Colour perception of single and mixed monochromatic lights in the blowfly Lucilia cuprina

Colour perception of spectral lights and mixtures of two monochromatic lights of blue and yellow wavelengths was studied in the blowfly Lucilia cuprina by using a generalization test in which the fly had to compare these lights in memory with coloured papers (blue, green, yellow and red) represented in the test array. Flies trained to a monochromatic light in the wavelength range of 429–491 nm responded to blue; those trained to 502–511 nm to green; and those trained to 522–582 nm to yellow. The maximal generalization for blue was found at 429 nm and that for yellow at 543 nm. Flies trained to the mixtures responded neither to blue, green nor yellow, when the blue component was mixed with the yellow component in a ratio of approximately 1 3. It seems that the fly perceives the mixtures as a neutral or an achromatic light. Colour loci of coloured papers, spectral lights and mixtures of two monochromatic lights used formed blue, yellow and neutral clusters in a colour triangle with respect to generalization responses to test colours.     

Colour choices of naive bumble bees and their implications for colour perception

The innate preferences of inexperienced bumble bees, Bombus terrestris, for floral colour stimuli were studied using artificial flowers. The artificial flowers provided a colour pattern and consisted of a star-shaped corolla and of central colour patches similar to the nectar guide of natural flowers. The innate choice behaviour was assessed in terms of the number of approach flights from some distance towards the artificial flowers and the percentage of approach flights terminating in antennal contact with the floral guide. The colours of the floral guide, the corolla and the background were varied. It was shown that the innate flower colour preference in bumble bees has two components. 1. The frequency of approaches from a distance is correlated with the colour difference between the corolla and the background against which it is presented. If the corolla colour was constant but its background colour varied, the relative attractiveness of the corolla increased with its colour difference to the background. The colour difference assessment underlying this behaviour on a perceptual basis can be attained by means of colour opponent coding, a system well-established in Hymenoptera. 2. The frequency of antennal contacts with the floral guides relative to that of approach flights cannot be accounted for by colour opponent coding alone. Whether the approach flights are interrupted, or whether they end in an antennal contact with the nectar guide is strongly dependent on the direction (sign) of the colour difference, not only its magnitude. The choice behaviour requires a unique perceptual dimension, possibly that of colour saturation or that of hue perception comparable to components of colour perception in humans.     

Learning and discrimination of coloured papers in the walking blowfly,Lucilia cuprina

Summary A new training and testing paradigm for walking sheep blowflies, Lucilia cuprina, is described. A fly is trained by presenting it with a droplet of sugar solution on a patch of coloured paper. After having consumed the sugar droplet, the fly starts a systematic search. While searching, it is confronted with an array of colour marks consisting of four colours displayed on the test cardboard (Fig. 1). Colours used for training and test include blue, green, yellow, orange, red, white and black.Before training, naive flies are tested for their spontaneous colour preferences on the test array. Yellow is visited most frequently, green least frequently (Table 2). Spontaneous colour preferences do not simply depend on subjective brightness (Table 1).The flies trained to one of the colours prefer this colour significantly (Figs. 5 and 9–11). This behaviour reflects true learning rather than sensitisation (Figs. 6–7). The blue and yellow marks are learned easily and discriminated well (Figs. 5, 9, 11). White is also discriminated well, although the response frequencies are lower than to blue and yellow (Fig. 11). Green is discriminated from blue but weakly from yellow and orange (Figs. 5, 9, 10). Red is a stimulus as weak as black (Figs. 8, 9). These features of colour discrimination reflect the spectral loci of colours in the colour triangle (Fig. 14).The coloured papers seem to be discriminated mainly by the hue of colours (Fig. 12), but brightness may also be used to discriminate colour stimuli (Fig. 13).     

Dual-curing resin cement with colour indicator for adhesively cemented restorations to dental tissues: Change of colour by curing and some physical properties

The study was aimed to investigate a color indicator containing dual curing resin composite luting cement and to plot the color change to the time of solidification of the cement. In addition some physical properties were studied. Specimens were made of a dual-cure resin cement (Maxcem Elite™ Chroma, Kerr, Orange, CA, USA) and polymerized by autopolymerization only, or with light initiated polymerization. A spectrophotometer was used to quantify the color change of the cement as plotted with the curing time. The efficacy of the curing process was studied by measuring water sorption and the ultimate flexural properties of the cement. The results showed that the flexural strength of cement after autopolymerization was 27.3 MPa and after light initiated polymerization 48.1 MPa. Young’s modulus of bending was 2089.3 MPa and 3781.5 MPa respectively for the same cement samples. Water sorption after two weeks for the autopolymerization cement samples was −1.12 wt% and for the light initiated polymerization samples 0.56 wt%. Non-parametric Spearman’s correlation was measured for autopolymerized cement samples between variables for color and solidification load (N), which showed a strong correlation between curing process and color change (p < 0.05). There was a correlation between the color change and degree of monomer conversion of the dual curing resin composite luting cement which contained a color indicator system for polymerization reaction. The study also suggested that autopolymerization only resulted in suboptimal polymerization of the cement. By additional light curing considerably higher flexural properties were obtained.     

