Conspicuous Coloration Research Articles

Mating behavior and rapid concealing of nuptial coloration in males of the Fishgod Blenny Malacoctenus ebisui (Teleostei: Blenniiformes)

Courting males often face the trade-off of attracting the attention of both females and predators. Rapid color change, a relatively simple solution to this dilemma, is described for nuptial males of the Fishgod Blenny Malacoctenus ebisui (Teleostei: Blenniiformes) from direct observations at three rocky reefs in the Mexican Pacific. Nuptial males showed three dark bars on a white background that covered the anterior part of the body, and three dark bars posteriorly forming a solid dark patch along the midline. The head was black with a prominent white area on the lower portion of the iris of each eye, two white patches on the upper jaw, and one central white patch on the lower jaw. When an intensely colored male was disturbed the white patches on the eyes quickly disappeared, while the other white markings became muted apparently by rapid expansion of melanophores. This relatively simple system permits males of the Fishgod Blenny to rapidly suppress their conspicuous coloration in response to perceived threats. Mating behavior of the Fishgod Blenny observed at Bahia Chamela is similar to that reported for other labrisomid blennies, with males repeatedly nudging the side of the female and both sexes alternately performing quivering movements.

Study of the influence of cobalt in the high formability of the Au-Fe system

Since ancient times, gold has been used due to its especial properties. Among those properties are the resistance to corrosion (for being noble), its high electrical and thermal conductivity, and also its conspicuous coloration. Gold has been applied in a diversity of subjects such as economy, jewelry, electronic circuits and odontology. The fascinating properties of gold are likely to improve with the preparation of alloys; among those, the Au-Fe alloys constitute some of the most studied nowadays. In this research, we present our results concerning the microstructure of the Au-Fe and Au-Fe-Co alloys. We fabricated gold based alloys with 25% (weight) Fe and then compared their structure and formability to Au-24.5Fe-0.5Co (% weight) to determine the role of cobalt in the alloy. An induction furnace with controlled atmosphere (argon) and conductor crucibles coated with zirconium silicate was used. The samples were characterized by three processes: as-cast, with heat treatment (HT) at T=900°C (1h and 3h) and as-cast centrifuged.

Phenylthiophene-Containing Poly(2,5-dithienylpyrrole)s as Potential Anodic Layers for High-Contrast Electrochromic Devices

A new phenylthiophene-containing 2,5-dithienylpyrrole derivative, namely 2,5-di(thiophen-2-yl)-1-(4-(thiophen-2-yl)phenyl)-pyrrole (DTTPP), was synthesized and its corresponding homopolymer (PDTTPP) and copolymers (P(DTTPP-co-DTP (dithieno[3,2-b:2’,3’-d]pyrrole)) and P(DTTPP-co-DTC (3,6-di(2-thienyl)carbazole))) were prepared using electrochemical polymerization. Spectroelectrochemical studies showed that the PDTTPP film was yellowish-green, bluish purple, and deep bluish violet in neutral, oxidized, and highly oxidized states, respectively. The P(DTTPP-co-DTP) film exhibited a conspicuous color transition between five colors (orange brown at 0 V, coffee at 0.8 V, bluish gray at 1.0 V, bluish purple at 1.2 V, and deep bluish violet at 1.4 V). The maximum optical contrast (ΔTmax) of the PDTTPP, P(DTTPP-co-DTP), and P(DTTPP-co-DTC) films were estimated as 36.7% at 970 nm, 63.5% at 1216 nm, and 46.2% at 932 nm, respectively, and the coloration efficiency (η) of the PDTTPP and P(DTTPP-co-DTP) films were determined as 303.84 cm2 C−1 at 970 nm and 260.65 cm2 C−1 at 1216 nm, respectively, in an ionic liquid solution. A dual type PDTTPP/PProDOT-Et2 (poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4–b][1,4]dioxepine)) electrochromic device (ECD) attained a high ΔTmax (43.5%) and a high coloration efficiency (895.53 cm2 C−1) at 594 nm, whereas a P(DTTPP-co-DTP)/PProDOT-Et2 ECD realized a high ΔTmax (52.4%) at 592 nm and satisfactory long-term cycling stability and open circuit memory.

