Anatomical decomposition and genomic control of avian wing shape variation across evolutionary scales

The associations between wing morphology and various facets of avian life history have been objects of a century of ecomorphological study. Despite this, the individual contributions of anatomical components inside the wing to overall shape variation within and between bird species remain poorly characterized, and the genetic basis of this variation is unknown. Here, I use micro-CT scans of museum specimens to quantify integration and scaling among wing components at two phylogenetic scales: across subspecies within the song sparrow (\textit{Melospiza melodia}) and among 37 species spanning the songbird (\textit{Passeri}) radiation. Within song sparrows, relative wing length variation is driven by the lengths of the primary and secondary flight feathers, with negligible contribution from wing bones. In contrast, between songbird species, wing bones scale proportionally with the outer primaries in expectation even as they remain only weakly integrated with them. These results reveal a separation of evolutionary timescales in songbird wing morphology: feathers drive wing shape adaptation within species while bones covary with them on deeper timescales. To identify the regulatory basis of this variation, I align $\sim 450,000$ conserved noncoding elements across 32 of the sampled songbird species and use PhyloAcc-C to identify elements that covary in evolutionary rate with wing morphology. Regions adjacent to genes involved in embryonic patterning and anatomical development are enriched for co-acceleration with wing shape. The extragenic noncoding element with the strongest signal for co-acceleration is adjacent to an essential \textit{Wnt} co-receptor with known functions in both limb bone and feather development, providing a target for future evolutionary developmental studies of wing morphogenesis.