Conspicuous Coloration Research Articles

Domestic chicks primarily attend to colour, not pattern, when learning an aposematic coloration

Aposematic conspicuous coloration consists of one or a few bright colours, often in combination with a black defined internal pattern. The function of conspicuousness in aposematism has been ascrib ...

Gender Differences in Species Recognition and the Evolution of Asymmetric Sexual Isolation

Closely related sympatric species are expected to evolve strong species discrimination because of the reinforcement of mate preferences. Fitness costs of heterospecific matings are thought to be higher in females than in males, and females are therefore expected to show stronger species discrimination than males. Here, we investigated gender and species differences in sexual isolation in a sympatric species pair of Calopteryx damselflies. The genus Calopteryx is one of the classic examples of reproductive character displacement in evolutionary biology, with exaggerated interspecific differences in the amount of dark wing coloration when species become sympatric. Experimental manipulation of the extent of dark wing coloration revealed that sexual isolation results from both female and male mate discrimination and that wing melanization functions as a species recognition character. Female choice of conspecific males is entirely based on wing coloration, whereas males in one species also use other species recognition cues in addition to wing color. Stronger species discrimination ability in males is presumably an evolutionary response to an elevated male predation risk caused by conspicuous wing coloration. Gender differences in species discrimination and fitness costs of male courtship can thus shed new light on the evolution of asymmetric sexual isolation and the reinforcement of mate preferences.

Automimic frequency influences the foraging decisions of avian predators on aposematic prey

Avian predators learn to avoid defended insects on the basis of their conspicuous warning coloration. In many aposematic species, the level of chemical defence varies, with some individuals (automodels) being more defended than others (automimics). Production of defence chemicals is often costly, and automimics enjoy the benefits of the warning signal without paying the cost of chemical production. This is a problem for the evolutionary stability of aposematism, since automimics appear to be at a selective advantage. If predators sample aposematic prey and selectively reject automodels, aposematism could become evolutionarily stable. However, it is then unclear how automimicry persists in aposematic species. Using chicks as predators and coloured crumbs for prey, we investigated how birds selectively rejected aposematic prey at different automimic frequencies. We found that birds tasted and rejected automodels at a constant level regardless of automimic frequency, but the rejection rates of automimics decreased with increasing automimic frequency. Birds only discriminated between automodels and automimics at frequencies above 25%; below this automimics would be at a selective advantage over automodels since they do not pay the costs associated with toxicity. Selective rejection of aposematic prey by predators can therefore explain both why aposematism is evolutionarily stable, and how automimicry can persist in aposematic populations. We also found that birds relearned that red crumbs were palatable more quickly with increasing automimic frequency. Therefore, the benefit of automimicry may depend upon birds' previous experiences with unpalatable prey as well as the actual frequency of automimics in the population.

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

AbstractSexual 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.

The Importance of Visual Cues for Nocturnal Species: Eagle Owl Fledglings Signal with White Mouth Feathers

AbstractComplex begging display by bird offspring has predominantly been investigated in diurnal species, which have conspicuous gape colours or plumage features. In nocturnal species, in contrast, such visual communication has received little attention because the assumption is that they exclusively rely on vocal communication. Here, we use a field experiment to investigate whether eagle owls, Bubo bubo, communicate through visual signals at night. We artificially decreased the brightness of the white feathers surrounding fledgling eagle owls’ mouths during the post‐fledging dependence period, and investigated the effect of this treatment by comparing the condition of these birds to that of birds who received a control treatment. Several physiological parameters considered in our analyses indicate that control owlets were in better condition than owlets with brightness‐reduced mouth feathers, which suggests that they received more or better food from feeding parents who discriminated between those young. Brightness‐dependent reactions of parent owls suggest that visual signalling may be more widely employed than previously thought, and studying birds at night may reveal sophisticated strategies of animal communication.

