Conspicuous colouration attracts prey to a stationary predator

Abstract 1. Conspicuous body colouration is counter‐intuitive in stationary predators because sit‐and‐wait tactics frequently rely on concealed traps to capture prey. Consequently, bright colours and contrasting patterns should be rare in predators using traps as they may alert potential prey. Yet, some orb‐weaving spiders are brightly coloured and contrastingly patterned. How can conspicuousness of trap‐building sit‐and‐wait predators be favoured by natural selection? 2. Observations of spiny spiders Gasteracantha fornicata in north‐eastern Australia showed that the size of spiders relative to their orb webs correlated positively with relative prey numbers already captured in their webs. A possible explanation is that the relatively larger appearance of the yellow–black striped dorsal surface of this spider attracts more visually oriented prey items. Prey attracted to webs may get trapped, thereby increasing the spiders' foraging success. 3. To test this hypothesis for the function of conspicuous body colouration, a field experiment was conducted that documented the prey capture rates of spiny spiders after manipulating or sham‐manipulating their appearance. 4. As predicted, spiders that were dyed black on their striped dorsal surface caught relatively fewer prey items than did control spiders. Thus, conspicuous dorsal body colouration may be adaptive in spiny spiders because it increases foraging success and, presumably, survival rates and reproductive outputs. Overall, these data support the colour‐as‐prey‐attractant hypothesis in a stationary, trap‐building predator.     

Conspicuousness of Dickerson's collared lizard (Crotaphytus dickersonae) through the eyes of conspecifics and predators

Selection should favour coloration in organisms that is more conspicuous to their own visual system than to those of their predators or prey. We tested this prediction in Dickerson's collared lizard ( Crotaphytus dickersonae ), a sexually dichromatic desert reptile that preys on insects and smaller lizard species, and which in turn is prey for birds and snakes. We modelled the spectral sensitivities of the lizards and their avian and snake predators, and compared the conspicuousness of the lizards' entire colour patterns with each class of viewers. Almost all comparisons involving females strongly supported our prediction for greater chromatic and brightness conspicuousness against local terrestrial visual backgrounds to their own modelled visual system than to those of avian and snake predators. Males, in contrast, exhibited far fewer cases of greater conspicuousness to their own visual system than to those of their predators. Our own perception of spectral similarity between blue C. dickersonae males and a local nonterrestrial visual background (i.e. the Sea of Cortéz) prompted a further investigation. We compared sea (and sky) radiance with dorsum radiance of C. dickersonae males and with males from two distantly-related Crotaphytus collaris populations in which males possess blue bodies. In all three visual models, C. dickersonae males exhibited significantly lower chromatic contrast with the sea (and sky) than did their noncoastal, blue-bodied congeners. Among potential explanations, the blue body coloration that is unique to male C. dickersonae may offset, if only slightly, the cost of visibility to predators (and to prey) through reduced contrast against the extensive, local, nonterrestrial blue backgrounds of the sea and sky.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 749–765.     

Local adaptation and divergence in colour signal conspicuousness between monomorphic and polymorphic lineages in a lizard

Population differences in visual environment can lead to divergence in multiple components of animal coloration including signalling traits and colour patterns important for camouflage. Divergence may reflect selection imposed by different receivers (conspecifics, predators), which depends in turn on the location of the colour patch. We tested for local adaptation of two genetically and phenotypically divergent lineages of a rock‐inhabiting lizard, Ctenophorus decresii, by comparing the visual contrast of colour patches to different receivers in native and non‐native environments. The lineages differ most notably in male throat coloration, which is polymorphic in the northern lineage and monomorphic in the southern lineage, but also differ in dorsal and lateral coloration, which is visible to both conspecifics and potential predators. Using models of animal colour vision, we assessed whether lineage‐specific throat, dorsal and lateral coloration enhanced conspicuousness to conspecifics, increased crypsis to birds or both, respectively, when viewed against the predominant backgrounds from each lineage. Throat colours were no more conspicuous against native than non‐native rock but contrasted more strongly with native lichen, which occurs patchily on rocks inhabited by C. decresii. Conversely, neck coloration (lateral) more closely matched native lichen. Furthermore, although dorsal coloration of southern males was consistently more conspicuous to birds than that of northern males, both lineages had similar absolute conspicuousness against their native backgrounds. Combined, our results are consistent with local adaptation of multiple colour traits in relation to multiple receivers, suggesting that geographic variation in background colour has influenced the evolution of lineage‐specific coloration in C. decresii.     

