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Coloration
Kinds of Coloration Terms modified by Coloration Selected AbstractsPERSPECTIVE: THE EVOLUTION OF WARNING COLORATION IS NOT PARADOXICALEVOLUTION, Issue 5 2005Nicola M. Marples Abstract Animals that are brightly colored have intrigued scientists since the time of Darwin, because it seems surprising that prey should have evolved to be clearly visible to predators. Often this self-advertisement is explained by the prey being unprofitable in some way, with the conspicuous warning coloration helping to protect the prey because it signals to potential predators that the prey is unprofitable. However, such signals only work in this way once predators have learned to associate the conspicuous color with the unprofitability of the prey. The evolution of warning coloration is still widely considered to be a paradox, because it has traditionally been assumed that the very first brightly colored individuals would be at an immediate selective disadvantage because of their greater conspicuousness to predators that are naive to the meaning of the signal. As a result, it has been difficult to understand how a novel conspicuous color morph could ever avoid extinction for long enough for predators to become educated about the signal. Thus, the traditional view that the evolution of warning coloration is difficult to explain rests entirely on assumptions about the foraging behavior of predators. However, we review recent evidence from a range of studies of predator foraging decisions, which refute these established assumptions. These studies show that: (1) Many predators are so conservative in their food preferences that even very conspicuous novel prey morphs are not necessarily at a selective disadvantage. (2) The survival and spread of novel color morphs can be simulated in field and aviary experiments using real predators (birds) foraging on successive generations of artificial prey populations. This work demostrates that the foraging preferences of predators can regularly (though not always) result in the increase to fixation of a novel morph appearing in a population of familiar-colored prey. Such fixation events occur even if both novel and familiar prey are fully palatable and despite the novel food being much more conspicuous than the familiar prey. These studies therefore provide strong empirical evidence that conspicuous coloration can evolve readily, and repeatedly, as a result of the conservative foraging decisions of predators. [source] RELATIONSHIP BETWEEN THE COLORATION AND THE FIRING TECHNOLOGY USED TO PRODUCE SUSA GLAZED CERAMICS OF THE END OF THE NEOLITHIC PERIOD*ARCHAEOMETRY, Issue 5 2009S. LAHLIL Ancient decorated potteries from Susa (Mesopotamia) dating from 4200 to 3700 bc, were studied in order to determine the origin and the nature of the raw materials used, and to identify the technological processes applied to make the ceramic bodies and their decorations. Bulk compositions were determined by particle induced X-ray emission (PIXE), while the microstructure and the mineralogical phases were studied using scanning electron microscopy (SEM), energy dispersive X-ray analyses (EDX) and X-ray powder diffraction (XRD). The results showed that the raw materials used to elaborate these potteries were similar for all the ceramic bodies (carbonates and iron and magnesium-rich clays containing sand), and for all the decorations (iron oxides, silica, potassic and alumina sources). The variations of coloration of the ceramics and of their decorations were due to different firing temperatures. The ranges of firing temperatures used by potters were evaluated on the basis of mineral stability domains. [source] Innate and Learned Shoaling Preferences Based on Body Coloration in Juvenile Mollies, Poecilia latipinnaETHOLOGY, Issue 11 2008Jessica M. Ledesma Shoaling offers fish enhanced protection from predators through a phenomenon known as the confusion effect. This phenomenon depends on a high degree of phenotypic homogeneity within a shoal, which may confuse predators that have difficulty in targeting a single individual as prey. Accordingly, fish typically choose shoalmates with similar phenotypic characteristics to themselves. In the molly (Poecilia latipinna), dramatic differences in body coloration have been shown to affect shoalmate choice in adults. Here, we show that juvenile mollies (50 d old) were capable of shoaling and that early experience impacted shoalmate choice. When raised in isolation, mollies chose shoalmates with similar body coloration to their own. When raised with other juvenile mollies, test fish chose to associate with individuals of the same coloration as the fish with whom they had been reared. These results show that P. latipinna are capable of the behavioral plasticity that has been demonstrated in other fish species, and that early experience affects the impact of body coloration on shoaling decisions in this species. [source] Parental Effort in Relation to Structural Plumage Coloration in the Mountain Bluebird (Sialia currucoides)ETHOLOGY, Issue 9 2007Susan L. Balenger Indicator models of sexual selection suggest that costly ornaments signal reliable information regarding an individual's quality to potential mates. In species that produce altricial offspring, the amount of parental care provided by both males and females can