Crab spiders affect flower visitation by bees

In a field experiment, the bumblebee, B. ternarius , visited milkweed patches harboring crab spiders, Misumena vatia , at a lower frequency than patches free of crab spiders, and honeybees showed a similar but non-significant trend. Two other bumblebee species, B. terricola and B. vagans , did not avoid the spider patches. The latter two species are larger than B. ternarius and honeybees and suffer lower crab-spider predation. As far as we know, this is the first field study documenting negative effects of predators on flower visitation rate by pollinator populations. Our study suggests that pollinator response to predation may influence pollinator-plant interactions.     

Hues of a dragon's belly: morphological correlates of ventral coloration in water dragons

Sexual dichromatism is common in lizards, and may play an important role in sex recognition and mating systems. Nonetheless, relatively few published papers provide quantitative analyses of colour, deal with Australian taxa or are based on large-bodied species. Water dragons Physignathus lesueurii (Agamidae) from eastern Australia are very large (upto 1 m total length) and sexually dichromatic, with conspicuous red ventral coloration in adult males. We quantified coloration in three ventral regions (throat, chest and abdomen) of males and females using a spectroradiometer and looked for associations of colour with sex and with morphological traits predicted to correlate with fitness (body size, body condition, relative head size and asymmetry of femoral pores). Among adult males, larger individuals showed less red on the abdomen than did smaller animals, and males with relatively large heads had darker, less red abdomens than did males with smaller heads. Among adult females, larger animals had darker chests, and less red on the abdomen and chest, than did smaller females. The similarity in these trends between the sexes, and the location of the sexually dichromatic and size-sensitive colours in an area (under the abdomen) where they presumably are not visible to other lizards cast doubt on their utility as sexual or dominance signals. Hence, although we documented significant sex and body-size effects on ventral coloration, our results suggest that ventral colours in water dragons do not function in sex-specific displays.     

Rapid evolution of elaborate male coloration is driven by visual system in Australian fairy‐wrens (Maluridae)

The interplay between colour vision and animal signalling is of keen interest to behavioural ecologists and evolutionary biologists alike, but is difficult to address in terrestrial animals. Unlike most avian lineages, in which colour vision is relatively invariant among species, the fairy‐wrens and allies (Maluridae) show a recent gain of ultraviolet sensitivity (UVS). Here, we compare the rates of colour evolution on 11 patches for males and females across Maluridae in the context of their visual system. We measured reflectance spectra for 24 species, estimating five vision‐independent colour metrics as well as metrics of colour contrast among patches and sexual dichromatism in a receiver‐neutral colour space. We fit Brownian motion (BM) and Ornstein–Uhlenbeck (OU) models to estimate evolutionary rates for these metrics and to test whether male coloration, female coloration or dichromatism was driven by selective regimes defined by visual system or geography. We found that in general male coloration evolved rapidly in comparison with females. Male colour contrast was strongly correlated with visual system and expanded greatly in UVS lineages, whereas female coloration was weakly associated with geography (Australia vs. Papua New Guinea). These results suggest that dichromatism has evolved in Maluridae as males and females evolve at different rates, and are driven by different selection pressures.     

The ultraviolet colour component enhances the attractiveness of red flowers of a bee-pollinated plant

蜂媒花很少呈红色，这可能是由于蜂类的眼睛缺少红光受体，因而较难搜寻红色目标。尽管有实验研究过蜂类对红色的反应，但所用目标多为纯红色。而人类感受到的红色中其实包含细微的色调差别，这些差别还甚少受到关注。我们在本研究中检验了如下假说：红花中的紫外反射组分能够增加其彩调反差，因而增强其对蜂类的吸引力。紫草科的密花滇紫草(Onosma confertum)由熊蜂传粉，其花为红色，但紫外反射明显。本研究利用该植物设计了表型操控实验，在野外检验了紫外反射对传粉者访花行为的影响。我们还在受控环境下检验了无经验熊蜂的色彩偏好。利用两个色彩模型评估熊蜂的色彩感受，用彩调反差和明度反差两个参数进行估计。研究发现，自然状态下及无经验的饲养熊蜂均偏好访问具有紫外反射的红色目标。色彩模型分析表明，具紫外反射的红花对蜂而言色彩更纯，且与叶片背景的彩调反差更大；而它们与无紫外反射的红花在明度反差方面(以绿光受体的反差估计)表现相似。这些结果表明，密花滇紫草红色花朵中的紫外反射组分增加了其彩调反差，增强了其对熊蜂的吸引力。我们推测，由于某些传粉者(例如蜂类)无红光受体，对由它们传粉的红色花而言，光谱中的副反射特征(例如紫外反射)可能是其花色中的必要组分。     

