Shape discrimination by wasps (<Emphasis Type="Italic">Paravespula germanica</Emphasis>) at the food source: generalization among various types of contrast

Wasps (Paravespula germanica) were trained and tested at an artificial feeding site, using convex shapes that produced colour contrast, luminance contrast, or motion contrast against the background. With each of the three types of contrast, we tested the wasps capacity to discriminate the learned shape from novel shapes. In addition, in each experiment we tested the wasps capability to recognize the learned shape when it offered a different type of contrast than that it had during the training. With the coloured shapes, a side-glance at the colour discrimination performance of the wasps was possible in addition. Wasps are found to discriminate between a variety of convex shapes regardless of the type of contrast that they produce against the background. Mainly, they discriminate the learned shape from novel shapes even if the colour of the shapes or the type of contrast they produce against the background is altered in the test. Thus, wasps generalize the learned shape from one colour to another, as well as between colour contrast, luminance contrast, and motion contrast.     

Visual discrimination by the honeybee (Apis mellifera): the position of the common centre as the cue

Abstract. Bees can be trained to discriminate between a target with a 20° spot above a 10° spot of the same colour, and another target with the spots exchanged in position. Tests show that they do not remember the separate positions of spots of the same colour (including black) on the same target. The bees discriminate the difference in positions, in the vertical direction, of the common centres of the spots taken together, with or without green contrast.
Similar results are obtained in discriminations of a fixed T shape, each composed of two broad black bars subtending 8 by 24°, vs the same shape inverted. The trained bees fail to discriminate between the T shapes when the centroids are at the same level in the vertical direction. Moving the shapes in the horizontal direction in tests has less effect. Quite different results are obtained when the two bars of the T shape differ in colour. The bees discriminate the positions of the two colours separately, but they still fail to discriminate the shape of the T. The results can be explained by filters that detect the intensities within their fields, irrespective of shape, and weigh them according to their vertical angles from the horizontal midline. The normal function of these filters could be to detect the levels of objects relative to the horizon when the bee is in flight.     

The learning of a sequence of visual patterns by the ant Cataglyphis cursor

We used a maze to explore the ability of Cataglyphis cursor to store multiple visual patterns presented in a fixed sequence. Ants were trained individually to negotiate a linear maze that consisted of four boxes connected by tunnels and through which an ant travelled from a sucrose feeder back to its nest. Each box had one entrance and two possible exits. One exit led to a blocked tunnel and the other to an open tunnel leading to the entrance of the next box. The open and closed exits in each box were labelled by different solid, black shapes that were specific to each box. Ants learnt to negotiate the maze using the shapes for guidance rather than a fixed motor strategy. Trained ants could not only discriminate positive from negative shapes, but had also learnt which positive shape belonged to which box. For example, when the positive shape appropriate to box 1 (1+) was pitted against that appropriate to box 3 (3+), ants preferred 1+ to 3+ in box 1, but chose 3+ over 1+ in box 3. We conclude that ants can identify individual positive shapes and expect to encounter them in the correct order independently of extra-maze cues.     

Blue colour preference in honeybees distracts visual attention for learning closed shapes

Spatial vision is an important cue for how honeybees (Apis mellifera) find flowers, and previous work has suggested that spatial learning in free-flying bees is exclusively mediated by achromatic input to the green photoreceptor channel. However, some data suggested that bees may be able to use alternative channels for shape processing, and recent work shows conditioning type and training length can significantly influence bee learning and cue use. We thus tested the honeybees’ ability to discriminate between two closed shapes considering either absolute or differential conditioning, and using eight stimuli differing in their spectral characteristics. Consistent with previous work, green contrast enabled reliable shape learning for both types of conditioning, but surprisingly, we found that bees trained with appetitive-aversive differential conditioning could additionally use colour and/or UV contrast to enable shape discrimination. Interestingly, we found that a high blue contrast initially interferes with bee shape learning, probably due to the bees innate preference for blue colours, but with increasing experience bees can learn a variety of spectral and/or colour cues to facilitate spatial learning. Thus, the relationship between bee pollinators and the spatial and spectral cues that they use to find rewarding flowers appears to be a more rich visual environment than previously thought.     

