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     

Multisegmental motor activity in the segmentally restricted gin trap behavior in Manduca sexta pupae

Stimulation of sensory neurons innervating hairs in the gin traps on the abdomen of Manduca sexta pupae evokes a rapid bending of the abdomen that is restricted to one or more of the three articulating posterior segments. However, electrical stimulation of the gin trap sensory nerve in an isolated abdominal nerve cord evokes characteristic motor neuron activity in every abdominal segment. To determine if the segmentally distributed motor activity also occurred in intact animals and how it contributed to the segmentally restricted reflex movement, mechanical stimulation of the sensory hairs in intact animals was used to evoke reflex responses that were recorded as electromyograms synchronized with video recordings of the behavior. Motor activity was monitored during movements to determine if there was activity in many segments when the movement was restricted to one segment. Coordinated muscle activity was evoked throughout the abdomen in response to stimulation of any of the three gin traps, even when movement was restricted to one segment. Differences in the timing of ipsilateral and contralateral motor activity among segments allowed the closing of gin traps to be segmentally restricted. These findings suggest that the neural circuit underlying the gin trap reflex is distributed throughout the abdominal nerve cord. This network generates a complex, yet coordinated, motor pattern with muscular activity in many abdominal segments that produces a localized bending reflex. Accepted: 10 January 1997     

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     

Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system

The effects of l-arginine, and its analogues N ^ω-nitro-l-arginine methyl ester and N ^ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation. l-Arginine, at 10^–8 mol · l^–1induced a slight vasodilatory effect (max 10%). N ^ω-nitro-l-arginine methyl ester and N ^ω-Nitro-l-arginine in the range 10^–8–10^–4 mol · l^–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10^–4 mol · l^–1 N ^ω-nitro-l-arginine or N ^ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l^–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced a strong vasoconstriction (already significant at 10^–5 mol · l^–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine induced a biphasic response with vasodilation at low concentration (max 15% at 10^–8 mol · l^–1). Serotonin displayed a dose-response vasodilation in the range 10^–8–10^–4 mol · l^–1 (max 20%). These vasodilative effects were reduced or abolished by 10^–4 mol · l^–1 l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system. Accepted: 1 July 1996     

Highly independent olfactory receptor sites for naturally occurring bile acids in the sea lamprey, Petromyzon marinus

(1) Electro-olfactogram recording was used to determine whether the olfactory epithelium of adult sea lamprey is specifically sensitive to bile acids, some of which have been hypothesized to function as pheromones. Ten bile acids were selected from 38 which had already been pre-screened for olfactory activity. These compounds were first tested on their own, then as adapting stimuli, and finally as components of mixtures (2) The lamprey-specific bile acids, petromyzonol sulfate and allocholic acid, were the most potent compounds tested. Five other bile acids were also detectable at picomolar concentrations. Petromyzonol sulfate had a distinctive dose-response curve. (3) Cross-adaptation demonstrated that sensitivity to bile acids is attributable to at least four independent classes of olfactory receptor sites and that both the nature and position of conjugating group(s) are critical to receptor specificity. Notably, petromyzonol sulfate has its own highly specific and independent receptor site. The situation for unconjugated bile acids was more complex and there appeared to be several sub-classes of receptor sites for these compounds. (4) Mixture studies largely confirmed the cross-adaptation results, describing receptor site independence for the same four sets of odorants. Mixture enhancement was also seen when expected and there was no evidence of mixture suppression. (5) Together, these data demonstrate that conspecific bile acids are discriminated by the olfactory epithelium of the sea lamprey, supporting the possibility that these compounds may function as migratory pheromones. Accepted: 23 November 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     

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     

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     

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