Ultraviolet and carotenoid‐based coloration in the viviparous lizard Zootoca vivipara (Squamata: Lacertidae) in relation to age,sex, and morphology

Lizards display structural and pigment‐based colorations, and their visual system is sensitive to wavelengths of 300–700 nm. However, few studies in squamate reptiles have quantified interindividual colour variation that includes the structural ultraviolet (UV) component (300–400 nm). In the present study, we investigated variability of a ventral UV/yellow–red ornamentation in the common lizard Zootoca vivipara, including an analysis of spatial distribution, as well as sex and age differences. We also investigated whether the expression of coloration is related to body size and condition. Our analyses revealed two distinct patches: a gular patch with a strong UV reflectance and a belly patch with a dominant yellow–red reflectance. Males displayed a less saturated throat coloration with higher UV chroma and UV hue, and had a redder but duller belly coloration than females. Yearlings had less elaborate ornaments than adults, although they already displayed a yellow–red sexual dichromatism on the belly. UV sexual dichromatism was only apparent in adults as a result of a weaker UV reflectance in females, suggesting potential fitness costs of a bright UV coloration in that sex. Different colour traits were related to body size in both sexes, as well as to body condition in males. We discuss the potential evolutionary scenarios leading to the maintenance of this ornament in common lizards. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 128–141.     

Body‐colour variation in an orb‐web spider and its effect on predation success

Animal body coloration serves several functions such as thermoregulation, camouflage, aposematism, and intraspecific communication. In some orb‐web spiders, bright and conspicuous body colours are used to attract prey. On the other hand, there are other species whose body colour does not attract prey. Using a spider species showing individual body‐colour variation, the present study aimed to determine whether or not the variation in body colour shows a correlation with predation rates. We studied the orb‐web spider (Cyclosa argenteoalba) using both field observations and T‐maze experiments, in which the prey were exposed to differently coloured spiders. Cyclosa argenteoalba has silver‐ and black‐coloured areas on its dorsal abdomen, with the ratio of these two colours varying continuously among individuals. The bright and conspicuous silver area reflects ultraviolet light. Results of both field observations and colour choice experiments using Drosophila flies as prey showed that darker spiders have a greater chance of capturing prey than silver spiders. This indicates that body‐colour variation affects predation success among individuals and that the bright silver colour does not function to attract prey in C. argenteoalba.     

Dietary carotenoids change the colour of Southern corroboree frogs

Animal coloration can be the result of many interconnected elements, including the production of colour‐producing molecules de novo, as well as the acquisition of pigments from the diet. When acquired through the diet, carotenoids (a common class of pigments) can influence yellow, orange, and red coloration and enhanced levels of carotenoids can result in brighter coloration and/or changes in hue or saturation. We tested the hypothesis that dietary carotenoid supplementation changes the striking black and yellow coloration of the southern corroboree frog (Pseudophryne corroboree, Amphibia: Anura). Our dietary treatment showed no measurable difference in colour or brightness for black patches in frogs. However, the reflectance of yellow patches of frogs raised on a diet rich in carotenoids was more saturated (higher chroma) and long‐wave shifted in hue (more orange) compared to that of frogs raised without carotenoids. Interestingly, frogs with carotenoid‐poor diets still developed their characteristic yellow and black coloration, suggesting that their yellow colour patches are a product of pteridines manufactured de novo.     

