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Hybrid zones are dynamic areas where populations of two or more interbreeding species may change through an influx of novel genetic material resulting from hybridization or selection on standing genetic variation. Documenting changes in populations through time, however, is challenging because repeated samples are often missing or because long-term storage can affect trait morphologies, especially colour traits that may fade through time. We document a change in carotenoid-based orange breast feathers of Bullock's Orioles ( Icterus bullockii) from the Great Plains hybrid zone, USA. Contemporary Bullock's Orioles are more orange than historic individuals from the same location sampled approximately 60 years ago. Spectrophotometry revealed that contemporary Bullock's Orioles resemble orange colour profiles of Baltimore Orioles ( I. galbula ), the species with which they hybridize. Fading or changes in diet hypotheses do not appear to explain the shift in colour we report for Bullock's Orioles. We propose that these changes in colour are facilitated through introgression with Baltimore Orioles, and favoured by females that choose brighter, more orange males. Our study highlights the long memory of natural history collections and how they offer new insights to the dynamic roll of hybrid zones in trait evolution between interacting species.

The Baltimore–Bullock’s Oriole hybrid zone is one of the best-studied avian hybrid zones in North America, yet our understanding of the causes of selection against hybrids remains poor. We examine if endohelminth parasites may cause selection against hybrid orioles but found no evidence for this hypothesis. Of the 139 male orioles we examined, 43 individuals contained endohelminth parasites from at least 1 of these groups: Cestoda, Acanthocephala, or Nematoda. Across the hybrid zone, Baltimore Orioles (Icterus galbula) and Bullock’s Orioles (I. bullockii) differed in their parasite communities, such that Baltimore Orioles frequently contained both Acanthocephala and Cestoda parasites whereas Bullock’s Orioles primarily contained Cestoda parasites. Despite these differences in parasite communities between parental species, the frequency of hybrid orioles with parasites was similar to parentals, suggesting that hybrids were as susceptible to endohelminth parasites as parentals. Using a subset of 99 adult male orioles, we explored how parasites may be associated with the expression of orange carotenoid-based plumage in hybrids and parentals. Associations between carotenoid-based plumage color and parasites were most strongly expressed in Bullock’s Orioles, but patterns were subtle and counterintuitive because individuals with parasites often had more enhanced color measures compared to individuals without parasites. Taken together, these data suggest that endohelminth parasites impose little fitness costs to male orioles on the breeding grounds and likely do not cause selection against hybrids.

Hybridization represents a natural experiment that can provide insight into processes of speciation and diversification. Though considerable research has focused on hybrid zone dynamics, macroevolutionary investigations of the factors that influence hybridization are few. Here, we compile a database of avian hybrids and perform comparative analyses to determine whether several social and life-history variables influence broad patterns of hybridization. We perform three main analyses: phylogenetic logistic regression to examine variables that are associated with the presence of hybridization, phylogenetic Poisson regression of only those species exhibiting hybridization to determine which variables are associated with the extent of hybridization, and a phylogenetic logistic regression on a subset of data to assess potential pseudoreplication. After testing several social and life-history variables, we found that social bond duration is associated with the presence and extent of hybridization. Specifically, lengthy social bonds are negatively associated with the presence and extent of hybridization. In addition to social bond length, migration is positively linked with a greater likelihood of hybridization. The broad-scale correlations between species-specific traits and hybridization across diverse avian lineages suggest commonalities in the fine-scale processes involved in mating with heterospecifics, which in turn has implications for how we think about, study and understand hybridization processes and their influence on evolutionary trajectories.

