Plumage Variation Research Articles

Dräktvariation hos hannar i skandinaviska populationer av svarthakad buskskvätta Saxicola rubicola

In western Europe, the European Stonechat Saxicola rubicola, occurs in two subspecies; rubicola, with a large distribution in Europe, and hibernans, mainly distributed on the British Isles. A small population of presumed hibernans birds breed in Norway. However, difficulties in distinguishing hibernans from rubicola at an individual level has led to speculation regarding the origin of the Norwegian birds. There are no clear genetic differences between the subspecies and their plumage appearance can be considered to overlap within parts of the range. To investigate this, I studied the plumage variation among males during the breeding season in the Scandinavian populations of European Stonechats in Sweden, Norway and Denmark. The study is based on photos of 404 males during the period March–May. The presence or absence of six typical hibernans characteristics were registered for each individual. The results show that males with both hibernans and rubicola characteristics occur during the spring in the Scandinavian populations. There was a clear over-representation of males with hibernans characteristics in Norway as compared to Sweden, and to a lower degree also to Denmark. If the expansion of rubicola progresses in Scandinavia, one could expect a larger proportion of rubicola-like males in the Norwegian population.

High-throughput sequencing is revealing genetic associations with avian plumage color

Abstract Avian evolution has generated an impressive array of patterns and colors in the ~10,000 bird species that exist on Earth. Recently, a number of exciting studies have utilized whole-genome sequencing to reveal new details on the genetics of avian plumage color. These findings provide compelling evidence for genes that underlie plumage variation across a wide variety of bird species (e.g., juncos, warblers, seedeaters, and estrildid finches). While much is known about large, body-wide color changes, these species exhibit discrete color differences across small plumage patches. Many genetic differences appear to be located in regulatory regions of genes rather than in protein-coding regions, suggesting gene expression is playing a large role in the control of these color patches. Taken together, these studies have the potential to broadly facilitate further research of sexual selection and evolution in these charismatic taxa.

FIRST RECORD OF LEUCISM IN Hylocharis chrysura (SHAW, 1812) (AVES: TROQUILIDAE) IN SOUTHERN BRAZIL

Leucism is the most frequent mutation in birds, leading to a partial or total depigmentation of covering structures. Here we report the first record of partial leucism in the Gilded Hummingbird Hylocharis chrysura (Apodiformes: Trochilidae) in the south of Brazil. This record contributes to important information about plumage variability in this species and the behavior associated with this mutation.

Shallow genetic divergence and distinct phenotypic differences between two Andean hummingbirds: Speciation with gene flow?

AbstractEcological speciation can proceed despite genetic interchange when selection counteracts the homogenizing effects of migration. We tested predictions of this divergence-with-gene-flow model in Coeligena helianthea and C. bonapartei, 2 parapatric Andean hummingbirds with marked plumage divergence. We sequenced putatively neutral markers (mitochondrial DNA [mtDNA] and nuclear ultraconserved elements [UCEs]) to examine genetic structure and gene flow, and a candidate gene (MC1R) to assess its role underlying divergence in coloration. We also tested the prediction of Gloger’s rule that darker forms occur in more humid environments, and examined morphological variation to assess adaptive mechanisms potentially promoting divergence. Genetic differentiation between species was low in both ND2 and UCEs. Coalescent estimates of migration were consistent with divergence with gene flow, but we cannot reject incomplete lineage sorting reflecting recent speciation as an explanation for patterns of genetic variation. MC1R variation was unrelated to phenotypic differences. Species did not differ in macroclimatic niches but were distinct in morphology. Although we reject adaptation to variation in macroclimatic conditions as a cause of divergence, speciation may have occurred in the face of gene flow driven by other ecological pressures or by sexual selection. Marked phenotypic divergence with no neutral genetic differentiation is remarkable for Neotropical birds, and makes C. helianthea and C. bonapartei an appropriate system in which to search for the genetic basis of species differences employing genomics.

