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Photographs showing male black grouse holding their fan open during lek display, with examples of both tip and vane spots.
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There is growing evidence that achromatic plumage can act as honest indicators of male quality. In some species with areas of white plumage, black melanin spots can be found on parts of the feathers. The functional significance of these spots and the relationship with male quality is yet poorly understood. We investigated the relationship between b...
Contexts in source publication
Context 1
... dominant coloration of black grouse is eumelanin-based, that is black, but there are also depigmented patches on the upper and underside of the wing and the conspicuous white undertail coverts. These undertail coverts are held open in a fan shape during calling on the lek (Figure 1; Höglund et al. 1994). However, black grouse tail fans are not always totally white; melanin spotting of various sizes can be found in different parts of the feathers (Figure 1). ...
Context 2
... undertail coverts are held open in a fan shape during calling on the lek (Figure 1; Höglund et al. 1994). However, black grouse tail fans are not always totally white; melanin spotting of various sizes can be found in different parts of the feathers (Figure 1). Despite being used as individual identifiers on leks (e.g., Alatalo et al. 1992), the functional significance of these spots is unknown to date. ...
Context 3
... captured, the grouse holds the tail fan closed and concealed making it impossible to fully photograph the tail spread manually. Therefore, each feather of the white tail fan was manually inspected and for each individual, the total number of melanin spots and their location (at tip or within the main part of the vane) was recorded ( Figure 1). ...
Citations
... In the field, unequivocal identification of the causes of unusual plumages is not always possible (van Grouw, 2013) and even the definition of the specific causes may differ between authors (Husby, 2017;Izquierdo et al., 2018;van Grouw, 2021). Nonetheless, the understanding of colour aberrations requires further study (Soulsbury et al., 2016) as these traits are potentially linked to sexual selection and conspicuousness in species ecology (Roulin, 2016). This brief article consists of a compilation of information on male western capercaillies Tetrao urogallus with atypical white feathers sensu lato that was inspired by a casual observation of an anomaly in the plumage of a male of this species in the Pyrenees. ...
... Atypical white feathers might be more frequent in black grouse than in capercaillies (Couturier and Couturier, 1980). Numerous specimens are found in museum and other collections (van Grouw et al., 2019) and substantial advances have been made in the understanding of unusual feather colourations and melanin-based colour polymorphism in black grouse (Soulsbury et al., 2016). Isolation appears to be linked to white plumage parts in the black-billed capercaillie Tetrao parvirostris (Spiridonova et al., 2020) and is a key factor in the ecology and genetics in western capercaillie (Segelbacher et al., 2003). ...
Unusual plumage colours are of interest for environmental and evolutionary questions. This brief article reappraised information on male western capercaillies Tetrao urogallus individuals with atypical white feathers. It was inspired by a casual observation of T. u. aquitanicus in the Pyrenees. The presence of colour aberrations has been reported for several body parts in male western capercaillies. Updated quantifications of this phenomenon and the understanding of its causal factors remain pending for this species. Monitoring individual variability in plumage in tetraonids could contribute to assessing potential signs of population deterioration in species that are currently faced with population and habitat fragmentation and subject to climate change.
... Melanin can be costly to produce. Documented examples include melanic morphs with slower development and growth rates (Cotter et al., 2011;Marie-Orleach et al., 2014), smaller body sizes (Busso & Blanckenhorn, 2018;Kim et al., 2013), lower reproduction (Ortega et al., 2015;Roff & Fairbairn, 2013), and reduced survival (Dubovskiy et al., 2013;Soulsbury et al., 2016). A number of reasons may explain the cost of melanin phenotypes including genetic pleiotropy (Ducrest et al., 2008) and the production of toxic byproducts during synthesis (Dubovskiy et al., 2016). ...
Melanin, including both eu‐ and pheomelanin forms, is the most common pigment type in animals and plays numerous adaptive roles. However, the effect of diet on melanin pigmentation is not well reviewed or synthesized. Understanding how diet influences melanin may lead to valuable insights such as explaining intraspecific variation or explaining when melanin‐based traits are plastic or condition dependent versus when they are prioritized or canalized.
