Biomedical subjects

Rüdiger Wehner

Publications and source records attributed to Rüdiger Wehner.

30 records · Page 2Linked to original sources

PubMed2005

Path integration in a three-dimensional maze: ground distance estimation keeps desert ants Cataglyphis fortis on course.

In this study, we investigate the ability of desert ants to gauge the ground distances of sloped sections in a three-dimensional (3D) outbound path. Ground distance estimation, as opposed to a simple measurement of walking distances, is a necessary prerequisite for precise path integration in undulating terrain. We trained ants to visit a feeder along a path that included an angular turn as well as a 'hill', resulting in an outbound path with a distinct 3D structure. We then observed the ants' return path in a test field on level ground. From the angles of the ants' return path on the test field one can infer which property of the hill segment was fed into the ants' path integration module, the actual walking distance or the ground distance. The results show clearly that it is the ground distance that Cataglyphis fortis feeds into its path integrator, and suggest that the ants are able to keep an accurate home vector also in hilly terrain.

Animals↗

PubMed2005

Desert ants compensate for navigation uncertainty.

During foraging trips, desert ants Cataglyphis fortis do not rely only on their well-studied path integration system, they also use olfactory cues when approaching a familiar food source. When a wind is blowing from a constant direction, as is characteristic of their desert habitat, the ants do not approach the feeder directly. They rather steer some distance downwind of the food source to pick up odour filaments emanating from the food. They follow this odour trail upwind, and find the source quickly and reliably. This approach behaviour was examined in more detail in order to identify the underlying orientation strategy. First, the ants may employ a 'goal expansion strategy', using odour spread as a spatially limited indicator for the presence of food. In that case, the distance steered downwind of the feeder should be determined by the range of the odour plume (and, for instance, wind speed). It should be independent of the distance between nest and feeder. Second, the ants may apply an 'error compensation strategy', using odour filaments as a guideline towards the food source. Steering downwind by a margin just exceeding their maximum navigation error will lead the ants safely across the odour guide. In that case, the distance steered downwind of the feeder should increase more or less linearly with the nest-feeder distance. Our results unambiguously support the second strategy. When feeders were established at distances of 5-75 m from the nest, the distances steered downwind of the food increased from 0.7 m to 3.4 m in a linear fashion. This result was independent of wind speed or wind direction. It translates into an ant's estimate of its navigation error within a range of 3 degrees to 8 degrees.

Animals↗

PubMed2004

Path integration in desert ants, Cataglyphis: how to make a homing ant run away from home.

Path integration is an ant's lifeline on any of its foraging journeys. It results in a homebound global vector that continually informs the animal about its position relative to its starting point. Here, we use a particular (repeated training and displacement) paradigm, in which homebound ants are made to follow a familiar landmark route repeatedly from the feeder to the nest, even after they have arrived at the nest. The results show that during the repeated landmark-guided home runs the ant's path integrator runs continually, so that the current state of the homebound vector increasingly exceeds the reference state. The dramatic result is that the homing ants run away from home. This finding implies that the ants do not rely on cartographic information about the locations of nest and feeder (e.g. that the nest is always south of the feeder), but just behave according to what the state of their egocentric path integrator tells them.

Animals↗

PubMed2004

Path integration in desert ants controls aggressiveness.

Cataglyphis ants of the Sahara Desert are extremely aggressive toward members of other colonies if they are close to their nest entrance, but not once they have embarked on their wide foraging journeys. We show that the ants reach the same level of aggressiveness when they are far from their actual nesting site but their path integrator--their main navigational toolkit--tells them that they are close, indicating a role for the animal's path integrator beyond navigation.

Aggression↗

PubMed2004

Navigation in wood ants Formica japonica: context dependent use of landmarks.