Animals produce a wide array of sounds with highly variable acoustic structures. It is possible to understand the causes and consequences of this variation across taxa with phylogenetic comparative analyses. Acoustic and evolutionary analyses are rapidly increasing in sophistication such that choosing appropriate acoustic and evolutionary approaches is increasingly difficult. However, the correct choice of analysis can have profound effects on output and evolutionary inferences. Here, we identify and address some of the challenges for this growing field by providing a roadmap for quantifying and comparing sound in a phylogenetic context for researchers with a broad range of scientific backgrounds. Sound, as a continuous, multidimensional trait can be particularly challenging to measure because it can be hard to identify variables that can be compared across taxa and it is also no small feat to process and analyse the resulting high-dimensional acoustic data using approaches that are appropriate for subsequent evolutionary analysis. Additionally, terminological inconsistencies and the role of learning in the development of acoustic traits need to be considered. Phylogenetic comparative analyses also have their own sets of caveats to consider. We provide a set of recommendations for delimiting acoustic signals into discrete, comparable acoustic units. We also present a three-stage workflow for extracting relevant acoustic data, including options for multivariate analyses and dimensionality reduction that is compatible with phylogenetic comparative analysis. We then summarize available phylogenetic comparative approaches and how they have been used in comparative bioacoustics, and address the limitations of comparative analyses with behavioural data. Lastly, we recommend how to apply these methods to acoustic data across a range of study systems. In this way, we provide an integrated framework to aid in quantitative analysis of cross-taxa variation in animal sounds for comparative phylogenetic analysis. In addition, we advocate the standardization of acoustic terminology across disciplines and taxa, adoption of automated methods for acoustic feature extraction, and establishment of strong data archival practices for acoustic recordings and data analyses. Combining such practices with our proposed workflow will greatly advance the reproducibility, biological interpretation, and longevity of comparative bioacoustic studies.

Organismal appearances are shaped by selection from both biotic and abiotic drivers. For example, Gloger's rule describes the pervasive pattern that more pigmented populations are found in more humid areas. However, species may also converge on nearly identical colours and patterns in sympatry, often to avoid predation by mimicking noxious species. Here we leverage a massive global citizen-science database to determine how biotic and abiotic factors act in concert to shape plumage in the world's 230 species of woodpeckers. We find that habitat and climate profoundly influence woodpecker plumage, and we recover support for the generality of Gloger's rule. However, many species exhibit remarkable convergence explained neither by these factors nor by shared ancestry. Instead, this convergence is associated with geographic overlap between species, suggesting occasional strong selection for interspecific mimicry.

Urban environments present animals with many novel experiences, not the least of which is the physical presence of humans. However, most studies on urban predation do not take human presence into account. We examined behavioral and physiological responses of a songbird species (the house finch, Haemorhous mexicanus) that is abundant in both natural and urban areas to the presence of humans and to a native predator model to distinguish whether urban birds show consistently bolder behavior or if they differentially respond to a threatening native predator versus a potentially more benign human. During three field seasons (winter 2012, summer-fall 2012, and winter 2013), we captured birds at six sites (urban, suburban, and rural) and measured breath rate (an indicator of stress). We then tested behavioral reactions of caged finches to an approaching human and both a hawk (predator) and dove (control-bird) flyover. We found that rural birds had lower breath rates than urban birds, but that urban birds showed fewer activity behaviors (e.g., hops, flights) than rural birds in response to an approaching human. Urban and rural birds did not differ in their behavioral responses to either the hawk or dove mount, though there were seasonal differences. Because house finch behavioral responses varied as a function of type of stimulus presented, our results point to an example of plasticity rather than to a generalized bold urban phenotype and also implicate tolerance of human proximity as a key factor driving urban success in some avian species.

Dynamic color signals represent a rare signaling strategy but there are numerous parallels between rapid color changes and the vocalizations used to mediate aggressive interactions in other taxa. Here, we used a robochameleon to elicit color change from live chameleons and linked these signals to individual-specific performance and behavior.

Organismal appearances are shaped by selection from both biotic and abiotic drivers. For example, Gloger’s rule describes the pervasive pattern that more pigmented populations are found in more humid areas. However, species may also converge on nearly identical colours and patterns in sympatry, often to avoid predation by mimicking noxious species. Here we leverage a massive global citizen-science database to determine how biotic and abiotic factors act in concert to shape plumage in the world’s 230 species of woodpeckers. We find that habitat and climate profoundly influence woodpecker plumage, and we recover support for the generality of Gloger’s rule. However, many species exhibit remarkable convergence explained neither by these factors nor by shared ancestry. Instead, this convergence is associated with geographic overlap between species, suggesting occasional strong selection for interspecific mimicry., Many abiotic and biotic factors shape the macroevolution of phenotype, but these factors are rarely disentangled across large radiations. Here, Miller et al. investigate plumage evolution across woodpeckers, finding influences of habitat and climate, but also convergence apparently driven by mimicry

Summary Behaviors are among the most complex phenotypes, making the genetic dissection of behavioral differences extremely challenging. A careful dissection of ontogenetic differences in burrowing behavior between mouse species highlights the importance of integrative approaches to the study of behavioral evolution.