Colour alone matters: no predator generalization among morphs of an aposematic moth

Local warning colour polymorphism, frequently observed in aposematic organisms, is evolutionarily puzzling. This is because variation in aposematic signals is expected to be selected against due to predators' difficulties associating several signals with a given unprofitable prey. One possible explanation for the existence of such variation is predator generalization, which occurs when predators learn to avoid one form and consequently avoid other sufficiently similar forms, relaxing selection for monomorphic signals. We tested this hypothesis by exposing the three different colour morphs of the aposematic wood tiger moth, Arctia plantaginis, existing in Finland to local wild-caught predators (blue tits, Cyanistes caeruleus). We designed artificial moths that varied only in their hindwing coloration (white, yellow and red) keeping other traits (e.g. wing pattern and size) constant. Thus, if the birds transferred their aversion of one morph to the other two we could infer that their visual appearances are sufficiently similar for predator generalization to take place. We found that, surprisingly, birds showed no preference or aversion for any of the three morphs presented. During the avoidance learning trials, birds learned to avoid the red morph considerably faster than the white or yellow morphs, confirming previous findings on the efficacy of red as a warning signal that facilitates predator learning. Birds did not generalize their learned avoidance of one colour morph to the other two morphs, suggesting that they pay more attention to conspicuous wing coloration than other traits. Our results are in accordance with previous findings that coloration plays a key role during avoidance learning and generalization, which has important implications for the evolution of mimicry. We conclude that, in the case of wood tiger moths, predator generalization is unlikely to explain the unexpected coexistence of different morphs.

Patterns of variation in eggshell colour of Mountain Bluebirds (Sialia currucoides) provide mixed support for the sexually selected eggshell colour hypothesis

Determining the functional significance of ornamental traits and whether they are shaped by sexual selection requires understanding how they vary among individuals, and their relationship with other measures of quality. Conspicuous eggshell coloration is a trait that may have evolved through sexual selection as a signal of female quality. This hypothesis is based on the possibility that the pigment used to colour blue-green eggs is limited and potentially costly to allocate to eggshells. We investigated the signalling potential of blue-green eggshell colour by quantifying patterns of within- and among-clutch colour variation in Mountain Bluebirds (Sialia currucoides) to determine if pigment was limited and if egg colour traits are intrinsic to individual females. We also explored relationships over two breeding seasons between eggshell colour and other female traits and investment in eggs. Eggshell colour was highly repeatable within clutches for most measures, and relatively consistent between breeding events in different years, indicating that eggshell colour is an intrinsic trait. Eggs in second clutches within a season had less saturated blue-green colour than in first clutches, and within clutches, later-laid eggs were brighter but generally less blue-green in colour than earlier laid eggs, providing evidence of pigment limitation. However, associations between eggshell colour and other female traits and investment in eggs were less clear, and inconsistent among study years. Our findings suggest that there is potential for blue-green egg colour to function as a signal of female quality, but further study is needed to determine if blue-green eggshell colour is a truly informative signal.

Responses of Galápagos Lava Lizards (Microlophus bivittatus) to Manipulation of Female Nuptial Coloration on Lizard Robots

Abstract Females of some lizard species exhibit conspicuous coloration during the breeding cycle (“nuptial coloration”) that elicits male courtship. We conducted two field experiments with San Cristobal Lava Lizards (Microlophus bivittatus) in the Galapagos Islands to determine how the presence and extent of nuptial coloration on lizard robots affected responses of adult males and females. Robots programmed to perform conspecific bobbing displays had a morphological appearance that mimicked (1) a conspecific female without nuptial coloration (non-red control stimulus); (2) a conspecific female with nuptial coloration (normal red stimulus); or (3) a female with an extent of nuptial coloration beyond the range of conspecific variation (super-normal red stimulus). In Experiment 1, subjects witnessed two stimuli in sequence, being presented first with the side of a robot that exhibited conspecific nuptial coloration or with the opposite side of the same robot that lacked nuptial coloration. Results showed no ...

How to fight multiple enemies: target-specific chemical defences in an aposematic moth.