Biological significance of distinguishing between similar colours in spectrally variable illumination: bumblebees (<Emphasis Type="Italic">Bombus terrestris</Emphasis>) as a case study

Individual bumblebees were trained to choose between rewarded target flowers and non-rewarded distractor flowers in a controlled illumination laboratory. Bees learnt to discriminate similar colours, but with smaller colour distances the frequency of errors increased. This indicates that pollen transfer might occur between flowers with similar colours, even if these colours are distinguishable. The effect of similar colours on reducing foraging accuracy of bees is evident for colour distances high above discrimination threshold, which explains previous field observations showing that bees do not exhibit complete flower constancy unless flower colour between species is distinct. Bees tested in spectrally different illumination conditions experienced a significant decrease in their ability to discriminate between similar colours. The extent to which this happens differs in different areas of colour space, which is consistent with a von Kries-type model of colour constancy. We find that it would be beneficial for plant species to have highly distinctive colour signals to overcome limitations on the bees performance in reliably judging differences between similar colours. An exception to this finding was flowers that varied in shape, in which case bees used this cue to compensate for inaccuracies of colour vision.     

Simultaneous and successive colour discrimination in the honeybee (Apis mellifera)

The colour discrimination of individual free-flying honeybees (Apis mellifera) was tested with simultaneous and successive viewing conditions for a variety of broadband reflectance stimuli. For simultaneous viewing bees used form vision to discriminate patterned target stimuli from homogeneous coloured distractor stimuli, and for successive discrimination bees were required to discriminate between homogeneously coloured stimuli. Bees were significantly better at a simultaneous discrimination task, and we suggest this is explained by the inefficiency with which the bees brain can code and retrieve colour information from memory when viewing stimuli successively. Using simultaneous viewing conditions bees discriminated between the test stimuli at a level equivalent to 1 just-noticeable-difference for human colour vision. Discrimination of colours by bees with simultaneous viewing conditions exceeded previous estimates of what is possible considering models of photoreceptor noise measured in bees, which suggests spatial and/or temporal summation of colour signals for fine discrimination tasks. The results show that when behavioural experiments are used to collect data about the mechanisms facilitating colour discrimination in animals, it is important to consider the effects of the stimulus viewing conditions on results.     

Patterns of chromatic information processing in the lobula of the honeybee, Apis mellifera L

The honeybee, Apis mellifera L., is one of the living creatures that has its colour vision proven through behavioural tests. Previous studies of honeybee colour vision has emphasized the relationship between the spectral sensitivities of photoreceptors and colour discrimination behaviour. The current understanding of the neural mechanisms of bee colour vision is, however, rather limited. The present study surveyed the patterns of chromatic information processing of visual neurons in the lobula of the honeybee, using intracellular recording stimulated by three light-emitting diodes, whose emission spectra approximately match the spectral sensitivity peaks of the honeybee. The recorded visual neurons can be divided into two groups: non-colour opponent cells and colour opponent cells. The non-colour opponent cells comprise six types of broad-band neurons and four response types of narrow-band neurons. The former might detect brightness of the environment or function as chromatic input channels, and the latter might supply specific chromatic input. Amongst the colour opponent cells, the principal neural mechanism of colour vision, eight response types were recorded. The receptive fields of these neurons were not centre surround as observed in primates. Some recorded neurons with tonic post-stimulus responses were observed, however, suggesting temporal defined spectral opponency may be part of the colour-coding mechanisms.     

Mouth colour is a reliable signal of need in begging canary nestlings

Begging passerine chicks display brightly coloured mouths as they solicit food from their parents. Despite a range of hypotheses, the function of vivid nestling mouth colour remains unknown. Here I report that mouth colour functions as a signal of need in canary nestlings, in the days immediately following hatching. Changes in mouth colour accurately reflect a nestling''s state of need: the more food deprived the chick, the more intensely coloured its mouth. In controlled experiments with two nestlings, parents were offered the opportunity to choose which nestling to feed. When the mouth colour of one offspring was artificially reddened using food colouring, parents gave it more food. These results demonstrate a novel function for nestling mouth colour and are consistent with recent models of the resolution of parent–offspring conflict.     

