Dana J. Rashid, Roger Bradley, Alida M. Bailleul, Kevin Surya, Holly N. Woodward, Ping Wu, Yun-Hsin (Becky) Wu, Douglas B. Menke, Sergio G. Minchey, Ben Parrott, Samantha L. Bock, Christa Merzdorf, Emma Narotzky, Nathan Burke, John R. Horner & Susan C. Chapman (2020)
Distal spinal nerve development and divergence of avian groups.
Scientific Reports 10, Article number: 6303
doi:
https://doi.org/10.1038/s41598-020-63264-5https://www.nature.com/articles/s41598-020-63264-5Free pdf:
https://www.nature.com/articles/s41598-020-63264-5.pdfThe avian transition from long to short, distally fused tails during the Mesozoic ushered in the Pygostylian group, which includes modern birds. The avian tail embodies a bipartite anatomy, with the proximal separate caudal vertebrae region, and the distal pygostyle, formed by vertebral fusion. This study investigates developmental features of the two tail domains in different bird groups, and analyzes them in reference to evolutionary origins. We first defined the early developmental boundary between the two tail halves in the chicken, then followed major developmental structures from early embryo to post-hatching stages. Differences between regions were observed in sclerotome anterior/posterior polarity and peripheral nervous system development, and these were consistent in other neognathous birds. However, in the paleognathous emu, the neognathous pattern was not observed, such that spinal nerve development extends through the pygostyle region. Disparities between the neognaths and paleognaths studied were also reflected in the morphology of their pygostyles. The ancestral long-tailed spinal nerve configuration was hypothesized from brown anole and alligator, which unexpectedly more resembles the neognathous birds. This study shows that tail anatomy is not universal in avians, and suggests several possible scenarios regarding bird evolution, including an independent paleognathous long-tailed ancestor.
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IvÃn de la Hera, Irene HernÃndezâTÃllez, Josà PÃrezâRigueiro, Javier PÃrezâTris, Francisco Javier Rojo & Josà Luis TellerÃa (2020)
Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine.
Journal of Evolutionary Biology (advance online publication)
doi:
https://doi.org/10.1111/jeb.13630https://onlinelibrary.wiley.com/doi/10.1111/jeb.13630Current avian migration patterns in temperate regions have been developed during the glacial retreat and subsequent colonization of the iceâfree areas during the Holocene. This process resulted in a geographic gradient of greater seasonality as latitude increased that favoured migrationârelated morphological and physiological (co)adaptations. Most evidence of avian morphological adaptations to migration comes from the analysis of variation in the length and shape of the wings, but the existence of intraâfeather structural adjustments has been greatly overlooked despite their potential to be under natural selection. To shed some light on this question, we used data from European robins Erithacus rubecula overwintering in Campo de Gibraltar (Southern Iberia), where sedentary robins coexist during winter with conspecifics showing a broad range of breeding origins and, hence, migration distances. We explicitly explored how wing length and shape, as well as several functional (bending stiffness), developmental (feather growth rate) and structural (size and complexity of feather components) characteristics of flight feathers varied in relation to migration distance, which was estimated from the hydrogen stable isotope ratios of the summerâproduced tail feathers. Our results revealed that migration distance not only favoured longer and more concave wings, but also promoted primaries with a thicker dorsoventral rachis and shorter barb lengths, which in turn conferred more bending stiffness to these feathers. We suggest that these intraâfeather structural adjustments could be an additional, largely unnoticed, adaptation within the avian migratory syndrome that might have the potential to evolve relatively quickly to facilitate the occupation of seasonal environments.