Melanic Phenotypes Research Articles

Being Dark is Better: A Feral Pigeon Plumage Polymorphism as a Response to Urban Environments in Slovakia

Abstract The purpose of this study was to determine the distribution and plumage phenotypes of the feral pigeon, Columba livia forma urbana (Gmelin, 1789), in Slovakia. Censuses carried out in the built-up areas of 16 towns and cities from November to February (2012–2018) counted and evaluated 3,123 individual birds. The most frequent were melanic colored birds (checker, T-pattern and spread phenotypes), which predominated in the population (51.6%, n = 1,613), followed by paler ones (42.1%, n = 1,316) and other types (6.2%, n = 194). A statistically significant difference was confirmed among the melanic and paler plumage phenotypes (χ2 = 81.49, df = 15, p < 0.0001). Correlation confirmed the different importance of city area and human density on the maintenance of dark and/or pale pigeons living in cities.

First record of a highly melanic morph of Cyphostethus tristriatus (Fabricius, 1787) (Hemiptera: Heteroptera: Acanthosomatidae).

The term 'melanism' means the occurrence of variant(s) that is/are mostly or completely dark in pigmentation either as intraspecific polymorphisms or as fixed differences between closely related species. Melanism can refer to variation involving discrete melanic and non-melanic phenotypes (melanic and typical morphs) or to cases of continuously varying pigmentation (True 2003). Melanism of moths inhabiting areas with industrial pollution is a very well-known example involving melanic polymorphisms in insects. However, melanism is also known in other insect orders, e.g. Coleoptera and Diptera (Majerus 1998, True 2003).

The Genetic Basis of Adaptation following Plastic Changes in Coloration in a Novel Environment

Phenotypic plasticity has been hypothesized to precede and facilitate adaptation to novel environments [1-8], but examples of plasticity preceding adaptation in wild populations are rare (but see [9,10]). We studied a population of side-blotched lizards, Uta stansburiana, living on a lava flow that formed 22,500 years ago [11] to understand the origin of their novel melanic phenotype that makes them cryptic on the black lava. We found that lizards living on and off of the lava flow exhibited phenotypic plasticity in coloration but also appeared to have heritable differences in pigmentation. We sequenced the exomes of 104 individuals and identified two known regulators of melanin production, PREP and PRKAR1A, which had markedly increased levels of divergence between lizards living on and off the lava flow. The derived variants in PREP and PRKAR1A were only found in the lava population and were associated with increased pigmentation levels in an experimental cohort of hatchling lizards. Simulations suggest that the derived variants in the PREP and PRKAR1A genes arose recently and were under strong positive selection in the lava population. Overall, our results suggest that ancestral plasticity for coloration facilitated initial survival in the lava environment and was followed by genetic changes that modified the phenotype in the direction of the induced plastic response, possibly through de novo mutations. These observations provide a detailed example supporting the hypothesis that plasticity aids in the initial colonization of a novel habitat, with natural selection subsequently refining the phenotype with genetic adaptations to the new environment. VIDEO ABSTRACT.

MC1R polymorphism associated with plumage color variations in Coturnix chinensis.

The melanocortin 1 receptor (MC1R) gene was investigated as a candidate for plumage variations in Chinese painted quail, Coturnix chinensis. Four silent and two missense nucleotide polymorphisms were identified. The correspondent amino acid changes, p.Glu92Lys and p.Pro292Leu, were found in Blue Face and Red Breasted animals respectively. Blue Face is a melanic phenotype similar to the co-dominant Extended Brown of Japanese quail, and both share the p.Glu92Lys mutation. The association of p.Pro292Leu with the recessive Red Breasted was confirmed in 23 animals from an experimental F2 cross.

