Orientation-sensitive Neurons in the Brain of the Honey Bee (Apis mellifera)

Recent behavioural experiments have shown that bees are able to distinguish vertically presented patterns with orientation cues, although the locations of areas of black are randomized. To discriminate between two orientations, the bees must possess more than one orientation-sensitive neuron type. Therefore, the aim is to search for different types of orientation-sensitive cells of the honey bee, and measure their receptive field, velocity sensitivity and contrast sensitivity. Orientation-sensitive cells with two different types of orientation tuning-curves were recorded intracellularly in the mid-brain of the honey bee when the stimulus was a narrow bar (bar width = 5 degrees ). These cells are sensitive to bar movement within their large receptive field, which covers the visual field of one eye. They are quite distinct from the well-known directional motion detectors. The contrast sensitivity of the orientation-sensitive cells recorded in this study corresponds to results from behavioural experiments. The velocity-sensitivity curves of the orientation-sensitive cells differ from those of the direction-sensitive cells. Measurements of orientation sensitivity and contrast sensitivity when the stimulus is a wide bar (bar width = 10 degrees ), done in different eye regions, suggest that each orientation-sensitive cell receives visual signals from an array of orientational subunits within its receptive field. The correspondence between these physiological results and the results of recent behavioural experiments are discussed. Copyright 1997 Elsevier Science Ltd. All rights reserved     

Behavioural type in newly emerged steelhead Oncorhynchus mykiss does not predict growth rate in a conventional hatchery rearing environment

Behavioural assays were conducted on newly emerged steelhead Oncorhynchus mykiss to investigate the presence of behavioural syndromes and to determine whether behavioural type in young fish predicts growth rate in a conventional hatchery rearing environment. Individual fry were consistent in their position choice and activity behaviours across safe and unsafe contexts, as well as among assays conducted on different days. Position choice and activity behaviours, however, were not necessarily correlated to each other. Both behaviours predicted feeding rates during behavioural assays, but there was no relationship between fry behaviour and subsequent growth rate or survival during the first 3 months of hatchery rearing. These results support the hypothesis that selection in captivity may be relaxed with respect to behavioural type rather than directional, allowing for increased behavioural variance in domesticated populations. Modest magnitudes of correlations among fry behaviours, however, suggest that behavioural type may be unstable at the onset of the juvenile feeding stage.     

Directional sensitivity along the upper limb in humans

The capacity of four neurologically healthy young adults to distinguish opposing directions of cutaneous motion was determined at five different sites along the proximal-distal axis of the upper limb. Constant-velocity brushing stimuli (ranging from 0.5 to 32.0 cm/sec) were delivered through an aperture in a Teflon plate that was securely positioned in light contact with the skin. In one series of experiments, directional sensitivity in d' units was assessed at each site, using an aperture length of 0.75 cm. In a second series of experiments, the aperture length required to obtain the same criterion level of directional sensitivity at each site was determined. To attain the sensitivity reached at distal sites, a proximal stimulus had to traverse a longer chord of skin. Specifically, chords 5.9 times longer on average (range = 5.4-6.2) were required on the proximal forearm than on the index finger pad. This finding suggests that relative directional sensitivity increases sixfold from the proximal forearm to the finger pad. Moreover, relative directional sensitivity on the shoulder was comparable to that observed on the proximal forearm for two of the subjects, and approximately one-half that observed on the proximal forearm for the other two subjects. In addition to such a prominent spatial gradient in relative directional sensitivity, the velocity of stimulus motion at which directional sensitivity was highest increased systematically as the test site was shifted from the finger pad to the proximal forearm. Specifically, the optimal velocity on the finger pad varied among subjects from 1.5 to 9.4 cm/sec (mean = 5.4 cm/sec), and on the proximal forearm from 11.5 to 31.2 cm/sec (mean = 18.6 cm/sec). The optimal velocity on the shoulder was not significantly different from that observed on the proximal forearm. The results suggest that effective and informed clinical testing of patients' capacity to distinguish opposing directions of motion on cutaneous regions that differ in peripheral innervation density requires appreciation of the sensitivities of different skin regions, as well as the unique velocity dependency of direction discrimination at each skin site.     

