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1. Feather Gene Expression Elucidates the Developmental Basis of Plumage Iridescence in African Starlings

   https://doi.org/10.1093/jhered/esab014  

   Rubenstein, Dustin R; Corvelo, André; MacManes, Matthew D; Maia, Rafael; Narzisi, Giuseppe; Rousaki, Anastasia; Vandenabeele, Peter; Shawkey, Matthew D; Solomon, Joseph (April 2021, Journal of Heredity)

   vonHoldt, Bridgett (Ed.)

   Abstract Iridescence is widespread in the living world, occurring in organisms as diverse as bacteria, plants, and animals. Yet, compared to pigment-based forms of coloration, we know surprisingly little about the developmental and molecular bases of the structural colors that give rise to iridescence. Birds display a rich diversity of iridescent structural colors that are produced in feathers by the arrangement of melanin-containing organelles called melanosomes into nanoscale configurations, but how these often unusually shaped melanosomes form, or how they are arranged into highly organized nanostructures, remains largely unknown. Here, we use functional genomics to explore the developmental basis of iridescent plumage using superb starlings (Lamprotornis superbus), which produce both iridescent blue and non-iridescent red feathers. Through morphological and chemical analyses, we confirm that hollow, flattened melanosomes in iridescent feathers are eumelanin-based, whereas melanosomes in non-iridescent feathers are solid and amorphous, suggesting that high pheomelanin content underlies red coloration. Intriguingly, the nanoscale arrangement of melanosomes within the barbules was surprisingly similar between feather types. After creating a new genome assembly, we use transcriptomics to show that non-iridescent feather development is associated with genes related to pigmentation, metabolism, and mitochondrial function, suggesting non-iridescent feathers are more energetically expensive to produce than iridescent feathers. However, iridescent feather development is associated with genes related to structural and cellular organization, suggesting that, while nanostructures themselves may passively assemble, barbules and melanosomes may require active organization to give them their shape. Together, our analyses suggest that iridescent feathers form through a combination of passive self-assembly and active processes. 

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2. Pachyrhynchus Weevils Use 3D Photonic Crystals with Varying Degrees of Order to Create Diverse and Brilliant Displays

   https://doi.org/10.1002/smll.202200592  

   Parisotto, Alessandro; Steiner, Ullrich; Cabras, Analyn Anzano; Van Dam, Matthew H.; Wilts, Bodo D. (April 2022, Small)

   Abstract The brilliant appearance of Easter Egg weevils, genusPachyrhynchus(Coleoptera, Curculionidae), originates from complex dielectric nanostructures within their elytral scales and elytra. Previous work, investigating singular members of thePachyrhynchusshowed the presence of either quasi‐ordered or ordered 3D photonic crystals based on the single diamond () symmetry in their scales. However, little is known about the diversity of the structural coloration mechanisms within the family. Here, the optical properties withinPachyrhynchusare investigated by systematically identifying their spectral and structural characteristics. Four principal traits that vary their appearance are identified and the evolutionary history of these traits to identify ecological trends are reconstructed. The results indicate that the coloration mechanisms across the Easter Egg weevils are diverse and highly plastic across closely related species with features appearing at multiple independent times across their phylogeny. This work lays a foundation for a better understanding of the various forms of quasi‐ordered and ordered diamond photonic crystal within arthropods. 

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3. Convergent evolution of disordered lipidic structural colour in the fruits of Lantana strigocamara (syn. L. camara hybrid cultivar)

   https://doi.org/10.1111/nph.18262  

   Sinnott‐Armstrong, Miranda A.; Ogawa, Yu; van de Kerkhof, Gea Theodora; Vignolini, Silvia; Smith, Stacey D. (June 2022, New Phytologist)