Polymorphisms in MC1R and ASIP genes and their association with coat color phenotypes in llamas (Lama glama)

The melanocortin 1-receptor (MC1R) and the agouti signaling protein (ASIP) are the major genes controlling the type and location of pigments produced in mammals. In recent years, polymorphisms in these genes have been associated with coat color variation in a number of species. Llamas (Lama glama) are characterized by a great diversity of coat colors. However, the genetic basis of coat color determination is still unknown. Here, we sequenced the MC1R and ASIP genes in llamas and studied the association between the polymorphisms identified and the coat color. Sequence analysis revealed ten nonsynonymous single nucleotide polymorphisms in the MC1R gene. Three main haplotypes were identified, none of which were completely associated to a particular color phenotype. However, significant association was detected between the MC1R*1 haplotype and the presence of pigmented coat (P<0.0001). Compared to the wild allele, MC1R*1 carried two amino acid substitutions, p.G126S and p.V87M. This last replacement occurs at a highly conserved residue among mammals and the same substitution has been previously associated to melanic phenotypes in avian species. Furthermore, two polymorphisms in ASIP exon 4, a 57bp deletion (c.325_381del) and c.292C>T that are both predicted to have a deleterious effect on the protein, were found in homozygous state or combined in most llamas with eumelanic coat.

Integrated Cytogenetic and Mitochondrial DNA Analyses Indicate That Two Different Phenotypes of Hypancistrus (L066 and L333) Belong to the Same Species.

The diversity of Hypancistrus species in the Xingu River is remarkable and the variation in color morphs represents a real challenge to taxonomists to delimit species boundaries. One of the most recognizable Hypancistrus complexes is the worm-lined species, known in the aquarium trade as King Tiger Plec in English, Hypancistrus "pão" in Portuguese or under the L-numbers L066 and L333 that represent two melanic pigment pattern phenotypes. To assess the identity of these two phenotypes, we described their karyotypes and sequenced part of the mitochondrial cytochrome oxidase I gene (DNA barcode). These fishes have 52 chromosomes (40 meta-submetacentric and 12 subtelo-acrocentric) and a strong heteromorphism in chromosome pair 21 was observed, which does not correlate with the two phenotypes or sex. DNA barcodes separated the samples analyzed from Hypancistrus zebra and other publicly available sequences of Loricariidae showing no divergence between the two phenotypes. The data set indicates that worm-lined Hypancistrus from the Xingu form a single species with clear chromosomal and melanic pigment pattern polymorphisms.

First Nearctic Records for Orius (Dimorphella) sibiricus Wagner (Hemiptera: Heteroptera: Anthocoridae), a Eurasian Steppe Inhabitant

Orius sibiricus Wagner, a dark-colored minute pirate bug widespread in the Eurasian Steppe, is recorded from sites near the Yukon River in Yukon, Canada. This species is distinguished from the melanic phenotype of Orius diespeter Herring by the more deeply and uniformly punctured dorsum, the subangular anterolateral angles of the pronotum of the female, the lack of denticles on the forefemora of the male, the entirely dark embolium, and the shape of the paramere. Collection sites for O. sibiricus in Yukon are in ecoregions that contain sun-warmed steppe in or near East Beringia. The species has also been collected in eastern Siberia from steppe sites within the boundaries of West Beringia. Specimens of O. sibiricus from East Beringia and West Beringia have very similar genitalic structures. Orius sibiricus has been collected from the plant genera Artemisia, Caragana and Spiraea, as well as from unidentified herbaceous vegetation. The geographical distribution of O. sibiricus suggests a relatively recent dispersal across the Bering Land Bridge.

Population-Specific Covariation between Immune Function and Color of Nesting Male Threespine Stickleback.

Multiple biological processes can generate sexual selection on male visual signals such as color. For example, females may prefer colorful males because those males are more readily detected (perceptual bias), or because male color conveys information about male quality and associated direct or indirect benefits to females. For example, male threespine stickleback often exhibit red throat coloration, which females prefer both because red is more visible in certain environments, and red color is correlated with male immune function and parasite load. However, not all light environments favor red nuptial coloration: more tannin-stained water tends to favor the evolution of a melanic male phenotype. Do such population differences in stickleback male color, driven by divergent light environments, lead to changes in the relationship between color and immunity? Here, we show that, within stickleback populations, multiple components of male color (brightness and hue of four body parts) are correlated with multiple immune variables (ROS production, phagocytosis rates, and lymphocyte:leukocyte ratios). Some of these color-immune associations persist across stickleback populations with very different male color patterns, whereas other color-immune associations are population-specific. Overall, lakes with red males exhibit stronger color-immune covariance while melanic male populations exhibit weak if any color-immune associations. Our finding that color-immunity relationships are labile implies that any evolution of male color traits (e.g., due to female perceptual bias in a given light environment), can alter the utility of color as an indicator of male quality.