Discrimination of coloured patterns by honeybees through chromatic and achromatic cues

We investigated pattern discrimination by worker honeybees, Apis mellifera, focusing on the roles of spectral cues and the angular size of patterns. Free-flying bees were trained to discriminate concentric patterns in a Y-maze. The rewarded pattern could be composed of either a cyan and a yellow colour, which presented both different chromatic and achromatic L-receptor contrast, or an orange and a blue colour, which presented different chromatic cues, but the same L-receptor contrast. The non-rewarded alternative was either a single-coloured disc with the colour of the central disc or the surrounding ring of the pattern, a checkerboard pattern with non-resolvable squares, the reversed pattern, or the elements of the training pattern (disc or ring alone). Bees resolved and learned both colour elements in the rewarded patterns and their spatial properties. When the patterns subtended large visual angles, this discrimination used chromatic cues only. Patterns with yellow or orange central discs were generalised toward the yellow and orange colours, respectively. When the patterns subtended a visual angle close to the detection limit and L-receptor contrast was mediating discrimination, pattern perception was reduced: bees perceived only the pattern element with higher contrast.     

Alternative use of chromatic and achromatic cues in a hawkmoth

The diurnal hummingbird hawkmoth Macroglossum stellatarum can learn the achromatic (intensity-related) and the chromatic (wavelength-related) aspect of a spectral colour. Free-flying moths learn to discriminate two colours differing in the chromatic aspect of colour fast and with high precision. In contrast, they learn the discrimination of two stimuli differing in the achromatic aspect more slowly and less reliably. When trained to use the chromatic aspect, they disregard the achromatic aspect, and when trained to use the achromatic aspect, they disregard the chromatic aspect, at least to some degree. In a conflicting situation, hummingbird hawkmoths clearly rely on the chromatic aspect of colour. Generally, the moths pay attention to the most reliable cue that allows them to discriminate colours in the learning situation. This is usually the chromatic aspect of the colour but they can learn to attend to the achromatic aspect instead. There is no evidence for relative colour learning, i.e. moths do not learn to choose the longer or shorter of two wavelengths, but it is possible that they learn to choose the darker or brighter shade of a colour, and thereby its relative intensities.     

Size,shape and hue modulate attraction and landing responses of the braconid parasitoid <Emphasis Type="Italic">Fopius arisanus</Emphasis> to fruit odour-baited visual targets

Female parasitoids are guided by multisensory information, including chemical and physical cues during host location. In the present study, we investigated the behavioural responses of naïve Fopius arisanus (Sonan) females to visual targets baited with guava odour. In non-choice wind tunnel tests, the attraction and landing responses of parasitoids to spheres painted with different colours, and targets of different shapes and sizes were evaluated. Females were more frequently attracted and landed more often on dark yellow targets than on targets with other colours. There was no correlation between the brightness of each colour and the attraction or landing responses. In contrast, both responses were correlated with relative reflectance (hue) of the coloured targets. A positive correlation was observed between attraction and hue, and a negative correlation between landing and hue. F. arisanus was attracted to and landed more often on spheres than on other shape models. The attraction response of this parasitoid was affected by the size of the targets, with spheres of 10 and 12 cm diameter being more attractive than spheres of 8, 6 and 4 cm diameter. The fact that F. arisanus females were able to discriminate among visual targets that differ in colour, shape and size stresses the importance of vision during host location by this species.     

Visual discrimination by the spraying characid,Copeina arnoldi Regan

Visual discrimination by male spraying characids, Copeina arnoldi, during spawn splashing was studied. Apparently the spawn is not used per se in directing parental splashing. Males discriminated between the standard 12·7-cm disc and a square, a triangle, a white disc, and a small disc in successive and/or simultaneous presentations. They did not discriminate between the standard disc and a large disc in succession, nor between the standard (green) disc and a white disc presented simultaneously. Although they can discriminate between objects differing in shape, colour, and/or brightness, these are probably not the major cues used in nature for selecting the spawn substrate from other proximal stimuli. However, large size differences may be important in spawn substrate discrimination.     

Do female tamarins use visual cues to detect fruit rewards more successfully than do males?

Primates are unique among eutherian mammals for possessing trichromatic colour vision. It is generally proposed that trichromacy evolved to aid detection of ripe fruits against mature foliage. However, while trichromacy is routine in all Old World monkeys and apes (the catarrhines), a cone opsin polymorphism in New World monkeys (the platyrrhines) results in foraging groups with mixed capacities for chromatic distinction. Although 50-66% of female platyrrhines are trichromatic, all males are dichromatic. Here, we test the hypothesis that trichromatic platyrrhines use visual cues to detect fruit rewards more successfully than do males. Specifically, we ask whether female emperor tamarins, Saguinus imperator imperator, and saddleback tamarins, S. fuscicollis weddelli, are the first members of their foraging group to locate food patches; and, furthermore, whether they are more successful than males in using colour, shape and size cues to discriminate between sham and reward feeding sites. Our results show that females and males do not differ in their ability to locate or discriminate between feeding sites. We conclude that trichromatic vision in female tamarins does not confer an advantage for detecting yellow fruit rewards against mature foliage. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Female mate preferences on high‐dimensional shape variation for male species recognition traits