In order to assess the state of the literature and the current understanding of the effects of diet on melanin pigmentation we conducted a systematic literature search. We use the search results to highlight common patterns across animals. In particular we focus on three questions: Which dietary components can influence melanin? Which aspects of melanin‐based traits are influenced by diet? What factors can mediate the influence of diet on melanin?
The effect of diet on melanin is complex and multifaceted. Diet itself can vary in a number of ways including diet quantity, protein content, fatty acid content and amount of metals and other micronutrients. We discuss the mechanisms by which these components influence melanin pigmentation.
Diet can influence the size, darkness and colour of melanin‐based traits. Often, diet influences one of these aspects but not another, which may reflect the processes of melanin synthesis and distribution.
Factors that mediate whether melanin pigmentation responds to dietary variation include the type of trait, life stage, sex and environmental stress. Methodology (e.g. degree of manipulation relative to natural conditions) can also influence results. These nuances should be considered when developing hypotheses about the effects of diet on melanin pigmentation.
We conclude with important areas for future research, including the proximate mechanisms connecting diet and melanin, how diet affects internal melanin, how diet mediates costs of melanin pigmentation and how diet affects the evolution of melanin‐based traits. Overall, diet has important and complex effects on melanin and likely plays an important role in the ecology and evolution of melanin pigmentation.
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... In birds, plumage dot patterns are very common (Somveille et al. 2016), and some of them are known to function as sexual or social signals (Alatalo et al. 1992;Roulin 1999;Crowhurst et al. 2012;Zanollo et al. 2012;Soulsbury et al. 2016;Soma and Garamszegi 2018). Individual birds with more conspicuous dot patterns (e.g. ...
... Visual attention to white dots can affect individual fitness in two ways. First, plumage dots in the species are highly likely to function as sexual and social signals (Crowhurst et al. 2012;Soulsbury et al. 2016;Soma and Garamszegi 2018), considering the sexual and among-individual variations in dot patterns. Second, images of dot patterns can indicate the presence of food sources, such as tiny seeds and termites (Goodwin 1982;Payne 2010). ...
... Evidence from previous research indirectly supports the idea that dots can play a role in within-species communication, i.e. sexual/social signalling (Alatalo et al. 1992;Roulin 1999;Summers et al. 1999;Siddiqi et al. 2004;Reynolds and Fitzpatrick 2007;Cummings 2008, 2009;Crothers et al. 2011;Crowhurst et al. 2012;Zanollo et al. 2012;Soulsbury et al. 2016;Soma and Garamszegi 2018). Like many Estrildid or other species that are characterised by dotted plumage patterns functioning for within-species signalling (Roulin 1999;Crowhurst et al. 2012;Zanollo et al. 2012;Soulsbury et al. 2016;Soma and Garamszegi 2018), star finches also bear conspicuous white dots covering from face to flank, wherein their visual attention to white dots would facilitate identification of conspecifics or potential mates. ...
Many animals have polka dot patterns on their body surface, some of which are known to have signalling functions; however, their evolutionary origins remain unclear. Dot patterns can trigger a fear response (trypophobia) in humans and are known to function as aposematic signals in non-human animals, suggesting that dots may deserve attention for biological reasons. Interestingly in many birds, plumage dot patterns serve for social/sexual signalling. To understand their evolution, we have focused on the sensory bias hypothesis, which predicts the role of pre-existing sensory preference driven by natural selection in shaping signal design. Our previous phylogenetic comparative study supported the hypothesis and showed that diet-driven visual preference promoted the evolution of plumage patterns, as there was an evolutionary correlation between termite-eating (white roundish gregarious prey) and the presence of plumage dot patterns in species of the family Estrildidae. This suggests that these species possess an intrinsic preference for dots. To test this, we compared the responses of an Estrildid species with dot plumage pattern (star finch Neochmia ruficauda ) towards simultaneously presented monochrome-printed white dot vs white stripe patterns under both food-deprived and -supplied conditions. Overall, star finches preferred dots to stripes. They showed foraging-like behaviours almost only toward dots when hungry and gazed at dots frequently even when food was available, suggesting both hunger-related and hunger-neutral dot preferences. These results are rather surprising, given how strongly the subjects were attracted to abstract dot patterns without organic structure, but provided good support for the sensory bias hypothesis.
