Why birds eat colourful grit: colour preferences revealed by the colour of gizzard stones

Colour preferences from sexual or social contexts are assumed to have arisen owing to preferences for specific kinds of food, representing a sensory bias, but once colour preferences have evolved in a sexual context, they may also be expressed during foraging. We tested whether preferences for specific body colours (i.e. plumage and soft parts) were related to colour preferences for grit ingested by birds. Birds eat grit to facilitate break down of food by the gizzard, and this function is independent of the colour of grit, but depends on the physical properties of stones. Bird species were significantly consistent in colour of grit, and grit of different colours varied in prevalence among species, even when analyses were restricted to a sample from a single locality. There were positive correlations between presence of lilac and red grit in the gizzard and presence of sexually dichromatic lilac and red colour on the body. There was a positive correlation between red grit colour and red sexually monochromatic body colour. Bird species with many different sexual colours, but not sexually monochromatic colours on their body had many different colours of grit. Males had more lilac and red grit than females, with this effect differing among species, whereas that was not the case for grit of other colours. These findings are consistent with the sensory bias hypothesis that birds express preferences for grit of specific colours and a high diversity of colours related to sexual colouration of the body, even when the colour of such grit is only visible to the individual at the moment of ingestion.     

The effects of the visual environment on responses to colour by domestic chicks

It is well known that development of vision is affected by experience, but there are few studies of environmental effects on colour vision. Natural scenes contain predominantly a restricted range of reflectance spectra, so such effects might be important, perhaps biasing visual mechanisms towards common colours. We investigated how the visual environment affects colour preferences of domestic chicks ( Gallus gallus), by training week-old birds to select small food containers distinguished from an achromatic alternative either by an orange or by a greenish-blue colour. Chicks that had been raised in control conditions, with long-wavelength-dominated reflectance spectra, responded more readily to orange than to blue. This was not due to avoidance of blue, as increasing saturation enhanced the chicks' preference for the same hue. The advantage of orange was, however, reduced or abolished for chicks raised in an environment dominated by blue objects. This indicates that responses to coloured food are affected by experience of non-food objects. If colours of ordinary objects in the environment do influence responses to specialised visual signals this might help explain why biological signals directed at birds are often coloured yellow, orange or red; long-wavelength-dominated spectra being more prevalent than short-wavelength-dominated spectra.     

A mutation in the MATP gene causes the cream coat colour in the horse

In horses, basic colours such as bay or chestnut may be partially diluted to buckskin and palomino, or extremely diluted to cream, a nearly white colour with pink skin and blue eyes. This dilution is expected to be controlled by one gene and we used both candidate gene and positional cloning strategies to identify the "cream mutation". A horse panel including reference colours was established and typed for different markers within or in the neighbourhood of two candidate genes. Our data suggest that the causal mutation, a G to A transition, is localised in exon 2 of the MATP gene leading to an aspartic acid to asparagine substitution in the encoded protein. This conserved mutation was also described in mice and humans, but not in medaka.     

Corticosterone regulates multiple colour traits in Lacerta [Zootoca] vivipara males

Ornamental colours usually evolve as honest signals of quality, which is supported by the fact that they frequently depend on individual condition. It has generally been suggested that some, but not all types of ornamental colours are condition dependent, indicating that different evolutionary mechanisms underlie the evolution of multiple types of ornamental colours even when these are exhibited by the same species. Stress hormones, which negatively affect condition, have been shown to affect colour traits based on different pigments and structures, suggesting that they mediate condition dependence of multiple ornament types both among and within individuals. However, studies investigating effects of stress hormones on different ornament types within individuals are lacking, and thus, evidence for this hypothesis is scant. Here, we investigated whether corticosterone mediates condition dependence of multiple ornaments by manipulating corticosterone levels and body condition (via food availability) using a two‐factorial design and by assessing their effect on multiple colour traits in male common lizards. Corticosterone negatively affected ventral melanin‐ and carotenoid‐based coloration, whereas food availability did not affect coloration, despite its significant effect on body condition. The corticosterone effect on melanin‐ and carotenoid‐based coloration demonstrates the condition dependence of both ornaments. Moreover, corticosterone affected ventral coloration and had no effect on the nonsexually selected dorsal coloration, showing specific effects of corticosterone on ornamental ventral colours. This suggests that corticosterone simultaneously mediates condition dependence of multiple colour traits and that it therefore accounts for covariation among them, which may influence their evolution via correlational selection.     

