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One of the two lineages of extant birds resulting from its deepest split, Palaeognathae, has been reported not to exhibit structural coloration in feathers, affecting inferences of ancestral coloration mechanisms in extant birds. Structural coloration in facial skin and eggshells has been shown in this lineage, but has not been reported in feathers. We present the first evidence for two distinct mechanisms of structural color in palaeognath feathers. One extinct volant clade, Lithornithidae, shows evidence of elongate melanin-containing organelles uniquely associated with glossy/iridescent color, a structural color mechanism found in fossil outgroups and neognath birds. We also demonstrate a structural basis for the exceptional gloss in extant cassowary feathers. We propose gloss as an intermediate phenotype between matte and iridescent plumage, conferred by a thick and smooth feather rachis. Rachis-based structural color has not been previously investigated. The new data illuminate the relationships between avian melanin-based coloration and feather structure.
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News:
Microscopic feather features reveal fossil birds' colors and explain why cassowaries shine
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Gang Song, Ruiying Zhang, Fernando MachadoâStredel, Per AlstrÃm, Ulf S. Johansson Martin, Irestedt, Herman L. Mays, Bailey D. McKay, Isao Nishiumi, Yalin Cheng, Yanhua Qu, Per G. P. Ericson, Jon FjeldsÃ, Andrew Townsend Peterson & Fumin Lei (2020)
Great journey of Great Tits (Parus major group): Origin, diversification and historical demographics of a broadly distributed bird lineage.
Journal of Biogeography (advance online publication)
doi:
https://doi.org/10.1111/jbi.13863https://onlinelibrary.wiley.com/doi/10.1111/jbi.13863
Aim
The Pleistocene glacial cycles play a prominent role in shaping phylogeographical patterns of organisms, while few studies have focused on the regional difference of glacial effects. By acquiring comprehensive knowledge of the origin, diversification and historical demography of an intensively studied passerine species complex, Great Tit, we aim to test the regional variation of the Late Pleistocene glaciation impacts on this widely distributed bird lineage.
Location
Eurasia and associated peninsulas and archipelagos.
Taxa
Parus major species complex.
Methods
Phylogeny, divergence times and demographic dynamics were estimated with Bayesian methods. Population structure, genetic diversity and correlation between genetic and physical distances were estimated based on mtDNA variation. Glacialâtoâpresent distributional changes were assessed via ecological niche modelling (ENM).
Results
Five major clades (Central Asia, Eastern Asia, Eastern Himalaya, Northern and Western Eurasia and Southern Asia) were detected, with divergence times ranging 1.57â0.50 million years ago. Genetic diversity values and Bayesian skyline plots suggest that the three eastern clades had a deeper population history. A more complex geographic structure was observed in East Asia. Demographic expansion during the last glacial cycle was indicated for all five clades. ENM results showed broad conservatism of traits related to climate tolerances, and generally broader and more continuous distributional patterns under glacial conditions.
Main Conclusions
The Great Tit complex probably originated in Southeast Asia. Geographic barriers, such as the deserts of Central Asia and the Qinghai-Tibet Plateau appear to be related to the lineage divergence. Late Pleistocene climate cycles influenced both demographic dynamics and divergence, especially in terms of eastâwest differences in relation to geographic complexity.
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