Organismal appearances are shaped by selection from both abiotic and biotic drivers 1–5. For example, Gloger’s rule describes the pervasive pattern that more pigmented populations are found in more humid areas 1,6,7, and substrate matching as a form of camouflage to reduce predation is widespread across the tree of life 8–10. Sexual selection is a potent driver of plumage elaboration 5,11, and species may also converge on nearly identical colours and patterns in sympatry, often to avoid predation by mimicking noxious species 3,4 To date, no study has taken an integrative approach to understand how these factors determine the evolution of colour and pattern across a large clade of organisms. Here we show that both habitat and climate profoundly shape avian plumage. However, we also find a strong signal that many species exhibit remarkable convergence not explained by these factors nor by shared ancestry. Instead, this convergence is associated with geographic overlap between species, suggesting strong, albeit occasional, selection for interspecific mimicry. Consequently, both abiotic and biotic factors, including interspecific interactions, are potent drivers of phenotypic evolution.

Ornaments used in courtship often vary wildly among species, reflecting the evolutionary interplay between mate preference functions and the constraints imposed by natural selection. Consequently, understanding the evolutionary dynamics responsible for ornament diversification has been a longstanding challenge in evolutionary biology. However, comparing radically different ornaments across species, as well as different classes of ornaments within species, is a profound challenge to understanding diversification of sexual signals. Using novel methods and a unique natural history dataset, we explore evolutionary patterns of ornament evolution in a group—the birds-of-paradise—exhibiting dramatic phenotypic diversification widely assumed to be driven by sexual selection. Rather than the tradeoff between ornament types originally envisioned by Darwin and Wallace, we found positive correlations among cross-modal (visual/acoustic) signals indicating functional integration of ornamental traits into a composite unit—the “courtship phenotype.” Furthermore, given the broad theoretical and empirical support for the idea that systemic robustness—functional overlap and interdependency—promotes evolutionary innovation, we posit that birds-of-paradise have radiated extensively through ornamental phenotype space as a consequence of the robustness in the courtship phenotype that we document at a phylogenetic scale. We suggest that the degree of robustness in courtship phenotypes among taxa can provide new insights into the relative influence of sexual and natural selection on phenotypic radiations., Author summary Animals frequently vary widely in ornamentation, even among closely related species. Understanding the patterns that underlie this variation is a significant challenge, requiring comparisons among drastically different traits—like comparing apples to oranges. Here, we use novel analytical approaches to quantify variation in ornamental diversity and richness across the wildly divergent birds-of-paradise, a textbook example of how sexual selection can profoundly shape organismal phenotypes. We find that color and acoustic complexity, along with behavior and acoustic complexity, are positively correlated across evolutionary timescales. Positive links among ornament classes suggests that selection is acting on correlated suites of traits—a composite courtship phenotype—and this integration may be partially responsible for the extreme variation in signal form that we see in birds-of-paradise.

Animal behaviors are dynamic in both space and time, and this variation is the raw material for exceptional behavioral adaptations in the animal kingdom. Here we argue that this same dynamism characterizes color signals in nature and that comparable approaches, both conceptually and methodologically, should be taken to comprehensively assess the production, perception, function, and evolution of dynamic animal colors. We review and synthesize recent findings in these emerging areas of color research and highlight the complex and interactive dynamics of color communication between senders and receivers. We also advance opportunities for new areas of research, especially centered on visual and neural plasticity of color reception as well as the intricate signaling interactions between co-expressed display behaviors and colors.

Summary Aphids are diverse sap-sucking insects [ 1 ] that can be serious agricultural pests and vectors of plant disease [ 2 ]. Some species, including pea aphids (Acyrthosiphon pisum), are susceptible to infection by epiphytic bacteria that are commonly found on plant surfaces [ 3 , 4 , 5 ]. Pea aphids appear unable to recover from these infections, possibly because pea aphids are missing apparent orthologs of some immune response genes [ 6 ], and these aphids exhibit relatively low immune responses after pathogen exposure [ 7 ]. We therefore tested the ability of pea aphids to use avoidance as a non-immunological defense against Pseudomonas syringae, a widespread plant epiphyte and aphid pathogen [ 8 , 9 ]. Pea aphids avoided highly virulent strains of P. syringae, but not all strains, and avoidance led to a significant reduction in infection among aphids. We found that aphids can use visual cues to detect the ultraviolet (UV)-based fluorescence of the bacterial siderophore pyoverdine [ 10 ] produced by virulent strains. Avoided epiphytic bacteria caused light leaving the surface of leaves to be richer in wavelengths that were tightly linked to both aphid visual sensitivities and the fluorescent emission spectra of pyoverdine, suggesting that pyoverdine fluorescence mediates avoidance and may be a visual cue used by aphids to detect epiphytic pathogens. Although pyoverdine production in Pseudomonas species may be a broadly reliable indicator of bacterial virulence within the phyllosphere, it was not directly responsible for virulence to aphids. Aphids may be under selection to avoid fluorescence on leaves, a phenomenon with potential use for the control of agricultural pest insects.

