The colours of extant mammals

Investigating the morphology and genetics of scalp and facial hair characteristics for phenotype prediction

Microscopic traits and ultrastructure of hair such as cross-sectional shape, pigmentation, curvature, and internal structure help determine the level of variations between and across human populations. Apart from cosmetics and anthropological applications, such as determining species, somatic origin (body area), and biogeographic ancestry, the evidential value of hair has increased with rapid progression in the area of forensic DNA phenotyping (FDP). Individuals differ in the features of their scalp hair (greying, shape, colour, balding, thickness, and density) and facial hair (eyebrow thickness, monobrow, and beard thickness) features. Scalp and facial hair characteristics are genetically controlled and lead to visible inter-individual variations within and among populations of various ethnic origins. Hence, these characteristics can be exploited and made more inclusive in FDP, thereby leading to more comprehensive, accurate, and robust prediction models for forensic purposes. The present article focuses on understanding the genetics of scalp and facial hair characteristics with the goal to develop a more inclusive approach to better understand hair biology by integrating hair microscopy with genetics for genotype-phenotype correlation research.

Seven Shades of Grey: A Follow-Up Study on the Molecular Basis of Coat Colour in Indicine Grey Cattle Using Genome-Wide SNP Data

Shades of grey and brown are a dominant component in mammal coat colours, representing a fundamental trait involved in a great number of processes including cryptism, sexual selection and signalling. The genetic mechanisms of the grey colouration in mammals are very complex and controlled by hundreds of genes whose effects and interactions are still largely unclear. In this study, we adopted a robust multi-cohort Fst outlier approach based on pairwise contrasts between seven grey indicine cattle breeds and both taurine and indicine non-grey cattle breeds in order to find genomic regions potentially related to the grey colouration. On the basis of three main drawn settings, built in order to control both the effect of the sample size and the genetic structure, we have identified some signals common to those obtained in a previous work employing only taurine cattle. In particular, using the top 1% Fst approach, we detected a candidate region (22.6–23.8 megabases) on chromosome 14 in which genes related to pigmentation have been already documented. In addition, when we constructed a phylogenetic tree using the significant markers identified in this study and including also the genotyping data at these loci of both the grey taurine and the extinct wild auroch, we found a topological repartition consistent with breed colour pattern rather than with the known bovine evolutionary history. Thus, on the basis of this evidence, together with the geographical distribution of the current taurine grey cattle, an ancestral indicine origin for the grey phenotype would seem to be a conceivable interpretation. In this context, a higher thermo-tolerance and less UV-induced damage of the grey phenotype might have favoured the retention of advantageous genes into the taurine genome during the post-Neolithic human-mediated cattle expansions.

The natural history and ecology of melanism in red wolf and coyote populations of the southeastern United States – evidence for Gloger’s rule

Background

Gloger’s rule postulates that animals should be darker colored in warm and humid regions where dense vegetation and dark environments are common. Although rare in Canis populations, melanism in wolves is more common in North America than other regions globally and is believed to follow Gloger’s rule. In the temperate forests of the southeastern United States, historical records of red wolf (Canis rufus) and coyote (Canis latrans) populations document a consistent presence of melanism. Today, the melanistic phenotype is extinct in red wolves while occurring in coyotes and red wolf-coyote hybrids who occupy the red wolf's historical range. To assess if Gloger’s rule could explain the occurrence and maintenance of melanistic phenotypes in Canis taxa, we investigated differences in morphology, habitat selection, and survival associated with pelage color using body measurements, GPS tracking data, and long-term capture-mark-recapture and radio-telemetry data collected on coyotes and hybrids across the southeastern United States.

Results

We found no correlation between morphometrics and pelage color for Canis taxa. However, we observed that melanistic coyotes and hybrids experienced greater annual survival than did their gray conspecifics. Furthermore, we observed that melanistic coyotes maintained larger home ranges and exhibited greater selection for areas with dense canopy cover and wetlands than did gray coyotes.