Natural and sexual selection on male behaviour and morphology,and female choice in a wild field cricket population: spatial,temporal and analytical components

We used multiple regression, path analysis and non-parametric selection surface visualisation to investigate natural and sexual selection and, in addition, cross-sectional female choice statistics to analyse female choice in a wild population of the field cricket Gryllus campestris L. in central Germany. Adults (167 males, 75 females) were individually marked and followed daily over the entire adult stage. Two morphological traits (pronotum width, body condition) and two behavioural traits (burrow occupation time, daily displacement) were measured for each male and used in selection analyses. Individuals mated multiply and male mating success was strongly right skewed with less than 6% of the population achieving 50% of the copulations. In males, analysis of natural selection in terms of lifespan revealed positive directional selection on burrow occupation time and stabilising selection on daily displacement. Analysis of sexual selection in term of mating success showed positive directional selection on pronotum width and lifespan. Path analysis confirmed the close association between natural and sexual selection and illustrated indirect effects of the behavioural variables on mating success via their effect on lifespan. Multiple regression analysis further indicated positive quadratic (disruptive) sexual selection on lifespan but the non-parametric cubic spline regression showed this to be an artefact of the quadratic approach. In fact, lifespan was under “threshold selection” i.e. it was not under selection below a threshold and under positive directional sexual selection above the threshold. A positive correlational selection gradient between lifespan and body condition revealed that a high body condition is advantageous among long-lived males. Female choice statistics showed that females chose large and heavy males in the beginning of the season only and that choosiness decreases with increasing distance to potential alternative mates. Our findings highlight the benefits of combining several analytical methods to uncover selection patterns and to avoid misinterpretations based on single methods.     

Correlational selection does not explain the evolution of a behavioural syndrome

Correlated suites of behaviours, or behavioural syndromes, appear to be widespread, and yet few studies have explored how they arise and are maintained. One possibility holds that correlational selection can generate and maintain behavioural syndrome if certain behavioural combinations enjoy greater fitness than other combinations. Here we test this correlational selection hypothesis by comparing behavioural syndrome structure with a multivariate fitness surface based on reproductive success of male water striders. We measured the structure of a behavioural syndrome including dispersal ability, exploration behaviour, latency to remount and sex recognition sensitivity in males. We then measured the relationship between these behaviours and mating success in a range of sex ratio environments. Despite the presence of some significant correlational selection, behavioural syndrome structure was not associated with correlational selection on behaviours. Although we cannot conclusively reject the correlational selection hypothesis, our evidence suggests that correlational selection and resulting linkage disequilibrium might not be responsible for maintaining the strong correlations between behaviours. Instead, we suggest alternative ways in which this behavioural syndrome may have arisen and outline the need for physiological and quantitative genetic tests of these suggestions.     

Temporally patterned pulse trains affect directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus

The directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, was studied under free field stimulation conditions with 3 temporally patterned trains of sound pulses which differed in pulse repetition rate and duration. The directional sensitivity curves of 92 neurons studied can be described as hemifield, directionally-selective, or non-directional according to the variation in the number of impulses with pulse train direction. When these neurons were stimulated with all 3 pulse trains, the directional sensitivity curves of 50 neurons was unchanged but that of the other 42 neurons changed from one type into another. When these pulse trains were delivered at high pulse repetition rate and short pulse duration, they significantly sharpened the directional sensitivity of two thirds of the neurons examined by reducing the angular range and increasing the slope of their impulse directional sensitivity curves. These pulse trains also sharpened the slope of the threshold directional sensitivity curves of 25 neurons studied. However, when directional sensitivity of collicular neurons was determined with pulse trains that differed only in pulse repetition rate or in pulse duration, significant sharpening of directional sensitivity was rarely observed in all experimental conditions tested. Possible mechanisms underlying these findings are discussed.     

Neural inhibition sharpens auditory spatial selectivity of bat inferior collicular neurons

This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed. Accepted: 18 January 2000     

Low doses of a neonicotinoid insecticide modify pheromone response thresholds of central but not peripheral olfactory neurons in a pest insect