Ultraviolet vision and foraging in terrestrial vertebrates

Tetrachromatic colour vision, based on four ‘main’ colours and their combinations, is probably the original colour vision in terrestrial vertebrates. In addition to human visible waveband of light (400–700 nm) and three main colours, it also includes the near ultraviolet part of light spectrum (320–400 nm). The ecological importance of ultraviolet (UV) vision in animals has mainly been studied in the context of intra‐ and inter‐sexual signalling, but recently the importance of UV vision in foraging has received more attention. Foraging animals may use either UV cues (reflectance or absorbance) of food items or UV cues of the environment. So far, all diurnal birds studied (at least 35 species), some rodents (4 species), many reptilians (11 species) and amphibians (2 species) are likely able to see near UV light. This probably allows e.g. diurnal raptors as well as frugivorous, nectarivorous and insectivorous birds to use foraging cues invisible to humans. The possible role of UV cues and existing light conditions should be taken into account when food selection of vertebrate animals is studied, particularly, in experiments with artificial food items.     

Bright autumn colours of deciduous trees attract aphids: nutrient retranslocation hypothesis

We propose an alternative hypothesis to the handicap-signalling hypothesis, to explain the high number of specialist aphids on tree species having bright autumn colour. Since birch aphids actively seek the first yellowing leaves for breeding in autumn, it is obvious that autumn colour of foliage does not repel migrating aphids. We suggest that aphids use bright colours as a cue to detect individual trees and leaves that are good sources of nitrogen in the form of amino acids in autumn. The active formation of bright-coloured pigments in leaves is needed to protect them from photo inhibition during energy consuming nutrient retranslocation under cold autumn conditions. During nutrient export from leaves, nitrogen is in the form of amino acids in the sieve elements and easily available for aphids. Therefore, bright colours may act as a signal of easily available high-quality food for viviparous aphid migrants that are selecting suitable trees for their sexual offspring reproduction. The females of sexual generation grown on the better quality food probably can oviposit the over-wintering eggs to the twigs in higher numbers, which may have an adaptive advantage in competition with conspecific females.     

食用天然色素开发利用中的一些问题

本文扼要讨论了食用天然色素的开发和利用,其中包括历史发展、安全性、着色力与稳定性、分析检测、规格标准、综合利用等。     

Food selection by chicks: Effects of colour,density and frequency of food types

Previous studies have shown that birds, including 3-day old chicks, show frequency-dependent selection when feeding on a food population made up of two types. Two experiments using 5-day old chicks are described here. In one, foods of three colours were presented in their three pairwise combinations, at five different relative frequencies. It was found that measures of selection were transitive: that is, selection of red versus yellow could be predicted from selection for red versus green and for green versus yellow. Selection was not frequency-dependent. In the second experiment, total food density, as well as relative frequency, was varied. Selection was density-dependent, being strongest at the middle one of the three densities. It was also irregularly frequency-dependent, being weaker at one (inter-mediate) frequency than at the other four, among which there was little variation.     