Conclusions

In the southeastern United States, pelage color influenced habitat selection by coyotes and annual survival of coyotes and hybrids providing evidence that Gloger’s rule is applicable to canids inhabiting regions with dense canopy cover and wetlands. Greater annual survival rates observed in melanistic Canis may be attributed to better concealment in areas with dense canopy cover such as coastal bottomland forests. We suggest that the larger home range sizes of melanistic coyotes may reflect the trade-off of reduced foraging efficiency in lower quality wetland habitat for improved survival. Larger home ranges and differential use of land cover by melanistic coyotes may facilitate weak assortative mating in eastern coyote populations, in which melanistic animals may have lower success of finding compatible mates in comparison to gray conspecifics. We offer that our observations provide a partial explanation for why melanism is relatively low (< 10%) but consistent within coyote populations throughout southeastern parts of their range.

The giant panda is cryptic

The giant panda (Ailuropoda melanoleuca) is an iconic mammal, but the function of its black-and-white coloration is mysterious. Using photographs of giant pandas taken in the wild and state-of-the-art image analysis, we confirm the counterintuitive hypothesis that their coloration provides camouflage in their natural environment. The black fur blends into dark shades and tree trunks, whereas white fur matches foliage and snow when present, and intermediate pelage tones match rocks and ground. At longer viewing distances giant pandas show high edge disruption that breaks up their outline, and up close they rely more on background matching. The results are consistent across acuity-corrected canine, feline, and human vision models. We also show quantitatively that the species animal-to-background colour matching falls within the range of other species that are widely recognised as cryptic. Thus, their coloration is an adaptation to provide background matching in the visual environment in which they live and simultaneously to afford distance-dependent disruptive coloration, the latter of which constitutes the first computational evidence of this form of protective coloration in mammals.

Aposematism in mammals

Aposematic coloration is traditionally considered to signal unpalatability or toxicity. In mammals, most research has focused on just one form of defense, namely, noxious anal secretions, and its black-and-white advertisement as exemplified by skunks. The original formulation of aposematism, however, encompassed a broader range of morphological, physiological, and behavioral defenses, and there are many mammal species with black-and-white contrasting patterns that do not have noxious adaptations. Here, using Bayesian phylogenetic models and data from 1726 terrestrial nonvolant mammals we find that two aspects of conspicuous coloration, black-and-white coloration patterns on the head and body, advertise defenses that are morphological (spines, large body size), behavioral (pugnacity), and physiological (anal secretions), as well as being involved with sexual signaling and environmental factors linked to crypsis. Within Carnivora, defensive anal secretions are associated with complex black-and-white head patterns and longitudinal black-and-white body striping; in primates, larger bodied species exhibit irregular patches of black-and-white pelage; and in rodents, pugnacity is linked to sharp countershading and irregular blocks of white and black pelage. We show that black-and-white coloration in mammals is multifunctional, that it serves to warn predators of several defenses other than noxious anal secretions, and that aposematism in mammals is not restricted to carnivores.

Generalist camouflage can be more successful than microhabitat specialisation in natural environments

BACKGROUND

Crypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward. To cope with heterogeneous backgrounds, animals could either specialise on particular microhabitat patches, appearing cryptic in some areas but mismatching others, or adopt a compromise strategy, providing partial matching across different patch types. Existing studies have tested the effectiveness of compromise strategies in only a limited set of circumstances, primarily with small targets varying in pattern, and usually in screen-based tasks. Here, we measured the detection risk associated with different background-matching strategies for relatively large targets, with human observers searching for them in natural scenes, and focusing on colour. Model prey were designed to either 'specialise' on the colour of common microhabitat patches, or 'generalise' by matching the average colour of the whole visual scenes.

RESULTS

In both the field and an equivalent online computer-based search task, targets adopting the generalist strategy were more successful in evading detection than those matching microhabitat patches. This advantage occurred because, across all possible locations in these experiments, targets were typically viewed against a patchwork of different microhabitat areas; the putatively generalist targets were thus more similar on average to their various immediate surroundings than were the specialists.

CONCLUSIONS

Demonstrating close agreement between the results of field and online search experiments provides useful validation of online citizen science methods commonly used to test principles of camouflage, at least for human observers. In finding a survival benefit to matching the average colour of the visual scenes in our chosen environment, our results highlight the importance of relative scales in determining optimal camouflage strategies, and suggest how compromise coloration can succeed in nature.