Animals have evolved different defensive strategies to survive predation, among which chemical defences are particularly widespread and diverse. Here we investigate the function of chemical defence diversity, hypothesizing that such diversity has evolved as a response to multiple enemies. The aposematic wood tiger moth (Arctia plantaginis) displays conspicuous hindwing coloration and secretes distinct defensive fluids from its thoracic glands and abdomen. We presented the two defensive fluids from laboratory-reared moths to two biologically relevant predators, birds and ants, and measured their reaction in controlled bioassays (no information on colour was provided). We found that defensive fluids are target-specific: thoracic fluids, and particularly 2-sec-butyl-3-methoxypyrazine, which they contain, deterred birds, but caused no aversive response in ants. By contrast, abdominal fluids were particularly deterrent to ants, while birds did not find them repellent. Our study, to our knowledge, is the first to show evidence of a single species producing separate chemical defences targeted to different predator types, highlighting the importance of taking into account complex predator communities in studies on the evolution of prey defence diversity.

Controllable Electrochromic Polyamide Film and Device Produced by Facile Ultrasonic Spray-coating

Thermally stable TPA-OMe polyamide films with high transmittance modulation in response to applied potential are formed by facile ultrasonic spray-coating. Four processing conditions (Film A, Film B, Film C and Film D) through tuning both solution concentrations and deposition temperatures can be utilized for the formation of wet and dry deposited films with two film thickness intervals. The electrochromic results show that the dry deposited rough films at higher deposition temperature generally reveal a faster electrochromic response, lower charge requirements (Q) and less conspicuous color changes (smaller optical density change (ΔOD) and lightness change (ΔL*)) during the oxidation process as compared to the wet deposited smooth films at lower deposition temperature. Moreover, thicker electrochromic films from increased solution concentration exhibit more obvious changes between coloration and bleaching transition. All these four polyamide films display colorless-to-turquoise electrochromic switching with good redox stability. The large scale patterned electrochromic film and its application for assembled device (10 × 10 cm2 in size) are also produced and reversibly operated for color changes. These represent a major solution-processing technique produced by ultrasonic spray-coating method towards scalable and cost-effective production, allowing more freedoms to facilitate the designed electrochromic devices as required.

Facile preparation of urchin-like NiCo2O4 microspheres as oxidase mimetic for colormetric assay of hydroquinone

The hierarchical urchin-like NiCo2O4 microspheres were successfully fabricated by facile two-step method, including template-free hydrothermal and calcination. The prepared NiCo2O4 microspheres with amounts of absorbed oxygen were found to possess oxidase-like activity. They could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) without the exogenous addition of H2O2, causing typical color reaction. But hydroquinone (HQ) could induce the reduction of oxTMB and result in a conspicuous blue color fading. In this paper, a simple and rapid colorimetric method for detecting trace amount of HQ was explored in-depth. Excellent linear relationship (5–110μM) and a low detection limit of 2.7μM were achieved. Meaningfully, this method could be well applied in real environmental samples with outstanding recoveries ranging from 97.07% to 103.52%. These primary results demonstrated that the NiCo2O4 microspheres have a great potential for applications in environmental chemistry.

Integration of graphene sensor with electrochromic device on modulus-gradient polymer for instantaneous strain visualization

In nature, some animals change their deceptive coloration for camouflage, temperature preservation or communication. This astonishing function has inspired scientists to replicate the color changing abilities of animals with artificial skin. Recently, some studies have focused on the smart materials and devices with reversible color changing or light-emitting properties for instantaneous strain visualization. However, most of these works only show eye-detectable appearance change when subjected to large mechanical deformation (100%–500% strain), and conspicuous color change at small strain remains rarely explored. In the present study, we developed a user-interactive electronic skin with human-readable optical output by assembling a highly sensitive resistive strain sensor with a stretchable organic electrochromic device (ECD) together. We explored the substrate effect on the electromechanical behavior of graphene and designed a strategy of modulus-gradient structure to employ graphene as both the highly sensitive strain sensing element and the insensitive stretchable electrode of the ECD layer. Subtle strain (0–10%) was enough to evoke an obvious color change, and the RGB value of the color quantified the magnitude of the applied strain. Such high sensitivity to smaller strains (0–10%) with color changing capability will potentially enhance the function of wearable devices, robots and prosthetics in the future.