impact reproductive success. The Good Parent Hypothesis proposes that ornamentation in biparental species can act as an honest signal of parental ability to potential mates. We tested this hypothesis using the mountain bluebird (Sialia currucoides), a sexually dichromatic, socially monogamous species in which both sexes have structurally based ornamental plumage coloration. A male's plumage color predicted neither the rate at which it provisioned nestlings nor brood growth rate. The same was true for females. We also found no indication of assortative mating by color or body condition. Feeding rates within pairs were positively correlated, which we suggest may be due to pairs responding similarly to the perceived needs of nestlings or to local area prey availability. In sum, our results do not support the Good Parent Hypothesis as an explanation for the evolution of ornamental plumage color in mountain bluebirds. We suggest alternative hypotheses for the evolution of ornamental plumage color in this species. [source] Dominance, Status Signals and Coloration in Male Mandrills (Mandrillus sphinx)ETHOLOGY, Issue 1 2005Joanna M. Setchell Where individuals contest access to a resource, escalated physical fighting presents a risk to all involved. The requirement for mechanisms of conflict management has led to the evolution of a variety of decision rules and signals that act to reduce the frequency of aggression during competitive encounters. We examined strategies of conflict management in male mandrills (Mandrillus sphinx) living in two semi-free-ranging groups in Gabon. Adult male mandrills are large (31 kg), with long canines, making the costs of conflict potentially very high. We found that males formed dominance hierarchies, but that male,male relationships were characterized by avoidance, appeasement and ignoring. Fights were rare, but could result in death. Examination of the relationship between dominance and signaling showed that males use facial and gestural signals to communicate dominance and subordinance, avoiding escalated conflict. Male mandrills also possess rank-dependent red coloration on the face, rump and genitalia, and we examined the hypothesis that this coloration acts as a ,badge of status', communicating male fighting ability to other males. If this is the case, then similarity in color should lead to higher dyadic rates of aggression, while males that differ markedly should resolve encounters quickly, with the paler individual retreating. Indeed, appeasement (the ,grin' display), threats, fights and tense ,stand-off' encounters were significantly more frequent between similarly colored males, while clear submission was more frequent where color differences were large. We conclude that male mandrills employ both formal behavioral indicators of dominance and of subordination, and may also use relative brightness of red coloration to facilitate the assessment of individual differences in fighting ability, thereby regulating the degree of costly, escalated conflict between well-armed males. [source] Role of Structural Fe(III) and Iron Oxide Nanophases in Mullite ColorationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001Amédée Djemai Six mullite samples, derived from heat-treated natural kaolinites with various iron content, were investigated and compared to synthetic monophasic mullite. They were analyzed by X-ray diffraction, diffuse reflectance spectroscopy, and electron paramagnetic resonance. To quantify mullite coloration, the CIE colorimetric system was used. In contrast to synthetic mullite, samples showed charge transfer bands involving O2, and Fe3+ ions as well as ferric crystal-field transitions due to Fe3+ ions in iron oxide nanoparticles. Absorption edges showed red shifts. The resulting yellowness, saturation of which increased with the content of iron oxide nanoparticles, is direct evidence for the coloring effect of Fe3+ ions. [source] Coloration of monodispersed polystyrene nanoparticles prepared via the RAFT reactionPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2006Ju Sung Kim Abstract Highly monodispersed polystyrene (PS) nanoparticles were prepared via the reversible addition fragmentation transfer (RAFT) living radical emulsion polymerization technique using a sur-iniferter, 4-(2-hydroxyethyl)piperazine-1-carbodithioicacid benzylether (HPCB). The monodispersed nanoparticles were colored by various methods, namely random and block copolymeriztion, the end group reaction and the adsorption method. For the coloration of the block and random copolymer monodispersed nanoparticles, a color pre-monomer was previously synthesized with a vinyl functional site. Dynamic light scattering and scanning electron microscopy were the main tools used to analyze the size and distribution of the prepared nanoparticles. Copyright © 2006 John Wiley & Sons, Ltd. [source] Role of oxygen vacancies in the coloration of 0.65Pb(Mg1/3Nb2/3)O3 -0.35PbTiO3 single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007Zhiguo Xia Abstract The coloration and oxygen vacancies in 0.65Pb(Mg1/3Nb2/3)O3 -0.35PbTiO3 (PMN-PT(65/35)) (starting composition) single crystals grown by a so-called modified Bridgman technique were investigated in this paper. Light yellow and dark brown colored crystals were generally observed for the typical as-grown PMN-PT(65/35) single crystals. X-ray diffraction results demonstrated that they were both of pure perovskite structure, but good electric properties were only obtained for the light yellow crystal. X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of its components. The O 1s photoelectron spectra of the dark brown colored crystals located at the higher binding energy side, which meant the existence of the more oxygen vacancies. It accordingly led to the formation of the low valence cations associated with the coloration of the crystals, which is also testified by the obtained X-ray photoelectron spectra of Ti and Nb. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Greater cuticular melanism is not associated with greater immunogenic response in adults of the polymorphic mountain stone weta, Hemideina maoriECOLOGICAL ENTOMOLOGY, Issue 6 2003T. Robb Abstract., 1.,Greater immune function is associated with the high-density melanic phase of polyphenic insects, appearing to compensate for density-dependent increases in susceptibility to parasites and/or pathogens. Other types of discrete variation in cuticular colour occur in insects (which may or may not be associated with melanin pigmentation), but whether this variation is predictive of immune ability has not been investigated. 2.,In the mountain stone weta Hemideina maori, a black morph and yellow banded morph occur. These morphs are not seasonally polyphenic and have discrete haplotype genetic markers. Black individuals are typically found at lower local densities than yellow individuals, contrary to relations between cuticular melanism and density seen in polyphenic insects. 3.,Yellow males and females had greater melanotic encapsulation responses upon immune challenge than did black males and females, but these differences were not associated with differences in temperature selection between morphs. Morph differences in melanotic encapsulation responses were somewhat related to differences between morphs in haemocyte concentrations. 4.,These results indicate that a common form of immune expression is not heightened with dark coloration in the mountain stone weta. Thus, earlier findings of greater immunity associated with darker cuticles in phase polyphenic insects cannot be extended to insects with other forms of discrete colour variation. These findings will help in elucidating causes and consequences of such colour polymorphism, which is widespread in several insect orders. [source] Influence of ambient light on the evolution of colour signals: comparative analysis of a Neotropical rainforest bird communityECOLOGY LETTERS, Issue 4 2004Doris Gomez Abstract Rainforests offer two contrasted light environments: a bright canopy rich in blue and UV and a dark understorey, rich in green and orange. Therefore, natural selection for crypsis should favour dark brown signals in understorey and bright green signals in canopy, whereas sexual selection for conspicuousness should favour bright yellow-red signals in understorey and dark blue and UV signals in canopy. Using spectrometry and comparative analyses, we examined the relationship between ambient light and colour signals in a bird community of French Guiana. It appears that brightness and hue are mostly naturally selected, while UV content of plumage is more likely sexually selected. At each height, both sexes present similar coloration but males display more conspicuous sexually selected patterns than females. These results show that ambient light drives the evolution of colour signals at community scale, and should be considered when studying signalling in other communities and light-contrasted ecosystems. [source] Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life historiesECOLOGY OF FRESHWATER FISH, Issue 1 2003A. Klemetsen Abstract ,,,Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3,5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour. [source] Legibility evaluation with oculomotor analysis.ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 9 2010The relationship between contrast, legibility Abstract Web page legibility is important because of the widespread use of the World Wide Web, and color combinations between the foreground and background are crucial to assuring sufficient legibility. In our previous studies, the visibilities of several web-safe color combinations were examined using a psychological method. In those studies, simple stimuli were used because of experimental restrictions. In this study, the legibility of sentences on Web sites was examined using an oculomotor-based psychophysiological method, and the effect of achromatic color combinations, that is, the contrast, was examined in terms of the calculated reading time. The presentation stimuli were positive colorations, whose font color luminance was lower than the background color, and negative colorations, whose font color luminance was higher than the background color. The number of characters per line was arranged to be the same on each page, and four levels of achromatic contrast (the contrast between the background color and the font color), namely, 92.5%, 75.0%, 50.0%, and 25.0%, were examined. It was shown that the reading time increased when the contrast decreased. However, with negative coloration, there were great differences between individuals. Therefore, considering web accessibility, legibility is found to be improved when using a positive coloration. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(9): 27,33, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10243 [source] Host plant changes produced by the aphid Sipha flava: consequences for aphid feeding behaviour and growthENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2002W.L. Gonzáles Abstract Induced plant responses may affect the behaviour and growth of the attacking herbivore insect. The aphid Sipha flava (Forbes) produces reddish spots on the infested leaf of its host plant Sorghum halepense (L.). In order to assess the consequences on the aphid of this presumptive induced plant response, we studied the feeding behaviour and growth of S. flava on previously infested and non-infested leaves of S. halepense. Considering that the reddish pigment could play a defensive role, its effect on aphid survival was determined in artificial diets. In addition, changes in the histology of the leaf and the chemical nature of the induced pigment were also studied. Aphids devoted a significantly shorter total time to non-penetration activities in infested than in non-infested leaves. Time before the first phloem ingestion tended to be shorter in infested leaves. The mean relative growth rate of S. flava nymphs was significantly higher on infested than on non-infested leaves. Survival of aphids on diet containing the reddish extract was not significantly different from that on the control diet. Infestation of S. halepense by S. flava produced a reddish coloration in the leaf, which was identified as an anthocyanin by UV-visible spectrometry. Light microscopy showed that only mesophyll cells of previously infested plants presented swelled, dispersed, and heterogeneously stained chloroplasts with a higher accumulation of starch granules, no grana arranged in stacks, and reduction in the amount of inner membranes (thylakoids), relatively to chloroplasts of non-infested leaves. Scanning electron micrographs of leaf surface revealed reduced presence of crystalline epicuticular waxes of epidermal cells in infested leaves as compared to non-infested ones. The main conclusion is that the attack of S. flava to S. halepense leaves induced plant susceptibility where aphid feeding behaviour and growth were both enhanced on previously infested leaves. [source] Plant biological warfare: thorns inject pathogenic bacteria into herbivoresENVIRONMENTAL MICROBIOLOGY, Issue 3 2007Malka Halpern Summary Thorns, spines and prickles are among the rich arsenal of antiherbivore defence mechanisms that plants have evolved. Many of these thorns are aposematic, that is, marked by various types of warning coloration. This coloration was recently proposed to deter large herbivores. Yet, the mechanical defence provided by thorns against large herbivores might be only the tip of the iceberg in a much more complicated story. Here we present evidence that thorns harbour an array of pathogenic bacteria that are much more dangerous to herbivores than the painful mechanical wounding by the thorns. Pathogenic bacteria like Clostridium perfringens, the causative agent of the life-threatening gas gangrene, and others, were isolated and identified from date palm (with green-yellow-black aposematic spines) and common hawthorn (with red aposematic thorns). These thorn-inhabiting bacteria have a considerable potential role in antiherbivory, and may have uniquely contributed to the common evolution of aposematism (warning coloration) in thorny plants. [source] Plesiomorphic Escape Decisions in Cryptic Horned Lizards (Phrynosoma) Having Highly Derived Antipredatory DefensesETHOLOGY, Issue 10 2010William E. Cooper Jr Escape theory predicts that the probability of fleeing and flight initiation distance (predator,prey distance when escape begins) increase as predation risk increases and decrease as escape cost increases. These factors may apply even to highly cryptic species that sometimes must flee. Horned lizards (Phrynosoma) rely on crypsis because of coloration, flattened body form, and lateral fringe scales that reduce detectability. At close range they sometimes squirt blood-containing noxious substances and defend themselves with cranial spines. These antipredatory traits are highly derived, but little is known about the escape behavior of horned lizards. Of particular interest is whether their escape decisions bear the same relationships to predation risk and opportunity costs of escaping as in typical prey lacking such derived defenses. We investigated the effects of repeated attack and direction of predator turning on P. cornutum and of opportunity cost of fleeing during a social encounter in P. modestum. Flight initiation distance was greater for the second of two successive approaches and probability of fleeing decreased as distance between the turning predator and prey increased, but was greater when the predator turned toward than away from a lizard. Flight initiation distance was shorter during social encounters than when lizards were solitary. For all variables studied, risk assessment by horned lizards conforms to the predictions of escape theory and is similar to that in other prey despite their specialized defenses. Our findings show that these specialized, derived defenses coexist with a taxonomically widespread, plesiomorphic method of making escape decisions. They suggest that escape theory based on costs and benefits, as intended, applies