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.     

Signal and preference divergence among populations of the non‐endemic basal Lake Malawi cichlid fish Astatotilapia calliptera (Perciformes: Cichlidae)

In Lake Malawi and Lake Victoria, cichlid fishes have diversified into hundreds of species, many reproductively isolated by mate choice. Territorial males tend to be more aggressive to similar‐coloured males, facilitating coexistence of divergent colour morphs or species. Behavioural mate choice and aggression biases of species and allopatric populations of specialized rocky shore cichlids are influenced by divergent signals such as male colour. Believed to be basal to the Lake Malawi haplochromine radiation, and inhabiting shallow weedy areas of the lake and neighbouring water bodies, Astatotilapia calliptera also shows allopatric variation in colour. Here, it is demonstrated that such signal divergence is associated with tendencies of females to mate with males of their own population and also for males to preferentially attack males of their own population, indicating that preference divergence related to signal divergence in allopatry may have operated throughout the adaptive radiation of the Malawian cichlids. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 180–188.     

Discrimination of chemical stimuli in conspecific fecal pellets by a visually adept iguanid lizard,Crotaphytus collaris

Iguanid lizards are known for visual acuity and a diminished vomeronasal organ, which has led to mixed conclusions on whether iguanids use chemical cues. The collared lizard, Crotaphytus collaris, is a territorial iguanid that lives in open rocky habitats. Fecal pellets placed prominently on open rocky perches may provide an ideal mechanism for intraspecific chemical signaling. In order to determine whether collared lizards can discriminate between chemical stimuli found in conspecific fecal pellets, we collected 24 males and 25 females to analyze sex-specific behavioral responses via tongue-flicks and a newly observed behavior for the species, gular pumps, to cotton swabs containing water, cologne, chemical stimuli from conspecific male and female fecal pellets, and the lizard’s own fecal pellet. Both sexes were able to discriminate chemical stimuli from water via at least one behavior. Male collared lizards exhibited greater rates of response (tongue-flick and gular pumps) toward male fecal pellets when compared to the negative water control. Our results also suggest individuals may be able to discriminate between fecal pellets, as indicated by generally greater (but non-significant) counts of male tongue-flick responses to male fecal pellets when compared to their own. Collared lizard chemical discrimination appears to utilize tongue-flick and gular pump behaviors, possibly associated with distinct chemosensory modes (vomerolfaction and olfaction). Based on this study, we suggest that chemical signals may play a greater role in intraspecific communication than previously thought in this highly visual lizard.     

Warning colouration in pseudocerotid flatworms (Platyhelminthes,Polycladida). A preliminary study

Many species of tropical and subtropical pseudocerotid flatworms are noted for their brilliant colour patterns and conspicuous behaviour and are suitable candidates for the investigation of aposematic colouration. This study gives the first experimental evidence of aposematic colouration in pseudocerotid flatworms. Coloured and uncoloured agar models of flatworms were used to determine whether a fish predator, the moon wrasse Thalassoma lunare, could learn to avoid colourful flatworms on the basis of their colour pattern. The results showed that uncoloured models were more significantly attacked than coloured models (1% significance) and that there was no significant difference between attacks made to live flatworms and their respective models. These results clearly indicate the operation of aposematism in brightly coloured flatworms and demonstrate the operation of mimicry as the agar models were essentially non-living mimics of the flatworms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Avoidance of an aposematically coloured butterfly by wild birds in a tropical forest