Molecular and morphological differentiation among Torrent Duck (Merganetta armata) populations in the Andes

AbstractBirds living in riverine environments may show weak population structure because high dispersal abilities required to track habitat dynamics can result in gene flow over broad spatial scales. Alternatively, the configuration of river networks may result in restricted dispersal within river courses or basins, leading to high genetic structure. Although several bird species are riverine specialists in the Andes, no study has extensively evaluated the population genetic structure of any of them. We examined evidence from genetic and morphological data to address questions about the biogeography and taxonomy of the Torrent Duck (Merganetta armata), a riverine specialist bird with a broad distribution in Andean riverine habitats which certainly comprises different subspecies and may comprise more than one species. We found deep subdivisions of Torrent Duck populations from the northern, central and southern portions of the Andes. These lineages, which partly coincide with subspecies described based on plumage variation and body size, do not share mtDNA haplotypes, have private nuclear alleles and exhibit marked differences in morphometric traits. Some geographic barriers presumably restricting gene flow between groups partially coincide with those associated with major genetic breaks in forest species with similar distributions along the Andes, suggesting that bird assemblages including species occupying different habitats were likely affected by common biogeographical events. The three groups of Torrent Ducks may be considered different species under some species definitions and are distinct evolutionary lineages to be conserved and managed separately.

Speciation, gene flow, and seasonal migration in Catharus thrushes (Aves:Turdidae)

New World thrushes in the genus Catharus are small, insectivorous or omnivorous birds that have been used to explore several important questions in avian evolution, including the evolution of seasonal migration and plumage variation. Within Catharus, members of a clade of obligate long-distance migrants (C. fuscescens, C. minimus, and C. bicknelli) have also been used in the development of heteropatric speciation theory, a divergence process in which migratory lineages (which might occur in allopatry or sympatry during portions of their annual cycle) diverge despite low levels of gene flow. However, research on Catharus relationships has thus far been restricted to the use of small genetic datasets, which provide limited resolution of both phylogenetic and demographic histories. We used a large, multi-locus dataset from loci containing ultraconserved elements (UCEs) to study the demographic histories of the migratory C. fuscescens-minimus-bicknelli clade and to resolve the phylogeny of the migratory species of Catharus. Our dataset included more than 2000 loci and over 1700 variable genotyped sites, and analyses supported our prediction of divergence with gene flow in the fully migratory clade, with significant gene flow among all three species. Our phylogeny of the genus differs from past work in its placement of C. ustulatus, and further analyses suggest historic gene flow throughout the genus, producing genetically reticulate (or network) phylogenies. This raises questions about trait origins and suggests that seasonal migration and the resulting migratory condition of heteropatry is likely to promote hybridization not only during pairwise divergence and speciation, but also among non-sisters.

Variation in plumage reflects avian habitat associations not revealed by abundance

For bird species in which plumage characteristics are associated with social dominance, the analysis of status badges may reveal habitat preferences. We analyzed the extent of male Chestnut-sided Warbler (Setophaga pensylvanica) chestnut-colored plumage in relation to age and body size to determine whether badge size was a potential indicator of resource-holding potential. We then modeled badge size in relation to habitat variables including habitat patch size, patch shape, and microhabitat characteristics in 101 different silvicultural openings in western Massachusetts during 2014 and 2015. Overall, older and larger Chestnut-sided Warblers had larger badges. Badge size showed a strong positive relationship with patch area. Notably, our findings reveal a greater sensitivity to area than was apparent from a different study's analysis of abundance at the same study site during the same time period. Badge size was positively related to patch shape complexity—an environmental variable not previously identified as important for this species by other studies. Our findings indicate that remote assessments of avian status badges may serve as reliable indicators of habitat preferences and suggest that this approach has the potential to reveal responses to gradients in habitat not reflected by abundance.