Carotenoid-based nestling colouration and parental favouritism in the great tit

While elaborate carotenoid-based traits in adult birds may have evolved as honest signals of individual quality in the context of sexual selection or other social interactions, the function of carotenoid-based colours in juveniles is less well understood. We investigated the hypothesis that carotenoid-based nestling colouration has evolved in response to parental preference of intensely coloured offspring during food provisioning. In a field experiment, we manipulated nestling plumage colouration by a carotenoid-supplementation and analysed the parental food provisioning behaviour before feather appearance and at the end of the nestling stage. Carotenoids per se did not influence the nestlings begging behaviour or parental feeding decisions and we found no evidence that carotenoid-based colouration in nestling great tits has a signalling function in parent-offspring interactions. Parents did not discriminate between intensely coloured and control offspring in their food provisioning and in accordance with this finding intensely coloured nestlings were not heavier or larger at the end of the nestling stage. Alternative explanations for the evolution of carotenoid-based colours in nestling birds are discussed.     

Influence of visual cues on host‐searching and learning behaviour of the egg parasitoids Telenomus podisi and Trissolcus basalis

Insect parasitoids use a variety of chemical and physical cues when foraging for hosts and food. Parasitoids can learn cues that lead them to the hosts, thus contributing to better foraging. One of the cues that influence host‐searching behaviour could be colour. In this study, we investigated the ability of females of the parasitoid wasps Telenomus podisi Ashmead and Trissolcus basalis Wollaston (both Hymenoptera: Scelionidae) to respond to colours and to associate the presence of hosts – eggs of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) – with coloured substrates after training (associative learning). Two sets of experiments were conducted: in one the innate preference for substrate colours was examined, in the other associative learning of substrate colour and host presence was tested in multiple‐choice and dual‐choice experiments. In the associative learning experiments, Te. podisi and Tr. basalis were trained to respond to differently coloured substrates containing hosts in two sessions of 2 h each, with 1‐h intervals. In multiple‐choice experiments, the wasps displayed innate preference for yellow substrates over green, brown, black, or white ones. Even after being trained on substrates of different colours, both parasitoids continued to show preference for yellow substrates. The response to the colours of substrates of both parasitoids was related with the orientation to the plant foliage during the search for hosts.     

A genome-wide scan study identifies a single nucleotide substitution in ASIP associated with white versus non-white coat-colour variation in sheep (Ovis aries)

In sheep, coat colour (and pattern) is one of the important traits of great biological, economic and social importance. However, the genetics of sheep coat colour has not yet been fully clarified. We conducted a genome-wide association study of sheep coat colours by genotyping 47 303 single-nucleotide polymorphisms (SNPs) in the Finnsheep population in Finland. We identified 35 SNPs associated with all the coat colours studied, which cover genomic regions encompassing three known pigmentation genes (TYRP1, ASIP and MITF) in sheep. Eighteen of these associations were confirmed in further tests between white versus non-white individuals, but none of the 35 associations were significant in the analysis of only non-white colours. Across the tests, the s66432.1 in ASIP showed significant association (P=4.2 × 10⁻¹¹ for all the colours; P=2.3 × 10⁻¹¹ for white versus non-white colours) with the variation in coat colours and strong linkage disequilibrium with other significant variants surrounding the ASIP gene. The signals detected around the ASIP gene were explained by differences in white versus non-white alleles. Further, a genome scan for selection for white coat pigmentation identified a strong and striking selection signal spanning ASIP. Our study identified the main candidate gene for the coat colour variation between white and non-white as ASIP, an autosomal gene that has been directly implicated in the pathway regulating melanogenesis. Together with ASIP, the two other newly identified genes (TYRP1 and MITF) in the Finnsheep, bordering associated SNPs, represent a new resource for enriching sheep coat-colour genetics and breeding.     

Genetic control of green curd colour in cauliflower

A genetic model was fitted to observed curd colours in a segregating cauliflower population derived from crosses between white and green curded types. The model was of a gene (Wi wi) giving white dominant over yellow, and an independent codominant gene (gr1 gr2) for green-ness.     

