Novelty effects in a multimodal warning signal

The warning signals of toxic insects are often 'multimodal', combining bright coloration with sounds or odours (or both). Pyrazine (a common insect warning odour) can elicit an intrinsic avoidance in domestic chicks Gallus gallus domesticus, both against novel coloured food, and also against food colours that are specifically associated with aposematism, namely yellow and red. In three experiments, we investigated the role of novelty in this innate bias against yellow coloured food in the presence of pyrazine. Naive chicks were familiarized either to pyrazine odour or to coloured food before being tested for a bias against yellow (warningly coloured) food as opposed to green (nonwarningly coloured) food. In experiment 1, pyrazine novelty was shown to be vital for eliciting a bias against yellow food. However, experiment 2 suggested that colour novelty was not important: chicks familiarized with coloured crumbs still avoided yellow crumbs when pyrazine was presented. In a third experiment that gave chicks an even greater degree of pre-exposure to coloured crumbs, the bias against yellow food eventually waned, although pyrazine continued to elicit an aversion to yellow even after birds had had experience of up to 24 palatable yellow crumbs. Pyrazine novelty has been an important pressure in the evolution of multimodal warning signals, and can continue to promote the avoidance of warningly coloured food, even when it is relatively familiar. The implications for warning signals are discussed. Copyright 1999 The Association for the Study of Animal Behaviour.     

Spring versus autumn leaf colours: Evidence for different selective agents and evolution in various species and floras

Red colouration is common in young and old leaves of broadleaf woody species. Assuming that leaf colours are adaptive, we examined, by comparing the colouration in young versus old leaves, the possibility that different selection agents may have operated on spring versus autumn leaf colouration. We observed spring versus autumn colouration in three very different woody floras (Finland, Japan and Israel) in order to allow for a broad ecological and evolutionary spectrum. The null hypothesis was that if the same selective agents operated in spring and autumn, it is expected that when spring leaves are red, they should always be red in autumn, and when spring leaves are green, they should be green or yellow in autumn. We found that green spring leaves are almost exclusively associated with yellow leaf colour at senescence in autumn. Species with red autumn leaves almost always have at least some red colouration in their spring leaves. However, about half of the species with red spring leaves have yellow autumn leaves. Brown autumn leaves were not common in the species we studied. As about half of the species with red spring leaves have yellow autumn leaves but not vice versa, we conclude that there are many cases in which the selecting agents for spring versus autumn leaf colour were not the same.     

An analysis of avoidance generalization and food preference transitivity in goldfish,Carassius auratus

To examine the effect of novelty in food selection by fishes, goldfish were trained by feeding them on red or green food pellets. Individual fish and fish in shoals of two, three, and five were then given a choice between equal numbers of familiar pellets and novel (yellow) pellets. In experimental groups, the yellow pellets were soaked in 15% quinine hydrochloride to make them unpalatable. Fish were next presented with equal numbers of familiar and a second novel pellet. It was expected that fish would generalize from their experience with the unpalatable pellets and demonstrate avoidance to sampling a second novel food item. However, as groups, neither controls nor experimentals were reluctant to sample the second novel pellets. Also, fish did not eat significantly more familiar than novel pellets when both were palatable. A third set of experiments examined food preference transitivity in which each pellet type was presented alone and in three pair-wise combinations to individual fish. Although red and yellow pellets were preferred over green, they were preferred equally, indicating an absence of transitivity in pellet choice and, perhaps, a “preference” for a mixture of red and yellow pellets.     

Familiarity interferes with filial imprinting

The present study was performed to investigate whether and how pre-exposure to an object affects subsequent filial imprinting to that object. In Experiment 1 junglefowl chicks (Gallus gallus spadiceus) were first exposed to either a red object alone (control group), or a red and a yellow object simultaneously (experimental group; phase 1). Subsequently, all chicks were exposed to the yellow object in the presence of a black and blue one (phase 2). At the end of phase 1, most experimental chicks had developed a preference for the red object over the yellow one. At the end of phase 2, preferences of experimental chicks were shifted away from the yellow object towards the novel black and blue object, relative to preferences of control chicks. This shows that pre-exposure may interfere with imprinting. Experiment 2 revealed that when control chicks were tested with the yellow object at the end of phase 1, filial responses were as strong as in experimental chicks. This shows that the yellow object had not acquired control over filial behaviour during phase 1, and also that the relatively impaired imprinting on that object in phase 2 was not due to reduced generalization from the red object. One possible explanation why pre-exposure may interfere with imprinting is that familiarity alters the level of attention attracted by an object, a mechanism suggested to underlie ‘latent inhibition’ in conditioning.     