Stabbing Spines: A review of the Biomechanics and Evolution of Defensive Spines

Spines are ubiquitous in both plants and animals, and while most spines were likely originally used for defense, over time many have been modified in a variety of ways. Here we take an integrative approach to review the form, function, and evolution of spines as a defensive strategy in order to make new connections between physical mechanisms and functional behavior. While this review focuses on spines in mammals, we reference and draw ideas from the literature on spines in other taxa, including plants. We begin by exploring the biomechanics of defensive spines, their varied functions, and nondefensive modifications. We pay particular attention to the mechanics involved in passive puncture and the ways organisms have overcome limitations associated with the low energy input. We then focus on the ecological, physiological, and behavioral factors that promote the evolution of spiny defenses, including predator- and habitat-mediated hypotheses. While there is considerable evidence to support both, studies have generally found that (1) defensive spines are usually effective against one class of attacker (e.g., larger predators) but ineffective against or even facilitate predation by others and (2) species that are more visible or exposed to predators are under much stronger selection to evolve defensive spines or some other robust defense. What type of defensive morphology that evolves, however, is less predictable and probably strongly dependent on both the dominant source of predation and the habitat structure of the organism (e.g., arboreal, terrestrial, and fossorial). We then explore traits that often are correlated with defensive spines and armor, potentially forming armor syndromes, suites of traits that evolve together with body armor in a correlated fashion. In mammals, these include aposematic warning coloration, locomotion style, diet, metabolic rate, and relative brain size. Finally, we encourage integration of mechanistic, behavioral, and evolutionary studies of defensive spines and suggest future avenues of research in the biomechanics, evolution, and behavior of spines and spiny organisms.

Examining the molecular basis of coat color in a nocturnal primate family (Lorisidae)

Organisms use color for camouflage, sexual signaling, or as a warning sign of danger. Primates are one of the most vibrantly colored Orders of mammals. However, the genetics underlying their coat color are poorly known, limiting our ability to study molecular aspects of its evolution. The role of the melanocortin 1 receptor (MC1R) in color evolution has been implicated in studies on rocket pocket mice (Chaetodipus intermediusi), toucans (Ramphastidae), and many domesticated animals. From these studies, we know that changes in MC1R result in a yellow/red or a brown/black morphology. Here, we investigate the evolution of MC1R in Lorisidae, a monophyletic nocturnal primate family, with some genera displaying high contrast variation in color patterns and other genera being monochromatic. Even more unique, the Lorisidae family has the only venomous primate: the slow loris (Nycticebus). Research has suggested that the contrasting coat patterns of slow lorises are aposematic signals for their venom. If so, we predict the MC1R in slow lorises will be under positive selection. In our study, we found that Lorisidae MC1R is under purifying selection (ω = 0.0912). In Lorisidae MC1R, there were a total of 75 variable nucleotides, 18 of which were nonsynonymous. Six of these nonsynonymous substitutions were found on the Perodicticus branch, which our reconstructions found to be the only member of Lorisidae that has predominantly lighter coat color; no substitutions were associated with Nycticebus. Our findings generate new insight into the genetics of pelage color and evolution among a unique group of nocturnal mammals and suggest putative underpinnings of monochromatic color evolution in the Perodicticus lineage.

Apparent piebald variants in quolls (Dasyurus): examples of three recent cases in the spotted-tailed quoll Dasyurus maculatus

Pelage patterning plays an important role in animal behaviour. Variation in pelage patterns can change with pigment distribution and quantity in individuals. We present three cases of apparent piebaldism – a condition where the body is patchily unpigmented – in the spotted-tailed quoll Dasyurus maculatus. Using a comprehensive dataset of historical descriptions (from Dunlop et al. 2020), we conclude that these cases represent the first description of this phenotype in the genus Dasyurus, but acknowledge capture and testing of these individuals is required to be certain of the cause. Little is known about the implications of pelage patterning in quoll species and further investigation is required to understand the evolutionary and functional role of unaffected and unpigmented variants.