The costs of colour: plasticity of melanin pigmentation in an outbreaking polymorphic forest moth

AbstractOutside the context of industrial melanism, little is known about the physiological and ecological importance of genetic melanic polymorphisms in moths. Melanin pigments are synthesized from amino acid precursors and should therefore be costly to produce in nitrogen‐limited insects. A genetic melanic polymorphism is present in adult Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae), a widespread forest moth with outbreaking population dynamics. We test the hypotheses that melanin‐based colouration is physiologically costly in M. disstria, that expression of melanin‐based colouration is a plastic trait which varies with population density and nutrition, and that the genetically based melanic phenotype is disadvantaged under nutritionally poor conditions. Two experiments were used to test these hypotheses. A field study compared pigmentation and phenotypic frequencies in moths collected from high‐ and low‐density populations. A laboratory experiment investigated the effects of larval nitrogen availability on adult pigmentation and phenotypic frequencies. High population density and nitrogen limitation reduced pigmentation and size of all moths, but phenotypic frequencies were not affected in either experiment. The effects of diet on both pigmentation and size were stronger for melanic moths than for typical moths. Our results show that adult melanism in M. disstria is physiologically costly, that colour expression is plastic despite its genetic component, and that the melanic phenotype may be disadvantaged under poor conditions but favoured under good conditions. We suggest that temporal variation in selection and trait plasticity help maintain polymorphism stability.

The adaptive function of melanin-based plumage coloration to trace metals

Trace metals produced by anthropogenic activities are of major importance in urban areas and might constitute a new evolutionary force selecting for the ability to cope with their deleterious effects. Interestingly, melanin pigments are known to bind metal ions, thereby potentially sequestering them in inert body parts such as coat and feathers, and facilitating body detoxification. Thus, a more melanic plumage or coat coloration could bring a selective advantage for animals living in polluted areas. We tested this hypothesis by investigating the link between melanin-based coloration and zinc and lead concentrations in feathers of urban feral pigeons, both at capture time and after one year of captivity in standardized conditions. Results show that differently coloured pigeons had similar metal concentrations at capture time. Metal concentrations strongly decreased after one year in standardized conditions, and more melanic pigeons had higher concentrations of zinc (but not lead) in their feathers. This suggests that more melanic pigeons have a higher ability to store some metals in their feathers compared with their paler counterparts, which could explain their higher success in urbanized areas. Overall, this work suggests that trace metal pollution may exert new selective forces favouring more melanic phenotypes in polluted environments.

Genetic basis of stage-specific melanism: a putative role for a cysteine sulfinic acid decarboxylase in insect pigmentation

Melanism, the overall darkening of the body, is a widespread form of animal adaptation to particular environments, and includes bookcase examples of evolution by natural selection, such as industrial melanism in the peppered moth. The major components of the melanin biosynthesis pathway have been characterized in model insects, but little is known about the genetic basis of life-stage specific melanism such as cases described in some lepidopteran species. Here, we investigate two melanic mutations of Bicyclus anynana butterflies, called Chocolate and melanine, that exclusively affect pigmentation of the larval and adult stages, respectively. Our analysis of Mendelian segregation patterns reveals that the larval and adult melanic phenotypes are due to alleles at different, independently segregating loci. Our linkage mapping analysis excludes the pigmentation candidate gene black as the melanine locus, and implicates a gene encoding a putative pyridoxal phosphate-dependant cysteine sulfinic acid decarboxylase as the Chocolate locus. We show variation in coding sequence and in expression levels for this candidate larval melanism locus. This is the first study that suggests a biological function for this gene in insects. Our findings open up exciting opportunities to study the role of this locus in the evolution of adaptive variation in pigmentation, and the uncoupling of regulation of pigment biosynthesis across developmental stages with different ecologies and pressures on body coloration.

