The use of visual landmarks by gerbils: Reaching a goal when landmarks are displaced

Summary Gerbils (Meriones unguiculatus) can specify the location of a goal by means of visual landmarks and will return to such a goal from different starting positions in the vicinity of the landmarks. To discover whether landmark-cues are used continuously during an approach to the goal, gerbils were trained to forage for sunflower seeds close to a single illuminated light-bulb on the floor of an arena. As they approached the bulb, it was switched off and another bulb in a variable position with respect to the first turned on. On 52 out of 71 trials the gerbils changed their trajectory (latency ca. 240 ms) to aim for the newly lit bulb (Fig. 1 A, B). On the remaining trials, gerbils maintained their original course towards the first bulb as though it were still lit and then paused after a longer delay before eventually changing direction (Fig. 1C). Thus, an approach to a beacon is usually under continuous visual control. This ensures that the gerbil will reach its goal correctly despite any inaccuracies in its initial computation of its approach.When switches were made between more complex arrays of landmarks, the gerbils' behaviour was less clear-cut. Possible reasons for this difference are suggested.     

Evidence for averaging of distance from landmarks in the domestic dog

Several studies in landmark use have shown that animals locate spatial positions by predominantly using perpendicular distance from extended surfaces over distance from individual landmarks. In the current study, I investigated whether the domestic dog encodes perpendicular distance from surfaces and whether they estimate distances from multiple cues. Dogs were first trained to locate a ball hidden at an equal and constant distance between an individual landmark and one wall (Experiment 1) or two walls (Experiment 2). On occasional unrewarded tests, the landmark was shifted laterally, perpendicularly or diagonally relative to one wall. Data revealed that the dogs largely determined where to search by averaging the distance from the walls of the room and the distance from the individual landmark. This study provides additional evidence that domestic dogs use metric properties of space to find a spatial location by use of landmarks. Although the present results are in accordance with the vector sum model, they are also consistent with current theories of spatial memory.     

Detection of coloured stimuli by honeybees: minimum visual angles and receptor specific contrasts

Honeybees Apis mellifera were trained to distinguish between the presence and the absence of a rewarded coloured spot, presented on a vertical, achromatic plane in a Y-maze. They were subsequently tested with different subtended visual angles of that spot, generated by different disk diameters and different distances from the decision point in the device. Bees were trained easily to detect bee-chromatic colours, but not an achromatic one. Chromatic contrast was not the only parameter allowing learning and, therefore, detection: _min, the subtended visual angle at which the bees detect a given stimulus with a probability P ₀ = 0.6, was 5° for stimuli presenting both chromatic contrast and contrast for the green photoreceptors [i.e. excitation difference in the green photoreceptors, between target and background (green contrast)], and 15° for stimuli presenting chromatic but no green contrast. Our results suggest that green contrast can be utilized for target detection if target recognition has been established by means of the colour vision system. The green-contrast signal would be used as a far-distance signal for flower detection. This signal would always be detected before chromatic contrast during an approach flight and would be learned in compound with chromatic contrast, in a facilitation-like process.     

Gender differences in landmark learning for virtual navigation: the role of distance to a goal

We used a new virtual program in two experiments to prepare subjects to perform the Morris water task (www.nesplora.com). The subjects were Psychology students; they were trained to locate a safe platform amidst the presence of four pinpoint landmarks spaced around the edge of the pool (i.e., two landmarks relatively near the platform and two landmarks relatively distant away from it). At the end of the training phase, we administered one test trial without the platform and recorded the amount of time that the students had spent in the platform quadrant. In Experiment 1, we conducted the test trial in the presence of one or two of the distant landmarks. When only one landmark was present during testing, performance fell to chance. However, the men outperformed the women when the two distant landmarks were both present. Experiment 2 replicated the previous results and extended it by showing that no sex differences exist when the searching process is based on the near landmarks. Both the men and the women had similarly good performances when the landmarks were present both individually and together. When present together, an addition effect was found. Far landmark tests favor configural learning processes, whereas near landmark tests favor elemental learning. Our findings suggest that other factors in addition to the use of directional cues can underlie the sex differences in the spatial learning process. Thus, we expand upon previous research in the field.     

