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opencc-zeroDec 2010View details →

Data from: Testicular melanization has evolved in birds with high mtDNA mutation rates

Melanin is mainly found in the integument of animals, but it also appears in several extracutaneous tissues. The presence of melanin in testes has been anecdotally reported in all vertebrate groups, but the causes and functions of this melanin remain unknown. Similar to other extracutaneous melanins, testicular melanin may protect male germ cells from oxidative stress. Given the high respiratory activity of spermatozoa, oxidative stress generated by mitochondrial dysfunction as a consequence of mtDNA mutations directly affects sperm viability. Thus, natural selection may favour testicular melanization in males of species with high historical mutation rates in the mitochondrial genome. Here, we tested this hypothesis using information on occurrence of testicular melanization and mutation accumulation as reflected by cytochrome b mtDNA base pair substitution rates in a large set of 134 species of birds, controlling for the confounding effects of body mass, reproductive activity and phylogeny. We found that testicular melanization has evolved in species with high rates of accumulated mitochondrial mutations and propose that this is an adaptive response related to the protective capacity of melanin against oxidative stress. In support of this hypothesis, testicular melanization was more frequently observed during the breeding season of birds (i.e. when spermatogenesis is likely to occur) than during reproductive inactivity. In contrast to other extracutaneous melanins whose abundance seems to reflect skin and coat colour, we did not find a correlation between the proportion of plumage coloured by melanins and occurrence of testicular melanization. Whereas future experimental studies should test these hypotheses, our study highlights for the first time that melanization patterns in animals may evolve as a response to historical mutation rates.

opencc-zeroDec 2016View details →

Data from: Do trace metals influence visual signals? Effects of trace metals on iridescent and melanic feather colouration in the feral pigeon

Trace metals are chemical pollutants of prime concern nowadays given their implication in several human diseases and their noxious effects on wildlife. Previous studies demonstrated their negative (e.g. lead, cadmium) or positive (e.g. zinc) effects on body condition, immunity and reproductive success in birds. Because of their effects on bird condition, trace metals are likely to influence the production of condition-dependent plumage colours, that may be used in mate choice. In the feral pigeon Columba livia, we investigated iridescent colouration in response to lead and zinc experimental (i.e. metal supplementation in standardized conditions) and natural exposure (i.e. metal concentrations in feathers of wild urban pigeons), and melanic feather colouration in response to experimental lead and zinc exposure. Both studies (i.e. experimental and correlative) consistently showed that lead exposure decreased iridescent neck feather brightness independently of colour morph. Moreover, lead, when provided alone, decreased melanic feather reflectance in the middle wavelengths while zinc supplementation increased melanic feather reflectance in the violet-wavelength. In conclusion, our study suggests that the colouration of iridescent and melanic feathers depends on the exposure to pollutants. Whether trace metal exposure affected the ability of birds to produce melanin pigments, to grow the microstructural feather elements required for maximum colour display, or to cope with bacteria that degrade feather microstuctures remains unclear. Future studies should investigate whether these metal-induced modifications of plumage colouration affect behaviours involved in sexual selection.

Figure 4 from: Schmitt M, Uhl G (2017) Oulema septentrionis and O. erichsonii are neither conspecific nor melanic variants of O. melanopus as assessed by micro CT analysis of their lectotypes (Insecta, Coleoptera, Chrysomelidae, Criocerinae). In: Chaboo CS, Schmitt M (Eds) Research on Chrysomelidae 7. ZooKeys 720: 121-130. https://doi.org/10.3897/zookeys.720.19760

Figure 4 - Oulema erichsonii , lectotype; a median lobe with flagellum lateral b apex of median lobe with flagellum dorsal c flagellum (not to scale). 3D reconstructed microCT-scans.

Figure 2 from: Schmitt M, Uhl G (2017) Oulema septentrionis and O. erichsonii are neither conspecific nor melanic variants of O. melanopus as assessed by micro CT analysis of their lectotypes (Insecta, Coleoptera, Chrysomelidae, Criocerinae). In: Chaboo CS, Schmitt M (Eds) Research on Chrysomelidae 7. ZooKeys 720: 121-130. https://doi.org/10.3897/zookeys.720.19760

Figure 2 - Oulema septentrionis , lectotype; a: median lobe with flagellum lateral b apex of median lobe with flagellum dorsal; c: flagellum (not to scale). 3D reconstructed microCT-scans.

Figure 3 from: Schmitt M, Uhl G (2017) Oulema septentrionis and O. erichsonii are neither conspecific nor melanic variants of O. melanopus as assessed by micro CT analysis of their lectotypes (Insecta, Coleoptera, Chrysomelidae, Criocerinae). In: Chaboo CS, Schmitt M (Eds) Research on Chrysomelidae 7. ZooKeys 720: 121-130. https://doi.org/10.3897/zookeys.720.19760

Figure 3 - Oulema erichsonii (Suffrian, 1841), lectotype. a dorsal b lateral from left c labels. Scale bars: 1 mm.