   Summary The majority of plant colours are produced by anthocyanin and carotenoid pigments, but colouration obtained by nanostructured materials (i.e. structural colours) is increasingly reported in plants. Here, we identify a multilayer photonic structure in the fruits ofLantana strigocamaraand compare it with a similar structure inViburnum tinusfruits.We used a combination of transmission electron microscopy (EM), serial EM tomography, scanning force microscopy and optical simulations to characterise the photonic structure inL. strigocamara. We also examine the development of the structure during maturation.We found that the structural colour derives from a disordered, multilayered reflector consisting of lipid droplets ofc.105 nm that form a plate‐like structure in 3D. This structure begins to form early in development and reflects blue wavelengths of light with increasing intensity over time as the structure develops. The materials used are likely to be lipid polymers.Lantana strigocamarais the second origin of a lipid‐based photonic structure, convergently evolved with the structure inViburnum tinus. Chemical differences between the lipids inL. strigocamaraand those ofV. tinussuggest a distinct evolutionary trajectory with implications for the signalling function of structural colours in fruits. 

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4. Taxonomy, nomenclature, and identification of the giant hummingbirds ( Patagona spp.) (Aves: Trochilidae)

   https://doi.org/10.1093/zoolinnean/zlaf036  

   Williamson, Jessie L; Gadek, Chauncey R; Robinson, Bryce W; Bautista, Emil; Bauernfeind, Selina M; Baumann, Matthew J; Gyllenhaal, Ethan G; Marra, Peter P; Ricote, Natalia; Singh, Nadia D; et al (June 2025, Zoological Journal of the Linnean Society)

   Abstract Giant hummingbirds (Patagona spp.) are extraordinarily large hummingbirds whose taxonomy has been muddled for two centuries. Patagona systematics were recently redefined in a study of migration, physiology, and genomics, revealing two species: the Northern Giant Hummingbird and Southern Giant Hummingbird. Here, we re-evaluate taxonomy and nomenclature of the genus in light of its newly clarified biology and species limits, analysing data from 608 specimens and wild-caught individuals spanning 1864–2023. The forms gigas and peruviana were both described based on multiple syntypes. The possible syntypes for Patagona gigas are dubious, so we designate a neotype for this taxon. The genetic identity of the peruviana lectotype remains untested, but its plumage appears to match the northern species. We critically considered the identity and usage of gigas and peruviana, respectively, and examined identification challenges that fostered taxonomic uncertainty. We endorse the name Patagona gigas for the Southern Giant Hummingbird and Patagona peruviana for the Northern Giant Hummingbird. We found that ~33% of specimens (74 of 226) in major museum collections that are labeled peruviana are actually misidentified gigas and we include this full list to correct the historical record. Finally, to facilitate identification and future study of these two cryptic species, we provide comprehensive information on plumage, measurements, and seasonal ranges. 

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5. The mechanistic, genetic and evolutionary causes of bird eye colour variation

   https://doi.org/10.1111/ibi.13276  

   Corbett, Eamon C; Brumfield, Robb T; Faircloth, Brant C (April 2024, Ibis)

   Birds display a rainbow of eye colours, but this trait has been little studied compared with plumage coloration. Avian eye colour variation occurs at all phylogenetic scales: it can be conserved throughout whole families or vary within one species, yet the evolutionary importance of this eye colour variation is under‐studied. Here, we summarize knowledge of the causes of eye colour variation at three primary levels: mechanistic, genetic and evolutionary. Mechanistically, we show that avian iris pigments include melanin and carotenoids, which also play major roles in plumage colour, as well as purines and pteridines, which are often found as pigments in non‐avian taxa. Genetically, we survey classical breeding studies and recent genomic work on domestic birds that have identified potential ‘eye colour genes’, including one associated with pteridine pigmentation in pigeons. Finally, from an evolutionary standpoint, we present and discuss several hypotheses explaining the adaptive significance of eye colour variation. Many of these hypotheses suggest that bird eye colour plays an important role in intraspecific signalling, particularly as an indicator of age or mate quality, although the importance of eye colour may differ between species and few evolutionary hypotheses have been directly tested. We suggest that future studies of avian eye colour should consider all three levels, including broad‐scale iris pigment analyses across bird species, genome sequencing studies to identify loci associated with eye colour variation, and behavioural experiments and comparative phylogenetic analyses to test adaptive hypotheses. By examining these proximate and ultimate causes of eye colour variation in birds, we hope that our review will encourage future research to understand the ecological and evolutionary significance of this striking avian trait. 

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