Use of visual landmarks by young trout (Salmo trutta) during their diel downstream post-emergence displacement in experimental channels

The diel timing of displacement of emerging brown trout ( Salmo trutta ) was studied by trapping the alevins at the downstream end of three experimental channels. The presence of phosphorescent landmarks on the substrate delayed the catches during the first hours of complete darkness, but increased them during twilight. During daylight, the presence of the landmarks was associated with greatly increased numbers of free-swimming fishes.     

Discrimination of coloured stimuli by honeybees: alternative use of achromatic and chromatic signals

Using a Y-maze experimental set-up, honeybees Apis mellifera were trained to a coloured disc presented against an achromatic background. In subsequent tests they were given a choice between the trained disc and an alternative disc that differed either in its chromatic properties, or in the amount of achromatic green contrast that it produced against the background. Tests were conducted in two experimental situations: one in which discs subtended a visual angle of 30° (as viewed by the bee at the decision point in the Y-maze), and another in which the angle was 6.5° or 5° (depending on the experiment). At the visual angle of 30°, the bees' choice behaviour was governed by the differences in chromatic properties, and not by the differences in the amount of green contrast. With the 6.5°- and 5°-discs, on the other hand, it was governed by the differences in the amount of green contrast, and not by the differences in chromatic properties. Consequently, in the present discrimination task, bees use either chromatic or achromatic cues, depending on the visual angle subtended by the stimuli at the eye. Results of a further experiment, in which the trained disc was tested against discs that produced various amounts of green contrast, confirm the above conclusion and show, in addition, that bees learn the green-contrast difference between a trained and a non-rewarded alternative. Accepted: 25 October 1996     

The deduction of the level of the human larynx from bony landmarks: Its relevance to the evolutionos speech

It has been claimed that the capacity for speech in hominids is related to the level of the larynx relative to its surrounding structures. Lower positioned larynges, such as those found in modern humans, have been said to be a prerequisite for articulate speech. In certain fossil hominids, the level of the larynx has been deduced from the angulation of the styloid process and the distance from the posterior nasal spine to the basion (the distance PB). The hypothesis that correlations exist between these bony features and the level of the larynx was tested in this study. The inclination of the styloid process and the level of the larynx were measured on human cadavers and on lateral x-ray cephalograms of the same cadavers. In addition, the distance PB and the level of the larynx were measured on lateral cephalograms of living adult humans. The inclination of the styloid process and the distance PB were also measured on a series of adult dry skulls. Pearson's correlation coefficients for the three sets of measurements were calculated. Only slight correlations between the inclination of the styloid process, the distance PB, and the level the larynx were found. The results of this study indicate that accurate prediction of the level of the larynx from the inclination of the styloid process and the distance PB is not possible.     

Wind drift,compensation, and the use of landmarks by nocturnal bird migrants

In this paper we describe fall nocturnal migration at three localities in eastern New York, one adjacent to the Hudson River, the other two 30 km to the west in a topographically more uniform area. Migrants at both study areas moved southwest in winds not out of the west and were, therefore, seemingly unaffected by the river. In west winds, however, birds away from the river moved south-southeast whereas those in the vicinity of the river flew a track west of south paralleling the river. In addition, a relative increase in the number of migrants along the river compared to away was observed in west winds as birds presumably became concentrated near the river. We conclude that on most autumn nights migrants passing through this area have a preferred track direction toward the southwest and in strong winds from the west and northwest they are drifted. Upon reaching the vicinity of the Hudson River, some birds alter their headings yielding a track direction that closely parallels the river resulting in at least a partial compensation for wind drift. No alternative hypothesis is consistent with all the data.     

Impact assessment in SLCA: sorting the sLCIA methods according to their outcomes

Background, aims, and scope  

Social Life Cycle Assessment (SLCA) is a tool assessing the social aspects of products and services. This article is a step forward from the Guidelines and wishes to clarify the different impact assessment (IA) methods covered in the Guidelines and how these different methods would provide different types of information regarding the social aspects of the product system.     