Population divergence and gene flow in two East Asian shorebirds on the verge of speciation

Genetic isolation of populations over evolutionary time leads to the formation of independent species. We examined a pair of shorebirds – the Kentish Plover Charadrius alexandrinus and the enigmatic White-faced Plover C. dealbatus – which display strong plumage differentiation, yet show minimal genetic divergence based on previous mitochondrial and microsatellite work. Two scenarios may lead to this situation: (1) they represent clinal or poorly diverged populations with limited genomic differentiation despite substantial plumage variation, or (2) they are diverging taxa at the cusp of speciation, with ongoing limited gene flow obliterating signals of differentiation in traditional genetic markers. We compared the genotypes of 98 plovers (59 Kentish Plovers, 35 White-faced Plovers and 4 genomic hybrids) sampled in eastern Asia and Europe using ddRADSeq to harvest over 8000 genome-wide SNPs. In contrast to previous studies, our analyses revealed two well defined genomic clusters, with limited hybridization and a narrow contact zone. We also uncovered significant differences in bill length and further sex-specific differences in size, which may signal differences in mate choice between Kentish and White-faced Plovers. Our results support the hypothesis that this shorebird duo is on the verge of speciation.

Reed warblers in the Marquesas Islands: song divergence and plumage convergence of two distinct lineages

ABSTRACTThe Pacific Ocean is the site of the most important diversification of insular reed warblers (Acrocephalus). In the Marquesas Islands (Eastern Polynesia), reed warblers belong to two distinct lineages that have reached the archipelago independently. We used mitochondrial sequences and microsatellite markers and found evidence of gene flow between the two lineages. One island in particular, Nuku Hiva, seems to act as the main contact zone between the two taxa. We then used reflectance spectrometry to evaluate the variation of carotenoid colouration among all populations. Marquesan reed warblers exhibit convergent evolution in carotenoid-based plumage colouration, but variation among islands was important. Having two different phylogenetic origins, the two lineages acquired their yellow colour independently and there is stochastic variation in plumage among islands. Finally, we analysed the songs of reed warblers from the main islands. Multifactorial analysis showed that vocalisations of Marquesan reed warblers differ slightly between species, significant differences between islands leading to different dialects. Vocal characteristics may act as the main pre-zygotic barriers when birds from different lineages come into contact. This study provides another example of convergence in plumage evolution in insular bird species. Furthermore, it highlights the importance of integrative analyses, using both genetic and phenotypical characters, for the study of the evolutionary history of the Pacific Ocean avifauna.

Sexual selection predicts the rate and direction of colour divergence in a large avian radiation

Sexual selection is proposed to be a powerful driver of phenotypic evolution in animal systems. At macroevolutionary scales, sexual selection can theoretically drive both the rate and direction of phenotypic evolution, but this hypothesis remains contentious. Here, we find that differences in the rate and direction of plumage colour evolution are predicted by a proxy for sexual selection intensity (plumage dichromatism) in a large radiation of suboscine passerine birds (Tyrannida). We show that rates of plumage evolution are correlated between the sexes, but that sexual selection has a strong positive effect on male, but not female, interspecific divergence rates. Furthermore, we demonstrate that rapid male plumage divergence is biased towards carotenoid-based (red/yellow) colours widely assumed to represent honest sexual signals. Our results highlight the central role of sexual selection in driving avian colour divergence, and reveal the existence of convergent evolutionary responses of animal signalling traits under sexual selection.

Epistatic mutations under divergent selection govern phenotypic variation in the crow hybrid zone.

The evolution of genetic barriers opposing inter-specific gene flow is key to the origin of new species. Drawing from information of over 400 admixed genomes sourced from replicate transects across the European hybrid zone between all-black carrion crows and grey-coated hooded crows, we decipher the interplay between phenotypic divergence and selection at the molecular level. Over 68% of plumage variation was explained by epistasis between the gene NDP and a ~2.8 Mb region on chromosome 18 with suppressed recombination. Both pigmentation loci showed evidence for divergent selection resisting introgression. This study reveals how few, large-effect loci can govern prezygotic isolation and shield phenotypic divergence from gene flow.