Colour association influences honey bee choice between sucrose concentrations

Certain colours associated with floral food resources are more quickly learned by honey bees (Apis mellifera) than are other colours. But the impact of colour, and other floral cues, on bee choice behaviour has not yet been determined. In these experiments, colour association and sugar concentration of reward were varied to assess how they interact to affect bee choice behaviour. Thirty-five bees were individually given binary choices between blue and yellow artificial flowers that contained either the same rewards or rewards of different sucrose concentrations. Honey bee choice between sucrose concentrations was affected by colour association and this effect was greatest when absolute difference between rewards was the lowest. The honey bee's ability to maximize energetic profitability during foraging is constrained by floral cue effectiveness.     

Induction of mitotic gene conversion by browning reaction products and its modulation by naturally occurring agents

Mitotic gene conversion in the D7 strain of Saccharomyces cerevisiae was significantly enhanced by exposure to non-enzymatic browning reaction products. These products were formed during the heating of sugar (caramelization reaction) or sugar-amino acid mixtures (Maillard reaction) at temperatures normally used during the cooking of food. Several modulating factors of this convertogenic activity were identified. These factors included two main groups: (1) trace metals which are widely distributed in the environment; and (2) several cellular enzymatic systems. The convertogenic activities of a heated glucose-lysine mixture and a commercial caramel powder were completely suppresses when yeast were concurrently exposed to these products and to either FeIII or CuII. Equimolar concentrations of MnII or sodium selenite had no effect on the convertogenic activity of the products of either model system. Horse-radish peroxidase, beef liver catalase and rat liver S9 preparations each decreased the frequency of gene conversion induced by the caramel powder and the heated glucose-lysine products. This modulating activity of the enzymes was lost if they were heat-inactivated. These studies indicate the presence of a variety of protective mechanisms which can modify genotoxic components in complex food mixtures.     

Do autumn leaf colours serve as a reproductive insurance against sucking herbivores?

Although autumn leaf colours of deciduous trees have been shown to protect against photo-oxidative damage, they are sometimes seen as signals to pests and predators. Here I modify the coevolution hypothesis of autumn leaf colours. I suggest that much of the within-population variation in autumn leaf colours can be explained by differences in the allocation of resources to sexual reproduction. According to the novel hypothesis, reproductively active woody plants produce early and intense autumn leaf colours in order to protect seeds and other reproductive tissues from pests that lay eggs in the autumn. If many seeds mature at times of leaf senescence or during the next summer, a woody plant will reallocate plenty of nitrogen to seeds. If sucking insects reproduce on such hosts, their flightless offspring will suffer poor-quality food after the ripening of seeds. Before this, however, insects will probably concentrate around the ripening seeds to forage on nitrogen-rich veins. This will decline the quality and quantity of developing seeds. If, on the other hand, insects are able to recognize reproductively active plants while laying eggs in the autumn, both the insects and the plants benefit. The flightless offspring of insects feeds on plants that supply sufficiently nitrogen for longer than reproducing plants do, while these optimise their reproduction by avoiding pests, which also contributes to the abundance of specialist pests. Hence, I suppose that while physiological factors are the origin of autumnal colour changes of deciduous leaves, the visible cue utilized by insects has evolved several times to an honest signal that reveals the unsuitability of the potential host in the near future. The reproductive insurance hypothesis may help us to understand why bright autumn leaf colours are rare among herbaceous plants, and why plants at high altitudes and latitudes are often brightly coloured in autumn.     

Effects of low pH and humus on the survivorship, growth and feeding of Gammarus pulex (L.) (Amphipoda)

SUMMARY. 1. The toxicity to the freshwater amphipod Gammarus pulex (L.) of soft water (pH6.0) with three concentrations of XAD-extracted aquatic humus was treated in the laboratory.
2. Exposure to pH6.0 water without humus added resulted in 92% mortality after 3 weeks. Humus, added at concentrations of 7 and 20 g Cm ³, decreased the mortality to 80% and 64% in the same period.
3. Surviving animals kept at pH6.0 had a lower growth rate, lower food conversion efficiency and higher body water content than animals kept at pH 7.3.
4. Humus had no significant effects on growth, food conversion or body composition of G. pulex kept at pH 6.0. However, there was a tendency for growth and food conversion to increase, and for body water content to decrease with increased humus concentration. The effects of humus on growth and food conversion of G. pulex observed in this study do not support the contention that humus acts as a free coupler to lower metabolic efficiency. On the contrary, humus tended to benefit food conversion.
5. It is suggested that low concentrations of humus can be directly beneficial to organisms in acidified water in ways other than by complexing toxic metals.     