Secondary sexual trait expression can be influenced by fixed individual factors (such as genetic quality) as well as by dynamic factors (such as age and environmentally induced gene expression) that may be associated with variation in condition or quality. In particular, melanin‐based traits are known to relate to condition and there is a well‐characterized genetic pathway underpinning their expression. However, the mechanisms linking variable trait expression to genetic quality remain unclear. One plausible mechanism is that genetic quality could influence trait expression via differential methylation and differential gene expression. We therefore conducted a pilot study examining DNA methylation at a candidate gene (agouti‐related neuropeptide: AgRP) in the black grouse Lyrurus tetrix. We specifically tested whether CpG methylation covaries with age and multilocus heterozygosity (a proxy of genetic quality) and from there whether the expression of a melanin‐based ornament (ultraviolet‐blue chroma) correlates with DNA methylation. Consistent with expectations, we found clear evidence for age‐ and heterozygosity‐specific patterns of DNA methylation, with two CpG sites showing the greatest DNA methylation in highly heterozygous males at their peak age of reproduction. Furthermore, DNA methylation at three CpG sites was significantly positively correlated with ultraviolet‐blue chroma. Ours is the first study to our knowledge to document age‐ and quality‐dependent variation in DNA methylation and to show that dynamic sexual trait expression across the lifespan of an organism is associated with patterns of DNA methylation. Although we cannot demonstrate causality, our work provides empirical support for a mechanism that could potentially link key individual factors to variation in sexual trait expression in a wild vertebrate.
In-person counts of sage-grouse at leks are vital for informed sage-grouse management, but conducting these counts can be logistically difficult. Camera traps (i.e. automated trail or wildlife cameras) have been used in conjunction with numerous studies of wildlife species, but rarely on grouse leks. In a pilot study, we deployed five camera traps at known leks in central Wyoming over an approximately 10-day span. These cameras successfully captured images of sage-grouse using both ambient illumination and with the
aid of built-in infrared flash. Grouse were visible almost every evening at all leks, and less commonly around midnight and after. We conclude that camera traps can be an effective tool when used in a targeted manner for documenting the presence of birds at leks. Further research is needed to develop methodology to achieve counts that are comparable to in person counts by human observers. Additionally, the frequent evening lek attendance we observed could indicate the occurrence of critical breeding behaviors at this time; therefore, future efforts to control disturbance at sage-grouse leks may need to consider at dusk activity as well as dawn.
Colour patterns (e.g. irregular, spotted or barred forms) are widespread in the animal kingdom, yet their potential role as signals of quality has been mostly neglected. However, a review of the published literature reveals that pattern itself (irrespective of its size or colour intensity) is a promising signal of individual quality across species of many different taxa. We propose at least four main pathways whereby patterns may reliably reflect individual quality: (i) as conventional signals of status, (ii) as indices of developmental homeostasis, (iii) by amplifying cues of somatic integrity and (iv) by amplifying individual investment in maintenance activities. Methodological constraints have traditionally hampered research on the signalling potential of colour patterns. To overcome this, we report a series of tools (e.g. colour adjacency and pattern regularity analyses, Fourier and granularity approaches, fractal geometry, geometric morphometrics) that allow objective quantification of pattern variability. We discuss how information provided by these methods should consider the visual system of the model species and behavioural responses to pattern metrics, in order to allow biologically meaningful conclusions. Finally, we propose future challenges in this research area that will require a multidisciplinary approach, bringing together inputs from genetics, physiology, behavioural ecology and evolutionary-developmental biology. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