Direct and correlated responses to laboratory selection for body melanisation inD. melanogaster: support for melanism- desiccation resistance hypothesis.

For Drosophila melanogaster, cuticular melanisation is a quantitative trait, varying from no melanin to completely dark. Variation in melanisation has been linked with stress resistance, especially desiccation, in D. melanogaster and other species. As melanism has a genetic component, we selected melanic and non-melanic phenotypes of D. melanogaster in order to confirm the association of desiccation resistance and rate of water loss with cuticular melanisation previously reported for this species. A bidirectional selection experiment for dark (D1-D4) and light (L1-L4) body colour in D. melanogaster was conducted for 60 generations. We observed a 1.6-fold increase in abdominal melanisation in selected dark strains and a 14-fold decrease in selected light strains compared with control populations. Desiccation resistance increased significantly in the dark-selected morphs as compared with controls. The observed increase in desiccation resistance appeared as a consequence of a decrease in cuticular permeability. Our results show that traits related to water balance were significantly correlated with abdominal melanisation and were simultaneously selected bidirectionally along with melanisation.

The molecular basis of the plumage colour polymorphism in the Tahiti reed-warbler Acrocephalus caffer

Th e endemic Tahiti reed-warbler Acrocephalus caff er occurs in two distinct morphs, a typical or ‘ yellow ’ morph and a melanic or ‘ dark ’ morph, which are found together in the valleys of the eastern and central parts of the island of Tahiti (Society Islands, French Polynesia). We investigated the molecular basis of the plumage colour polymorphism in this species using sequences of the melanocortin-1 receptor (MC1R), a gene often found associated to melanism in birds. We found that the MC1R genotype was perfectly associated with plumage colour in the Tahiti reed-warbler, with the same nonsynonymous substitution that showed a correlation with phenotype in the Caribbean bananaquit Coereba fl aveola . An heterozygous reed-warbler at this site presented a melanic phenotype, suggesting that the melanic allele is dominant. All other Polynesian reed-warbler species, which do not have a melanic morph, shared the ‘ yellow ’ nucleotide at this position. Th ese results suggested that the same mutation point was linked to a melanic polymorphism in two unrelated passerine birds. Polymorphism in colour is a widespread phenomenon in birds and in other vertebrates: it is generally defi ned by the presence within a species of individuals of the same sex and age that have diff erent genetically determined coloration (Buckley 1987). Th e term ‘ morph ’ was fi rst proposed by Huxley (1955) and is generally used for the discrete categories of plumage. In their review of avian polymorphism, Galeotti et al. (2003) showed that changes in the distribution of the melanic pigments, with the defi nition of a ‘ dark ’ or melanic morph, is the most frequent polymorphism

Local adaptation and matching habitat choice in female barn owls with respect to melanic coloration

Local adaptation is a major mechanism underlying the maintenance of phenotypic variation in spatially heterogeneous environments. In the barn owl (Tyto alba), dark and pale reddish-pheomelanic individuals are adapted to conditions prevailing in northern and southern Europe, respectively. Using a long-term dataset from Central Europe, we report results consistent with the hypothesis that the different pheomelanic phenotypes are adapted to specific local conditions in females, but not in males. Compared to whitish females, reddish females bred in sites surrounded by more arable fields and less forests. Colour-dependent habitat choice was apparently beneficial. First, whitish females produced more fledglings when breeding in wooded areas, whereas reddish females when breeding in sites with more arable fields. Second, cross-fostering experiments showed that female nestlings grew wings more rapidly when both their foster and biological mothers were of similar colour. The latter result suggests that mothers should particularly produce daughters in environments that best match their own coloration. Accordingly, whiter females produced fewer daughters in territories with more arable fields. In conclusion, females displaying alternative melanic phenotypes bred in habitats providing them with the highest fitness benefits. Although small in magnitude, matching habitat selection and local adaptation may help maintain variation in pheomelanin coloration in the barn owl.