very generally, even to highly cryptic prey that have specialized defense mechanisms. [source] Risk Assessment and Withdrawal Behavior by Two Species of Aposematic Poison Frogs, Dendrobates auratus and Oophaga pumilio, on Forest TrailsETHOLOGY, Issue 4 2009William E. Cooper Jr Many chemically defended prey advertize toxicity to predators by aposematic coloration. When aposematic prey are approached, they often move slowly or not at all, allowing predators to evaluate their unprofitability. Poison frogs (Dendrobatidae) are toxic, aposematically colored, forage openly and diurnally, and are much easier to capture than many palatable frogs. Although protected against diverse predators, they are sometimes attacked and are subjected to injury by large animals without predatory intent. We predicted that they have limited escape behavior, but retain ability to assess and respond to risk. When we approached Dendrobates auratus and Oophaga pumilio on forest trails, both species hopped by the shortest route to the nearer forest edge and stopped there. When approached, D. auratus moved after shorter latency at an angle closer to perpendicular to the forest edge, were more likely to leave the trail, and left the trail sooner with fewer changes in direction after moving a shorter distance than when not approached. In agreement with predictions of optimal escape theory based on risk, flight initiation distance by D. auratus was greater when approached directly than indirectly and rapidly than slowly, and was greater when frogs were in the open than partially concealed. Frogs neither attempted rapid escape nor entered refuges. Both species hopped leisurely and remained visible after stopping. They exhibit the diminished escape behavior of aposematic prey, yet retain the capacity to assess risk and adjust behavior accordingly. Their behavior demonstrates continued need for escape behavior by highly toxic aposematic prey. [source] Innate and Learned Shoaling Preferences Based on Body Coloration in Juvenile Mollies, Poecilia latipinnaETHOLOGY, Issue 11 2008Jessica M. Ledesma Shoaling offers fish enhanced protection from predators through a phenomenon known as the confusion effect. This phenomenon depends on a high degree of phenotypic homogeneity within a shoal, which may confuse predators that have difficulty in targeting a single individual as prey. Accordingly, fish typically choose shoalmates with similar phenotypic characteristics to themselves. In the molly (Poecilia latipinna), dramatic differences in body coloration have been shown to affect shoalmate choice in adults. Here, we show that juvenile mollies (50 d old) were capable of shoaling and that early experience impacted shoalmate choice. When raised in isolation, mollies chose shoalmates with similar body coloration to their own. When raised with other juvenile mollies, test fish chose to associate with individuals of the same coloration as the fish with whom they had been reared. These results show that P. latipinna are capable of the behavioral plasticity that has been demonstrated in other fish species, and that early experience affects the impact of body coloration on shoaling decisions in this species. [source] Parental Effort in Relation to Structural Plumage Coloration in the Mountain Bluebird (Sialia currucoides)ETHOLOGY, Issue 9 2007Susan L. Balenger Indicator models of sexual selection suggest that costly ornaments signal reliable information regarding an individual's quality to potential mates. In species that produce altricial offspring, the amount of parental care provided by both males and females can impact reproductive success. The Good Parent Hypothesis proposes that ornamentation in biparental species can act as an honest signal of parental ability to potential mates. We tested this hypothesis using the mountain bluebird (Sialia currucoides), a sexually dichromatic, socially monogamous species in which both sexes have structurally based ornamental plumage coloration. A male's plumage color predicted neither the rate at which it provisioned nestlings nor brood growth rate. The same was true for females. We also found no indication of assortative mating by color or body condition. Feeding rates within pairs were positively correlated, which we suggest may be due to pairs responding similarly to the perceived needs of nestlings or to local area prey availability. In sum, our results do not support the Good Parent Hypothesis as an explanation for the evolution of ornamental plumage color in mountain bluebirds. We suggest alternative hypotheses for the evolution of ornamental plumage color in this species. [source] The role of melanin- and carotenoid-based plumage coloration in nest defence in the Great TitETHOLOGY, Issue 7 2007Javier Quesada Although plumage coloration is recognized to convey valuable information about the bearer's parental abilities, few studies have explored the relationship between coloration and nest defence. In this study in Great Tit Parus major, we analysed the relationship between nest defence and melanin- as well as carotenoid-based plumage coloration, after controlling for ecological variables known to influence nest defence. A principal components analysis was applied to classify birds according to how vigorously they defended the nest, and the intensity of nest defence was tested against plumage coloration. Males with a