Insect pest management relies mainly on neurotoxic insecticides, including neonicotinoids, leaving residues in the environment. There is now evidence that low doses of insecticides can have positive effects on pest insects by enhancing various life traits. Because pest insects often rely on sex pheromones for reproduction, and olfactory synaptic transmission is cholinergic, neonicotinoid residues could modify chemical communication. We recently showed that treatments with different sublethal doses of clothianidin could either enhance or decrease behavioural sex pheromone responses in the male moth, Agrotis ipsilon. We investigated now effects of the behaviourally active clothianidin doses on the sensitivity of the peripheral and central olfactory system. We show with extracellular recordings that both tested clothianidin doses do not influence pheromone responses in olfactory receptor neurons. Similarly, in vivo optical imaging does not reveal any changes in glomerular response intensities to the sex pheromone after clothianidin treatments. The sensitivity of intracellularly recorded antennal lobe output neurons, however, is upregulated by a lethal dose 20 times and downregulated by a dose 10 times lower than the lethal dose 0. This correlates with the changes of behavioural responses after clothianidin treatment and suggests the antennal lobe as neural substrate involved in clothianidin-induced behavioural changes.     

Local population success in heterogeneous habitats: reciprocal transplant experiments completed on a desert spider

Reciprocal transplant experiments were completed to test for selection against the mixing of behavioural phenotypes in a desert spider. Most Agelenopsis aperta populations experience low prey abundances and competition for web‐sites that provide shelter from thermal extremes. These conditions favour aggressiveness towards both prey and conspecifics (an ‘arid‐land behavioural phenotype’). The spider also occupies narrow stretches of riparian habitat bordering spring‐fed streams and rivers. Here it is released from competition for prey and foraging sites, but is subject to predation by birds. A less aggressive/more fearful behaviour is selected for in these riparian habitats (a ‘riparian behavioural phenotype’). Previous work with this spider indicates that there is genetic differentiation between arid‐land and riparian populations. However, the degree to which genetic differentiation is achieved may be limited by gene flow. Reciprocal sets of enclosures were established in: (1) a dry evergreen woodland site (arid‐land phenotype) and (2) a neighbouring riparian site (riparian phenotype) in south‐eastern Arizona. Equal numbers of field collected, early instar A. aperta were introduced into native and transplant enclosures in each habitat. After 6 months of site‐imposed selection, survivorship was determined and growth estimates and behavioural trials completed on spiders remaining in the different enclosures. The same behavioural test was subsequently applied to lab‐reared offspring of the spiders surviving the respective selection regimes. Riparian transplants showed both poor survival and retarded growth in the dry woodland habitat when compared with both arid‐land and riparian natives. Arid‐land transplants that survived, however, grew equally well in riparian habitat as did dry woodland and riparian natives. Behavioural assays conducted on test subjects after selection and on their offspring reared in a controlled laboratory environment indicate that phenotypes that were inappropriate to the respective habitats were selected against in the transplant experiments. The frequency distribution of transplant spider behaviour on a continuum from fearful to aggressive was intermediate between that exhibited by respective native riparian and dry woodland spiders. It is concluded that while arid‐land and riparian behavioural ecotypes do exist, directional gene flow of arid‐land phenotypes into riparian habitat limits population subdivision.     

Linking behavioural syndromes and cognition: a behavioural ecology perspective

With the exception of a few model species, individual differences in cognition remain relatively unstudied in non-human animals. One intriguing possibility is that variation in cognition is functionally related to variation in personality. Here, we review some examples and present hypotheses on relationships between personality (or behavioural syndromes) and individual differences in cognitive style. Our hypotheses are based largely on a connection between fast-slow behavioural types (BTs; e.g. boldness, aggressiveness, exploration tendency) and cognitive speed-accuracy trade-offs. We also discuss connections between BTs, cognition and ecologically important aspects of decision-making, including sampling, impulsivity, risk sensitivity and choosiness. Finally, we introduce the notion of cognition syndromes, and apply ideas from theories on adaptive behavioural syndromes to generate predictions on cognition syndromes.     

Long rise times of sound pulses in grasshopper songs improve the directionality cues received by the CNS from the auditory receptors