Effects of polymorphic melanism and larval diet on life history traits of Malacosoma disstria moths

In this study we investigated the presence and possible genetic basis of polymorphic melanism in the forest tent caterpillar (Malacosoma disstria) moth. Adult moths were classified into pattern-based phenotypes and wing darkness was measured to quantify the degree of melanization. We found that two distinct phenotypes, melanic and simple, are present in these moths. Although the full melanic phenotype is sex-limited to males, it is partially expressed in females. We also provide support for the theory that the melanic allele is autosomal and dominant. The effects of larval diet quality on the survival, development and wing melanization of each phenotype were studied by rearing larvae on the foliage of either a primary or secondary host. Diet quality did not differentially affect the two phenotypes; however, melanic males were found to be smaller than simple males regardless of larval diet. Such inherent developmental differences between the two phenotypes could have important consequences for the frequencies of the two morphs.

Disruption of an N-acetyltransferase gene in the silkworm reveals a novel role in pigmentation

The pigmentation of insects has served as an excellent model for the study of morphological trait evolution and developmental biology. The melanism (mln) mutant of the silkworm Bombyx mori is notable for its strong black coloration, phenotypic differences between larval and adult stages, and its widespread use in strain selection. Here, we report the genetic and molecular bases for the formation of the mln morphological trait. Fine mapping revealed that an arylalkylamine N-acetyltransferase (AANAT) gene co-segregates with the black coloration patterns. Coding sequence variations and expression profiles of AANAT are also associated with the melanic phenotypes. A 126 bp deletion in the mln genome causes two alternatively spliced transcripts with premature terminations. An enzymatic assay demonstrated the absolute loss of AANAT activity in the mutant proteins. We also performed RNA interference of AANAT in wild-type pupae and observed a significant proportion of adults with ectopic black coloration. These findings indicate that functional deletion of this AANAT gene accounts for the mln mutation in silkworm. AANAT is also involved in a parallel melanin synthesis pathway in which ebony plays a role, whereas no pigmentation defect has been reported in the Drosophila model or in other insects to date. To the best of our knowledge, the mln mutation is the first characterized mutant phenotype of insects with AANAT, and this result contributes to our understanding of dopamine metabolism and melanin pattern polymorphisms.

Disruption of an N-acetyltransferase gene in the silkworm reveals a novel role in pigmentation

The pigmentation of insects has served as an excellent model for the study of morphological trait evolution and developmental biology. The melanism (mln) mutant of the silkworm Bombyx mori is notable for its strong black coloration, phenotypic differences between larval and adult stages, and its widespread use in strain selection. Here, we report the genetic and molecular bases for the formation of the mln morphological trait. Fine mapping revealed that an arylalkylamine N-acetyltransferase (AANAT) gene co-segregates with the black coloration patterns. Coding sequence variations and expression profiles of AANAT are also associated with the melanic phenotypes. A 126 bp deletion in the mln genome causes two alternatively spliced transcripts with premature terminations. An enzymatic assay demonstrated the absolute loss of AANAT activity in the mutant proteins. We also performed RNA interference of AANAT in wild-type pupae and observed a significant proportion of adults with ectopic black coloration. These findings indicate that functional deletion of this AANAT gene accounts for the mln mutation in silkworm. AANAT is also involved in a parallel melanin synthesis pathway in which ebony plays a role, whereas no pigmentation defect has been reported in the Drosophila model or in other insects to date. To the best of our knowledge, the mln mutation is the first characterized mutant phenotype of insects with AANAT, and this result contributes to our understanding of dopamine metabolism and melanin pattern polymorphisms.