Plumage coloration follows Gloger's rule in a ring species

AbstractAimAnimal coloration is expected to differ between populations in different habitats according to Gloger's rule, with darker animals found in more humid, vegetated or warmer environments. Yet despite considerable support across the globe, the mechanisms behind this biogeographical rule are currently still unclear. Exploiting a ring species with plumage coloration from crimson to pale yellow, we test Gloger's rule and the mechanisms behind phenotypic divergence.LocationSouth‐eastern Australia.Major taxa studiedCrimson rosellas (Platycercus elegans).MethodsWe combined three modelling approaches (spatial regression; random decision forest species distribution and conditional inference tree) to test the association between 10 environmental variables (based on long‐term climate data and remotely sensed reflectance of the land) and plumage coloration across the distribution of P. elegans. We also took in‐situ measurements of background coloration of dominant vegetation to examine the relationship between (a) background coloration measured locally and remotely, (b) P. elegans coloration and (c) known differences in visual sensitivity of the subspecies using species‐specific visual models.ResultsOn both a continental and a local scale, the distribution of yellow‐red plumage coloration was strongly predicted by average rainfall, summer temperature and the Earth's reflectance between 620–670 nm. Remotely sensed radiance measures correlated strongly and positively with reflectance of the leaves of the dominant tree species at sites across the P. elegans distribution. Visual modelling indicated that differences in background colour could affect signalling efficacy in dim‐light conditions.Main conclusionsOur study shows that the highly variable plumage coloration conforms to Gloger's rule, and indicates that background coloration of the vegetation and thermoregulation are likely to be important mechanisms. Our results also show that Gloger's rule can explain variation in pigmentary systems other than melanin, and highlight that selection from environmental variation could be an important force behind the geographic diversity found in ring species.

Notes on the distribution and plumage variation of Varied and Mangrove Honeyeaters

Considered conspecific in some recent literature, the Varied Gavicalis versicolor and Mangrove Honeyeaters G. fasciogularis have long been thought to intergrade in and around the city of Townsville, Queensland. Here we update knowledge concerning the distribution of these two species and their variation in plumage colour and pattern in the Townsville region. A lack of records between Lucinda and Townsville seems to reflect a real gap. Further work is required to clarify whether elsewhere Varied Honeyeaters may occasionally exclude Mangrove Honeyeaters in a given locality. If so, this may explain the seemingly inconsistent reports of one or the other at particular localities. Mangrove Honeyeaters immediately south of Townsville may be slightly yellower ventrally than populations further south. However, we argue that this is consistent with our genetic findings reported elsewhere and is not, we conclude, indicative of an undescribed subspecies.

Experimental trait mismatches uncover specificity of evolutionary links between multiple signaling traits and their interactions in hummingbirds.

Many animal signals co-occur, and these signals may coevolve due to their interactive properties. Previous work has demonstrated ecological drivers of evolutionary relationships between signals and the environment, which leads to questions about why specific signal pairs evolved among species that possess multiple signals. We asked whether the coloration of different species was optimized for presentation with its natural behavioral display. We investigated this in "bee" hummingbirds, where males exhibit angle-dependent structurally-colored plumage and a stereotyped courtship (shuttle) display, by experimentally creating mismatches between the behavior and plumage of five species and quantifying how these mismatches influenced male color appearance during a display. Specifically, we photographed the plumage from a given species as we moved its feathers through the position-and-orientation-specific courtship display path of other species and quantified the resulting color appearance during the display in order to compare the mismatched color appearance to each species' natural color appearance. We found that mismatches significantly altered display flashiness (% change in coloration during displays) compared to the natural plumage-behavior pairings, and that such departures in flashiness were predicted by differences in shuttle behaviors alone. These results illustrate a tight evolutionary relationship between shuttle displays and color flashiness in these hummingbirds. Further, we found that interspecific variation in male plumage, behavior, and natural color appearance predicted deviations between natural and mismatched flashy color appearance. Altogether, our work provides a new method for testing signal coevolution and highlights the complex evolutionary relationships between multiple signals and their interactions.