Getting to the start line: how bumblebees and honeybees are visually guided towards their first floral contact

Much of the literature on foraging behaviour in bees focuses on what they learn after they have had rewarded experience with flowers. This review focuses on how honeybees and bumblebees are drawn to candidate food sources in the first place: the foundation on which learning is built. Prior to rewarded foraging experience, flower-naïve bumblebees and honeybees rely heavily on visual cues to discover their first flower. This review lists methodological issues that surround the study of flower-naïve behaviour and describes technological advances. The role of distinct visual properties of flowers in attracting bees is considered: colour, floral size, patterning and social cues. The research reviewed is multi-disciplinary and takes the perspectives of both the bees and the plants they visit. Several avenues for future research are proposed.     

The use of visual cues in host evaluation by aphidiid wasps

We examined host evaluation behaviour in three species of aphid parasitoids, Ephedrus californicus Baker, Monoctonus paulensis (Ashmead), and Praon pequodorum Viereck (Hymenoptera: Aphidiidae). Mated females were provided with pairwise choices among three kinds of hosts in the laboratory: (green) pea aphid, Acyrthosiphon pisum (Harris), and a green and a pink colour morph of alfalfa aphid, Macrosiphum creelii Davis. Patterns of attack and host acceptance were species-specific. Females of E. californicus did not respond to the presence of aphids prior to making antennal contact. Variations in rates of parasitization (pea aphid>green alfalfa aphid>pink alfalfa aphid) were consistent with differences in aphid defensive behaviours; no ‘preference’ for any host type was evident when aphids were anaesthetized with carbon dioxide. In M. paulensis, the order of preference (pea aphid>green alfalfa aphid>pink alfalfa aphid) did not vary when aphids were immobilized, or presented in the dark, or both. Host movement did not influence the rate of attack by M. paulensis. In contrast, the ranked order of preference in P. pequodorum varied with circumstance. In the light, females attacked pea aphid and green alfalfa aphid with equal frequency, but parasitized significantly more of the former; both kinds of aphids were attacked and parasitized at higher rates than pink alfalfa aphid. In the dark, P. pequodorum females parasitized green and pink alfalfa aphids equally and at higher rates than pea aphids. Whereas E. californicus was more successful ovipositing in immobilized hosts, P. pequodorum females attacked and laid more eggs in normal than anaesthetized aphids. Patterns of host recognition and evaluation are compared across six species representing four genera in the family Aphidiidae.     

From antenna to antenna: lateral shift of olfactory memory recall by honeybees

Honeybees, Apis mellifera, readily learn to associate odours with sugar rewards and we show here that recall of the olfactory memory, as demonstrated by the bee extending its proboscis when presented with the trained odour, involves first the right and then the left antenna. At 1-2 hour after training using both antennae, recall is possible mainly when the bee uses its right antenna but by 6 hours after training a lateral shift has occurred and the memory can now be recalled mainly when the left antenna is in use. Long-term memory one day after training is also accessed mainly via the left antenna. This time-dependent shift from right to left antenna is also seen as side biases in responding to odour presented to the bee's left or right side. Hence, not only are the cellular events of memory formation similar in bees and vertebrate species but also the lateralized networks involved may be similar. These findings therefore seem to call for remarkable parallel evolution and suggest that the proper functioning of memory formation in a bilateral animal, either vertebrate or invertebrate, requires lateralization of processing.     

The ecology of sewage treatment gradients in relation to their use by waterbirds

The distribution and abundance of waterbirds along sewage treatment gradients at the Western Treatment Plant (Victoria, Australia) were studied in late summer/early autumn 2000. In general, the highest densities and diversity of waterbirds, and of zooplankton, were found in the ponds towards the end of a treatment series. Filter-feeding waterfowl (Anatidae) probably used these ponds because of the availability of zooplankton as a food-source. Dissolved oxygen concentration generally increased along the treatment gradient and un-ionised sulphide concentration decreased, and it is possible that either one, or both, of these played a key role in determining the distribution of zooplankton.