Colour categorization by domestic chicks

Spectral stimuli form a physical continuum, which humans divide into discrete non-overlapping regions or categories that are designated by colour names. Little is known about whether non-verbal animals form categories on stimulus continua, but work in psychology and artificial intelligence provides models for stimulus generalization and categorization. We compare predictions of such models to the way poultry chicks (Gallus gallus) generalize to novel stimuli following appetitive training to either one or two colours. If the two training colours are (to human eyes) red and greenish-yellow or green and blue, chicks prefer intermediates, i.e. orange rather than red or yellow and turquoise rather than green or blue. The level of preference for intermediate colours implies that the chicks interpolate between the training stimuli. However, they do not extrapolate beyond the limits set by the training stimuli, at least for red and yellow training colours. Similarly, chicks trained to red and blue generalize to purple, but they do not generalize across grey after training to the complementary colours yellow and blue. These results are consistent with a modified version of a Bayesian model of generalization from multiple examples that was proposed by Shepard and show similarities to human colour categorization.     

An investigation of colour discrimination with horses (Equus caballus)

The ability of four horses (Equus caballus) to discriminate coloured (three shades of blue, green, red, and yellow) from grey (neutral density) stimuli, produced by back projected lighting filters, was investigated in a two response forced-choice procedure. Pushes of the lever in front of a coloured screen were occasionally reinforced, pushes of the lever in front of a grey screen were never reinforced. Each colour shade was randomly paired with a grey that was brighter, one that was dimmer, and one that approximately matched the colour in terms of brightness. Each horse experienced the colours in a different order, a new colour was started after 85% correct responses over five consecutive sessions or if accuracy showed no trend over sessions. All horses reached the 85% correct with blue versus grey, three horses did so with both yellow and green versus grey. All were above chance with red versus grey but none reached criterion. Further analysis showed the wavelengths of the green stimuli used overlapped with the yellow. The results are consistent with histological and behavioural studies that suggest that horses are dichromatic. They differ from some earlier data in that they indicate horses can discriminate yellow and blue, but that they may have deficiencies in discriminating red and green.     

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).     

卷蛾分索赤眼蜂雌蜂的颜色偏好性

为了确定卷蛾分索赤眼蜂Trichogrammatoidea bactrae Nagaraja 雌蜂的颜色偏好性, 在室内通过在培养皿底部黏贴彩纸的方法测定卷蛾分索赤眼蜂雌蜂对红、 黄、 黑、 紫、 绿、 白、 蓝7种颜色的行为趋性反应。结果表明, 卷蛾分索赤眼蜂雌蜂在红、 黄、 紫、 绿和蓝5种颜色上的滞留时间都极显著地高于对照（P<0.01）, 在黑和白2种颜色上的滞留时间与对照没有显著差异（P>0.05）; 对黄色的首次选择率极显著高于对照(P< 0.01), 对红、 紫、 绿和蓝色的首次选择率均显著高于对照(P＜0.05), 对黑色和白色的首次选择率与对照没有显著差异。当雌蜂分别在黄与红、 紫、 绿和蓝两两颜色之间选择时, 雌蜂在黄色彩纸上的滞留时间显著长于其他4种颜色。当雌蜂对红、 紫、 绿、 蓝和黄色5种颜色一起选择时, 在首次选择率、 滞留次数上5种颜色间都没有明显差异(P＞0.05); 但在红色和蓝色上的滞留时间显著长于紫色(P＜0.05), 在这3种颜色上的滞留时间与在黄色和绿色上的滞留时间均无显著差异(P＞0.05)。卷蛾分索赤眼蜂雌蜂在7种颜色卵卡上分别与透明纸（对照）上的米蛾卵的选择寄生时, 在黄色卵卡上的寄生卵量极显著多于对照(P＜0.01), 黑色卵卡上的寄生卵量极显著少于对照(P＜0.01), 其他5种颜色的卵卡上的寄生卵量与对照没有显著差异(P＞0.05)。结果说明, 卷蛾分索赤眼蜂雌蜂对黄色最为偏好, 其次偏好红、 紫、 绿和蓝色, 较不喜好白色和黑色。     