How variation in prey aposematic signals affects avoidance learning, generalization and memory of a salticid spider

Most studies of aposematism focus on the effect of warning signals on vertebrate predators, especially birds. In our experiments, we used jumping spiders, Evarcha arcuata (Araneae: Salticidae) as predators, and larvae of three colour forms (red, white, yellow) of an unpalatable firebug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae) as prey. The experiments were divided into four successive steps, focusing on different aspects of predator–prey interaction. (1) When presented with a firebug for the first time, the spiders captured the white, least conspicuous colour form more often than the other two. No differences in the attack latencies were observed between the colour forms. (2) In the avoidance-learning test, the spiders were offered in succession five firebugs of one of the three colour forms. The attack and capture rate decreased in all colour forms, more notably in the red, most conspicuous form. (3) After five presentations of the same prey, the spiders were presented with a different firebug colour form. The results of the generalization process were asymmetric: spiders' attack rate increased when the red prey was followed by the yellow or white one, but decreased when the red form was presented after the other colour forms. (4) Spiders attacked the same prey more often the next day, but the attacks were seldom fatal. Similarly to the initial reaction, spiders captured the white firebugs more often. Our results show that for E. arcuata , the red coloration can represent an effective aposematic signal. Red prey coloration decreased the attack rate during the avoidance-learning process and favoured the prey in generalization between different colour forms. Yellow coloration was moderately effective against E. arcuata , whereas white coloration was the least effective because of low innate bias against this signal.

Colour vision in Finlayson’s squirrel (Callosciurus finlaysonii): is conspicuous pelage colour useful for species recognition?

Finlayson’s squirrel, Callosciurus finlaysonii, is distributed in lowland forests throughout South-East Asia. Its pelage colour is conspicuous and polymorphic (red, black, white and a mixture of these colours), which is characteristic of the species, with 16 subspecies described based on pelage colour patterns. Two closely related species, the brown C. erythraeus and the orange C. caniceps, are also distributed throughout the region. To examine whether the conspicuous pelage colour is a visual clue for species/subspecies discrimination, we experimentally assessed the colour vision of C. finlaysonii. Optically measured pelage colours of the dorsal body differed greatly among seven subspecies of C. finlaysonii and also differed among the three species of the region. Colour vision tests revealed that C. finlaysonii can discriminate the colour of conspecific white, black, and red pelages from the orange pelages of C. caniceps. They can also discriminate the brown pelages of C. erythraeus and conspecific white...

Bright birds are cautious: seasonally conspicuous plumage prompts risk avoidance by male superb fairy-wrens.

Increased predation risk is considered a cost of having conspicuous colours, affecting the anti-predator behaviour of colourful animals. However, this is difficult to test, as individual factors often covary with colour and behaviour. We used alarm call playback and behavioural observations to assess whether individual birds adjust their response to risk according to their plumage colour. Male superb fairy-wrens (Malurus cyaneus) change from a dull brown to conspicuous blue plumage each year, allowing the behaviour of different coloured birds to be compared while controlling for within-individual effects. Because the timing of colour change varies among males, blue and brown birds can also be compared at the same time of year, controlling for seasonal effects on behaviour. While blue, fairy-wrens fled more often in response to alarm calls, and took longer to emerge from cover. Blue fairy-wrens also spent more time foraging in cover and being vigilant. Group members appeared to benefit from the presence of blue males, as they reduced their response to alarms, and allocated less time to sentinel behaviour when a blue male was close by. We suggest that fairy-wrens perceive themselves to be at a higher risk of predation while in conspicuous plumage and adjust their behaviour accordingly.