Wood ants Formica japonica can steer their outbound (foraging) and inbound (homing) courses without using celestial compass information, by relying exclusively on landmark cues. This is shown by training ants to run back and forth between the nest and an artificial feeder, and later displacing the trained ants either from the nest (when starting their foraging runs: outbound full-vector ants) or from the feeder (when starting their home runs: inbound full-vector ants) to various nearby release sites. In addition, ants that have already completed their foraging and homing runs are displaced after arrival either at the feeder (outbound zero-vector ants) or at the nest (inbound zero-vector ants), respectively, to the very same release sites. Upon release, the full-vector ants steer their straight courses by referring to panoramic landmark cues, while the zero-vector ants presented with the very same visual scenery immediately search for local landmark cues defining their final goal. Hence, it depends on the context, in this case on the state of the forager's round-trip cycle, what visual cues are picked out from a given set of landmarks and used for navigation.

Animals↗

PubMed2003

Landmark memories are more robust when acquired at the nest site than en route: experiments in desert ants.

Foraging desert ants, Cataglyphis fortis, encounter different sequences of visual landmarks while navigating by path integration. This paper explores the question whether the storage of landmark information depends on the context in which the landmarks are learned during an ant's foraging journey. Two experimental set-ups were designed in which the ants experienced an artificial landmark panorama that was placed either around the nest entrance (nest marks) or along the vector route leading straight towards the feeder (route marks). The two training paradigms resulted in pronounced differences in the storage characteristics of the acquired landmark information: memory traces of nest marks were much more robust against extinction and/or suppression than those of route marks. In functional terms, this result is in accord with the observation that desert ants encounter new route marks during every foraging run but always pass the same landmarks when approaching the nest entrance.

Animals↗

PubMed2002

Honey bees store landmarks in an egocentric frame of reference.

Honey bees are well known to rely on stored landmark information to locate a previously visited site. While various mechanisms underlying insect navigation have been thoroughly explored, little is yet known about the degree of integration of spatial parameters to form higher-level spatial representations. In this paper we explore the basic interactions between landmark cues and directional cues, which stand at the basis of our understanding of piloting mechanisms. A novel experimental paradigm allowed us independent manipulation of each parameter in a highly controlled environment. The approach taken was twofold: cue-conflict experiments were first conducted to examine the interactions between positional cues and directional cues. The bees were then successively deprived of sensory cues to question the dependence of landmark navigation on context cues. Our results confirm previous findings that landmark cues are used in concert with external directional cues if present. Conversely, the bees' ability to locate a food site was not disrupted in the absence of an external directional reference. Thus, bees store landmark memories in an egocentric frame of reference and only loose and facultative associations between visual memories and compass cues are formed.

Animals↗

PubMed2002

Dufour gland contents of ants of the Cataglyphis bicolor group.

The species of desert-dwelling ants of the Cataglyphis bicolor (Hymenoptera: Formicidae) group are difficult to distinguish by morphological features. Analysis of the secretion from the Dufour glands of workers of a number of colonies was undertaken to see if it provided a clear test of species. Linked 6c-ms showed in all samples straight and branched-chain alkanes, linear alkenes, ketones, aldehydes, acetates, and a group of C22 to C28 esters not previously identified in this genus. Contents of the Dufour glands of C. savignyi from Tunisia and Egypt were similar, and comprised straight and branched-chain alkanes, alkenes and small amounts of esters. C. bicolor from Tunisia contained compounds similar to C. savignyi but was distinguished from the latter by larger amounts of the esters. The major compound in the glands of C. viaticus was tridecane, in contrast to the pentadecane of other species. It also contained a branched alkane, 3-methyltridecane as a major component. Branched-chain esters and a wide variety of acetates were also found in this species. C. diehlii had a limited range of compounds, with branched alkanes almost completely absent and high proportions of pentadecene and dodecyl acetate. C bombycinus, a sympatric species. but recognized as not belonging to the bicolor group by its different mandibular gland substances, was notable in having butanoate esters in its Dufour glands. Despite these differences among species, both the great variability of individuals from a single colony and the among between conspecific colonies make species diagnosis from a few individuals difficult, in contrast with postpharyngeal glands, which, as recently reported, give a clearer indication of species.

Animals↗

PubMed2002

Visual navigation in desert ants Cataglyphis fortis: are snapshots coupled to a celestial system of reference?