Genetics and Evolution of Mammalian Coat Pigmentation

The diversity of mammalian coat colors, and their potential adaptive significance, have long fascinated scientists as well as the general public. The recent decades have seen substantial improvement in our understanding of their genetic bases and evolutionary relevance, revealing novel insights into the complex interplay of forces that influence these phenotypes. At the same time, many aspects remain poorly known, hampering a comprehensive understanding of these phenomena. Here we review the current state of this field and indicate topics that should be the focus of additional research. We devote particular attention to two aspects of mammalian pigmentation, melanism and pattern formation, highlighting recent advances and outstanding challenges, and proposing novel syntheses of available information. For both specific areas, and for pigmentation in general, we attempt to lay out recommendations for establishing novel model systems and integrated research programs that target the genetics and evolution of these phenotypes throughout the Mammalia.

Bar, stripe and spot development in sand-dwelling cichlids from Lake Malawi

Background

Melanic patterns such as horizontal stripes, vertical bars and spots are common among teleost fishes and often serve roles in camouflage or mimicry. Extensive research in the zebrafish model has shown that the development of horizontal stripes depends on complex cellular interactions between melanophores, xanthophores and iridophores. Little is known about the development of horizontal stripes in other teleosts, and even less is known about bar or spot development. Here, we compare chromatophore composition and development of stripes, bars and spots in two cichlid species of sand-dwellers from Lake Malawi—Copadichromis azureus and Dimidiochromis compressiceps.

Results

(1) In D. compressiceps, stripes are made of dense melanophores underlaid by xanthophores and overlaid by iridophores. Melanophores and xanthophores are either loose or absent in interstripes, and iridophores are dense. In C. azureus, spots and bars are composed of a chromatophore arrangement similar to that of stripes but are separated by interbars where density of melanophores and xanthophores is only slightly lower than in stripes and iridophore density appears slightly greater. (2) Stripe, bar and spot chromatophores appear in the skin at metamorphosis. Stripe melanophores directly differentiate along horizontal myosepta into the adult pattern. In contrast, bar number and position are dynamic throughout development. As body length increases, new bars appear between old ones or by splitting of old ones through new melanophore appearance, not migration. Xanthophore and iridophore distributions follow melanophore patterns. (3) Metamorphic pigmentation arises in cichlids in a fashion similar to that described in zebrafish: melanophore progenitors derived from the medial route of neural crest migration migrate from the vicinity of the neural tube to the skin during metamorphosis.

Conclusion

The three pigment cell types forming stripes, bars and spots arise in the skin at metamorphosis. Stripes develop by differentiation of melanophores along horizontal myosepta, while bars do not develop along patent anatomical boundaries and increase in number in relation with body size. We propose that metamorphic melanophore differentiation and migratory arrest upon arrival to the skin lead to stripe formation, while bar formation must be supported by extensive migration of undifferentiated melanophores in the skin.

Venom in Furs: Facial Masks as Aposematic Signals in a Venomous Mammal

The function of colouration in animals includes concealment, communication and signaling, such as the use of aposematism as a warning signal. Aposematism is unusual in mammals, and exceptions help us to understand its ecology and evolution. The Javan slow loris is a highly territorial venomous mammal that has a distinctive facial mask and monochromatic vision. To help understand if they use aposematism to advertise their venom to conspecifics or predators with different visual systems, we studied a population in Java, Indonesia. Using ImageJ, we selected colours from the facial masks of 58 individuals, converted RBG colours into monochromatic, dichromatic and trichromatic modes, and created a contrast index. During 290 captures, we recorded venom secretion and aggressiveness. Using Non-metric Multidimensional Scaling and generalised additive models for location, scale and shape, we found that young slow lorises differ significantly from adults, being both more contrasting and more aggressive, with aggressive animals showing fewer wounds. We suggest aposematic facial masks serve multiple purposes in slow lorises based on age. Change in colouration through development may play a role in intraspecific competition, and advertise toxicity or aggressiveness to competitors and/or predators in juveniles. Aposematic signals combined with intraspecific competition may provide clues to new venomous taxa among mammals.