The behavior of animals is an intrinsically fascinating topic for students from a wide array of backgrounds. We describe a learning experience using animal behavior that we created for middle school students as part of a graduate-student outreach program, Graduate Partners in Science Education, at Arizona State University in collaboration with a K–8 public school. This activity capitalizes on the interest that animal behavior can generate to introduce and reinforce student understanding of the scientific method. Specifically, our activity highlights the general utility of the scientific method and uses this method to examine ant social behavior, with emphasis on generating and testing hypotheses. Furthermore, this activity introduces the idea of animal societies and encourages students to apply the concepts they learn to other species, including humans. By collecting ants locally, from schoolyards or nearby habitats, this experience situates learning in the context of students’ own communities. We also provide optional assessment materials that teachers can use to assess learning objectives and standard mastery.

Research on intraspecific aggression has typically focused on dominant individuals, but a better understanding of the consequences and mechanisms of agonistic encounters requires a balanced perspective that includes knowledge of subordinate animal behaviors. In contrast to signals of fighting ability, signals of submission are an understudied component of agonistic communication that could provide important insights into the dynamics, function, and evolution of intraspecific competition. Here, I use a series of staged agonistic trials between adult male veiled chameleons Chamaeleo calyptratus to test the hypothesis that rapid skin darkening serves as a submissive signal to resolve agonistic activity. Concordant with this hypothesis, I found that losing chameleons darkened over the course of aggressive trials while winners brightened, and the likelihood of darkening increased when individuals were attacked more aggressively. Additionally, I found that the degree of brightness change exhibited by individual chameleons was tied to both overall and net aggression experienced during a trial, with chameleons who received high levels of aggression relative to their own aggression levels darkening to a greater extent than individuals receiving relatively less aggression. Lastly, I found that aggression increased for losers and winners prior to the onset of darkening by the eventual loser but that both chameleons reduced aggression after the losing chameleon began to darken. Based on the theoretical prediction that signals of submission should be favored when retreat options are restricted, I suggest that limited escapability imposed by chameleon morphology, physiology, and ecology favored the evolution of a pigment-based signal of submission in this group.

International audience; Rapid human urbanization can have strong and varied impacts on the behavior and fitness of wild animals. The “credit-card hypothesis” predicts that low predation and high food predictability in cities lead to the presence of many weak competitors in urban populations. However, no experimental studies to date have found support for this hypothesis. Here, we studied the relationship betweenurbanization and aggressiveness in males of a widespread North American songbird (the house finch, Haemorhous mexicanus) whiletaking into account the degree of sexual signal elaboration (plumage coloration), which is known to impact competitive outcomes. Inpaired laboratory experiments, we found that colorful urban males were less aggressive than drab urban males, whereas there wasno significant difference in aggressiveness between colorful and drab rural males. Moreover, we found that colorful urban males wereless aggressive than colorful rural males, whereas there was no significant difference in aggressiveness between drab urban and drabrural males. In 4-bird trials (i.e., trials with colorful and drab males from both urban and rural environments), we found that colorfulurban males were consistently less aggressive than all others. Taken together, these results support the credit-card hypothesis andthe idea that plumage color is an important predictor of social status in urban environments. Finally, in a model-presentation study, wefound that urban males with lower body condition avoided drab male models. Urban settings, along with the social and foraging conditions they create, may exert novel selection pressures that shape the competitiveness and status signaling systems of animals.

