Fruit color and contrast in seasonal habitats – a case study from a cerrado savanna

Communication contributes to mediate the interactions between plants and the animals that disperse their genes. As yet, seasonal patterns in plant–animal communication are unknown, even though many habitats display pronounced seasonality e.g. when leaves senescence. We thus hypothesized that the contrast between fruit displays and their background vary throughout the year in a seasonal habitat. If this variation is adaptive, we predicted higher contrasts between fruits and foliage during the fruiting season in a cerrado–savanna vegetation, southeastern Brazil. Based on a six‐year data base of fruit ripening and a one‐year data set of fruit biomass, we used reflectance measurements and contrast analysis to show that fruits with distinct colors differed in the beginning of ripening and the peak of fruit biomass. Black, and particularly red fruits, that have a high contrast against the leaf background, were highly seasonal, peaking in the wet season. Multicolored and yellow fruits were less seasonal, not limited to one season, with a bimodal pattern for yellow ones, represented by two peaks, one in each season. We further supported the hypothesis that seasonal changes in fruit contrasts can be adaptive because fruits contrasted more strongly against their own foliage in the wet season, when most fruits are ripe. Hence, the seasonal variation in fruit colors observed in the cerrado–savanna may be, at least partly, explicable as an adaptation to ensure high conspicuousness to seed dispersers.     

Conspicuousness, not colour as foraging cue in plant–animal signalling

The global prevalence of red and black fruits has still not been explained. Hypotheses based on innate consumer preferences have been tested and rejected. Though colour itself plays an important role in animal foraging, it is only one component of signals. Another major component are colour contrasts against background achieving the conspicuousness of signals. In order to evaluate which signal component determines consumers behaviour, we measured fruit colour and colour contrasts of 43 species against their natural background under ambient light conditions. Red and black fruits exhibit stronger contrasts and are therefore more conspicuous to consumers than fruits of other colours. Subsequently, trials were carried out to determine whether colour or conspicuousness influences avian food choice. Four bird species strongly preferred contrasting red–green or black–green over uni-coloured red, green, or black fruit displays, while no preference for particular hues was found. We therefore hypothesize that conspicuousness determines avian food selection and define the contrast hypothesis: Diurnal dispersers select fruit colours based on their conspicuousness and not their colour itself.
Because colour vision is an ancient trait, the entire heterogeneous group of frugivorous birds most likely perceives conspicuousness uniformly over evolutionary time spans. Conspicuousness has thus the potential to explain the global prevalence of red and black fruits.     

The role of chromatic and achromatic signals for fruit detection by birds

Fruit color changes during ripening are typically viewed asan adaptation to increase signal efficacy to seed dispersers.Plants can increase signal efficacy by enhancing chromatic (wavelengthrelated) and/or achromatic (intensity related) contrasts betweenfruit and background. To assess how these contrasts determinethe detectability of fruit signals, we conducted 2 experimentswith free-flying crows (Corvus ossifragus) under seminaturalconditions in a 2025 m² aviary. Crows searched first for artificialred and black fruits and detected red fruits from a larger distance.Because artificial red fruits had higher chromatic and lowerachromatic contrasts against foliage than artificial black fruits,crows apparently prioritized chromatic contrasts. Thus, thecommon change in fruit color from red to black during ripeningdoes not increase signal efficacy to crows. In a second trial,crows searched for UV-reflecting and black blueberries (Vaccinummyrtillus) against backgrounds of foliage and sand. Againstfoliage, UV-reflecting berries had higher chromatic and achromaticcontrasts than black berries, and crows detected them from alarger distance. Against sand, UV-reflecting berries had lowachromatic contrasts and black berries low chromatic contrasts.Crows detected both fruit types equally, suggesting that theyused chromatic contrasts to detect UV-reflecting berries andachromatic contrasts to detect black berries. Birds prioritizedchromatic contrasts when searching for artificial red fruitsin foliage but not when searching for blueberries on sand. Wesuggest that the relative importance of chromatic and achromaticcontrasts is contingent on the chromatic and achromatic varianceof the background. Models of signal perception can be improvedby incorporating background-specific effects.     