Figure 1 from: Schmitt M, Uhl G (2017) Oulema septentrionis and O. erichsonii are neither conspecific nor melanic variants of O. melanopus as assessed by micro CT analysis of their lectotypes (Insecta, Coleoptera, Chrysomelidae, Criocerinae). In: Chaboo CS, Schmitt M (Eds) Research on Chrysomelidae 7. ZooKeys 720: 121-130. https://doi.org/10.3897/zookeys.720.19760

Figure 1 - Oulema septentrionis (Weise, 1880), lectotype. a dorsal b lateral from left c labels. Scale bars: 1 mm.

opencc-by-4.0Mar 2017View details →

Figure 13 in The dark side of birds: melanism-facts and fiction

Figure 13. Gould's Chestnut-coloured Partridge Ortyx castanea, which was a melanistic Northern Bobwhite Colinus virginianus; the normal black head markings have overrun their boundaries, whilst the rest of the plumage is darker as well, the latter mainly due to increased phaeomelanin hence 'Chestnut-coloured' (Hein van Grouw, © Natural History Museum, London)

opencc-zeroDec 2017View details →

Data from: Metabolic physiology explains macroevolutionary trends in the melanic colour system across amniotes

Metabolism links organisms to their environment through its effects on thermoregulation, feeding behaviour, and energetics. Genes involved in metabolic processes have known pleiotropic effects on some melanic colour traits. Understanding links between physiology and melanic colour is critical for understanding the role of, and potential constraints on, colour production. Despite considerable variation in metabolic rates and presumed ancestral melanic colouration in vertebrates, few studies have looked at a potential relationship between these two systems in a comparative framework. Here, we test the hypothesis that changes in melanosome shape in integumentary structures track metabolic rate variation across amniotes. Using multivariate comparative analyses and incorporating both extant and fossil taxa, we find significantly faster rates of melanosome shape evolution in taxa with high metabolic rates, as well as both colour- and clade-specific differences in the relationship between metabolic rate and melanosome shape. Phylogenetic tests recover an expansion in melanosome morphospace in maniraptoran dinosaurs, as well as rate shifts within birds (in songbirds) and mammals. These findings indicate another core phenotype influenced by metabolic changes in vertebrates. They also provide a framework for testing clade-specific gene expression patterns in the melanocortin system, and may improve colour reconstructions in extinct taxa.

opencc-zeroOct 2019View details →

Melanism protects alpine zooplankton from DNA damage caused by ultraviolet radiation

Melanism is widely observed among animals, and is adaptive in various contexts for its thermoregulatory, camouflaging, mate-attraction, or photoprotective properties. Many organisms exposed to ultraviolet radiation show increased fitness resulting from melanin pigmentation; this has been assumed to result in part from reduced UV-induced damage to DNA. However, to effectively test the hypothesis that melanin pigmentation reduces UV-induced DNA damage requires quantification of UV-specific DNA damage lesions following UV exposure under controlled conditions using individuals that vary in pigmentation intensity. We accomplished this using alpine genotypes of the freshwater microcrustacean Daphnia melanica for which we quantified cyclobutane pyrimide dimers in DNA, a damage structure that can only be generated by UV exposure. For genotypes with carapace melanin pigmentation, we found that individuals with greater melanin content sustained lower levels of UV-induced DNA damage. Individuals with more melanin were also more likely to survive exposure to ecologically relevant levels of UV-B radiation. Parallel experiments with conspecific genotypes that lack carapace melanin pigmentation provide additional support for our conclusion that melanism protects individuals from UV-induced DNA damage. Finally, within-genotype comparisons with asexually-produced clonal siblings demonstrate that melanin content influences DNA damage even among genetically identical individuals raised in the same environment.

opencc-zeroDec 2012View details →

Data from: The costs of being dark: the genetic basis of melanism and its association with fitness-related traits in the sand cricket

Melanism is an important component of insect cuticle and serves numerous functions that enhance fitness. Despite its importance, there is little information on its genetic basis or its phenotypic and genetic correlation with fitness-related traits. Here, we examine the heritability of melanism in the wing dimorphic sand cricket and determine its phenotypic and genetic correlation with wing morphology, gonad mass and size of the dorso-longitudinal muscles (the principle flight muscles). Previously demonstrated trade-offs among these traits are significant factors in the evolution of life history variation. Using path analysis, we show that melanization is causally related to gonad mass, but not flight muscle mass. Averaged over the sexes, the heritability of melanism was 0.61, the genetic correlation with gonad mass was −0.36 and with wing morph was 0.51. The path model correctly predicted the ranking of melanization score in lines selected for increased ovary mass, increased flight muscle mass, an index that increased both traits and an unselected control. Our results support the general hypothesis that melanization is costly for insects and negatively impacts investment in early reproduction.

opencc-zeroAug 2021View details →

Secondary sexual trait melanization in black scavenger flies: nutritional plasticity and its evolution

The black scavenger fly Sepsis thoracica exhibits polyphenic development resulting in alternate small black and large amber male morphs. Although the behavior, ecology, and physiology of both morphs are being scrutinized, the evolutionary origins of the nutritional polyphenism remain poorly understood. I here use a comparative approach to study variation in the degree of melanization of the forefemur —a secondary sexual trait. Melanization showed nutritional plasticity in all species and character mapping suggests polyphenic development to represent the ancestral character state that was lost repeatedly. That is, interspecific variation among the studied species is mainly caused by the loss and not the gain of polyphenic development. Coevolution between male melanization and mating system differences further implicates sexual selection in the evolution of male melanization. These findings highlight the usefulness of comparative and natural history data in shedding new light on the evolution of phenotypic variation.