The function and evolution of avian plumage colouration has been the subject of many studies over the past decade, but virtually all of this research has focused on the plumages of sexually mature individuals. The colours and patterns of juvenal plumage, which is worn by altricial songbirds only for the first few months of life, have been the focus of few studies. We develop the idea that distinctive juvenile appearance may be a signal of sexual immaturity, serving to reduce aggression from conspecific adults. We use a comparative phylogenetic approach to test this hypothesis in the thrushes (Family Turdidae). Honest signals of reproductive immaturity should be more valuable when juveniles fledge into environments with aggressive adult conspecifics. Therefore, we predicted that distinctive juvenile appearance would be more likely to evolve in species with extended breeding seasons and high levels of territoriality. Because many tropical bird species exhibit year-round territoriality and elongated breeding seasons, we used breeding latitude as a proxy for these variables. As predicted, distinctive juvenile appearance was significantly correlated with occupancy of tropical latitudes. While alternative explanations cannot be ruled out and more tests of the hypothesis are needed, the observed associations between breeding latitude and distinctiveness of juvenal plumage are consistent with our hypothesis that distinctive juvenal plumage evolved as a signal of sexual immaturity.

Introduced species can exert outsized impacts on native biota through both direct (predation) and indirect (competition) effects. Ants frequently become established in new areas after being transported by humans across traditional biological or geographical barriers, and a prime example of such establishment is the red imported fire ant (Solenopsis invicta). Introduced to North America in the 1930's, red imported fire ants are now firmly established throughout the southeastern United States. Although these invasive predators can dramatically impact native arthropods, their effect on vertebrates through resource competition is essentially unknown. Using a paired experimental design, we compared patterns of foraging and rates of provisioning for breeding eastern bluebirds (Sialia sialis) in unmanipulated (control) territories to those in adjacent (treated) territories where fire ants were experimentally reduced. Bluebirds inhabiting treated territories foraged nearer their nests and provisioned offspring more frequently than bluebirds inhabiting control territories with unmanipulated fire ant levels. Additionally, nestlings from treated territories were in better condition than those from control territories, though these differences were largely confined to early development. The elimination of significant differences in body condition towards the end of the nestling period suggests that bluebird parents in control territories were able to make up the food deficit caused by fire ants, potentially by working harder to adequately provision their offspring. The relationship between fire ant abundance and bluebird behavior hints at the complexity of ecological communities and suggests negative effects of invasive species are not limited to taxa with which they have direct contact.

Many annual monitoring programs assume that availability—the probability that an animal will be visible, make an audible sound, or leave other evidence of its presence—is not changing systematically from year to year. Until recently, this assumption of unchanging availability seemed reasonable, but recent studies report changes in breeding phenology that are presumed to be linked to climate change. Because the rate of bird song is often correlated with stage of breeding, earlier breeding could shift timing of peak bird availability, changing the number of birds counted during annual surveys on set dates. Such changes could be erroneously interpreted as population trends. To better understand how changes in phenology might affect the probability of detecting birds, we modeled availabilities of 31 species in southern Alabama through the breeding season, documenting strong seasonal variation in availability. Then, using our availability estimates, we investigated whether changes in detection probab...

The hypothesis that nestlings are a significant driver of arbovirus transmission and amplification is based upon findings that suggest nestlings are highly susceptible to being fed upon by vector mosquitoes and to viral infection and replication. Several previous studies have suggested that nestlings are preferentially fed upon relative to adults in the nest, and other studies have reported a preference for adults over nestlings. We directly tested the feeding preference of nestling and adult birds in a natural setting, introducing mosquitoes into nesting boxes containing eastern bluebirds (Sialia sialis), collecting blood-fed mosquitoes, and matching the source of mosquito blood meals to individual birds using microsatellite markers. Neither nestlings nor adults were fed upon to an extent significantly greater than would be predicted based upon their relative abundance in the nests, although feeding upon mothers decreased as the age of the nestlings increased.