1. Birds are considered to be the primary selective agents for warning colouration in butterflies, and select for aposematic mimicry by learning to avoid brightly coloured prey after unpleasant experiences. It has long been thought that bright colouration plays an important role in promoting the avoidance of distasteful prey by birds. 2. The hypothesis that warning colouration facilitates memorability and promotes predator avoidance was tested by means of a field experiment using distasteful model butterflies. Artificial butterflies with a Heliconius colour pattern unknown to local birds were generated using bird vision models, either coloured or achromatic, and hung in tree branches in a tropical forest. Two sequential trials were conducted at each site to test avoidance by naïve and experienced predators. 3. There was a significant reduction in predation in the second trial. Also, coloured models were attacked less than achromatic models. Specifically, coloured butterflies were attacked significantly less in the second trial, but there was no significant decrease in predation on achromatic models. 4. The present results imply an important role for colour in enhancing aversion of aposematic butterflies. It has also been demonstrated that previous experience of distasteful prey can lead to enhanced avoidance in subsequent trials, supporting mimicry theory.     

Individual selection, kin selection, and the shifting balance in the evolution of warning colours: the evidence from butterflies

It is difficult to imagine how warning colours evolve in unpalatable prey. Firstly, novel warningly coloured variants gain no protection from their colours, since predators have not previously encountered and learnt their colour patterns. This leads to a frequency-dependent disadvantage of a rare variant within a species. Secondly, novel warningly coloured variants may be more conspicuous than non-aposematic prey.
Nevertheless, it is obvious that many palatable butterflies have bright colours used in intraspecific communication and in duping predators. Other palatable butterflies are already warningly coloured. Should such butterflies evolve unpalatability, perhaps because of a host-plant shift, these bright colours would be preadapted to a warning role. Warning colours could then continue to evolve by enhancement of memorable characteristics of these patterns, or by mimicry.
Even within lineages of warningly coloured, unpalatable butterflies, colour patterns have continued to evolve rapidly. This diversity of warning colour patterns could have evolved in a number of ways, including individual and kin selection, and by the shifting balance. Evidence for these mechanisms is discussed, as are the similarities between the evolution of warning colours and more general evolutionary processes, including sexual selection and speciation.     

Foraging Benefits in a Colour Polymorphic Neotropical Orb Web Spider

Conspicuous body colouration in sedentary predators such as orb web spiders seems paradoxical as potential prey can see and avoid the webs. Several studies have demonstrated that rather than deterring prey, the colours act as sensory traps for flower‐seeking insects. In chromatically polymorphic species, the existence of more than one colour morph may lead to differing levels of prey attraction. To explore these issues, we studied a neotropical orb web spider, Verrucosa arenata, which shows colour polymorphism with predominantly white or yellow abdomen colours. We asked whether a particular morph is dominant in the population, and whether a particular morph is associated with enhanced foraging success and body condition. Here we showed that although yellow morphs attracted more prey, white morphs were in better body condition. We showed that model prey such as honeybees are able to discriminate between the morphs. We discuss these findings in relation to the functional significance of bright body colouration and colour polymorphism in spiders.     

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.     

Phylogeography of the Trans‐Volcanic bunchgrass lizard (Sceloporus bicanthalis) across the highlands of south‐eastern Mexico

We quantify the population divergence processes that shaped population genetic structure in the Trans‐Volcanic bunchgrass lizard (Sceloporus bicanthalis) across the highlands of south‐eastern Mexico. Multilocus genetic data from nine nuclear loci and mitochondrial (mt)DNA were used to estimate the population divergence history for 47 samples of S. bicanthalis. Bayesian clustering methods partitioned S. bicanthalis into three populations: (1) a southern population in Oaxaca and southern Puebla; (2) a population in western Puebla; and (3) a northern population with a broad distribution across Hidalgo, Puebla, and Veracruz. The multilocus nuclear data and mtDNA both supported a Late Pleistocene increase in effective population size, and the nuclear data revealed low levels of unidirectional gene flow from the widespread northern population into the southern and western populations. Populations of S. bicanthalis experienced different demographic histories during the Pleistocene, and phylogeographical patterns were similar to those observed in many co‐distributed highland taxa. Although we recommend continuing to recognize S. bicanthalis as a single species, future research on the evolution of viviparity could gain novel insights by contrasting physiological and genomic patterns among the different populations located across the highlands of south‐eastern Mexico. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 852–865.     