large black tie defended their nests more vigorously, but no such effect was found for yellow breast coloration. This suggests that melanin-based coloration in the Great Tit is associated with aggression, including both dominance-aggression and nest defence, whereas carotenoid-based coloration is not. The challenge in future studies will be to demonstrate whether females use this trait as an ornament to assess male quality and whether they trade off between the different ornaments a male may exhibit. [source] Dominance, Status Signals and Coloration in Male Mandrills (Mandrillus sphinx)ETHOLOGY, Issue 1 2005Joanna M. Setchell Where individuals contest access to a resource, escalated physical fighting presents a risk to all involved. The requirement for mechanisms of conflict management has led to the evolution of a variety of decision rules and signals that act to reduce the frequency of aggression during competitive encounters. We examined strategies of conflict management in male mandrills (Mandrillus sphinx) living in two semi-free-ranging groups in Gabon. Adult male mandrills are large (31 kg), with long canines, making the costs of conflict potentially very high. We found that males formed dominance hierarchies, but that male,male relationships were characterized by avoidance, appeasement and ignoring. Fights were rare, but could result in death. Examination of the relationship between dominance and signaling showed that males use facial and gestural signals to communicate dominance and subordinance, avoiding escalated conflict. Male mandrills also possess rank-dependent red coloration on the face, rump and genitalia, and we examined the hypothesis that this coloration acts as a ,badge of status', communicating male fighting ability to other males. If this is the case, then similarity in color should lead to higher dyadic rates of aggression, while males that differ markedly should resolve encounters quickly, with the paler individual retreating. Indeed, appeasement (the ,grin' display), threats, fights and tense ,stand-off' encounters were significantly more frequent between similarly colored males, while clear submission was more frequent where color differences were large. We conclude that male mandrills employ both formal behavioral indicators of dominance and of subordination, and may also use relative brightness of red coloration to facilitate the assessment of individual differences in fighting ability, thereby regulating the degree of costly, escalated conflict between well-armed males. [source] Fruit Colour Preferences of Redwings (Turdus iliacus): Experiments with Hand-Raised Juveniles and Wild-Caught AdultsETHOLOGY, Issue 6 2004Johanna Honkavaara 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. [source] Do Male Veiled Chameleons, Chamaeleo calyptratus, Adjust their Courtship Displays in Response to Female Reproductive Status?ETHOLOGY, Issue 6 2002Erin C. Kelso Variation in male courtship behavior may be due to inherent differences among males or may arise from males adjusting their courtship displays according to female responsiveness. Female veiled chameleons, Chamaeleo calyptratus, exhibit two distinctive suites of body coloration and behavior patterns that vary according to receptive and non-receptive stages of their reproductive cycle. We presented male chameleons with both receptive and non-receptive females, and recorded differences in their mating frequency, courtship intensity and courtship behavior patterns. As expected, males were more likely to court and attempt mating with receptive females. Although fewer males courted non-receptive females, their courtship displays were significantly longer than those directed towards receptive females. Males also adjusted the contents of their displays according to female reproductive condition. Certain behavior patterns were unique to courtship displays directed towards each class of females. Males exhibited the behavior pattern `head roll' only when paired with receptive females, and `chin rub' was displayed only during courtship of non-receptive females. We hypothesize that these differences in male courtship frequency, intensity and content reflect differences in female reproductive value. Although males may benefit from mating with both receptive and non-receptive females, the costs associated with courtship may depend on female responsiveness. Thus, males adjust their courtship tactics accordingly. [source] BACKGROUND MATCHING AND COLOR-CHANGE PLASTICITY IN COLONIZING FRESHWATER SCULPIN POPULATIONS FOLLOWING RAPID DEGLACIATIONEVOLUTION, Issue 6 2009Andrew R. Whiteley Anthropogenic-induced change is forcing organisms to shift their distributions and colonize novel habitats at an increasing rate, which leads to complex interactions among evolutionary processes. Coastrange sculpin (Cottus aleuticus) have colonized recently deglaciated streams of Glacier Bay in Alaska within the last 220 years. We examined divergence among populations in background matching coloration and tested the hypothesis that observed variation is due to morphological color plasticity. To examine how color-change plasticity has interacted with other evolutionary processes, we also determined the influence of colonization on neutral genetic diversity. We observed clinal variation in substrate-matching fish color along the chronological continuum of streams. Microsatellites