Females in many animal species must discriminate between conspecific and heterospecific males when choosing mates. Such mating preferences that discriminate against heterospecifics may inadvertently also affect the mating success of conspecific males, particularly those with more extreme phenotypes. From this expectation, we hypothesized that female mate choice should cause Enallagma females (Odonata: Coenagrionidae) to discriminate against conspecific males with more extreme phenotypes of the claspers males use to grasp females while mating – the main feature of species mate recognition in these species. To test this, we compared cerci sizes and shapes between males that were captured while mating with females to males that were captured at the same time but not mating in three Enallagma species. In contrast to our hypothesis, we found only one of forty comparisons of shape variation that was consistent with females discriminating against males with more extreme cerci shapes. Instead, differences in cerci shape between mating and single males suggested that females displayed directional preferences on 1–4 aspects of cerci shape in two of the species in our samples. These results suggest that whereas some directional biases in mating based on cerci shape occur, the intraspecific phenotypic variation in male cerci size and shape is likely not large enough for females to express any significant incidental discrimination among conspecifics with more extreme shapes.     

Colour preferences of flower-naive honeybees

Flower-naive honeybees Apis mellifera L. flying in an enclosure were tested for their colour preferences. Bees were rewarded once on an achromatic (grey, aluminium or hardboard), or on a chromatic (ultraviolet) disk. Since naive bees never alighted on colour stimuli alone, a scent was given in combination with colour. Their landings on twelve colour stimuli were recorded. Results after one reward (“first test”) were analysed separately from those obtained after few rewards (“late tests”).

1. After pre-training to achromatic signals, bees preferred, in the first test, bee-uv-blue and bee-green colours. With increasing experience, the original preference pattern persisted but the choice of bee-blue and bee-green colours increased.
2. Neither colour distance of the test stimuli to the background or to the pre-training signal, nor their intensity, nor their green contrast, accounted for the colour choice of bees. Choices reflected innate preferences and were only associated with stimulus hue.
3. Bees learned very quickly the pre-trained chromatic stimulus, the original colour preferences being thus erased.
4. Colour preferences were strongly correlated with flower colour and its associated nectar reward, as measured in 154 flower species.
5. Colour preferences also resemble the wavelength dependence of colour learning demonstrated in experienced bees.

     

Pattern discrimination by the honeybee (Apis mellifera ) is colour blind for radial / tangential cues

Bees were trained to discriminate between two patterns, one of which was associated with a reward, in a Y-choice apparatus with the targets presented vertically at a distance at an angular subtense of 50°. Previous work with this apparatus has found discrimination between two patterns of coloured gratings or radial sectors that are fixed in different orientations during the training. When there was contrast to the blue receptors alone, gratings of period 6° were resolved, and 4° when there was contrast to the green receptors. In the present work, bees discriminate between a pattern containing tangentially arranged edges and one containing radially arranged edges, both with no average edge orientation. The targets were rotated every 5 min to make the locations of areas useless as cues. The edges remained consistently radial or tangential and were therefore the only cues. Tests with patterns of selected colours and various levels of grey show that for each colour there is a level of grey at which discrimination fails. Discrimination is therefore colour-blind. The same patterns were made with combinations of coloured papers that give no contrast to the green receptors or alternatively to the blue receptors. The bees discriminate only if the edges between colours present a contrast to the green receptors. The system that discriminates generalized radial and tangential cues is therefore colour blind because the inputs are restricted to the green receptors, not because receptor outputs are added together. The same result was obtained with a very coarse pattern of period 20°. Accepted: 10 January 1999     

Behavioural evidence for visual recognition of predators by the mangrove climbing crab Sesarma leptosoma

The climbing crab Sesarma leptosoma colonizes the mangrove roots and canopy of East African mangrove swamps, an intricate three-dimensional habitat in which it orients itself visually. To ascertain if vision helps this tree crab to detect dangers such as predators, we used dummy objects: (1) a preserved specimen of its predator, the crab Epixanthus dentatus in its typical ambush posture; (2) a piece of wood with real E. dentatus claws attached to it, the same size as, and painted to resemble (to the human eye), this predator; and (3) a piece of wood the same size and colour as a live crab but without claws. When these dummies were presented to migrating S. leptosoma in the field, they stopped their normal migratory flow only when they were able to see the open claws of the predator. Thus S. leptosoma showed a considerable ability to perceive shape, being able to distinguish motionless objects of different shapes but similar size and to associate the detected shapes with the presence of danger.     