The colour phases of the European red squirrel in Ukraine: Similarities and differences by craniometric characters

The different colour phases of the European red squirrel occuring in Ukraine were analysed in a morphological context. They are indicated in the literature as different subspecies of Sciurus vulgaris L. and described only based on their coat colouration. In Ukraine, at least three colour phases occur: dark (black and brown), red, and light red, which in natural habitats occur separately from one another. These phases co-occur in human settlements and at different altitudes, in particular at the boundary of the lowland and piedmont zones and of piedmont and mountainbelts. The aim of the present study was to find some other morphological differences between the red squirrel’s phases in Ukraine beyond their coat colouration and to reveal the possible interaction between colouration and morphological variation of the squirrels. Eighteen craniometric and four external characters were measured and analysed. Results have shown that the squirrel’s colour phases differ among themselves by some characters, although the most visible differences were revealed when all measurents were analysed together. It has been revealed that the three colour phases are stabilized types (populations) manifested in a multidimensional space as different populations with minimal overlap (up to 10%). The population of dark squirrels in Ukraine is morphologically the most distant from the light red phase and less so from the red one. The dark phase significantly differs from the red phase by 9 of 18 craniometric characters with Mayr’s coefficient of divergence (CDmin = 0.62, CDmax = 0.96). The dark phase significantly differs from the light red phase by two craniometric characters according to ANOVA, but only by one character according to Mayr’scoefficient of divergence (CD = 0.96). The red and light red phases significantly differ by four parameters having CDmin = 0.64 and CDmax = 0.76. The geographically transitional red phase is morphologically intermediate according to the results of discriminant analysis.

Social communication in bats

Bats represent one of the most diverse mammalian orders, not only in terms of species numbers, but also in their ecology and life histories. Many species are known to use ephemeral and/or unpredictable resources that require substantial investment to find and defend, and also engage in social interactions, thus requiring significant levels of social coordination. To accomplish these tasks, bats must be able to communicate; there is now substantial evidence that demonstrates the complexity of bat communication and the varied ways in which bats solve some of the problems associated with their unique life histories. However, while the study of communication in bats is rapidly growing, it still lags behind other taxa. Here we provide a comprehensive overview of communication in bats, from the reasons why they communicate to the diversity and application of different signal modalities. The most widespread form of communication is the transmission of a signaller's characteristics, such as species identity, sex, individual identity, group membership, social status and body condition, and because many species of bats can rely little on vision due to their nocturnal lifestyles, it is assumed that sound and olfaction are particularly important signalling modes. For example, research suggests that secretions from specialized glands, often in combination with urine and saliva, are responsible for species recognition in several species. These olfactory signals may also convey information about sex and colony membership. Olfaction may be used in combination with sound, particularly in species that emit constant frequency (CF) echolocation calls, to recognize conspecifics from heterospecifics, yet their simple structure and high frequency do not allow much information of individual identity to be conveyed over long distances. By contrast, social calls may encode a larger number of cues of individual identity, and their lower frequencies increase their range of detection. Social calls are also known to deter predators, repel competitors from foraging patches, attract group mates to roost sites, coordinate foraging activities, and are used during courtship. In addition to sound, visual displays such as wing flapping or hovering may be used during courtship, and swarming around roost sites may serve as a visual cue of roost location. However, visual communication in bats still remains a poorly studied signal modality. Finally, the most common form of tactile communication known in bats is social grooming, which may be used to signal reproductive condition, but also to facilitate and strengthen cooperative interactions. Overall, this review demonstrates the rapid advances made in the study of bat social communication during recent years, and also identifies topics that require further study, particularly those that may allow us to understand adaptation to rapidly changing environmental conditions.

Molecular cloning and expression analysis of tyr and tyrp1 genes in normal and albino yellow catfish Tachysurus fulvidraco