Characterizing background heterogeneity in visual communication

How is a visual signal effectively transmitted through an environment triggering a response by a perceiver? Experimental and theoretical works in disparate fields, such as sexual selection and plant–animal interactions, have demonstrated selection based on signal conspicuousness. However, to properly describe the conspicuousness of a signal, it is necessary to quantify the spatial and temporal heterogeneity of background coloration of a signaler. We intend to compare the effectiveness of four methods developed to characterize background heterogeneity. To describe the background in a seasonal vegetation, we collected reflectance data in dry and wet seasons of (i) target leaves (those leaves against which a signal is predominantly displayed); (ii) overall leaves (leaves from the most common plant species in the community); (iii) frames in a limited area in space, by measuring the reflectance of all material found in the background; and (iv) background items from the most common species, based on their abundance along transects. We analyzed seasonal color changes in terms of hue, chroma and brightness and described the conspicuousness of fruit coloration according to avian vision. All methods found significant differences in the background coloration between seasons, with higher reflectance values in the dry season. Hue values were higher in the dry season, and chroma values were higher in the wet season. Only the methods most restricted in space (target leaves and frames) recorded seasonal differences in fruit conspicuousness. The transects and frames methods are useful for describing the backgrounds of non-stationary signals (i.e., those of most animals). For plant signals, which are displayed against a fixed background in space, we recommend specific sampling of target leaves. Our results support the importance of measuring the seasonal heterogeneity of the background but also indicate that a monthly sampling design is not necessary to evaluate the conspicuousness of fruit signals.     

Evolution of color variation in dragon lizards: quantitative tests of the role of crypsis and local adaptation

Abstract Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions “exposed” to visual predators more cryptic than “hidden” body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast (“hue’ of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast (“brightness’ of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation.     

Why are fruits colorful? The relative importance of achromatic and chromatic contrasts for detection by birds

The colors of fruits and flowers are traditionally viewed as an adaptation to increase the detectability of plant organs to animal vectors. The detectability of visual signals increases with increasing contrasts between target and background. Contrasts consist of a chromatic aspect (color) and an achromatic aspect (light intensity), which are perceived separately by animals. To evaluate the relative importance of fruits’ chromatic and achromatic contrasts for the detection by avian fruit consumers we conducted an experiment with artificial fruits of four different colors in a tropical forest. We displayed the fruits against two different backgrounds, an artificial background and a natural one, because they differed in achromatic properties. We found no effect of the type of background on fruit detection rates. Detection rates differed for the four fruit colors. The probability of detection was explained by the chromatic contrast between fruits and their background, not by the achromatic contrasts. We suggest that birds attend primarily to chromatic contrast probably because these are more reliably detected under variable light conditions. Consistent with this hypothesis, we found habitat-specific differences in the conspicuousness of natural fruit colors in the study area. Fruits of understory species that are subjected to the variable light conditions within a forest displayed higher chromatic contrasts than species growing in the open restinga forest with constant bright illumination. There was no such difference for achromatic contrasts. In sum, we suggest that fruit colors differ between habitats because fruit colors that have strong chromatic contrasts against background can increase plants’ reproductive success, particularly under variable light conditions.     

Diversity in warning coloration is easily recognized by avian predators

Warning coloration is a widespread strategy to alert predators about prey unprofitability. The success of this strategy partly depends on predators being able to learn and recognize certain signals as indicators of toxicity, and theory predicts that this is easier if signals converge on similar colours. However, the diversity in warning signal form is astonishing, contradicting predictions. Here, we quantified ladybird signal diversity with respect to avian vision, measuring how unique and discernible each signal is from one another. In addition, we measured signal conspicuousness against a series of backgrounds, namely an average green, average brown, and where we collected each species, to determine whether signals are more contrasting against the ladybirds’ local substrates than compared to average ones. This allowed us to establish whether there are local adaptations in conspicuousness that promote signal diversity. We found that while ladybird signals are unique and recognizable, specialist species are more contrasting against the background they are most commonly found on. However, overall our study suggests that warning signals have evolved to be effective against a wide range of natural backgrounds, partly explaining the success of this strategy in nature.     