Methodology for the testing of food dyes for genotoxic activity: experiments with red 2G (C.I. 18050).

A methodology for investigating genotoxicity of food colours using the fluctuation and DNA-repair assays with bacteria is described. In addition, a liquid repair test, developed to permit incorporation of microsomes and the quantitative estimation of cell viability, has been characterised with a number of positive control agents. Results obtained in these systems suggest that the food colour Red 2G induces repairable DNA damage and base-substitution mutation, but only in the presence of a rat-liver microsomal preparation. The significance of the data in the light of other toxicological information is discussed.     

Bumblebees (Bombus terrestris) and honeybees (Apis mellifera) prefer similar colours of higher spectral purity over trained colours

Differences in the concentration of pigments as well as their composition and spatial arrangement cause intraspecific variation in the spectral signature of flowers. Known colour preferences and requirements for flower-constant foraging bees predict different responses to colour variability. In experimental settings, we simulated small variations of unicoloured petals and variations in the spatial arrangement of colours within tricoloured petals using artificial flowers and studied their impact on the colour choices of bumblebees and honeybees. Workers were trained to artificial flowers of a given colour and then given the simultaneous choice between three test colours: either the training colour, one colour of lower and one of higher spectral purity, or the training colour, one colour of lower and one of higher dominant wavelength; in all cases the perceptual contrast between the training colour and the additional test colours was similarly small. Bees preferred artificial test flowers which resembled the training colour with the exception that they preferred test colours with higher spectral purity over trained colours. Testing the behaviour of bees at artificial flowers displaying a centripetal or centrifugal arrangement of three equally sized colours with small differences in spectral purity, bees did not prefer any type of artificial flowers, but preferentially choose the most spectrally pure area for the first antenna contact at both types of artificial flowers. Our results indicate that innate preferences for flower colours of high spectral purity in pollinators might exert selective pressure on the evolution of flower colours.     

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.     

Identification of target genes for a MYB-type anthocyanin regulator in Gerbera hybrida

Genetic modification of the flavonoid pathway has been used to produce novel colours and colour patterns in ornamental plants as well as to modify the nutritional and pharmaceutical properties of food crops. It has been suggested that co-ordinate control of multiple steps of the pathway with the help of regulatory genes would lead to a more predictable control of metabolic flux. Regulation of anthocyanin biosynthesis has been studied in a common ornamental plant, Gerbera hybrida (Asteraceae). An R2R3-type MYB factor, GMYB10, shares high sequence similarity and is phylogenetically grouped together with previously characterized regulators of anthocyanin pigmentation. Ectopic expression of GMYB10 leads to strongly enhanced accumulation of anthocyanin pigments as well as to an altered pigmentation pattern in transgenic gerbera plants. Anthocyanin analysis indicates that GMYB10 specifically induces cyanidin biosynthesis in undifferentiated callus and in vegetative tissues. Furthermore, in floral tissues enhanced pelargonidin production is detected. Microarray analysis using the gerbera 9K cDNA array revealed a highly predicted set of putative target genes for GMYB10 including new gene family members of both early and late biosynthetic genes of the flavonoid pathway. However, completely new candidate targets, such as a serine carboxypeptidase-like gene as well, as two new MYB domain factors, GMYB11 and GMYB12, whose exact function in phenylpropanoid biosynthesis is not clear yet, were also identified.