Factors shaping the evolution of colour patterns in Australian agamid lizards (Agamidae): a comparative study

Identifying general patterns of adaptive coloration in animals can help to elucidate the evolutionary processes that generate them. We examined the evolution of colour patterns in Australian agamid lizards, a morphologically and ecologically diverse group that relies primarily on visual communication. We tested whether certain types of colour (yellow–reds and black) were likely to be used as sexual signals, as indicated by their association with indices of sexual selection, namely, sexual dichromatism and sexual dimorphism in body size and head shape. We then tested whether sexually dichromatic colours are associated with specific patterns (uniform, mottled, striped, blotched, reticulated) or ecological variables such as habitat openness, arboreality, and substrate type. The presence of yellow–red on lateral and ventral body regions and black on ventral body regions was significantly more common in males than females. Lateral yellow–red in males was associated with the total extent of sexual dichromatism and size dimorphism, whereas ventral yellow–red was associated with sexual dichromatism. Both lateral and ventral yellow–red were associated with uniform patterning, suggesting that sexual signals in male agamid lizards may often comprise uniform patches or flushes of yellow–red. Although ventral black coloration was more prevalent on males (i.e. strongly sexually dichromatic), it was not associated with indices of sexual selection, suggesting that, in agamid lizards, yellow–red coloration is more likely to be sexually selected than black. Sexually dichromatic coloration was not strongly associated with any of the ecological variables measured. We found some associations, however, between female dorsal patterns and ecological variables, suggesting that female patterns are influenced by natural selection. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 101–112.     

Why do red and dark-coloured cars lure aquatic insects? The attraction of water insects to car paintwork explained by reflection-polarization signals

We reveal here the visual ecological reasons for the phenomenon that aquatic insects often land on red, black and dark-coloured cars. Monitoring the numbers of aquatic beetles and bugs attracted to shiny black, white, red and yellow horizontal plastic sheets, we found that red and black reflectors are equally highly attractive to water insects, while yellow and white reflectors are unattractive. The reflection-polarization patterns of black, white, red and yellow cars were measured in the red, green and blue parts of the spectrum. In the blue and green, the degree of linear polarization p of light reflected from red and black cars is high and the direction of polarization of light reflected from red and black car roofs, bonnets and boots is nearly horizontal. Thus, the horizontal surfaces of red and black cars are highly attractive to red-blind polarotactic water insects. The p of light reflected from the horizontal surfaces of yellow and white cars is low and its direction of polarization is usually not horizontal. Consequently, yellow and white cars are unattractive to polarotactic water insects. The visual deception of aquatic insects by cars can be explained solely by the reflection-polarizational characteristics of the car paintwork.     

Temporal hierarchy of the visual perceptive systems in the Mondrian world.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50-100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure--an abstract multi-coloured scene with no recognizable objects--against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.     

Ultraviolet dermal reflexion and mate choice in the guppy, Poecilia reticulata

Some fish, including the guppy, have the ability to perceive ultraviolet (UV) wavelengths. Female guppies prefer to associate with males that are viewed under light conditions that include UV-A, in preference to conditions lacking these wavelengths. We used reflexion spectrophotometry to show that male guppies reflect UV light from both their structural (purple, green and white) and pigment (orange) colour patches and that males differ in the levels of UV light reflected. Varying components of UV may affect both the brightness and hue of particular colour patches. This may produce nonspectral colours that are visible to the guppy but that are outside human perception. We used video analysis to quantify male reflexion in the UV and visible wavebands. Male guppies with high and low UV reflexion, but similar human-visible coloration and area of coloration, were paired for use in mate choice experiments. Female guppies shown pairs of males differing in their levels of UV reflexion had no preference for either high or low UV reflexion. This suggests that UV reflexion does not provide particularly significant information relating to male quality or influence female preference in this population of guppies. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Nuptial coloration varies with ambient light environment in a freshwater fish

Visual signals play a vital role in many animal communication systems. Signal design, however, often varies within species, raising evolutionarily important questions concerning the maintenance of phenotypic diversity. We analysed nuptial colour variation within and among nine populations of southern pygmy perch (Nannoperca australis Günther) along an environmental light gradient. Within populations, larger males were redder and blacker, and better-condition males were blacker. Among populations, red colour was positively correlated with the amount of orange-red light present, suggesting that males are likely optimizing signal conspicuousness by producing proportionally larger and redder patches in broad spectrum environments with more orange-red light. Signal contrast, in this regard, is maximized when red colour, appearing bright because of the prevalence of red wavelengths, is viewed against the water-column background. Together, our results are concordant with the sensory drive hypothesis; selection favours signal adaptations or signal plasticity to ensure communication efficacy is maximized in different light environments.     