寄主挥发物、叶色在B型烟粉虱寄主选择中的作用

在室温条件下,研究B型烟粉虱Bemisia tabaci(Gennadius)对不同寄主植物和颜色的行为趋性。笼罩实验的结果显示,烟粉虱雌虫对共存的5种寄主植物偏好存在显著差异,总体上表现为对番茄的趋性最强(35·0%),甘蓝次之(27·7%),烟草和棉花再次之,辣椒最低(7·1%);且随着时间的延长,烟粉虱数量在番茄上逐渐增加,在甘蓝上呈下降趋势,在烟草、棉花和辣椒上变动幅度不大,但数量总体上仍是番茄(48·8%)>甘蓝(18·4%)>烟草、棉花>辣椒(3·4%)。但烟粉虱在不同寄主植物上的产卵量则表现为:甘蓝>番茄>棉花、烟草>辣椒;其中甘蓝和番茄上卵量分别占总卵量的56·8%和28·2%;而烟草、棉花和辣椒上的卵量均不到总卵量的6·0%。"Y"型嗅觉仪进一步测定表明:寄主植物番茄和甘蓝气味对烟粉虱具有显著引诱作用,且表现为番茄>甘蓝,辣椒不具引诱作用;烟粉虱对3种植物(番茄、甘蓝、辣椒)的叶片颜色均有显著趋性,选择率在75%左右,但在三者之间的趋性差异不明显;烟粉虱雌虫对黄色和绿色均具有显著趋性,且对黄色的趋性显著大于对绿色的趋性,但对红色无趋性。综合分析表明,在对寄主定向和定位过程中,B型烟粉虱的视觉和嗅觉均起作用,但在对同种颜色(绿色)的寄主进行选择和定位的过程中,嗅觉起主要作用,而对不同种颜色(红、黄、绿)的选择和定位时,其视觉起决定作用。     

Ontogenetic development of conditioned food aversion in chickens

Development of conditioned food aversion (CFA) was studied in 25-, 35-, and 45-day Leghorn chicks. Food-deprived birds had 10-min access to normal food on days 1 and 2, and to green coloured food CS on day 3. Injection of LiCl (0.15 M, 3–4% body weight) administered 10 min after CS on day 3 served as the US. Control groups were injected with the same volume of saline. Retention was tested on day 4 in three 3-min presentations of normal food alternating with two presentations of green food. Number of pecks and amount of food consumed were measured. Significant neophobic rejection of green food was observed in 25- but not in 35- and 45-day-old control birds. Neophobia in the youngest chicks was further accentuated by CFA which could be observed in pure form in the 45-day-old experimental group. Comparison of pecking rate and food intake showed that CFA in younger birds was accomplished predominantly by inhibition of pecking, and in older birds also by reduction of peck volume. It is concluded that protection against poisoning in chickens shifts between 25 and 45 days of posthatching age from neophobia to CFA.     

Field tests of density-and frequency-dependent selection in Erigeron annuus (Compositae)

Selection may maintain genetic diversity in natural populations if the physical or biotic environment is variable over space and-or time. Because density and genotype frequencies can be heterogeneous, and because genotypes may differ in competitive ability, both density-and frequency-dependent selection have been considered to be potentially important evolutionary processes. To address the possibility that intraspecific interactions among plants are a source of fitness variation in Erigeron annuus, we conducted field experiments over 2 yr that were designed to examine the potential of population density, genotype frequency, and their interaction to act as selective agents. In both experiments, apomictic genotypes of Erigeron were paired. Seedlings were planted into plots that differed in density and the identity of minority and majority genotype. There was evidence for a differential effect of density among genotypes for only one year's experiment, suggesting that density-dependent selection is either weak or temporally variable. Genotype frequency had no effect on fitness in either year, and thus there was no evidence for frequency-dependent selection. In addition, the lack of a frequency ;ts density interaction demonstrates that resource partitioning, one mechanism for frequency dependence, is not strong among Erigeron genotypes. If frequency-dependent selection does occur in this species, it is either too weak to detect even in large field experiments, or occurs only in the presence of a selective agent (e.g., pathogens) that was lacking in our experiments.     