Predators' Toxin Burdens Influence Their Strategic Decisions to Eat Toxic Prey

Toxic prey advertise their unprofitability to predators via conspicuous aposematic coloration [1]. It is widely accepted that avoidance learning by naive predators is fundamental in generating selection for aposematism [2, 3] and mimicry [4, 5] (where species share the same aposematic coloration), and consequently this cognitive process underpins current evolutionary theory [5, 6]. However, this is an oversimplistic view of predator cognition and decision making. We show that predators that have learned to avoid chemically defended prey continue to attack defended individuals at levels determined by their current toxin burden. European starlings learned to discriminate between sequentially presented defended and undefended mealworms with different color signals. Once birds had learned to avoid the defended prey at a stable asymptotic level, we experimentally increased their toxin burdens, which reduced the number of defended prey that they ingested in the subsequent trial. This was due to the birds making strategic decisions to ingest defended prey on the basis of their visual signals. Birds are clearly able to learn about the nutritional benefits and defensive costs of eating defended prey, and they regulate their intake according to their current physiological state. This raises new perspectives on the evolution of aposematism, mimicry, and defense chemistry.

Sexual Dichromatism, Dimorphism, and Condition-Dependent Coloration in Blue-Tailed Bee-Eaters

AbstractAbstract. The Blue-tailed Bee-eater (Merops philippinus) is a cooperatively breeding and socially monogamous member of the Coraciiformes that displays conspicuous coloration and elongated central rectrices (“streamers”). Humans cannot distinguish males from females; both sexes are brightly colored with a chestnut throat patch, a yellow chin, and green body coloration fading into a turquoise-blue rump and tail. We quantified coloration with ultraviolet- (UV) visible spectrometry and measured morphology to determine the extent of sexual dichromatism and dimorphism. Males displayed more exaggerated coloration, longer tail streamers, and were larger than females. Multiple plumage ornaments (measures of plumage coloration and streamer length) were positively correlated in both sexes. Males in better body condition expressed darker chestnut throats and more chromatic green body plumage. Females in better body condition, however, exhibited more chromatic blue rumps and yellow chins. This study represents the first objective description of plumage ornamentation in the order Coraciiformes.

Molecular phylogeny and diversification of freshwater shrimps (Decapoda, Atyidae, Caridina) from ancient Lake Poso (Sulawesi, Indonesia)—The importance of being colourful

Ancient Lake Poso on the Indonesian island Sulawesi hosts a highly diverse endemic fauna, including a small species flock of atyid Caridina shrimps, which are characterized by conspicuous colour patterns. We used a mtDNA based molecular phylogeny to test the assumption of a monophyletic origin and intralacustrine radiation of the species flock and to assess the species specificity of some colour morphs. Our data reveal a rapid radiation of Caridina in the entire Poso drainage system, but provide no strong evidence for a monophyletic radiation of the lake species. Nevertheless each lacustrine species shows a varying degree of substrate or trophic specialization, usually considered a hallmark of adaptive radiation. Two distinct colour forms previously attributed to a single species, C. ensifera, lack distinguishing qualitative morphological characters, but are shown to be two different species. In contrast, morphologically rather distinct lake species lacking specific colour patterns may be hybridizing with riverine taxa. These results suggest that colour may play a similar role in species recognition and possibly speciation in ancient lake Caridina as hypothesized, e.g. for some African cichlids.

The evolutionary process of bioluminescence and aposematism in cantharoid beetles (Coleoptera: Elateroidea) inferred by the analysis of 18S ribosomal DNA

Cantharoid beetles are distinctive for their leathery soft elytra and conspicuous color or bioluminescence, and many of the members are equipped with chemical defenses. Thus, the vivid coloration of Cantharidae and Lycidae and the bioluminescence in Lampyridae and Phengodidae appear to be aposematic signals. However, the evolutionary aspect of their aposematism is not well understood, because the classification of the families remains controversial. In this study, we performed molecular phylogenetic analyses of species from cantharoid families, based on nucleotide sequence comparisons of nuclear 18S ribosomal DNA. The results shows that the luminous species Rhagophthalmus ohbai, which had sometimes been classified in Lampyridae, is excluded from a lampyrid clade and associates with the taxa of Phengodidae. The molecular data also suggests that four major subfamilies of Cantharidae (Cantharinae, Chauliognathinae, Malthininae, and Silinae) form a clade. The six subfamilies of Lampyridae are grouped and classified into two sublineages: Amydetinae + Lampyrinae + Photurinae and Cyphonocerinae + Luciolinae +Ototretinae. Genera Drilaster and Stenocladius are the members of Ototretinae in Lampyridae. These results conform to traditional taxonomy but disagree with more recent cladistic analyses. Based on these findings, we propose an evolutionary process of bioluminescence and aposematism in cantharoids: the clades of Cantharidae, Lampyridae, Lycidae, and Phengodidae have evolved aposematic coloration; subsequently Lampyridae and Phengodidae acquired bioluminescence; and these four major cantharoid families achieved their current adaptive diversities.