Visual generalization in honeybees: evidence of peak shift in color discrimination

In the present study, we investigated color generalization in the honeybee Apis mellifera after differential conditioning. In particular, we evaluated the effect of varying the position of a novel color along a perceptual continuum relative to familiar colors on response biases. Honeybee foragers were differentially trained to discriminate between rewarded (S+) and unrewarded (S?) colors and tested on responses toward the former S+ when presented against a novel color. A color space based on the receptor noise-limited model was used to evaluate the relationship between colors and to characterize a perceptual continuum. When S+ was tested against a novel color occupying a locus in the color space located in the same direction from S? as S+, but further away, the bees shifted their stronger response away from S? toward the novel color. These results reveal the occurrence of peak shift in the color vision of honeybees and indicate that honeybees can learn color stimuli in relational terms based on chromatic perceptual differences.     

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.     

Avian colour perception predicts behavioural responses to experimental brood parasitism in chaffinches

Hosts of cuckoos have evolved defences allowing them to discriminate and reject parasite eggs. Mechanisms of discrimination are mostly visually mediated, and have been studied using approaches that do not account for what the receiver (i.e. host) actually can discriminate. Here, for the first time we apply a perceptual model of colour discrimination to study behavioural responses to natural variation in parasite egg appearance in chaffinches Fringilla coelebs. Discrimination of parasite eggs gradually increased with increasing differences in chromatic contrasts as perceived by birds between parasite and host eggs. These results confirm that colour differences of the eggs as perceived by birds are important integral parts of a matching signal used by chaffinch hosts.     

Mapping the variation in spider body colouration from an insect perspective

Colour variation is frequently observed in spiders. Such variation can impact fitness by affecting the way spiders are perceived by relevant observers such as prey (i.e. by resembling flower signals as visual lures) and predators (i.e. by disrupting search image formation). Verrucosa arenata is an orb-weaving spider that presents colour variation in a conspicuous triangular pattern on the dorsal part of the abdomen. This pattern has predominantly white or yellow colouration, but also reflects light in the UV part of the spectrum. We quantified colour variation in V. arenata from images obtained using a full spectrum digital camera. We obtained cone catch quanta and calculated chromatic and achromatic contrasts for the visual systems of Drosophila melanogaster and Apis mellifera. Cluster analyses of the colours of the triangular patch resulted in the formation of six clusters and three clusters in the colour space of D. melanogaster and A. mellifera, respectively. Significant differences were found between morphs for both visual systems in contrasts between the colour pattern and two backgrounds against which it would be viewed. Yellow spiders showed higher chromatic contrast than white spiders, while white spiders showed higher achromatic contrast. Therefore, there are perceptual differences between V. arenata colour morphs in the visual systems of potential relevant observers which could pose an important selective pressure on this trait. A variation in the contribution of colour channels to the colour pattern observed in colour maps constructed from reflectance values of individual pixels could influence the way the pattern is perceived, and its resemblance to attractive flower signals.     

The butterfly Papilio xuthus detects visual motion using chromatic contrast

Many insects’ motion vision is achromatic and thus dependent on brightness rather than on colour contrast. We investigate whether this is true of the butterfly Papilio xuthus, an animal noted for its complex retinal organization, by measuring head movements of restrained animals in response to moving two-colour patterns. Responses were never eliminated across a range of relative colour intensities, indicating that motion can be detected through chromatic contrast in the absence of luminance contrast. Furthermore, we identify an interaction between colour and contrast polarity in sensitivity to achromatic patterns, suggesting that ON and OFF contrasts are processed by two channels with different spectral sensitivities. We propose a model of the motion detection process in the retina/lamina based on these observations.     

Pattern recognition in honeybees: chromatic properties of orientation analysis

The spectral properties of the discrimination of pattern orientation in freely flying honeybees (Apis mellifera) were examined. Bees were trained to discriminate between two random black/white gratings oriented perpendicularly to each other, one of which was associated with a reward. Subsequently the bees were tested on two-colour gratings or gratings consisting of grey and coloured stripes, providing a range of different chromatic contrasts, luminance contrasts and specific channel contrasts. The results of these experiments indicate that orientation analysis in the honeybee is mediated almost exclusively by the green receptor channel, although the bee's visual system as a whole is endowed with excellent trichromatic colour vision.