Effects of ambient colour on colour preference and growth of juvenile rainbow trout Oncorhynchus mykiss (Walbaum)

Colour preference of individual juvenile rainbow trout Oncorhynchus mykiss was tested at 1 and 12° C, and also at 12° C after a 42 day growth experiment under white, blue, green, yellow or red ambient colour. All experiments were carried out under controlled laboratory conditions and the preference was assessed by the location of the fish in a preference tank with four chambers. Rainbow trout showed a preference for blue and green at 1° C and for green at 12° C. After the growth experiment the fish reared in blue tanks preferred blue and green but green was the most preferred colour for the fish reared in green, yellow and red tanks. Yellow and especially red chambers were avoided, irrespective of the ambient colour during the growth trial. The final mass of fish reared in the red aquaria was significantly smaller than that of the fish in green tanks. In addition, when the data of the preference tests were correlated with the data of the growth experiment using mean values of the four tested colours, a very good linear relationship was observed between the preference ( i.e. visit frequency in coloured compartments) and growth rate as well as food intake. When considering the results both from the preference and growth trials it is suggested that green is the best environmental colour for rearing juvenile rainbow trout while rearing in a red environment cannot be recommended.     

Visual memory of shapes in quail chicks: discrimination among 2-dimensional objects

Newly hatched chicks spontaneously peck at conspicuous objects, and soon learn to discriminate between edible food particles and inedible objects. To examine whether this discrimination is based on a chick's ability to memorize objects by shape cues, we analyzed the pecking behavior. One- to 3-day old quail chicks (Coturnix japonica) were presented with dry objects of different shapes (ball, disk, triangle and T-shape) of similar size (4 mm) and color (green). Habituation occurred after repeated presentation of any one of these objects (duration: 30 sec; interval: 4 min). When chicks showed significantly more pecks at a novel object (dishabituation), we assumed that chicks had memorized the habituated shapes and distinguished the novel object. Chicks did not show dishabituation between a ball and a disk. On the other hand, chicks discriminated a triangle or T-shape from the memorized image of disk, but did not memorize either triangle or T-shape by its shape. Similarly, chicks did not memorize the size of disks as a reference for subsequent pecking behavior. Chicks proved to have a limited ability to memorize shape and size cues for selective pecking behavior, in strong contrast to their accurate memorization of colors.     

Mechanisms promoting higher growth rate in arctic than in temperate shorebirds

We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.     

Fruit or aposematic insect? Context-dependent colour preferences in domestic chicks.

Colours are common stimuli in signalling systems. Requirements to function well as a signal sometimes conflict between different signallers, and the same colour stimulus is used to convey completely different messages to the same receiver. Fruits and aposematic insects both use red coloration as a signal, in the former case to signal profitability and in the latter case as a warning signal. In two experiments, we investigated whether the domestic chick, an omnivorous predator, differed in its unconditioned preference or avoidance of red and green stimuli depending on whether or not the stimulus was an insect. The experiments were designed as preference tests between red and green painted prey. The prey were live insects and artificial fruits (experiment 1), and, to investigate the effect of movement, live and dead insects (experiment 2). The chicks did not show any difference in pecking preference between red and green when fruit-like stimuli were used, but when the prey were insects, green prey were strongly preferred to red prey, and prey movement did not affect this bias. Thus, young chicks may recognize prey as insects and then discriminate between different prey colorations, or one type of food may elicit an unlearned colour preference-avoidance response that is absent with another type of food.     

A test for negative frequency-dependent mating success as a function of male colour pattern in the bluefin killifish

Rare male mating advantage (a form of negative frequency dependence) is frequently proposed as a mechanism for the maintenance of genetic variation within populations. This hypothesis is attractive for systems with pronounced male colour polymorphism because it can maintain particularly high levels of variation. We tested for negative frequency-dependent mating success between yellow and red male colour patterns in bluefin killifish, Lucania goodei . Lucania goodei populations harbour substantial colour pattern polymorphism, and a large proportion of this variation has a genetic basis. We established outdoor mesocosms with red and yellow males in three different ratios: yellow rare (one yellow ♂ : five red ♂), even (three yellow ♂ : three red ♂), and red rare (five yellow ♂ : one red ♂). We obtained eggs and used microsatellites to determine paternity. By contrast to expectations, we found no support for a rare male mating advantage. Red males had slightly higher spawning success than yellow males, particularly in replicates with large clutches and when red males were rare. However, yellow males did not have higher mating success when rare. We discuss alternative mechanisms for the maintenance of the polymorphism as well as the potential reasons for the lack of a rare male mating advantage.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 489–500.     