Relationship Between Algal-Foraging Ability and Expression of Sexually Selected Traits in Male Guppies

In the guppy Poecilia reticulata, males exhibit orange spots on their body and tail, and the orange spot patterns are often criteria for female mate choice. The orange spot coloration of males is determined by the intake of algae, a natural source of carotenoids. Therefore, males exhibiting conspicuous orange coloration are considered to possess high algal-foraging ability. In the present study, we examined the influence of algal-foraging ability, measured by algal-searching ability and algal-foraging frequency, on the expression of orange spot patterns and on other sexually selected traits in male guppies. Males exhibiting better performance in terms of both algal-searching ability and algal-foraging frequency grew larger. The size of the orange spots on males also increased with algal-foraging ability. However, neither algal-searching ability nor algal-foraging frequency influenced the coloration of the orange spots. In this experiment, a limited supply of carotenoids possibly prevented the males from completely developing their spots to the intrinsic size. The results of this study suggest that in male guppies under a carotenoid-limited situation, the allocation of carotenoids is directed toward enlargement of the size of the orange spots rather than enhancement of their coloration. Since both the body size and orange spot patterns of males contribute to their sexual attractiveness to females, high algal-foraging ability may enhance their mating success.

Steroid correlates of multiple color traits in the spiny lizard, Sceloporus pyrocephalus

Conspicuous coloration in females is less well studied compared to that in males. Adult female Mexican boulder spiny lizards (Sceloporus pyrocephalus) have conspicuously colored throat, or gular, regions, ranging from red to yellow, while adult males only weakly express such color in their gular region. Both sexes have dark blue-black gular stripes and venter stripes. Understanding proximate mechanisms underlying trait expression can aid in understanding trait function. To characterize the proximate mechanisms potentially influencing color variation among field-captured male and female S. pyrocephalus, we quantified three aspects of color (hue, saturation, brightness) for three body locations (gular region, gular stripes, venter stripes) and then assessed how color was related to reproductive state and concentrations of the plasma steroid hormones testosterone (T) and corticosterone (CORT) in males and T, CORT, and 17-beta estradiol (E(2)) in females. Testes volume was not related to variation in color or in hormones, perhaps because most males were in peak reproductive condition. Large vitellogenic follicles as opposed to oviductal eggs were associated with higher E(2) in females. Males with more dull gular stripes and females with dull venter stripes had significantly higher CORT. Females with red gular regions and pale grey gular stripes had higher T and E(2) concentrations compared to females with a more yellow gular region and darker gular stripes. Thus, gular region color in females could communicate reproductive state; dull gular stripes in males and dull venter stripes in females could communicate stress status.

Development of Self-Indicating Resin

Previously, we have reported the development and application of self-indicating resins (SIR), materials which can indicate presence or absence of amines in the reaction solution by the conspicuous color change of a phenolsulfophthalein type dye immobilized on resin beads [2a]. Although the functionality necessary for attaching the dye to the resins could be readily introduced by the Suzuki-Miyaura coupling during the synthesis of the SIR 1, this approach was only applicable to the dyes containing suitable functionality for the cross-coupling reaction. In this article we describe a new approach of immobilizing the indicating dyes onto the resin support. The dyes suitable for loading onto aminomethyl polystyrene (PS) resin were prepared by Friedel-Crafts reaction of 2-sulfoterephthalic anhydride with a wide range of phenols. Using this new route, the SIR 6c was readily prepared in >100g quantities. Use of the SIR 6c in the synthesis of a 144 member urea library was demonstrated and the SIR successfully indicated the endpoint of the reaction between amines and isocyanates.