A framework for analysing colour pattern geometry: adjacent colours

The analysis of colour pattern geometry is not as well advanced as the analysis of colour, although this reflects a lack of an analytical framework. The present study proposes an approach based on a consideration of which colours are adjacent to each other. Both vertebrate and invertebrate eyes do not take static images of the world but move across the field of view. As a consequence, the eye takes transects across the field of view responding to the colours and luminances within patches and to the colour and/or luminance transitions between patches. The framework and methods suggested here are based upon transects across colour patterns and make it possible to estimate colour pattern parameters that capture not only the relative areas of each patch class, but also the relative frequencies of colour/luminance transitions or adjacency. This allows tests of new hypotheses about colour patterns at the same time as including colour, pattern, and texture. Eleven groups of predictions are made with respect to the often conflicting needs of communication with conspecifics, avoiding predation, and finding food. New phenomena may be discovered as a result of these methods and predictions. For example, certain colour transitions may be used for species recognition even though the same colours are used by all species. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Molecular and functional studies of tilapia (Oreochromis mossambicus) NMDA receptor NR1 subunits

The Pin-tailed Manakin (Ilicura militaris) is a small, sexually dimorphic, frugivorous suboscine songbird (Pipridae; Passeriformes; Aves) endemic to the Atlantic Forest of Brazil. A variant individual of this species was recently described in which the red patches that characterise the male's Definitive plumage were replaced by orange-yellow ones. We show here that the pigments in the feathers of the colour variant are common dietary carotenoids (zeaxanthin, beta-cryptoxanthin), not carotenoids synthesised by birds, lending support to the suggestion that the individual is a colour mutant lacking the capability to transform yellow dietary pigments into the red pigments normally present in these feathers. By comparison, the yellow crown feathers of a close relative, the Golden-winged Manakin (Masius chrysopterus), contained predominantly endogenously produced epsilon-caroten-3'-ones. Surprisingly, the normal-coloured feathers of the male Pin-tailed Manakin owe their red hue to rhodoxanthin, an unusual carotenoid more commonly found in plants, rather than 4-keto-carotenoids typically found in red plumages and found lacking in previously characterised bird colour variants. The implication is that birds, like the tilapia fish, may be able to synthesise this unusual pigment endogenously from dietary precursors. A newly described carotenoid, 6-hydroxy-epsilon,epsilon-carotene-3,3'-dione, here named piprixanthin, present in the red feathers of the Pin-tailed Manakin, provides a plausible intermediate between epsilon,epsilon-carotene-3,3'-dione (canary-xanthophyll B), a bright yellow pigment found in this and other songbirds, and rhodoxanthin. It is apparent that pigeons (Columbidae, Columbiformes) also have the capability to produce rhodoxanthin, and a structurally related pigment, endogenously. The ability to synthesise rhodoxanthin might have arisen at least twice in birds.     

Spectral sensitivity of a colour changing spider

Vision plays a paramount role in some spider families such as the Salticidae, Lycosidae and Thomisidae, as it is involved in prey hunting, orientation or choice of substrate. In the thomisid Misumena vatia, for which the substrate colour affects the body colour, vision seems to mediate morphological colour changes. However, nothing is known about which component of visual signals from the substrate might be perceived, nor whether M. vatia possesses the physiological basis for colour vision. The aim of this study is thus to investigate the vision of this spider species by measuring the spectral sensitivities of the different pairs of eyes using electrophysiological methods. Extra- and intracellular electrophysiological recordings combined with selective adaptation revealed the presence of two classes of photoreceptor cells, one sensitive in the UV region of the spectrum (around 340 nm) and one sensitive in the green (around 520 nm) regions in the four pairs of eyes. We conclude that M. vatia possesses the physiological potential to perceive both chromatic and achromatic components of the environment.     