Males typically have greater variance in reproductive success than females, so mothers should benefit by producing sons under favourable conditions. Being paired with a better-than-average mate is one such favourable circumstance. High-quality fathers can improve conditions for their offspring by providing good genes, good resources, or both, so females paired to such males should invest preferentially in sons. Ornamentation has been linked to male quality in many birds, and, in support of differential allocation theory, females of several avian species invest more in entire broods when paired to attractive mates. Additionally, the females of some bird species apparently manipulate the primary sex ratio of their broods in relation to the attractiveness of their mates. However, empirical support for a link between mate ornamentation and preferential feeding of sons (another form of biased investment) is lacking. We tested for correlations between sex-biased parental investment and mate plumage colour in the eastern bluebird, Sialia sialis, a species in which juveniles have sexually dichromatic UV blue plumage. We found that the proportion of maternal feeding attempts to fledgling sons (versus fledgling daughters) was positively correlated with structurally coloured plumage ornamentation of fathers. Additionally, paternal feeding attempts to sons were correlated with plumage ornamentation of mothers and increased in fathers that had breast plumage characteristics typical of older males. These results provide further support for the idea that parental strategies are influenced by mate attractiveness and provide the first evidence that mate ornamentation can influence parental behaviour even after offspring have left the nest.

We observed and video-taped active- ly nesting adult Eastern Bluebirds (Sialia sialis) repeatedly feeding abandoned conspecific juveniles in a nearby nest. We used molecular techniques to confirm these nestlings were unrelated to the adults that fed them. The most likely explanation for the observed behavior is that it was a mistake resulting from parental

The role that different age classes of birds play in the amplification of arthropod-borne viruses depends critically on the feeding choices made by mosquitoes. To determine if mosquitoes are more likely to feed on nestling or adult birds, we introduced Culex quinquefasciatus mosquitoes into eastern bluebird Sialia sialis nest boxes after dark and recaptured them the following morning. We collected blood from each nestling and brooding mother and used molecular genotyping methods to trace the blood meals of individual mosquitoes to the individual bird fed upon (mothers or chicks). Of the 14 recaptured mosquitoes, whose blood meals were identified to the species level, 10 fed only on nestlings, three fed only on an adult, and one mosquito fed on an adult and two nestlings. These preliminary data show that microsatellite genotyping may be used to answer important questions concerning mosquito feeding patterns on different age classes of birds.

Juveniles of many avian species possess spotted or mottled plumage that is distinct from the plumage of adults. Such plumage has typically been assumed to aid in camouflaging vulnerable immature birds. Here, we propose that spotty plumage signals juvenile status, thereby decreasing aggression from territorial adults. We tested this hypothesis by measuring the aggressive responses of adult eastern bluebird males to different combinations of simultaneously presented taxidermic mounts. We found that territorial males attacked adult models significantly more than juvenile models, and that they attacked adult models with orange breasts (typical of adults) more frequently than they attacked adult models with spotty breasts (typical of juveniles). We found no difference in attack rates when models with white breasts (a novel trait) were presented with models possessing spotty breasts. These observations indicate that breast colour is a cue used by territorial adults when identifying conspecific intruders, but that adults do not recognize juvenile-specific plumage as such. Adults respond aggressively only to orange-breasted intruders.

The ornaments used by animals to mediate social interactions are diverse, and by reconstructing their evolutionary pathways we can gain new insights into the mechanisms underlying ornamental innovation and variability. Here, we examine variation in plumage carotenoids among the true finches (Aves: Fringillidae) using biochemical and comparative phylogenetic analyses to reconstruct the evolutionary history of carotenoid states and evaluate competing models of carotenoid evolution. Our comparative analyses reveal that the most likely ancestor of finches used dietary carotenoids as yellow plumage colorants, and that the ability to metabolically modify dietary carotenoids into more complex pigments arose secondarily once finches began to use modified carotenoids to create red plumage. Following the evolutionary “innovation” that enabled modified red carotenoid pigments to be deposited as plumage colorants, many finch species subsequently modified carotenoid biochemical pathways to create yellow plumage. However, no reversions to dietary carotenoids were observed. The finding that ornaments and their underlying mechanisms may be operating under different selection regimes—where ornamental trait colors undergo frequent reversions (e.g., between red and yellow plumage) while carotenoid metabolization mechanisms are more conserved—supports a growing empirical framework suggesting different evolutionary patterns for ornaments and the mechanistic innovations that facilitate their diversification.

The fundamental unit of rapid, physiological color change in vertebrates is the dermal chromatophore unit. This unit, comprised of cellular associations between different chromatophore types, is relatively conserved across the fish, amphibian, and reptilian species capable of physiological color change and numerous attempts have been made to understand the nature of the four major chromatophore types (melanophores, erythrophores, xanthophores, and iridophores) and their biochemical regulation. In this review, we attempt to describe the current state of knowledge regarding what classifies a pigment cell as a dynamic chromatophore, the unique characteristics of each chromatophore type, and how different hormones, neurotransmitters, or other signals direct pigment reorganization in a variety of vertebrate taxa.