Auditory receptors of the locust (Locusta migratoria) were investigated with respect to the directionality cues which are present in their spiking responses, with special emphasis on how directional cues are influenced by the rise time of sound signals. Intensity differences between the ears influence two possible cues in the receptor responses, spike count and response latency. Variation in rise time of sound pulses had little effect on the overall spike count; however, it had a substantial effect on the temporal distribution of the receptor's spiking response, especially on the latencies of first spikes. In particular, with ramplike stimuli the slope of the latency vs. intensity curves was steeper as compared to stimuli with steep onsets (Fig. 3). Stimuli with flat ramplike onsets lead to an increase of the latency differences of discharges between left and right tympanic receptors. This type of ramplike stimulus could thus facilitate directional hearing. This hypothesis was corroborated by a Monte Carlo simulation in which the probability of incorrect directional decisions was determined on the basis of the receptor latencies and spike counts. Slowly rising ramps significantly improved the decisions based on response latency, as compared to stimuli with sudden onsets (Fig. 4). These results are compared to behavioural results obtained with the grasshopper Ch. biguttulus. The stridulation signals of the females of this species consist of ramplike pulses, which could be an adaptation to facilitate directional hearing of phonotactically approaching males.Abbreviations HFR high frequency receptor - ILD interaural level difference - LFR low frequency receptor - SPL sound pressure level - WN white noise     

Evidence of a rheotactic component in the odour search behaviour of freshwater eels

The detection of food odour by the freshwater eels, Anguilla australis and Anguilla dieffenbachii released a behavioural response to flow that resulted in direct upstream movement toward the odour source. Changes in various orientation parameters were observed as eels neared the source. Eels had substantially lower swimming velocities and considerably more variable heading and course angles close to the odour source (≤0·9 m) than further away (>0·9 m). Observed changes in orientation parameters were primarily due to changes in the behaviour of a searcher following odour loss. Cross-stream movements were initiated when the eel moved beyond the lateral margins of the odour plume. The behavioural switch from odour-conditioned rheotaxis to cross-stream casting following odour loss occurred more frequently close to the odour source where the plume was most narrow. Odour-conditioned rheotaxis enables the searcher to move quickly and efficiently toward the odour source without the need to extract directional information from a highly intermittent and complex chemical signal.     

The role of the medial septum in the acoustic trachea of the cricket Gryllus bimaculatus

In the cricket Gryllus bimaculatus, it is demonstrated that the medial septum in the prothoracic trachea of the auditory system plays an important role in shaping the directional sensitivity of the ear.After perforation of the medial septum, the directional characteristic of intact animals, showing a mean right-to-left difference in sensitivity of 14 dB, becomes more omnidirectional with a mean right-to-left difference of only 7 dB. Correspondingly, the rate of change in auditory sensitivity for a sound source moving from frontal to contralateral is reduced to 0.78 dB/10° versus 1.5 dB/10° in intact animals (Figs. 2, 3).A computer simulation of phonotaxis based on these findings predicts a reduction in phonotactic performance in animals with a perforated septum. This prediction is in good quantitative agreement with experimental data (Fig. 4) and emphasizes the importance of an intact septum for effective phonotaxis in crickets.     

Hearing in tsetse flies? Morphology and mechanics of a putative auditory organ

Tympanal hearing organs are widely used by insects to detect sound pressure. Such ears are relatively uncommon in the order Diptera, having only been reported in two families thus far. This study describes the general anatomical organization and experimentally examines the mechanical resonant properties of an unusual membranous structure situated on the ventral prothorax of the tsetse fly, Glossina morsitans (Diptera: Glossinidae). Anatomically, the prosternal membrane is backed by an air filled chamber and attaches to a pair of sensory chordotonal organs. Mechanically, the membrane shows a broad resonance around 5.3-7.2 kHz. Unlike previously reported dipteran tympana, a directional response to sound was not found in G. morsitans. Collectively, the morphology, the resonant properties and acoustic sensitivity of the tsetse prothorax are consistent with those of the tympanal hearing organs in Ormia sp. and Emblemasoma sp. (Tachinidae and Sarcophagidae). The production of sound by several species of tsetse flies has been repeatedly documented. Yet, clear behavioural evidence for acoustic behaviour is sparse and inconclusive. Together with sound production, the presence of an ear-like structure raises the enticing possibility of auditory communication in tsetse flies and renews interest in the sensory biology of these medically important insects.     

Intraspecific sexual selection on a speciation trait, male coloration, in the Lake Victoria cichlid Pundamilia nyererei

The haplochromine cichlids of Lake Victoria constitute a classical example of explosive speciation. Extensive intra- and interspecific variation in male nuptial coloration and female mating preferences, in the absence of postzygotic isolation between species, has inspired the hypothesis that sexual selection has been a driving force in the origin of this species flock. This hypothesis rests on the premise that the phenotypic traits that underlie behavioural reproductive isolation between sister species diverged under sexual selection within a species. We test this premise in a Lake Victoria cichlid, by using laboratory experiments and field observations. We report that a male colour trait, which has previously been shown to be important for behavioural reproductive isolation between this species and a close relative, is under directional sexual selection by female mate choice within this species. This is consistent with the hypothesis that female choice has driven the divergence in male coloration between the two species. We also find that male territoriality is vital for male reproductive success and that multiple mating by females is common.     