Female Brazilian whiptail lizards (Cnemidophorus ocellifer) prefer males with high ultraviolet ornament reflectance

Conspicuous colouration is an important way of social communication in many taxa. The role of ultraviolet (UV) signals in intraspecific communication has only recently been studied in lizards, and there is not a general understanding of the adaptive role of UV colouration. Colour ornaments can signal male quality in mate choice and are therefore suitable for reliably predicting the outcome of female preference. Here, we tested the potential role of UV colouration in female spatial preference in a non-territorial teiid lizard, Cnemidophorus ocellifer. We experimentally manipulated the UV reflectance of size-matched male pairs and tested the effects of our treatment on females’ spatial distribution. We found that females associated with males of higher UV reflectance, suggesting that UV colour can be an important clue during mate preference decisions. Our results provide the first empirical evidence for the importance of UV colouration in female preference in a mutually ornamented lizard species.

Escape behaviour of aposematic (Oophaga pumilio) and cryptic (Craugastor sp.) frogs in response to simulated predator approach

Abstract:Crypsis and aposematism are common antipredator strategies that can each be coupled with behaviours that maximize predator deterrence or avoidance. Cryptic animals employ camouflage to conceal themselves within their environment and generally rely on immobility to avoid detection by predators. Alternatively, aposematic animals tend to rely on an association between conspicuous colouration and secondary defence to deter potential predators, and tend to exhibit slow movements in response to predators. The goal of the present study was to determine how cryptic Craugastor sp. and aposematic Oophaga pumilio respond to simulated human and bird model predators. Oophaga pumilio responded more often with movement to both the human (17/22) and bird (9/25) predators than Craugastor sp. (human: 2/21; bird: 0/21). The increased movement resulted in a greater average flight initiation distance, latency to move, and distance fled in O. pumilio. These findings suggest that cryptic Craugastor sp. rely on immobility to avoid detection, whereas aposematic O. pumilio utilize movement, possibly as a mechanism to increase the visibility of their warning signals to potential predators. Furthermore, O. pumilio exhibited greater movement in response to humans, suggesting that they actively avoid trampling by large threats, rather than considering them predators.

The evolutionary history and taxonomic reevaluation of the Japanese coral snake,Sinomicrurus japonicus(Serpentes, Elapidae), endemic to the Ryukyu Archipelago, Japan, by use of molecular and morphological analyses

Sinomicrurus japonicus has a conspicuous colour pattern of longitudinal black stripes and transverse sets of black and white bands with an orange-reddish background colour. The pattern varies markedly among island populations, and thus, three subspecies have been recognized. We conducted molecular phylogenetic analyses on the island populations to clarify the evolutionary trajectory of such colour patterns and reevaluate the current classification accordingly. The results indicated relatively deep allopatric divergences within S. j. boettgeri, paraphyly of S. j. boettgeri against other two subspecies, and two independent derivations of S. j. takarai from boettgeri-like ancestors. Detailed morphological analyses revealed that variations in the boettgeri and takarai forms were more or less continuous and that differences between the two takarai populations were very small. From these results, we propose synonymizing S. j. takarai with S. j. boettgeri. Morphological differences between the genetically most distant populations of S. j. boettgeri were also small, whereas the japonicus form was distinct from the remainder. Considering the possible evolution of S. j. japonicus through peripheral isolation, we propose retention of these two subspecies. This study provides a basis for future work on the adaptive significance of geographic variation in the colour pattern of S. japonicus.

Origin of an extensive network of non-tectonic synclines in Eocene limestones of the Western Desert, Egypt

Satellite images of the Western Desert of Egypt display conspicuous sinuous color patterning that previous workers have interpreted as erosional flutes formed by catastrophic flooding. Our work with high resolution satellite imagery shows that the patterning is not erosional but, rather, the result of a network of thousands of narrow synclines in the Eocene bedrock capping the Limestone Plateau. Synclines form as isolated, 200-400 meter-wide downwarps in otherwise flat-lying strata. Limb dips are shallow, and doubly plunging hinges form multiple basin closures along syncline lengths. Anticlines form “accidentally” in inter-syncline areas where two adjacent synclines lie close together. Synclines have two dominant orientations, WNW-ESE and NNW-SSE, parallel to two prominent joint and fault sets, and synclines branch, merge, and change orientation along their lengths. Synclines are all at the same scale with neither larger structures nor parasitic structures and are best described as non-tectonic sag synclines. An Egypt-wide inventory reveals that these synclines are both confined to Eocene limestones and developed, albeit it sporadically, over nearly 100,000 km2. The syncline network predates plateau gravels of the Katkut Formation, which have been interpreted as Oligocene or early Miocene in age, and the network is cut by faults related to Western Desert extension associated with Red Sea rifting. The mechanism that caused sag of overlying layers is not clear. Modern karst collapse, subsurface dissolution of evaporites, and collapse of paleokarst are all unlikely mechanisms given the timing of formation and the underlying stratigraphy. Silica diagenesis and downslope mobilization of underlying shales are possibilities, although uncertainty about the origin of silica in the limestones, plus the consistency of syncline orientations over large areas, make these models problematic. Hypogene karst, perhaps related to aggressive fluids associated with basaltic intrusions, may be the model most consistent with the admittedly limited data we currently have for the network.