Many animals display static coloration (e.g. of feathers or fur) that can serve as a reliable sexual or social signal, but the communication function of rapidly changing colours (as in chameleons and cephalopods) is poorly understood. We used recently developed photographic and mathematical modelling tools to examine how rapid colour changes of veiled chameleons Chamaeleo calyptratus predict aggressive behaviour during male–male competitions. Males that achieved brighter stripe coloration were more likely to approach their opponent, and those that attained brighter head coloration were more likely to win fights; speed of head colour change was also an important predictor of contest outcome. This correlative study represents the first quantification of rapid colour change using organism-specific visual models and provides evidence that the rate of colour change, in addition to maximum display coloration, can be an important component of communication. Interestingly, the body and head locations of the relevant colour signals map onto the behavioural displays given during specific contest stages, with lateral displays from a distance followed by directed, head-on approaches prior to combat, suggesting that different colour change signals may evolve to communicate different information (motivation and fighting ability, respectively).

Introduction Nutrient availability, assimilation, and allocation can have important and lasting effects on the immune system development of growing animals. Though carotenoid pigments have immunostimulatory properties in many animals, relatively little is known regarding how they influence the immune system during development. Moreover, studies linking carotenoids to health at any life stage have largely been restricted to birds and mammals. We investigated the effects of carotenoid supplementation on multiple aspects of immunity in juvenile veiled chameleons (Chamaeleo calyptratus). We supplemented half of the chameleons with lutein (a xanthophyll carotenoid) for 14 weeks during development and serially measured multiple aspects of immune function, including: agglutination and lysis performance of plasma, wound healing, and plasma nitric oxide concentrations before and after wounding. Results Though lutein supplementation effectively elevated circulating carotenoid concentrations throughout the developmental period, we found no evidence that carotenoid repletion enhanced immune function at any point. However, agglutination and lysis scores increased, while baseline nitric oxide levels decreased, as chameleons aged. Conclusions Taken together, our results indicate that body mass and age, but not carotenoid access, may play an important role in immune performance of growing chameleons. Hence, studying well-understood physiological processes in novel taxa can provide new perspectives on alternative physiological processes and nutrient function.

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early- and late-season breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs).

The relative amount of resources that avian parents provide to individual offspring within a brood represents a strategy that can have large effects on reproductive success. We tested whether parental feeding decisions of eastern bluebirds Sialia sialis are influenced by offspring plumage color by presenting pairs of differently colored fledglings side by side and observing how they were provisioned by parents. After a control period, we manipulated blue plumage color so that one sibling in each trial became relatively dark and one became relatively bright. During neither the control nor the experimental periods did either parent consistently feed naturally brighter or experimentally brightened sons more than drab sons. Under specific circumstances, however, both parents directed a higher proportion of their feeding attempts to more brightly colored sons. Paternal feeding attempts to brighter offspring during both the control and experimental periods increased in relation to the brightness of these fledglings relative to their brothers. Maternal feeding decision, on the other hand, were influenced by numerous variables during control and experimental periods including the date of the trial, the difference in mass between fledglings, the feeding behavior of fathers during the trial, the relative investment by fathers during the nestling stage, and the amount of UV chroma in fledgling plumage. Taken together, these results suggest that equal provisioning of offspring is the strategy most commonly adopted by eastern bluebirds but more brightly colored offspring will be fed preferentially when resources for offspring are limited. Copyright 2010, Oxford University Press.

The role that different age classes of birds play in the amplification of arthropod-borne viruses depends critically on the feeding choices made by mosquitoes. To determine if mosquitoes are more likely to feed on nestling or adult birds, we introduced Culex quinquefasciatus mosquitoes into eastern bluebird Sialia sialis nest boxes after dark and recaptured them the following morning. We collected blood from each nestling and brooding mother and used molecular genotyping methods to trace the blood meals of individual mosquitoes to the individual bird fed upon (mothers or chicks). Of the 14 recaptured mosquitoes, whose blood meals were identified to the species level, 10 fed only on nestlings, three fed only on an adult, and one mosquito fed on an adult and two nestlings. These preliminary data show that microsatellite genotyping may be used to answer important questions concerning mosquito feeding patterns on different age classes of birds.