The full-length complementary DNA of two genes related to vertebrate albinism, the tyrosinase gene tyr and tyrosinase-related protein 1 gene tyrp1, were cloned and analysed from normal and albino yellow catfish Tachysurus fulvidraco. The open reading frames (ORF) of tyr and tyrp1 encode putative peptides of 533 and 526 amino acids (amino-acid), both of which possess two conserved copper binding sites. The homologous identities of deduced amino-acid sequences showed that both Tyr and Tyrp1 of T. fulvidraco share considerable similarity with that of channel catfish Ictalurus punctatus. Both tyr and tyrp1 were expressed in a wide range of adult tissues. Tyr gene had the highest expression level in the brain of both normal and albino T. fulvidraco. Tyrp1 had the highest expression level in the skin of normal groups, and the fin of albino groups. The messenger (m)RNA expressions of tyr and tyrp1 were detectable at different early developmental stages and varied with embryonic and larval growth. Tyr and tyrp1 mRNA have obvious tissue specificity both in normal and albino T. fulvidraco and higher expression levels were detected in the normal group revealing that tyr and tyrp1 may have an important role in pigmentation. These results will provide useful data for understanding the molecular mechanism of melanin formation and the occurrence of albinism in T. fulvidraco.

Countershading and Stripes in the Theropod Dinosaur Sinosauropteryx Reveal Heterogeneous Habitats in the Early Cretaceous Jehol Biota

Countershading is common across a variety of lineages and ecological time [1-4]. A dark dorsum and lighter ventrum helps to mask the three-dimensional shape of the body by reducing self-shadowing and decreasing conspicuousness, thus helping to avoid detection by predators and prey [1, 2, 4, 5]. The optimal countershading pattern is dictated by the lighting environment, which is in turn dependent upon habitat [1, 3, 5, 6]. With the discovery of fossil melanin [7, 8], it is possible to infer original color patterns from fossils, including countershading [3, 9, 10]. Applying these principles, we describe the pattern of countershading in the diminutive theropod dinosaur Sinosauropteryx from the Early Cretaceous Jehol Biota of Liaoning, China. From reconstructions based on exceptional fossils, the color pattern is compared to predicted optimal countershading transitions based on 3D reconstructions of the animal's abdomen, imaged in different lighting environments. Reconstructed patterns match well with those predicted for animals living in open habitats. Jehol is presumed to have been a predominantly closed forested environment [3, 11, 12], but our results indicate a more heterogeneous range of habitats. Sinosauropteryx is also shown to exhibit a "bandit mask," a common pattern in many living vertebrates, particularly birds, that serves multiple functions including camouflage [13-18]. Sinosauropteryx therefore shows multiple color pattern features likely related to the habitat in which it lived. Our results show how reconstructing the color of extinct animals can inform on their ecologies beyond what may be obvious from skeletal remains alone. VIDEO ABSTRACT.

The colours of humanity: the evolution of pigmentation in the human lineage

Humans are a colourful species of primate, with human skin, hair and eye coloration having been influenced by a great variety of evolutionary forces throughout prehistory. Functionally naked skin has been the physical interface between the physical environment and the human body for most of the history of the genus Homo, and hence skin coloration has been under intense natural selection. From an original condition of protective, dark, eumelanin-enriched coloration in early tropical-dwelling Homo and Homo sapiens, loss of melanin pigmentation occurred under natural selection as Homo sapiens dispersed into non-tropical latitudes of Africa and Eurasia. Genes responsible for skin, hair and eye coloration appear to have been affected significantly by population bottlenecks in the course of Homo sapiens dispersals. Because specific skin colour phenotypes can be created by different combinations of skin colour-associated genetic markers, loss of genetic variability due to genetic drift appears to have had negligible effects on the highly redundant genetic 'palette' for the skin colour. This does not appear to have been the case for hair and eye coloration, however, and these traits appear to have been more strongly influenced by genetic drift and, possibly, sexual selection.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Zebra Stripes through the Eyes of Their Predators, Zebras, and Humans

The century-old idea that stripes make zebras cryptic to large carnivores has never been examined systematically. We evaluated this hypothesis by passing digital images of zebras through species-specific spatial and colour filters to simulate their appearance for the visual systems of zebras’ primary predators and zebras themselves. We also measured stripe widths and luminance contrast to estimate the maximum distances from which lions, spotted hyaenas, and zebras can resolve stripes. We found that beyond ca. 50 m (daylight) and 30 m (twilight) zebra stripes are difficult for the estimated visual systems of large carnivores to resolve, but not humans. On moonless nights, stripes are difficult for all species to resolve beyond ca. 9 m. In open treeless habitats where zebras spend most time, zebras are as clearly identified by the lion visual system as are similar-sized ungulates, suggesting that stripes cannot confer crypsis by disrupting the zebra’s outline. Stripes confer a minor advantage over solid pelage in masking body shape in woodlands, but the effect is stronger for humans than for predators. Zebras appear to be less able than humans to resolve stripes although they are better than their chief predators. In conclusion, compared to the uniform pelage of other sympatric herbivores it appears highly unlikely that stripes are a form of anti-predator camouflage.