State-dependent decision making: educated predators strategically trade off the costs and benefits of consuming aposematic prey

Aposematic prey advertise their defences, such as toxins or stings, to visually hunting predators using conspicuous warning coloration. Both the conspicuousness and the chemical content of prey determine the speed of avoidance learning by naive predators, and it has long been assumed that predator education is the main selective pressure in the evolution of aposematism. However, recent theoretical models have considered how educated predators could also exert significant selection pressures on aposematic prey by increasing their attack rates on defended prey in times of food shortage. Currently, there are no clear experimental data to support these models. In this study, we show that European starlings (Sturnus vulgaris) increase their attack rates on chemically defended insect larvae when their body masses and fat stores are experimentally reduced. In addition, the increase in attack rate is not simply due to indiscriminate attacks made when energy reserves are low but is based on knowledge about the prey’s defences. Taken together, these results suggest that educated adult predators will strategically trade off the energetic benefits of prey against their toxic costs according to their energetic needs. This result challenges classic theoretical models of the evolution of aposematism based purely on predator learning and forgetting rates and demonstrates the need to consider energy-toxin trade-offs in foraging decisions on defended prey. We discuss the implication of these results for the evolution of chemical defences and warning signals. Key words: aposematism, discrimination, energetic state, predation, quinine, receiver psychology. [Behav Ecol]

A new species of Temple Pitviper (Tropidolaemus Wagler, 1830) from Sulawesi, Indonesia (Squamata: Viperidae: Crotalinae)

The Asian Temple Pitviper Tropidolaemus wagleri is a widespread polytypic species complex with a complicated taxonomic history, a lengthy species synonymy list, and a geographic distribution encompassing Vietnam, Thailand, Malaysia, Singapore, Brunei, portions of Indonesia, and the Philippines. As a prelude to a comprehensive review of this species complex, we describe a new species of Temple Pitviper based on five historic museum specimens from the Indonesian island of Sulawesi. The new species can be distinguished from sympatric members of the Tropidolaemus subannulatus complex and other congeners on the basis of its conspicuous color pattern and scalation characters. Available collecting data suggest that the new species has a wide distribution in rainforests and lower montane wet forests of Sulawesi Utara and Sulawesi Tengah provinces.

Adaptive significance of maternal induction of density‐dependent phenotypes

Density has been demonstrated to impact life history traits such as growth, fecundity and survival. Some authors have proposed that morphological and behavioral traits have evolved in response to density conditions. To escape the adverse effect of density, individuals can either adapt to crowding or avoid crowding by dispersing. The aim of this work is to study the interplay between local adaptation and dispersal in four populations of the common lizard, Lacerta vivipara, where densities of both the maternal and juvenile environment have been experimentally manipulated. Density was decreased in the spring by removing a quarter of the population at two sites and was un‐manipulated in two other sites. One month later, we caught some pregnant females and kept them in the laboratory until parturition. To manipulate density of postnatal neonates and juveniles, we divided each clutch into two, and released half of the juveniles either in a reduced density site or in a control one. We then recaptured individuals a year after release and recorded their size and weight. When density was reduced, females increased their clutch size, but produced offspring of lower body condition than in the control sites. The conspicuous ventral color of females was likewise increased when density was reduced. However, offspring growth rate, local survival and dispersal were not influenced by maternal density. Juvenile females released in the reduced‐density site had lower survival rate than those released in the control density site. Contrary to expectations, offspring dispersal was significantly higher at the reduced compared to control density sites. There was no interaction between maternal density habitat and the juvenile release habitat indicating that maternal effects did not influence juvenile life history traits in a different way according to the level of density. Moreover, clutch size and offspring size had no effect on juvenile growth or survival.

Fiery red heads: female dominance among head color morphs in the Gouldian finch

Although the evolution of genetic color polymorphisms has received much theoretical interest, few empirical studies have investigated the adaptive function of alternative color morphs. Furthermore, most studies have focused almost exclusively on the evolution and adaptive expression of male coloration, leaving the role of conspicuous female coloration largely unknown. Using the color polymorphic Gouldian finch (Erythrura gouldiae), this study experimentally tests the status signaling function of head color (red, yellow, and black) among the 3 female color morphs. In standardized dominance contests between unfamiliar females of different head colors, red-headed females dominated both black- and yellow-headed females. During contests between the morphs, red-headed females passively displaced black- and yellow-headed opponents, whereas interactions between red-headed dyads were particularly aggressive and more frequent than interactions within dyads of the other color morphs. This effect of red dominance further persisted when head color was experimentally altered; red-manipulated females (of the other morphs) dominated both black- and yellow-headed females, whereas blackened red-headed females were dominated by naturally red-headed birds. Together with similar dominance-related differences among male morphs, these results suggest that the 3 color morphs may display alternative strategies in dominance behavior.