Host Specificity and Morphometrics of Four Populations of Heterodera glycines (Nematoda: Heteroderidae)

Four populations of Heterodera glycines from four different states differed considerably in numbers of adult females developed on five resistant soybean cultivars, mungbean and lespedeza. Differences were observed also in body, tail and tail terminus lengths of second-stage larvae. No attempt was made to assign these populations to recognized races, and it is suggested that race designations should be applied only to representative samples of field populations and not to selected greenhouse populations or isolates.     

Flower colour preferences of Aporia bieti (Lepidoptera: Pieridae) in the Xiama Forest Farm,Gansu, China

In addition to their ornamental value, butterflies provide value to flowering plants through pollination, which can improve their heterosis. Studying the relationship between butterflies and flowers is useful for understanding the adaptive relationship between them. By observing the pollinating and feeding behaviour of Aporia bieti in the Xiama forest, Gansu, we explored the adaptive relationship between A. bieti proboscis size and the corolla tube length of the flowers. To eliminate interference from the butterfly's sense of smell, we used foam flowers instead of real flowers. The results indicated that (1) of the red, yellow, pink, purple, and white flowers tested, yellow flowers were preferred; (2) there was no distinct difference in the preferences of A. bieti for large- (45 mm) and small- (25 mm) sized flowers; and (3) A. bieti proboscis length was significantly related to the corolla tube length of the flowers fed on by the butterfly, which suggests co-evolution between butterfly proboscis length and the length of the pollen tube.     

Parental preference for red mouth of chicks in a songbird

Parental preferences during feeding and care-giving may select for ornamental traits in young, such as bright coloration. For chicks of coots, there is experimental evidence for this idea. We examined the hypothesis that bright yellow, orange and red mouths of chicks of songbirds have been favoured by feeding preferences in parents. In a field experiment, the orange–yellow mouths of great tit nestlings were dyed brightly red, and the feeding response of parents recorded. In nest boxes with extra daylight through a window, experimental chicks were on average given twice as much food (biomass) as control chicks (sham dyed). In normal nest boxes, the tendency was similar, but not significant. Thus, at least in good light, great tit parents prefer to feed young with red mouths, a preference for colourfulness that helps explain the evolution of bright gapes in chicks of songbirds (passerine birds).     

Signals of profitability? Food colour preferences in migrating juvenile blackcaps differ for fruits and insects

Red is a common colour signal in both aposematic warning displays, and in fruit displays. One common feature is that red is conspicuous against the natural background of the prey and fruits. However, there is a potential conflict between fruits and aposematic prey in how a bird predator should react to red colours, where fruits aim to attract birds and aposematic insects aim to ward off, often the same bird individuals. Here we investigate possible differences in red/green colour preferences of frugivorous, wild-caught, young blackcaps (Sylvia atricapilla), when food is either a fruit or an insect. Birds in two groups were presented with a series of pairs of food items that had been artificially painted red and green, in the order of (I) fruits, crickets and maggots, or (II) crickets, fruits, and maggots. Birds first presented with crickets or fruits differed in first attacks directed at the two colours: They showed no colour preference between fruits, but showed a clear preference for green over red crickets. Also, birds in both experimental groups clearly preferred green to red maggots. These results provide evidence that wild, frugivorous birds are able to differentiate between prey types, and show different colour preferences depending on whether food is insect or fruit. We conclude that blackcaps show an attack bias against red insects, and that one important function of the signal in insects, is to inhibit attack after discovery. However, the lack of preference for red fruits suggests other functions to red fruit displays, such as facilitating discovery per se, rather than directly stimulating attack after discovery.     

Opponent colour coding is a universal strategy to evaluate the photoreceptor inputs in Hymenoptera

Summary Behavioural tests were carried out with 9 hymenopteran insect species, which ranked certain sets of coloured stimuli according to their subjective similarity to a previously memorized stimulus. Kendall's coefficient is employed for the analysis of correlation between these similarity rankings and the colour distance rankings predicted by various models of neural colour computation. The models are based on the measured spectral sensitivities of photoreceptor colour types and use a variety of simple colour coding systems to derive hypothetical colour distances. The correlation between the predictions of the models and the behavioural results serves as a measure for the likelihood of existence of a colour coding system. In all species, the similarity rankings can be best explained by assuming that colour is coded on a perceptual level by two colour opponent mechanisms. Brightness differences are ignored, indicating that an intensity-coding sub-system is not used in colour discrimination by the insects investigated. The weighting factors of the colour opponent mechanisms differ between species in detail, but not in the principles involved. It is thus possible to employ a standard measure of perceptual colour distance (colour hexagon distance) to predict the capacities of colour discrimination adequately in all the tested insects.     