Fruit Colour Preferences of Redwings (Turdus iliacus): Experiments with Hand-Raised Juveniles and Wild-Caught Adults

Certain fruit colours and their contrast with the background coloration are suggested to attract frugivorous birds. To test the attractiveness of different colours, we performed three experiments in laboratory with controlled light conditions. In the first two experiments, we studied the fruit colour preferences of naive juvenile redwings. In the third experiment, we continued to investigate whether the contrast of the fruit colour with the background coloration affects the preference of both naive juveniles and experienced adult redwings. In the first experiment, juvenile birds preferred black, UV‐blue and red berries, to white ones. In pairwise trials, a new set of juveniles still preferred red berries to white ones. When testing the effect of contrasts on their choice, juveniles preferred UV‐blue berries to red ones on a UV‐blue background. However, no preference was found, when the background was either red or green. Adult redwings preferred UV‐blue berries to red ones on all backgrounds. According to these results, juveniles seem to have an innate avoidance of white berries. Furthermore, the foraging decisions of fruit‐eating birds are affected more by fruit colour than its contrast with background coloration, at least when contrasting displays are encountered from relatively short distances. Differences in preferences of adult and juvenile birds also indicate that learning seems to play a role in fruit choices.     

The detectability of the colour pattern in the aposematic firebug,Pyrrhocoris apterus: an image‐based experiment with human ‘predators’

Crypsis and aposematism are often regarded as two opposite protective strategies. However, there is large variation in prey appearance within both strategies. In this article, we investigated the conspicuousness of the aposematic red‐and‐black firebug, Pyrrhocoris apterus, by presenting images of natural and digitally manipulated phenotypes in their natural habitat on a computer screen to human ‘predators’, and comparing the detection times. We asked whether the natural colour pattern can be made more or less conspicuous by rearranging the spatial distribution of colour elements. Hence, we created a phenotype in which the black colour elements were moved to the body outline to test for a possible disruptive effect. In the ‘black’ and ‘red’ manipulations, we removed one of the two colours, creating two uniform colour variants. We found that some of our manipulations increased, but none reduced, the detection time significantly; this indicates that the naturally coloured firebug is highly conspicuous. The detection time varied among backgrounds and there was a significant relationship between detection time and chromatic similarity between the bug and the background for the natural and black phenotypes. Although background colour composition has an important effect on the signal, we argue that the coloration of P. apterus has evolved for high conspicuousness. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 806–816.     

Effects of anthocyanin and carotenoid combinations on foliage and immature fruit color of Capsicum annuum L

Shades ranging from violet to black pigmentation in pepper (Capsicum annuum L.) are attributed to anthocyanin accumulation. High-performance liquid chromatography and mass spectrometry analysis of violet and black fruit tissue identified a single anthocyanin that was determined to be delphinidin-3-p-coumaroyl-rutinoside-5-glucoside. Leaf tissue of a black-pigmented foliage genotype contained the same anthocyanin found in fruit but at a considerably higher concentration in comparison to violet and black fruit tissue. Fruit chlorophyll concentration was approximately 14-fold higher in black fruit in comparison to violet fruit that contained relatively little chlorophyll. Beta-carotene, lutein, violaxanthin, and neoxanthin carotenoid concentrations in black fruit were also significantly greater in comparison to violet fruit. High concentrations of delphinidin in combination with chlorophyll and accessory carotenoid pigments produced the characteristic black pigmentation observed in fruits and leaves of selected genotypes. Anthocyanins were accumulated in the outer mesocarp of violet and black fruit and in the palisade and mesophyll cells of black leaves. Consistent with chlorophyll content of respective genotypes, chloroplast density was greater in cells of black fruits. Utilizing Capsicum pigment variants, we determine the biochemical factors responsible for violet versus black-pigmented pepper tissue in the context of described pepper color genes.     

