pigeon pectoralis was examined by measurement of blood lactate following exercise, total lactate dehydrogenase activity of pectoral muscle, and proportions of specific isoenzymes of pectoral muscle lactate dehydrogenase. Sprint-trained birds had the highest pectoral muscle lactate dehydrogenase activity (1409 IU · g⁻¹ wet tissue), while endurance-trained birds had the highest peak lactate levels (287 mg · dl⁻¹, extrapolated from decay curves) and fastest half-time of the lactate response (4.8 min) following exercise, but the lowest lactate dehydrogenase activity (115 IU · g⁻¹ wet tissue). Immobilization of one wing for 3 weeks following endurance training produced a marked increase in lactate dehydrogenase activity of the immobilized muscle, compared to that in the contralateral pectoralis and endurance-trained muscle. Aerobic forms of the lactate dehydrogenase enzyme (that favor conversion of lactate to pyruvate) predominated in pectoral muscle of endurance-trained birds, while cage-confined birds exhibited primarily the anaerobic isoenzymes. These results demonstrate that conversion of pectoral muscle lactate dehydrogenase isoenzymes, total lactate dehydrogenase activity, and half-time of lactate response after exercise is dependent on activity regime in pigeons. In this respect, pigeon pectoral muscle responds to training and disuse in a manner similar to that of mammalian skeletal muscle. Accepted: 10 September 1996     

Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands

The post-dispersal fate of seeds and fruit (diaspores) of three vertebrate-dispersed trees, Crataegus monogyna, Prunus mahaleb and Taxus baccata, was studied in the Andalusian highlands, south-eastern Spain. Exclosures were used to quantify separately the impact of vertebrates and invertebrates on seed removal in relation to diaspore density and microhabitat. The three plant species showed marked differences in the percentage of diaspores removed, ranging from only 5% for C. monogyna to 87% for T. baccata. Although chaffinches (Fringilla coelebs) fed on diaspores, rodents (Apodemus sylvaticus) were the main vertebrate removers of seed and fruit. Two species of ant (Cataglyphis velox and Aphaenogaster iberica) were the only invertebrates observed to remove diaspores. However, the impact of ants was strongly seasonal and they only removed P. mahaleb fruit to any significant extent. While removal of seed by rodents was equivalent to predation, ants were responsible for secondary dispersal. However, their role was limited to infrequent, small-scale redistribution of fruit in the vicinity of parent trees. Rodents and ants differed in their use of different microhabitats. Rodents foraged mostly beneath trees and low shrubs and avoided open areas while the reverse was true of ants. Thus, patterns of post-dispersal seed removal will be contigent on the relative abundance and distribution of ants and rodents. Studies which neglect to quantify separately the impacts of these two guilds of seed removers may fail to elucidate the mechanisms underlying patterns of post-dispersal seed removal. The coincidence of both increased seed deposition by the main avian dispersers (Turdus spp.) and increased seed predation with increasing vegetation height suggested that selection pressures other than post-dispersal seed predation shape the spatial pattern of seed dispersal. Rather than providing a means of escaping post-dispersal seed predators, dispersal appears to direct seeds to microhabitats most suitable for seedling survival. Nevertheless, the reliance of most vertebrate-dispersed trees on regeneration by seed and the absence of persistent soil seed banks imply that post-dispersal seed predators may exert a strong influence on the demography of the plants whose seeds they consume. Even where microsites are limited, the coincidence of the most suitable microhabitats for seedling establishment with those where seed predation is highest provide a means by which selective seed predators can influence community composition. Received: 19 August 1996 / Accepted: 25 January 1997     

Rhythmicity of torpor in a marsupial hibernator, the mountain pygmy-possum (Burramysparvus), under natural and laboratory conditions

Circadian rhythms have been observed in most mammals, but their importance and function remain controversial with respect to daily cycles during hibernation. We investigated the timing of arousals from and entries into hibernation for both free-living and captive mountain pygmy-possums (Burramys parvus). Under both natural and laboratory conditions most arousals and entries were entrained with the light-dark cycle. Entries occurred mainly during the night and arousals preferably around dusk, which coincides with the onset of the normal activity phase for the nocturnal pygmy-possums. This entrainment prevailed throughout the hibernation season although only the laboratory animals were constantly subjected to photoperiodic stimuli, whereas under natural conditions hibernacula are shielded from photic cues and diurnal temperature fluctuations. Nevertheless, possums left their hibernacula frequently throughout winter and were occasionally trapped close to the snow surface suggesting that during the periods of post-arousal normothermia they can be exposed to environmental stimuli. It thus appears that the synchronisation with the photocycle was governed by a temperature-compensated circadian clock which was reset periodically during short activity periods. For the mountain pygmy-possum, entrainment with the photocycle probably has two functions: 1. Entrainment ensures that foraging bouts during the hibernation season remain synchronised with the dark phase. 2. Information about the prevailing climatic conditions sampled during short activity periods enables them to time final spring emergence from hibernation when snow melt begins and ensures that the breeding season can commence as early as possible. Accepted: 26 August 1998     

Chromosome mapping of low-temperature induced Wcs120 family genes and regulation of cold-tolerance expression in wheat

 Low-temperature (LT) induced genes of the Wcs120 family in wheat (Triticum aestivum) were mapped to specific chromosome arms using Western and Southern blot analysis on the ditelocentric series in the cultivar Chinese Spring (CS). Identified genes were located on the long arms of the homoeologous group 6 chromosomes of all 3 genomes (A, B, and D) of hexaploid wheat. Related species carrying either the A, D, or AB genomes were also examined using Southern and Western analysis with the Wcs120 probe and the WCS120 antibody. All closely related species carrying one or more of the genomes of hexaploid wheat produced a 50 kDa protein that was identified by the antibody, and a Wcs120 homoeologue was detected by Southern analysis in all species. In the absence of chromosome arm 6DL in hexaploid CS wheat no 50 kDa protein was produced and the high-intensity Wcs120 band was missing, indicating 6DL as the location of Wcs120 but suggesting silencing of the Wcs120 homoeologue in the A genome. Levels of proteins that cross-reacted with the Wcs120 antibody and degrees of cold tolerance were also investigated in the Chinese Spring/Cheyenne (CS/CNN) chromosome substitution series. CNN chromosome 5A increased the cold tolerance of CS wheat. Densitometry scanning of Western blots to determine protein levels showed that the group 5 chromosome 5A had a regulatory effect on the expression of the Wcs120 gene family located on the group 6 chromosomes of all three hexaploid wheat genomes. Received: 10 July 1996 / Accepted: 30 September 1996