Phylogenetic comparative analysis supports aposematic colouration–body size association in millipede assassins (Hemiptera: Reduviidae: Ectrichodiinae)

The diversity of colour patterns and its importance in interactions with the environment make colouration in animals an intriguing research focus. Aposematic colouration is positively correlated with body size in certain groups of animals, suggesting that warning colours are more effective or that crypsis is harder to achieve in larger animals. Surprisingly, this relationship has not been recovered in studies investigating insects, which may have been confounded by a focus on aposematic taxa that are also gregarious. Millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae) comprise species with cryptic and aposematic colour patterns across a range of body sizes, are typically solitary as adults and are thus an excellent model for investigating a possible association between colouration and body size. Here, we use a comprehensive phylogeny for Ectrichodiinae, ancestral state reconstruction of colouration, and phylogenetic comparative methods to test for a colouration–body size association. The ancestor of Ectrichodiinae is reconstructed as cryptically coloured, with multiple subsequent transitions between aposematic and cryptic colouration. Aposematic colouration is positively associated with male body length and supports the hypothesis that selection on Ectrichodiinae body size may influence evolutionary transitions between aposematic and cryptic colouration or alternatively that selection for aposematic colouration influences body size evolution.     

Dietary conservatism may facilitate the initial evolution of aposematism

It has generally been assumed that warningly coloured organisms pay a cost associated with their increased visibility, because naïve predators notice and eat them. This cost is offset by their enhanced protection from educated predators who associate the colour pattern with unprofitability. However, some studies have suggested that avoidance of novel prey by avian predators ("dietary conservatism") can actually place novel colour morphs at a selective advantage over familiar ones, even when they are highly conspicuous. To test this idea, we experimentally simulated the appearance of a single novel-coloured mutant in small populations (20 individuals) of palatable artificial prey. The colour morph frequencies in each "generation" were determined by the relative survival of the previous generation under predation by birds. We used wild-caught European robins Erithacus rubecula foraging on pastry "prey" of different colours. The aim was to test whether prey selection by predators prevented or facilitated the novel colour morph persisting in the prey population over successive generations. We found that the novel colour morph quickly increased to fixation in 14/40 prey "populations", and at least once each in 8 of the 10 birds tested. Novel mutants of the classic aposematic colours (red and yellow) reached fixation most frequently, but even the green and blue novel morphs both increased to fixation in 2/40 trials. Novel colours reached fixation significantly faster than could be accounted for by drift, indicating active avoidance by the birds. These results suggest that a novel colour morph arising in a prey population can persist and increase under the selective pressure imposed by predators, even to the local exclusion of the original morph, despite being fully palatable. The consequences of this finding are discussed in relation to receiver psychology, the evolution of aposematism and the existence of polymorphism in Müllerian mimics.     

Prey selection by wild birds can allow novel and conspicuous colour morphs to spread in prey populations

Conspicuous warning coloration helps to protect prey because it signals to potential predators that the prey is unprofitable. However, such signals only work once predators have come to associate the conspicuous colour with the unprofitability of the prey. The evolution of warning coloration is generally considered to be paradoxical, because it has traditionally been assumed that the first brightly coloured individuals would be at an immediate selective disadvantage because of their greater conspicuousness to predators that are naïve to the meaning of the signal. As a result, it has been difficult to understand how a novel conspicuous colour morph could ever avoid rapid extinction, and instead survive and spread in the population until predators have become educated about the signal. In the present study, we experimentally simulated the appearance of a single novel coloured mutant in small populations (20 individuals) of palatable artificial pastry "prey". The colour morph frequencies in each "generation" of prey (presented on successive days of a trial) were determined by the relative survival of the previous generation under predation by free-living birds. We found that the novel colour morphs regularly persisted and increased from a starting frequency of 1/20 to reach fixation (100%), despite being fully palatable, even when the novel morph was much more conspicuous against the background than the familiar morph. This was true for both green (not normally considered a warning colour) and red (a classic warning colour) novel morphs. Novel colours reached fixation significantly faster than could be accounted for by random drift, indicating differential predation in relation to prey colour by the birds. Our experiments show that the immediate demise of a fully palatable new prey morph is not an inevitable outcome of predator behaviour, because even very conspicuous prey can gain protection from conservative foragers, simply by being novel.     