The aggregation behavior of Harmonia axyridis in its native range in Northeast China

Harmonia axyridis has become notorious as an urban pest in many of the regions where it has been introduced, despite its numerous contributions to the biological control of insects injurious to agriculture and horticulture. Aggregative behavior prior to overwintering leads to invasions of human habitations as beetles seek refuge from freezing temperatures. Here we describe the aggregation behavior of native H. axyridis populations of northeast China that breed in agricultural fields (mostly corn and rice) and shrub/forest habitats and then migrate through rural villages in autumn. More than 140,000 beetles were collected during direct observations in 16 villages in five townships in Jilin Province. Beetles aggregated on dwellings shortly after agricultural harvests, favoring white walls with southern exposures, the largest aggregations occurring in villages in mountainous townships at higher elevations. The sex ratio was consistently female-biased and succinic phenotypes were more than twice as abundant as melanic phenotypes in all locations. A special trap compared the relative attractiveness of different surface colors (white > yellow = black > green > red = natural wood) and potential baits (corn pollen = honey > caramel = cocoa > milk = blank control). All aggregations disappeared abruptly just prior to the first frost, whereupon beetles were discovered sheltering in montane caves with southern aspects at higher elevations. Villagers reported substantial expenditures on pesticides in efforts to eliminate beetles from their homes every autumn. Invasion of human habitations appears to be an intrinsic tendency of native H. axyridis populations in China, which is the result of behavioral adaptations for cold-avoidance.

The Genetic, Morphological, and Physiological Characterization of a Dark Larval Cuticle Mutation in the Butterfly, Bicyclus anynana

Studies on insect melanism have greatly contributed to our understanding of natural selection and the ultimate factors influencing the evolution of darkly pigmented phenotypes. Research on several species of melanic lepidopteran larvae have found that low levels of circulating juvenile hormone (JH) titers are associated with a melanic phenotype, suggesting that genetic changes in the JH biosynthetic pathway give rise to increased deposition of melanin granules in the cuticle in this group. But does melanism arise through different molecular mechanisms in different species? The present study reports on a Bicyclus anynana (Lepidoptera: Nymphalidae) dark larvae single locus mutation, in which larvae exhibit a darker cuticle relative to wild type. Unlike other lepidopteran melanic larvae mutations, this one is autosomal recessive and does not appear to involve a deficiency in JH titers. Unlike JH deficiency mutants, dark larvae mutants display similar growth rates and sexual behaviors as wild type, and topical application of a JH analogue failed to rescue the wild type cuticular coloration. Finally, transmission electron microscopy showed that sclerotization or deposition of diffuse melanin, rather than deposition of melanin granules, produces the dark coloration found in the cuticle of this species. We conclude that different molecular mechanisms underlie larval melanism in different species of Lepidoptera.

Melanism in Peromyscus Is Caused by Independent Mutations in Agouti

Identifying the molecular basis of phenotypes that have evolved independently can provide insight into the ways genetic and developmental constraints influence the maintenance of phenotypic diversity. Melanic (darkly pigmented) phenotypes in mammals provide a potent system in which to study the genetic basis of naturally occurring mutant phenotypes because melanism occurs in many mammals, and the mammalian pigmentation pathway is well understood. Spontaneous alleles of a few key pigmentation loci are known to cause melanism in domestic or laboratory populations of mammals, but in natural populations, mutations at one gene, the melanocortin-1 receptor (Mc1r), have been implicated in the vast majority of cases, possibly due to its minimal pleiotropic effects. To investigate whether mutations in this or other genes cause melanism in the wild, we investigated the genetic basis of melanism in the rodent genus Peromyscus, in which melanic mice have been reported in several populations. We focused on two genes known to cause melanism in other taxa, Mc1r and its antagonist, the agouti signaling protein (Agouti). While variation in the Mc1r coding region does not correlate with melanism in any population, in a New Hampshire population, we find that a 125-kb deletion, which includes the upstream regulatory region and exons 1 and 2 of Agouti, results in a loss of Agouti expression and is perfectly associated with melanic color. In a second population from Alaska, we find that a premature stop codon in exon 3 of Agouti is associated with a similar melanic phenotype. These results show that melanism has evolved independently in these populations through mutations in the same gene, and suggest that melanism produced by mutations in genes other than Mc1r may be more common than previously thought.