Lack of conspecific visual discrimination between second-year males and females in the Saffron Finch.

Sexually dichromatic birds often show delayed plumage maturation, but second-year (SY) males may or may not be distinguishable from females. In competitive contexts, SY males receive a reduced amount of adult males’ aggression, either by mimicking females or through signaling their sex and inexperience as subordinate males. To the human eye, reproductive dull SY male Saffron Finches are indistinguishable from females, whereas after second-year (ASY) males are golden yellow. Our aim is to establish whether SY males are sexually dichromatic with females to the eye of conspecifics. We describe plumage variation in females, SY and ASY males and, in particular, analyze assortative mating by color by comparing a previously disregarded yellow feather patch shared by the three groups. We measured plumage reflectance of the forehead, breast, belly, and axillaries, and used a two-step avian visual model analysis to estimate the ability of Saffron Finches to distinguish between SY males and females. We find that those groups are indistinguishable to conspecifics by color. Furthermore, we find non-significant evidence of assortative mating directly related to the coloration of comparable feather patches between females and each type of male, though body condition of SY males is associated to that of their mates. Our results are compatible with both the female-mimicry and the status signaling hypotheses of evolution and maintenance of delayed plumage maturation. However, the singing behavior of males reveals their presence within the breeding site; the combined effect of song and dull coloration suggest that SY males are honestly revealing their sex and status to conspecifics.

Significant Asia‐Europe divergence in the middle spotted woodpecker (Aves, Picidae)

AbstractPopulation divergence could be strongly affected by species’ ecology and might not be a direct response to climate‐driven environmental change. We tested this in the middle spotted woodpecker (Dendrocoptes medius), a non‐migratory, low‐dispersal habitat specialist associated with old deciduous forests of the Western Palearctic. We present the first phylogeographic study of this species integrating genetic data (three mitochondrial loci, one autosomal and one Z‐linked intron) with species distribution modelling. Based on this species’ ecology, we predicted that the middle spotted woodpecker could have colonized its current range from multiple Last Glacial Maximum (LGM) refugia and that strongly structured populations could be expected. Indeed, we discovered a strong genetic divergence between Asian and European populations, with a split estimated at around one million of years ago. This was surprising given only slight intraspecific variation in plumage and morphology. Although there was no significant phylogeographic structure within the Asian and European groups, we cannot exclude the possibility of multiple refugia within either group during the LGM. This has to be further investigated with more extensive geographic sampling and larger number of variable independently evolving markers. Future studies should also investigate potential differences in vocalizations and ecology between the two groups. Lineages showing similar level of genetic differentiation including woodpeckers are often treated as species‐level taxa. Comparison of our results with the phylogeographic history of other woodpeckers, suggests that sympatric species with similar life‐histories might have idiosyncratic phylogeographic patterns probably resulting from different ecological requirements or historic stochasticity.

The white neck-ring of the Eurasian Teal Anas crecca: rare mutation or stable morph? A first genetic and heuristic analysis

ABSTRACTCapsule: Individual Eurasian Teal Anas crecca with white neck-rings have been found in Italy and an extensive museum survey found this plumage character occurring with a low frequency, although no genetic difference was observed with respect to the normal phenotype.Aims: To estimate the relative frequency and distribution of this plumage variation and to provide a first genetic assessment to verify if this character could have a taxonomic basis or if it occurs by chance among populations.Methods: An extensive museum survey was conducted to check for the occurrence of white neck-ringed Eurasian Teals in preserved specimens from its distributional range. A genetic analysis was conducted at standard mitochondrial loci (D-loop and COI) of ten white neck-ringed Eurasian Teals from Venice lagoon, Italy. Haplotypes were compared with genetic data from Holarctic populations.Results: The museum survey uncovered additional cases of white neck-ringed Eurasian Teals in Italy and Europe. Moreover, this mutation has also been documented for the first time in the North American Green-winged Teal Anas carolinensis. The white neck-ring was found to be variable in size and occurred in both sexes and in different age classes in about 1.5% of examined individuals. The genetic analysis did not show any significant lineage differentiation between them and the normal phenotype, but the Italian samples showed high values of haplotype diversity indicating a key role of northeast Italy in attracting different migratory populations in winter.Conclusions: While the same variation occurs in many other species of the tribe Anatini, none of these cases clearly suggested the occurrence of hybridization, progressive greying, environmental causation or another kind of locally frequent mutation. It is most likely this plumage trait is a form of leucism or the expression of an ancestral phenotype, possibly occurring in different populations within the species’ range.