Conspicuousness, color resemblance, and toxicity in geographically diverging mimicry: The pan-Amazonian frogAllobates femoralis

Predation risk is allegedly reduced in Batesian and Müllerian mimics, because their coloration resembles the conspicuous coloration of unpalatable prey. The efficacy of mimicry is thought to be affected by variation in the unpalatability of prey, the conspicuousness of the signals, and the visual system of predators that see them. Many frog species exhibit small colorful patches contrasting against an otherwise dark body. By measuring toxicity and color reflectance in a geographically variable frog species and the syntopic toxic species, we tested whether unpalatability was correlated with between-species color resemblance and whether resemblance was highest for the most conspicuous components of coloration pattern. Heterospecific resemblance in colorful patches was highest between species at the same locality, but unrelated to concomitant variation in toxicity. Surprisingly, resemblance was lower for the conspicuous femoral patches compared to the inconspicuous dorsum. By building visual models, we further tested whether resemblance was affected by the visual system of model predators. As predicted, mimic-model resemblance was higher under the visual system of simulated predators compared to no visual system at all. Our results indicate that femoral patches are aposematic signals and support a role of mimicry in driving phenotypic divergence or mimetic radiation between localities.

Conspicuous plumage colours are highly variable.

Elaborate ornamental traits are often under directional selection for greater elaboration, which in theory should deplete underlying genetic variation. Despite this, many ornamental traits appear to remain highly variable and how this essential variation is maintained is a key question in evolutionary biology. One way to address this question is to compare differences in intraspecific variability across different types of traits to determine whether high levels of variation are associated with specific trait characteristics. Here we assess intraspecific variation in more than 100 plumage colours across 55 bird species to test whether colour variability is linked to their level of elaboration (indicated by degree of sexual dichromatism and conspicuousness) or their condition dependence (indicated by mechanism of colour production). Conspicuous colours had the highest levels of variation and conspicuousness was the strongest predictor of variability, with high explanatory power. After accounting for this, there were no significant effects of sexual dichromatism or mechanisms of colour production. Conspicuous colours may entail higher production costs or may be more sensitive to disruptions during production. Alternatively, high variability could also be related to increased perceptual difficulties inherent to discriminating highly elaborate colours. Such psychophysical effects may constrain the exaggeration of animal colours.

Disruptive selection on plumage coloration across genetically determined morphs

Sexual selection can drive the evolution of conspicuous visual signals that advertise individual quality to prospective mates. Reproductive strategy can influence the balance between selective pressures and whether sexually selected signals evolve. Alternatively, visual signals can serve other functions, including predator deterrence, species recognition and differentiating genetically determined morphs. In the dimorphic white-throated sparrow, Zonotrichia albicollis, we explored how selection on conspicuous coloration changes with reproductive strategy, and whether visual signals of morph identity are discrete from sexually selected signals of individual quality. In this species, white morph birds have more colourful plumage than tan morph birds, and white males are more promiscuous and aggressive than tan counterparts. White females are also more aggressive than tan females. White males with more contrasting coloration achieved higher lifetime fitness, whereas the opposite relationship occurred among tan males. Linear selection gradients indicated strong, positive selection on plumage contrast in white males, but negative selection on contrast in tan males. For both morphs, relationships between female coloration and fitness were weak. Results demonstrate disruptive selection on a visual signalling trait in a colour-polymorphic species and suggest that signals associated with an aggressive morph can also evolve to indicate individual quality within that morph.