Contrast versus colour in aposematic signals

Conspicuousness is an important feature of warning coloration. One hypothesis for its function is that it increases signal efficacy by facilitating avoidance learning. An alternative, based on the handicap hypothesis, suggests that the degree of conspicuousness holds information directly about the quality of the prey, and that predators associate and learn about the conspicuousness of the coloration, and not the actual colour pattern. We studied the relative importance of signal contrast and the colours of signals for predator attention during discrimination. We used young chicks, Gallus gallus domesticus, as predators and small blue or red paper cones on either matching or contrasting paper backgrounds as stimuli associated with palatable or unpalatable chick crumbs. In four treatment groups, birds could use either cone and/or background colour, cone colour only, background colour only or cone-to-background contrast as cues for discrimination. Only birds in the contrast treatment failed to learn their discrimination task. Birds that had a choice between cone and background colour as cues used the cone colour and they learned the task faster than did birds that had to use background colour as a cue. The results suggest that birds primarily attend to the colours of signals and disregard contrast in discrimination tasks; they thus fail to support a handicap function of conspicuous aposematic coloration. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Phenotypic variation in male guppies from natural inland populations: an additional test of Haskins' sexual selection/predation hypothesis

Synopsis In Venezuela, guppies,Poecilia reticulata, are found in a diversity of aquatic ecosystems fringing the western slope of the eastern Andes. These inland drainages are associated with large between-site variation in both physical and biotic environments. Numbers of potential guppy predators vary greatly between low diversity piedmont streams and high diversity llanos swamps. We analyze geographic variation in several phenotypic traits associated with conspicuousness of male guppies as an independent test of Haskins' (Haskins et al. 1961) hypothesis of natural balance between sexual selection (driving male conspicuousness) and predation (driving crypsis). Four sites were compared: a diverse llanos swamp (high predation), two Andean piedmont streams (intermediate and low predation), and a spring pool located south of Venezuela's Paría Peninsula (no aquatic predators). Because tropical wet and dry seasons are associated with varying degrees of environmental change at these sites, within-site seasonal samples provided an additional test of the role of selective predation on Male phenotypes. Phenotypic traits associated with both size and coloration supported the sexual selection/predation hypothesis. male guppies from the spring were generally more colorful than male guppies from inland drainages. Males from the diverse swamp site were smaller and less colorful than guppies from other sites. Males from the swamp population were smallest and least colorful during the early dry season, when diurnal aquatic piscivores were more diverse and abundant. Dominant spot pigments at each site were generally those that provided greatest contrast with the predominant environmental background color, lending further evidence that coloration patterns in male guppies enhance conspicuousness.     

Correlated evolution of fig size and color supports the dispersal syndromes hypothesis

The influence of seed dispersers on the evolution of fruit traits remains controversial, largely because most studies have failed to account for phylogeny and or have focused on conservative taxonomic levels. Under the hypothesis that fruit traits have evolved in response to different sets of selective pressures by disparate types of seed dispersers (the dispersal syndromes hypothesis), we test for two dispersal syndromes, defined as groups of fruit traits that appear together more often than expected by chance. (1) Bird syndrome fruits are brightly colored and small, because birds have acute color vision, and commonly swallow fruits whole. (2) Mammal syndrome fruits are dull-colored and larger on average than bird syndrome fruits, because mammals do not rely heavily on visual cues for finding fruits, and can eat fruits piecemeal. If, instead, phylogenetic inertia determines the co-occurrence of fruit size and color, we will observe that specific combinations of size and color evolved in a small number of ancestral species. We performed a comparative analysis of fruit traits for 64 species of Ficus (Moraceae), based on a phylogeny we constructed using nuclear ribosomal DNA. Using a concentrated changes test and assuming fruit color is an independent variable, we found that small-sized fruits evolve on branches with red and purple figs, as predicted by the dispersal syndromes hypothesis. When using diameter as the independent variable, results vary with the combination of algorithms used, which is discussed in detail. A likelihood ratio test confirms the pattern found with the concentrated changes test using color as the independent variable. These results support the dispersal syndromes hypothesis.     

Does individual variation in fruit profitability override color differences in avian choice of red or white <Emphasis Type="Italic">Ilex serrata</Emphasis> fruits?