Right-handed snakes: convergent evolution of asymmetry for functional specialization

External asymmetry found in diverse animals bears critical functions to fulfil ecological requirements. Some snail-eating arthropods exhibit directional asymmetry in their feeding apparatus for foraging efficiency because dextral (clockwise) species are overwhelmingly predominant in snails. Here, we show convergence of directional asymmetry in the dentition of snail-eating vertebrates. We found that snakes in the subfamily Pareatinae, except for non-snail-eating specialists, have more teeth on the right mandible than the left. In feeding experiments, a snail-eating specialist Pareas iwasakii completed extracting a dextral soft body faster with fewer mandible retractions than a sinistral body. The snakes failed in holding and dropped sinistral snails more often owing to behavioural asymmetry when striking. Our results demonstrate that symmetry break in dentition is a key innovation that has opened a unique ecological niche for snake predators.     

Sound transmission and directional hearing in field crickets: neurophysiological studies outdoors

Many studies provide detailed behavioural and neurophysiological information on the ability of crickets to localize a sound source under ideal acoustic conditions, but very little is known about how they perform in real habitats. We investigated directional hearing of crickets in the field using a neurophysiological approach, by recording the activity of the two prominent, bilaterally homologous AN1 neurons simultaneously in a cricket’s habitat. The discharge and latency differences of the pair of neurons in response to conspecific chirps presented at different distances and directions were taken as a measure of directional information. The maximum hearing distance differed between individuals and weather conditions from 1 to 15 m (mean 9.2 m). Although the AN1 activity generally decreased with increasing distance, large fluctuations in the magnitude of responses occurred with distance, indicating that the intensity gradient over distance is often irregular. The directional information provided in the discharge differences of the two neurons also varied with distance. Again, there was no simple directional gradient on the transmission channel; rather, with decreasing distance to the source there were receiver locations providing suprathreshold responses, but no directional information. The consequences for the ability of field crickets to communicate acoustically close to the ground are discussed.     

Directional sensitivity of wind-sensitive giant interneurons in the cave cricket Troglophilus neglectus.

Unlike the situation in most cockroach and cricket species studied so far, the wind-sensitive cerci of the cave cricket Troglophilus neglectus Krauss (Rhaphidophoridae, Orthoptera) are not oriented parallel to the body axis but perpendicular to it. The effects of this difference on the morphology, and directional sensitivity of cercal giant interneurons (GIs), were investigated. In order to test the hypothesis that the 90 degrees change in cercal orientation causes a corresponding shift in directional sensitivity of GIs, their responses in both the horizontal and vertical planes were tested. One ventral and four dorsal GIs (corresponding to GIs 9-1a and 9-2a, 9-3a, 10-2a, 10-3a of gryllid crickets) were identified. The ventral GI 9-1a of Troglophilus differed somewhat from its cricket homologue in its dendritic arborisation and its directional sensitivity in the horizontal plane. The morphology and horizontal directionality of the dorsal GIs closely resembled that of their counterparts in gryllids. In the vertical plane, the directionality of all GIs tested was similar. They were all excited mainly by wind puffs from the axon-ipsilateral quadrant. The results suggest that directional sensitivity to air currents in the horizontal plane is maintained despite the altered orientation of the cerci. This is presumably due to compensatory modifications in the directional pReferences of the filiform hairs.     

A learning-related variation in electroantennogram responses of a parasitic wasp

ABSTRACT Odour responses of parasitic insects, in search of their hosts, can change due to experience. Leptopilina heterotoma (Thomson) (Hymenoptera; Eucoilidae), a parasitic wasp of drosophilid larvae, is known to alter its preference for odours emanating from host food substrates through learning. These kinds of behavioural modifications in insects are assumed to be the result of complex processes in the brain. The results presented in this report, however, suggest that this learning-related behavioural variation is not restricted to brain processes but that it involves changes in sensitivity of olfactory receptor neurones.