Variation in radular teeth and acuspid side of the radula in Lacuna pallidula, L. parva and L. vincta (Gastropoda: Littorinidae) from the Isle of Wight, United Kingdom

The variation in the radula of three species of Lacuna has been investigated and the back of the rachidian tooth is proposed as providing a new character set of potentially high taxonomic value. The term basal plate is introduced for the back of the rachidian tooth. Cusp and tooth morphology are closely related to diet and wear, and are subject to considerable homoplasy, whereas the structure of the basal plate of the rachidian tooth provides a more neutral character set. The difference in this character set between the lacunids has been quantified using seven measurements and the exploratory multivariate statistical procedure principal component analysis. The basal plate of the rachidian tooth showed interspecific differences. The taxonomic value of this new character set should be evaluated in further studies of other prosobranchs. Received in revised form: 25 October 2000 Electronic Publication     

The effects of large and small-scale random events on the synchrony of metapopulation dynamics: a theoretical analysis

We present an analysis of the conditions under which migration and global random factors may determine large scale synchrony in the dynamics of spatially structured populations. We derive an analytic approximation which describes how the desynchronizing influence of local environmental stochasticity combines with the synchronizing influences of larger scale environmental stochastic variation and migration to determine population cross correlation coefficients. Despite the simplifications made by this analysis, computer simulations show that the behaviour of more complicated models is well described by our approximation over considerable regions of parameter space. We conclude that population synchrony is largely determined by the coefficients of variation (CVs) of the local and larger scale stochastic processes, and that migration alone is only likely to maintain population synchrony when the CV of the local stochastic process is very small.     

Microtubules in the epidermal cells of Carausius morosus (Br.). Their pattern and relation to pigment migration

The existence of one or several systems of microtubules, consisting of a central bundle that branches off towards the basal and distal ends of epidermal cells of Carausius morosus has been shown by indirect immuno-fluorescence microscopy using monospecific anti-tubulin. The pattern of microtubules coincides with the position of the ommochrome granules and their migration path during physiological colour change. The ommochrome granules stick to isolated bundles of microtubules. Small bundles of microtubules extend almost perpendicularly towards the apical cell membrane where they are attached. Distally they are covered by pore channels within the cuticle. Parallel to the basal cell membrane and in close contact with it, there are very small bundles of microtubules. These findings strongly support the idea that during physiological colour change the ommochrome granules migrate along a firmly fixed system of microtubules.     

The genetic basis of an adaptive radiation: warning colour in two Heliconius species

Mimetic colour pattern races of Heliconius butterflies provide a striking example of adaptive radiation and numerous crossing experiments have investigated the genetics of these racial differences. However, colour pattern differentiation between closely related Heliconius species has not been previously studied. Here we present data from crosses between H. erato cyrbia and its sister species, H. himera. The genetic architecture underlying colour pattern divergence between these species is identical to that observed between races of H. erato. As in inter-racial crosses, colour pattern differences resulted from segregation at a few major loci. Evidence from 1321 offspring in 4 F₁, 17 backcross, 7 F₂ and 21 further crosses showed that two major loci controlled most of the colour pattern differences between H. erato and H. himera. There were strong interactions between these loci in their patterns of expression and evidence for other loci with relatively minor phenotypic effects. More importantly, based on patterns of expression within broods and linkage with Aconitase, we conclude that these major loci were homologous with those known to be responsible for colour pattern differences within H. erato. Our crosses also permit a re-evaluation of the relationships between colour pattern races of H. erato. This suggests that H. e. hydara, which occurs across a major mtDNA break, is the ancestral phenotype from which other races have evolved. Based on this assumption, we find no evidence to support the recent suggestion that apparently homologous colour pattern alleles have arisen multiple times.     

周口店第一地点人类牙齿化石的时序性变异

周口店第一地点人类下颌牙齿材料显示出一定程度的时序性变异。该地点时代较晚的下颌牙齿与时代较早的相比,门齿偏大些,而犬齿和犬齿后各齿显得偏小,呈现出趋向早期智人牙齿尺寸格式的演变。该地点人类牙齿大小上的差异不能如魏敦瑞所主张的那样单纯地归因于两性差异。