Subspecific and Temporal Variation in the Structurally Based Coloration of the Ultramarine Grosbeak

AbstractAbstractUltramarine Grosbeaks (Cyanocompsa brissonii) possess a striking sexual dichromatism, with males dark blue and females brown. There are two subspecies in Argentina: the larger-bodied C. b. argentina, which is common in shrubs and semiopen areas, and the smaller C. b. sterea that inhabits forests. We measured reflectance spectra of six plumage patches from study skins to evaluate the possibility of color differences between males of each subspecies and temporal variation in plumage coloration. We found differences between subspecies in color brightness, hue, saturation, and UV chroma in the plumage patches of more conspicuous coloration, which could be related to ambient light differences between the environments that each subspecies inhabits. We also documented temporal color variation in some plumage patches, in particular a gradual decrease of UV reflectance and a gradual increase in hue after molting, possibly attributable to feather wear.

Feral populations of the Australian Red-Claw crayfish (Cherax quadricarinatus von Martens) in water supply catchments of Singapore

The Red-Claw crayfish, Cherax quadricarinatus von Martens, is native to freshwater habitats of northern Australia and Papua New Guinea. Owing to its large size and suitability for aquaculture, C. quadricarinatus has been widely translocated around the world. Unfortunately, C. quadricarinatus is also recognised as invasive, having already established feral populations in South Africa, Mexico, Jamaica and Puerto Rico. The hardiness and conspicuous colouration of C. quadricarinatus has also made it popular in the aquarium trade worldwide, including Singapore. Here, we report the establishment of feral populations of C. quadricarinatus in the water supply catchments of Singapore.

Unusual sex roles in a highly promiscuous parrot: the Greater Vasa ParrotCaracopsis vasa

We describe the unusual mating system of the Greater Vasa ParrotCaracopsis vasa. The dull black plumage of males and females is similar but females are significantly larger than males. Females are promiscuous and copulated with at least five different males. Copulations were either short (1–3 s) or very long (mean 35.9 min), and long copulations involved a copulatory tie facilitated by the male's enlarged cloacal protrusion. Multilocus DNA fingerprinting of 17 broods showed that all were of mixed paternity, and that some broods had three fathers. Males never visited nests directly, but during the incubation and chick‐rearing periods females came off the nest and were fed regurgitated fruit by multiple males. Four had band‐sharing coefficients that suggested they were unrelated. Males copulated with and provided food for several widely separated females simultaneously. During the chick‐rearing period females defended a territory around the nest from conspecific females, developed conspicuous orange skin on the head (through feather loss), and uttered loud, complex vocalizations that we refer to as ‘song’ from prominent perches near the nest. Males showed none of these traits. Females with high song rates attracted more males and as a result received more food than other females. Play‐back experiments in which female song rates were either increased or decreased, attracted more or fewer males respectively. We propose that female song, conspicuous head colour and territoriality have all evolved as a result of competition between females for the food provided by males. The selective pressures favouring this highly unusual breeding system in the Greater Vasa Parrot are unclear but some sort of ecological constraint, such as food availability, may be important.

SUBSPECIFIC AND TEMPORAL VARIATION IN THE STRUCTURALLY BASED COLORATION OF THE ULTRAMARINE GROSBEAK

Abstract ABSTRACT Ultramarine Grosbeaks (Cyanocompsa brissonii) possess a striking sexual dichromatism, with males dark blue and females brown. There are two subspecies in Argentina: the larger-bodied C. b. argentina, which is common in shrubs and semiopen areas, and the smaller C. b. sterea that inhabits forests. We measured reflectance spectra of six plumage patches from study skins to evaluate the possibility of color differences between males of each subspecies and temporal variation in plumage coloration. We found differences between subspecies in color brightness, hue, saturation, and UV chroma in the plumage patches of more conspicuous coloration, which could be related to ambient light differences between the environments that each subspecies inhabits. We also documented temporal color variation in some plumage patches, in particular a gradual decrease of UV reflectance and a gradual increase in hue after molting, possibly attributable to feather wear.