Although avian color preferences have been studied and documented in controlled experiments, they have not been demonstrated under natural conditions in most cases. We hypothesized that avian fruit choice reflects intraspecific variation in fruit characteristics other than color, rather than fruit color differences. By planting one Ilex serrata Thunb. (red form) and one I. serrata forma leucocarpa Beissner (white form), which produce red and white fruits, respectively, at each of five points, we examined the proportion of fruits removed per tree and fruit choice by three avian species based on fruit color and other fruit characteristics. The proportion of fruits removed increased with pulpy sugar concentration and fruit diameter, but it did not differ between fruit colors. The main foragers, resident brown-eared bulbuls Hypsypetes amaurotis, consumed fruits regardless of color, but correspondingly to fruit removal, and appeared to base their fruit choice on pulpy sugar concentration and fruit diameter rather than on color. In contrast, the minor foragers, migrant Daurian redstarts Phoenicurus auroreus (Pallas) and Siberian bluechats Tarsiger cyanurus (Pallas), tended to choose red fruits and were possibly attracted by them. In conclusion, fruit removal per tree reflected individual variation in fruit profitability more strongly than differences in fruit color, even though the individual variation was not remarkable. The importance of color in fruit choice differed based on species, residency status, and major/minor foragers.     

Sugar concentration of fruits and their detection via color in the Central American spider monkey (Ateles geoffroyi)

Although most arguments explaining the predominance of polymorphic color vision in platyrrhine monkeys are linked to the advantage of trichromacy over dichromacy for foraging for ripe fruits, little information exists on the relationship between nutritional reward and performance in fruit detection with different types of color vision. The principal reward of most fruits is sugar, and thus it seems logical to investigate whether fruit coloration provides a long-distance sensory cue to primates that correlates with sugar content. Here we test the hypothesis that fruit detection performance via trichromatic color vision phenotypes provides better information regarding sugar concentration than dichromatic phenotypes (i.e., is a color vision phenotype with sufficient red-green (RG) differentiation necessary to "reveal" the concentration of major sugars in fruits?). Accordingly, we studied the fruit foraging behavior of Ateles geoffroyi by measuring both the reflectance spectra and the concentrations of major sugars in the consumed fruits. We modeled detection performance with different color phenotypes. Our results provide some support for the hypothesis. The yellow-blue (YB) color signal, which is the only one available to dichromats, was not significantly related to sugar concentration. The RG color vision signal, which is present only in trichromats, was significantly correlated with sugar content, but only when the latter was defined by glucose. There was in fact a consistent negative relationship between fruit detection performance and sucrose concentration, although this was not significant for the 430 nm and 550 nm phenotypes. The regular trichromatic phenotypes (430 nm, 533 nm, and 565 nm) showed higher correlations between fruit performance and glucose concentration than the other two trichromatic phenotypes. Our study documents a trichromatic foraging advantage in terms of fruit quality, and suggests that trichromatic color vision is advantageous over dichromatic color vision for detecting sugar-rich fruits.     

Fruit color and fruit size of bird-disseminated plants in Japan

Fruit color, fruit size and phenology of bird-disseminated plants were examined in different climatic zones of Japan and the relationships between the plants and frugivorous birds were disscussed.Black fruit was the most common in warm-temperate areas and red was the most common in cool-temperate and subarctic zones. Red was more dominant in the lower layer of the forests in all climatic zones. Bicolor fruits were frequent in trees and were not found in herbs. Both in warm- and cool-temperate zones conspicuous fruits which are red and bicolored display were more frequent in summer than in winter.The diameter of most fruits were 4–11 mm. Fruits in warm-temperate were somewhat bigger than those in cooltemperate zone. In forest strata the fruits of shrubs were smaller than those of trees and herbs in width. However I found no relationships between fruit size and fruit color.The frugivorous birds could have influenced not only the evolution of seasonal differences in the proportion of fruit color between warm-temperate and cool-temperate region, but also affect the fruit size.     