Local adaptation versus historical isolation as sources of melanin‐based coloration in the white‐throated thrush Turdus assimilis

Local adaptation seems to be one of the causes of variation in melanin‐based colors in bird plumages, related mainly to the heterogeneity of the environmental conditions along the distribution of a species. Based on comparisons of genetic (mtDNA sequences), ecological (niche models), and quantitative colorimetric data, we explored variation in plumage coloration of the white‐throated thrush Turdus assimilis, a Mesoamerican species whose dorsal color varies from brown (northern and central Mexico) to dark gray (southern Mexico and Central America). Our results suggest the existence of two major patterns of coloration in this bird, which are congruent with the genetic structure, and comparisons of ecological niche models showed that population's niches were more similar than expected by chance, suggesting that color variation in plumage of T. assimilis is not consequence of local adaptation to different environmental conditions. Our results also showed that a greater geographic distance between populations is correlated with greater colorimetric differences, suggesting that color variation in T. assimilis may be consequence of historical isolation.

Dissection by genomic and plumage variation of a geographically complex hybrid zone between two Australian non-sister parrot species, Platycercus adscitus and Platycercus eximius

The study of hybrid zones advances understanding of the speciation process, and approaches incorporating genomic data are increasingly used to draw significant conclusions about the impact of hybridisation. Despite the progress made, the complex interplay of factors that can lead to substantially variable hybridisation outcomes are still not well understood, and many systems and/or groups remain comparatively poorly studied. Our study aims to broaden the literature on avian hybrid zones, investigating a potentially geographically and temporally complex putative hybrid zone between two native Australian non-sister parrot species, the pale-headed and eastern rosellas (Platycercus adscitus and Platycercus eximius, respectively). We analysed six plumage traits and >1400 RADseq loci and detected hybrid individuals and an unexpectedly complex geographic structure. The hybrid zone is larger than previously described due to either observer bias or its movement over recent decades. It comprises different subregions where genetic and plumage signals of admixture vary markedly in their concordance. Evidence of contemporary hybridisation (later generation and backcrossed individuals) both within and beyond the previously defined zone, when coupled with a lack of F1 hybrids and differential patterns of introgression among potentially diagnostic loci, indicates a lack of post-zygotic barriers to gene flow between species. Despite ongoing gene flow, species boundaries are likely maintained largely by strong pre-mating barriers. These findings are discussed in detail and future avenues for research into this system are proposed, which would be of benefit to the speciation and hybrid zone literature.

Taxonomic Status of the Streaked Saltator, Saltator striatipectus (Passeriformes: Thraupidae), from Puná Island, Ecuador.

The Streaked Saltator, Saltator striatipectus, is an uncommon to common resident of open areas, cultivated land, gardens, and forest edges, with ten subspecies recognized from west Costa Rica through west Peru (Brewer 2016). Patterns of plumage variation, especially mantle color and streaking pattern below, are complex across subspecies and age classes (Chapman 1926; Ridgely Tudor 2009; Brewer 2016). Until recently, S. striatipectus was considered conspecific with the Lesser Antillean Saltator S. albicollis, but separated on the basis of genetic differentiation despite overall plumage similarities (Seutin et al. 1993). Actually, S. striatipectus and S. albicollis are not each other's closest relatives (Chaves et al. 2013).