provided little evidence of genetic subdivision among sculpin populations. Fish color was significantly correlated to substrate color, but was not correlated to neutral population genetic structure. Furthermore, a laboratory experiment revealed that morphological color plasticity could explain much, but not all, of the observed fish color divergence. Our study demonstrates that sculpin in Glacier Bay have colonized and adapted to recently deglaciated habitat and suggests that color change plasticity has aided in this process. This research, therefore, highlights the important role phenotypic plasticity may play in the adaptation of species to rapid climate change. [source] PEAK SHIFT DISCRIMINATION LEARNING AS A MECHANISM OF SIGNAL EVOLUTIONEVOLUTION, Issue 6 2005Spencer K. Lynn Abstract "Peak shift" is a behavioral response bias arising from discrimination learning in which animals display a directional, but limited, preference for or avoidance of unusual stimuli. Its hypothesized evolutionary relevance has been primarily in the realm of aposematic coloration and limited sexual dimorphism. Here, we develop a novel functional approach to peak shift, based on signal detection theory, which characterizes the response bias as arising from uncertainty about stimulus appearance, frequency, and quality. This approach allows the influence of peak shift to be generalized to the evolution of signals in a variety of domains and sensory modalities. The approach is illustrated with a bumblebee (Bombus impatiens) discrimination learning experiment. Bees exhibited peak shift while foraging in an artificial Batesian mimicry system. Changes in flower abundance, color distribution, and visitation reward induced bees to preferentially visit novel flower colors that reduced the risk of flower-type misidentification. Under conditions of signal uncertainty, peak shift results in visitation to rarer, but more easily distinguished, morphological variants of rewarding species in preference to their average morphology. Peak shift is a common and taxonomically widespread phenomenon. This example of the possible role of peak shift in signal evolution can be generalized to other systems in which a signal receiver learns to make choices in situations in which signal variation is linked to the sender's reproductive success. [source] PERSPECTIVE: THE EVOLUTION OF WARNING COLORATION IS NOT PARADOXICALEVOLUTION, Issue 5 2005Nicola M. Marples Abstract Animals that are brightly colored have intrigued scientists since the time of Darwin, because it seems surprising that prey should have evolved to be clearly visible to predators. Often this self-advertisement is explained by the prey being unprofitable in some way, with the conspicuous warning coloration helping to protect the prey because it signals to potential predators that the prey is unprofitable. However, such signals only work in this way once predators have learned to associate the conspicuous color with the unprofitability of the prey. The evolution of warning coloration is still widely considered to be a paradox, because it has traditionally been assumed that the very first brightly colored individuals would be at an immediate selective disadvantage because of their greater conspicuousness to predators that are naive to the meaning of the signal. As a result, it has been difficult to understand how a novel conspicuous color morph could ever avoid extinction for long enough for predators to become educated about the signal. Thus, the traditional view that the evolution of warning coloration is difficult to explain rests entirely on assumptions about the foraging behavior of predators. However, we review recent evidence from a range of studies of predator foraging decisions, which refute these established assumptions. These studies show that: (1) Many predators are so conservative in their food preferences that even very conspicuous novel prey morphs are not necessarily at a selective disadvantage. (2) The survival and spread of novel color morphs can be simulated in field and aviary experiments using real predators (birds) foraging on successive generations of artificial prey populations. This work demostrates that the foraging preferences of predators can regularly (though not always) result in the increase to fixation of a novel morph appearing in a population of familiar-colored prey. Such fixation events occur even if both novel and familiar prey are fully palatable and despite the novel food being much more conspicuous than the familiar prey. These studies therefore provide strong empirical evidence that conspicuous coloration can evolve readily, and repeatedly, as a result of the conservative foraging decisions of predators. [source] EVOLUTION OF COLOR VARIATION IN DRAGON LIZARDS: QUANTITATIVE TESTS OF THE ROLE OF CRYPSIS AND LOCAL ADAPTATIONEVOLUTION, Issue 7 2004Devi M. Stuart-Fox 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. [source] VISUAL BACKGROUND COMPLEXITY FACILITATES THE EVOLUTION OF CAMOUFLAGEEVOLUTION, Issue 6 2003Sami Merilaita Abstract., Cryptic animal coloration or camouflage is an adaptation that decreases the risk of detection. The study of the evolution of camouflage has strongly emphasized the minimization of visual information that predators receive from prey, by means of background matching. However, the evolutionary effects of information processing