BRITAIN'S GAME FISHES: CELEBRATION AND CONSERVATION OF SALMONIDS. By M. Everard and P. Knight

This field study describes the camouflage pattern repertoire, associated behaviours and speed of pattern change of Nassau groupers Epinephelus striatus at Little Cayman Island, British West Indies. Three basic camouflaged body patterns were observed under natural conditions and characterized quantitatively. The mean speed of pattern change across the entire body was 4·44 s (range = 0·97–9·87 s); the fastest pattern change as well as contrast change within a fixed pattern occurred within 1 s. Aside from apparent defensive camouflage, E. striatus used camouflage offensively to approach crustacean or fish prey, and three successful predation events were recorded. Although animal camouflage is a widespread tactic, dynamic camouflage is relatively uncommon and has been studied rarely in marine teleosts under natural conditions. The rapid changes observed in E. striatus suggest direct neural control of some skin colouration elements, and comparative studies of functional morphology and behaviour of colour change in other coral‐reef teleosts are likely to reveal new mechanisms and adaptations of dynamic colouration.     

The interplay between multiple predators and prey colour divergence

Evolutionary divergence in the coloration of toxic prey is expected when geographic variation in predator composition and behavior favours shifts in prey conspicuousness. A fundamental prediction of predator‐driven colour divergence is that the local coloration should experience lower predation risk than novel prey phenotypes. The dorsal coloration of the granular poison frog varies gradually from populations of conspicuous bright red frogs to populations of dull green and relatively cryptic frogs. We conducted experiments with clay models in four populations to examine the geographic patterns of taxon‐specific predation. Birds avoided the local phenotype while lizards consistently selected for decreased conspicuousness and crab predation did not depend on frog coloration. Importantly, birds and lizards favoured low conspicuousness in populations where relatively cryptic green morphs have evolved. This study provides evidence for the interplay among distinct selective pressures, from multiple‐predator taxa, acting on the divergence in protective coloration of prey species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 580–589.     

The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.     

Size and sex matter: reproductive biology and determinants of offspring survival in Gazella marica

For prey, many behavioural traits are constrained by the risk of predation. Therefore, shifts between warning and cryptic coloration have been suggested to result in parallel changes in several behaviours. In the present study, we tested whether changes in chromatic contrast among eight populations of the strawberry poison‐dart frog, Dendrobates pumilio, co‐vary with behaviour, as expected if selection is imposed by predators relying on visual detection of prey. These eight populations are geographically isolated on different island in the Bocas del Toro region of Panama and have recently diverged morphologically and genetically. We found that aggression and explorative behaviour were strongly correlated and also that males tended to be more aggressive and explorative if they belonged to populations with conspicuously coloured individuals. We discuss how evolutionary switches between predator avoidance strategies and associated behavioural divergence between populations may affect reproductive isolation. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Behavioural,ecological, and evolutionary aspects of diversity in frog colour patterns

The role of colours and colour patterns in behavioural ecology has been extensively studied in a variety of contexts and taxa, while almost overlooked in many others. For decades anurans have been the focus of research on acoustic signalling due to the prominence of vocalisations in their communication. Much less attention has been paid to the enormous diversity of colours, colour patterns, and other types of putative visual signals exhibited by frogs. With the exception of some anecdotal observations and studies, the link between colour patterns and the behavioural and evolutionary ecology of anurans had not been addressed until approximately two decades ago. Since then, there has been ever‐increasing interest in studying how colouration is tied to different aspects of frog behaviour, ecology and evolution. Here I review the literature on three different contexts in which frog colouration has been recently studied: predator–prey interactions, intraspecific communication, and habitat use; and I highlight those aspects that make frogs an excellent, yet understudied, group to examine the role of colour in the evolution of anti‐predation strategies and animal communication systems. Further, I argue that in addition to natural‐history observations, more experiments are needed in order to elucidate the functions of anuran colouration and the selective pressures involved in its diversity. To conclude, I encourage researchers to strengthen current experimental approaches, and suggest future directions that may broaden our current understanding of the adaptive value of anuran colour pattern diversity.