Warning coloration in sawflyAthalia rosae larva and concealing coloration in butterflyPieris rapae larva feeding on similar plants evolved through individual selection

Green larvae of the butterfly Pieris rapae and black larvae of the sawfly Athalia rosae feed on green leaves of the same cruciferous plants. To demonstrate that P. rapae has concealing coloration and that A. rosae has warning coloration, the larvae of the two species were supplied to naive chicks Gallus gallus on white, green or black backgrounds. P. rapae larvae were palatable and their green body color acted as a concealing coloration. On the other hand, A. rosae larvae were unpalatable and their black body color acted as a warning coloration. There is a general consensus that warning coloration is an altruistic character which needs victims, and thus can evolve through kin selection or green beard selection. However, black A. rosae larvae were seldom injured by chicks' attack, in particular, on the green background. Therefore, the warning coloration of A. rosae larvae can be a selfish character and hence can evolve through individual selection as well as concealing coloration of P. rapae.     

Analysis of early growth of guppy strains,Poecilia reticulata,with different color patterns

Summary The guppy, Poecilia reticulata, is economically the most important species of freshwater ornamental fish cultured in Singapore. About 30 strains with different color patterns and fin shapes are reared in guppy farms practising monoculture in Singapore. To compare the growth rates of domesticated strains with different color patterns, newborn fry of 11 strains were obtained on the same day from a single farm in Singapore and were reared experimentally in the laboratory for about 100 days. Each strain was distributed randomly into 4 tanks with 30 fish/tank. Weekly weighings of 10 fish/tank were made from 17 to 100 days of age. Three strains were homozygous for the autosomal recessive blond gene which gives rise to a pale yellow background pigmentation (bb). These blond strains had significantly smaller body weights than corresponding ones with the same color pattern but with the wild-type grey-brown background coloration due to the dominant allele (BB). The strains with the red tail pattern due to a dominant X-linked gene (Rdt) had more rapid growth than those with other tail color patterns including the blue, black, green snakeskin and variegated. However, no significant differences were detected among the other color pattern strains. Thus among the strains studied, the blond strains were associated with slower growth while those with the red tail color were associated with faster growth.     

Fruit color polymorphism in a bird-dispersed shrub (Rhagodia parabolica) in Australia

Summary We examined the selective basis of fruit color, a trait assumed to affect the attractiveness of fruits to avian dispersal agents, inRhagodia parabolica in Victoria, Australia. The fleshy fruits ofR. parabolica are highly polymorphic in color; individual plants may bear red, white, or yellow fruits, or some combination of these. Red color is produced by betacyanins, yellow by betaxanthins, and white by some other flavonoid compounds. Red is the most common color, white less common, and yellow is relatively rare; red and white is the most common color combination. Fruits of these color-morphs do not differ in maximum size, weight, pulp-seed ratio, water content, or content of major nutrients (sugars, N, and lipids). The most common avian consumer,Zosterops lateralis, foraged at random on the color-morphs, although all fruit-eaters, collectively, slightly favored white fruits. Weekly fruit removal rates were equivalent for all four morphs. Seeds from color-morphs differed in seed germination behavior: seeds from red fruits germinated faster than seeds from yellow fruits, and seeds from white fruits showed the greatest response to passage throughZ. lateralis guts. Lack of strong foraging preferences by birds and the different germination behaviors may contribute to the maintenance of the color polymorphism.     

Unripe red fruits may be aposematic

The unripe fruits of certain species are red. Some of these species disperse their seeds by wind (Nerium oleander, Anabasis articulata), others by adhering to animals with their spines (Emex spinosa) or prickles (Hedysarum spinosissimum). Certainly neither type uses red coloration as advertisement to attract the seed dispersing agents. Fleshy-fruited species (Rhamnus alaternus, Rubus sanguineus and Pistacia sp.), which disperse their seeds via frugivores, change fruit color from green to red while still unripe and then to black or dark blue upon ripening. The red color does not seem to function primarily in dispersal (unless red fruits form advertisement flags when there are already black ripe fruits on the plant) because the red unripe fruits of these species are poisonous, spiny, or unpalatable. The unripe red fruits of Nerium oleander are very poisonous, those of Rhamnus alaternus and Anabasis articulata are moderately poisonous, those of Rubus sanguineus are very sour, those of Pistacia sp. contain unpalatable resin and those of Emex spinosa and Hedysarum spinosissimum are prickly. We propose that these unripe red fruits are aposematic, protecting them from herbivory before seed maturation.