Central-place foraging insects such as desert ants of the genus Cataglyphis use both path integration and landmarks to navigate during foraging excursions. The use of landmark information and a celestial system of reference for nest location was investigated by training desert ants returning from an artificial feeder to find the nest at one of four alternative positions located asymmetrically inside a four-cylinder landmark array. The cylindrical landmarks were all of the same size and arranged in a square, with the nest located in the southeast corner. When released from the compass direction experienced during training (southeast), the ants searched most intensely at the fictive nest position. When instead released from any of the three alternative directions of approach (southwest, northwest or northeast), the same individuals instead searched at two of the four alternative positions by initiating their search at the position closest to the direction of approach when entering the landmark square and then returning to the position at which snapshot, current landmark image and celestial reference information were in register. The results show that, in the ants' visual snapshot memory, a memorized landmark scene can temporarily be decoupled from a memorized celestial system of reference.

Animals↗

PubMed2002

Does reflection polarization by plants influence colour perception in insects? Polarimetric measurements applied to a polarization-sensitive model retina of Papilio butterflies.

Using imaging polarimetry, we have measured some typical reflection-polarization patterns of plant surfaces (leaves and flowers) under different illuminations. Using a quantitative model to determine photon absorptions in the weakly polarization-sensitive (PS approximately 2) photoreceptors of Papilio butterflies, we have calculated the influence of reflection polarization on the colours of leaves and flowers perceived by PAPILIO: Compared with a retina containing polarization-blind colour receptors, the colour loci of specularly reflecting and, thus, strongly polarizing areas on a plant are slightly shifted, which could cause the perception of false colours. However, the colour of specularly reflecting surfaces is strongly masked by white glare, which may prevent the perception of polarization-induced hue shifts. Although the perception of polarizational false colours by Papilio butterflies was previously demonstrated with artificial, strongly colour-saturated and totally linearly polarized stimuli, we expect that the weak polarization sensitivity of Papilio photoreceptors hardly influences colour perception under natural conditions.

Animals↗

PubMed2002

The visual centring response in desert ants, Cataglyphis fortis.

When negotiating their way through cluttered environments, desert ants, Cataglyphis fortis, tend to run along the midlines of the alleys formed by adjacent low shrubs. This 'centring response' was investigated by inducing foraging ants to walk through artificial channels. The sidewalls of the channel were either homogeneously black or provided with stationary or moving black-and-white gratings. The speed of motion and the spatial period of the gratings and the height of the walls could be varied independently on the left-hand and right-hand sides of the channel. The results clearly show that the ants, while exhibiting their centring responses, try to balance neither the self-induced image speeds nor the contrast frequencies seen in their left and right visual fields, but the vertical angle subtended by the landmarks on either side. When manoeuvring through the channel, the ants always adjust the lateral positions of their walking trajectories in such a way that the vertical angles subtended by the walls are identical for both eyes.

Animals↗

PubMed2002

First observation of the fourth neutral polarization point in the atmosphere.

In the clear sky there are three commonly known loci, the Arago, Babinet, and Brewster neutral points, where the skylight is unpolarized. These peculiar celestial points, bearing the names of their discoverers, have been the subject of many ground-based investigations, because their positions are sensitive indicators of the amount and type of atmospheric turbidity. According to theoretical considerations and computer simulations, there should exist an additional neutral point approximately opposite to the Babinet point, which can be observed only at higher altitudes in the air or space. Until now, this anonymous "fourth" neutral point has not been observed during air- or space-borne polarimetric experiments and has been forgotten, in spite of the fact that the neutral points were a basic tool in atmospheric research for a century. Here, we report on the first observation of this fourth neutral point from a hot air balloon. Using 180 degrees-field-of-view imaging polarimetry, we could observe the fourth neutral point at 450, 550, and 650 nm from different altitudes between 900 and 3500 m during and after sunrise at approximately 22 degrees - 40 degrees below the anti-solar point along the anti-solar meridian, depending on the wavelength and solar elevation. We show that the fourth neutral point exists at the expected location and has characteristics similar to those of the Arago, Babinet, and Brewster points. We discuss why the fourth neutral point has not been observed in previous air- or space-borne polarimetric experiments.

Journal Article↗