after its reception have been virtually ignored. I constructed a model that employs an artificial neural network and simulates the evolution of prey coloration in a visually complex and simple habitat. The model suggests: (1) the difficulty of a detection task is related to the visual complexity of the habitat; (2) it is easier to decrease the risk of detection by the means of camouflage in a visually complex habitat; (3) selection on camouflage can exploit limitations in predators information processing; and (4) there are shortcomings in using the degree of background matching as the measure of camouflage. [source] PERSPECTIVE: FEMALE REMATING, OPERATIONAL SEX RATIO, AND THE ARENA OF SEXUAL SELECTION IN DROSOPHILA SPECIESEVOLUTION, Issue 9 2002Therese Ann Markow Abstract., As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila. Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well. [source] COEVOLUTION OF COLOR PATTERN AND THERMOREGULATORY BEHAVIOR IN POLYMORPHIC PYGMY GRASSHOPPERS TETRIX UNDULATAEVOLUTION, Issue 2 2002Anders Forsman Abstract Ectothermic organisms, such as insects and reptiles, rely on external heat sources to control body temperature and possess physiological and behavioral traits that are temperature dependent. It has therefore been hypothesised that differences in body temperature resulting from phenotypic properties, such as color pattern, may translate into selection against thermally inferior phenotypes. We tested for costs and benefits of pale versus dark coloration by comparing the behaviors (i.e., basking duration and bouts) of pygmy grasshopper (Tetrix undulata) individuals exposed to experimental situations imposing a trade-off between temperature regulation and feeding. We used pairs consisting of two full-siblings of the same sex that represented different (genetically coded) color morphs but had shared identical conditions from the time of fertilization. Our results revealed significant differences in behavioral thermoregulation between dark and pale individuals in females, but not in males. Pale females spent more time feeding than dark females, regardless of whether feeding was associated with a risk of either hypothermia or overheating. In contrast, only minor differences in behavior (if any) were evident between individuals that belonged to the same color morph but had been painted black or gray to increase and decrease their heating rates. This suggests that the behavioral differences between individuals belonging to different color morphs are genetically determined, rather than simply reflecting a response to different heating rates. To test for effects of acclimation on behaviors, we used pairs of individuals that had been reared from hatchlings to adults under controlled conditions in either low or high temperature. The thermal regime experienced during rearing had little effect on behaviors during the experiments reported above, but significantly influenced the body temperatures selected in a laboratory thermal gradient. In females (but not in males) preferred body temperature also varied among individuals born to mothers belonging to different color morphs, suggesting that a genetic correlation exists between color pattern and temperature preferences. Collectively, these findings, at least in females, are consistent with the hypothesis of multiple-trait coevolution and suggest that the different color morphs represent alternative evolutionary strategies. [source] Phenotypic plasticity in insects: the effects of substrate color on the coloration of two ground-hopper speciesEVOLUTION AND DEVELOPMENT, Issue 3 2008Axel Hochkirch SUMMARY The question of how phenotypic variation is maintained within populations has long been a central issue in evolutionary biology. Most of these studies focused on the maintenance of genetic variability, but the phenotype of organisms may also be influenced by environmental cues experienced during ontogeny. Color polymorphism has received particular attention in evolutionary studies as it has strong fitness consequences. However, if body coloration is influenced by the environment, any conclusions on evolutionary consequences of fitness trade-offs can be misleading. Here we present data from a laboratory experiment on the influence of substrate color on three aspects of the coloration of two ground-hopper species, Tetrix subulata and Tetrix ceperoi. We reared hatchlings either on dark or on light substrates, using a split-brood design. Although the type of pronotal pattern changed mainly in response to nymphal development, the basic color was strongly influenced by the substrate color. In both species, black and dark olive color morphs were found more frequently on the dark substrate, whereas the gray color morph dominated on the light substrate. These findings have considerable implications for our understanding of color morph evolution as they show that color polymorphism may not only be maintained by natural selection acting on discrete color morphs, but also by phenotypic plasticity, which enables organisms to adjust to the environmental conditions experienced during ontogeny. This facultative morphology is opposing to the prevailing view of color morph adaptation, which assumes a purely genetic determination and co-evolution of discrete color morphs with life history traits. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||