Extensive hybridization reveals multiple coloration genes underlying a complex plumage phenotype

Coloration is an important target of both natural and sexual selection. Discovering the genetic basis of colour differences can help us to understand how this visually striking phenotype evolves. Hybridizing taxa with both clear colour differences and shallow genomic divergences are unusually tractable for associating coloration phenotypes with their causal genotypes. Here, we leverage the extensive admixture between two common North American woodpeckers—yellow-shafted and red-shafted flickers—to identify the genomic bases of six distinct plumage patches involving both melanin and carotenoid pigments. Comparisons between flickers across approximately 7.25 million genome-wide SNPs show that these two forms differ at only a small proportion of the genome (mean F_ST = 0.008). Within the few highly differentiated genomic regions, we identify 368 SNPs significantly associated with four of the six plumage patches. These SNPs are linked to multiple genes known to be involved in melanin and carotenoid pigmentation. For example, a gene (CYP2J19) known to cause yellow to red colour transitions in other birds is strongly associated with the yellow versus red differences in the wing and tail feathers of these flickers. Additionally, our analyses suggest novel links between known melanin genes and carotenoid coloration. Our finding of patch-specific control of plumage coloration adds to the growing body of literature suggesting colour diversity in animals could be created through selection acting on novel combinations of coloration genes.     

On the measurement and classification of colour in studies of animal colour patterns

In studies of animal colouration it is no longer necessary to rely on subjective assessments of colour and conspicuousness, nor on methods which rely upon human vision. This is important because animals vary greatly in colour vision and colour is context-dependent. New methods make it practical to measure the colour spectrum of pattern elements (patches) of animals and their visual backgrounds for the conditions under which patch spectra reach the conspecific's, predator's or prey's eyes. These methods can be used in both terrestrial and aquatic habitats. A patch's colour is dependent not only upon its reflectance spectrum, but also upon the ambient light spectrum, the transmission properties of air or water, and the veiling light spectrum. These factors change with time of day, weather, season and microhabitat, so colours must be measured under the conditions prevalent when colour patterns are normally used. Methods of measuring, classifying and comparing colours are presented, as well as techniques for assessing the conspicuousness of colour patterns as a whole. Some implications of the effect of environmental light and vision are also discussed.     

The significance of flower colour change in eight co-occurring shrub species

Flower colour changes from white or yellow to various shades of red at or near the sites of harvestable pollen in Calytrix glutinosa, Grevillea pilulifera, Isopogon dubius and Petrophile biloba , and over most of the flower in Hypocalymma angustifolium, Verticordia chrysantha and V. huegelii and over the pseudanthium in Darwinia citriodora. All bee, wasp, beetle, fly, butterfly and moth visitors select flowers in the white/yellow phase rather than the red or intermediate phase.
Nectar is produced by five species, harvestable pollen by four species and detectable perfume by three species, all of which features are usually absent from the red phase. The timing of the colour change in all species also corresponds to loss of stigma receptivity, completion of pollination and onset of ovule seed) swelling. Six species also undergo minor morphometric changes which discourage visitation. In all species, colour change is non-inducible by pollinators, taking 2–30 days to complete. In three protandrous species, all available pollen may be removed in the first visit, requiring transport of non-self pollen to rewardless flowers during the 10 h period of the yellow phase.
These species are highly floriferous and occur in dense patches. Since only a small proportion of flowers may be receptive at any one time, it is concluded that retention of flower parts essentially serves to enhance long-distance attraction, while colour change maximizes pollination and foraging efficiency.     

Red is not a proxy signal for female genitalia in humans

Red is a colour that induces physiological and psychological effects in humans, affecting competitive and sporting success, signalling and enhancing male social dominance. The colour is also associated with increased sexual attractiveness, such that women associated with red objects or contexts are regarded as more desirable. It has been proposed that human males have a biological predisposition towards the colour red such that it is 'sexually salient'. This hypothesis argues that women use the colour red to announce impending ovulation and sexual proceptivity, with this functioning as a proxy signal for genital colour, and that men show increased attraction in consequence. In the first test of this hypothesis, we show that contrary to the hypothesis, heterosexual men did not prefer redder female genitalia and, by extension, that red is not a proxy signal for genital colour. We found a relative preference for pinker genital images with redder genitalia rated significantly less sexually attractive. This effect was independent of raters' prior sexual experience and variation in female genital morphology. Our results refute the hypothesis that men's attraction to red is linked to an implied relationship to genital colour and women's signalling of fertility and sexual proceptivity.