Social huddling and physiological thermoregulation are related to melanism in the nocturnal barn owl

Endothermic animals vary in their physiological ability to maintain a constant body temperature. Since melanin-based coloration is related to thermoregulation and energy homeostasis, we predict that dark and pale melanic individuals adopt different behaviours to regulate their body temperature. Young animals are particularly sensitive to a decrease in ambient temperature because their physiological system is not yet mature and growth may be traded-off against thermoregulation. To reduce energy loss, offspring huddle during periods of cold weather. We investigated in nestling barn owls (Tyto alba) whether body temperature, oxygen consumption and huddling were associated with melanin-based coloration. Isolated owlets displaying more black feather spots had a lower body temperature and consumed more oxygen than those with fewer black spots. This suggests that highly melanic individuals display a different thermoregulation strategy. This interpretation is also supported by the finding that, at relatively low ambient temperature, owlets displaying more black spots huddled more rapidly and more often than those displaying fewer spots. Assuming that spot number is associated with the ability to thermoregulate not only in Swiss barn owls but also in other Tytonidae, our results could explain geographic variation in the degree of melanism. Indeed, in the northern hemisphere, barn owls and allies are less spotted polewards than close to the equator, and in the northern American continent, barn owls are also less spotted in colder regions. If melanic spots themselves helped thermoregulation, we would have expected the opposite results. We therefore suggest that some melanogenic genes pleiotropically regulate thermoregulatory processes.

Zebrafish stripes as a model for vertebrate colour pattern formation

Colour patterns are prominent features of many animals and have important functions in communication, such as camouflage, kin recognition and mate choice. As targets for natural as well as sexual selection, they are of high evolutionary significance. The molecular mechanisms underlying colour pattern formation in vertebrates are not well understood. Progress in transgenic tools, in vivo imaging and the availability of a large collection of mutants make the zebrafish (Danio rerio) an attractive model to study vertebrate colouration. Zebrafish display golden and blue horizontal stripes that form during metamorphosis as mosaics of yellow xanthophores, silvery or blue iridophores and black melanophores in the hypodermis. Lineage tracing revealed the origin of the adult pigment cells and their individual cellular behaviours during the formation of the striped pattern. Mutant analysis indicated that interactions between all three pigment cell types are required for the formation of the pattern, and a number of cell surface molecules and signalling systems have been identified as mediators of these interactions. The understanding of the mechanisms that underlie colour pattern formation is an important step towards deciphering the genetic basis of variation in evolution.

A Comparative Transcriptome Analysis between Wild and Albino Yellow Catfish (Pelteobagrus fulvidraco)

Body colours are important and striking features for individual survival and reproductive success, in particular in vertebrates where mating behaviour and mate preference may be strongly influenced by non-normal phenotypes. Pigmentation disorders may be generated by disruption of one or many independent genes as well as by environmental factors. The first discovery of albino yellow catfish (Pelteobagrus fulvidraco Richardson) with golden skin colour from fish farms in China provides us valuable material to study the molecular mechanism underlying the abnormalities of pigmentation. In this study, transcriptome sequencing of fin tissues corresponding to the distinct body colours, wild type and mutant albino yellow catfish, were performed using Illumina sequencing technology. Based on next-generation sequencing technology and de novo assembly, we generated a transcriptome of P. fulvidraco. A number of genes differentially expressed between the wild types and albinos were identified, suggesting their contribution to the different phenotypes and fitness. However, non-synonymous mutations result from single nucleotide substitutions residing in coding regions may not contribute to such differences. Based on the high-throughput expression data generated for the two different types of P. fulvidraco, we found that alterations of expression pattern may be more common than non-synonymous mutations. The transcriptome of P. fulvidraco will be an invaluable resource for subsequent comparative genomics and evolutionary analyses of this economically important fish.