Effects of local density and flower colour polymorphism on pollination and reproduction in the rewardless orchid Dactylorhiza sambucina (L.) Soò

The rewardless orchid Dactylorhiza sambucina shows a stable flower colour polymorphism, with both yellow- and red-flowered morphs growing sympatrically. Pollination biology and breeding system were investigated to examine the effects of density of plants, colour polymorphism, inflorescence dimension, and flower position within inflorescence on male and female reproductive success in three natural populations of D. sambucina. There were significant differences among sites in the number of pollinia removed and in fruit set per inflorescence. Number of removed pollinia and capsule production in D. sambucina were independent from flower and inflorescence size or flower position. As a whole, the red morphs showed the highest number of capsules produced, while the yellow morphs had the greatest male success. The relative male and female reproductive success were independent from plant density but were significantly correlated with the yellow morph frequency at the population level. Overall, our findings show that the contribution to the total reproductive success deriving from the two colour morphs does not conform with the predictions of negative frequency-dependent selection.     

Changes in learning ability and mechanism during development of grasshopper nymphs, Melanoplus bivittatus

Abstract. In an experimental arena, Melanoplus bivittatus (Say) (Orthoptera: Acrididae) nymphs of four stadia were observed to determine whether they learn to associate food with positional or light-related cues. Nymphs were observed for 4 h in the arena containing one yellow box and one green box, then they were trained by placing food in the green box overnight. Following training, the responses of nymphs to green and yellow boxes were observed for a second 4 h period.
Before training, nymphs of all stadia visited the yellow box more frequently than the green box. Training did not affect the behaviour of second-stadium nymphs, but training increased the relative frequency of visits to the green box by third, fourth and fifth instars. Effects of training on duration of visits to boxes were not evident. Investigations of the mechanism of learning showed that positional cues were used by third-stadium nymphs, but that fourth and fifth instars responded to light-related cues. The progression from no learning in second instars, through use of positional cues by third instars, to use of light-related cues by fourth and fifth instars is probably associated with the greater mobility, greater food consumption, and more varied diet of older nymphs.     

Association of red coloration with senescence of sugar maple leaves in autumn

We evaluated the association of red coloration with senescence in sugar maple (Acer saccharum Marsh.) leaves by assessing differences in leaf retention strength and the progression of the abscission layer through the vascular bundle of green, yellow, and red leaves of 14 mature open-grown trees in October 2002. Computer image analysis confirmed visual categorization of leaves as predominantly green, yellow or red, and chemical quantification of leaf pigment concentrations verified that leaf color reflected underlying differences in leaf biochemistry. Significantly lower chlorophyll concentrations within red and yellow leaves indicated that senescence was more advanced in leaves from these color categories relative to green leaves. Among leaf types, only red leaves contained high concentrations of anthocyanins. There were significant differences in leaf retention capacity among color categories, with the petioles of green leaves being the most firmly attached to twigs, followed by red and then yellow leaves. Microscopic analysis indicated that yellow leaves had the most advanced extension of the abscission layer through the vasculature, with green and red leaves having significantly less abscission layer progression than yellow. A more limited progression of the abscission layer through vascular bundles may be evidence of delayed leaf senescence that could extend resorption of mobile leaf constituents. Together, results from this study suggest an association between leaf anthocyanin content and functional delays in senescence.     

The influence of density on frequency-dependent selection by wild birds feeding on artificial prey

Previous work has demonstrated frequency-dependent selection by wild garden birds when feeding on green and brown pastry ''baits''. When the density of baits is low, the common colour is eaten disproportionately more than the rare colour (apostatic selection), and when the density is very high, the rare colour is eaten disproportionately more than the common (anti-apostatic selection). We explored the relationship between frequency-dependent predation and density in an experiment at 16 separate sites, using four levels of density and two frequencies of green and brown. Analysis of estimates of log-relative risk ratios showed little evidence for frequency-independent selection, but frequency-dependent selection changed gradually from apostatic at low density to anti-apostatic at high density. The validity of these conclusions in terms of individual bird behaviour was confirmed by Monte-Carlo simulations. We thus conclude that selection by wild birds feeding on green and brown artificial prey is frequency dependent, and that the strength and direction of this selection changes with prey density in a gradual and predictable manner.