Meeting Abstract

P3-154   -   Effect of locomotor development on vascular canal orientation in limb bones of the glaucous-winged gull Lee, AH*; Simons, ELR; Woodward, HN; Hayward, JL; Midwestern University; Midwestern University; Oklahoma State University; Andrews University alee712@gmail.com https://www.midwestern.edu/academics/our-faculty/andrew-h-lee-phd

Gulls hatch ready to walk but must grow to nearly full-size before flying. This asynchronous timing of locomotor development results in different patterns of compensatory growth in limb bones. Compensation by growing thick bones occurs early in the hindlimbs of chicks, whereas it is delayed in the forelimbs of subadults. Thus, gulls present a new model to test how locomotor development affects other properties of growing bone. Previous histological studies suggest that limb bones with an elevated proportion of circumferentially oriented vascular canals are adapted to resist torsional loads induced by locomotion. However, estimates of canal orientation based on 2D measurements from histology may not accurately represent the 3D complexity of the canal network. Here, we used 3D analysis to trace changes in vascular canal orientation in the major limb bones from a growth series of glaucous-winged gull. The whole midshaft of each bone was scanned with micro-CT. Vascular canals were digitally segmented from the scans using semi-automated algorithms. Centerline skeletonization of the canals was performed. Each canal was classified into one of four categories (longitudinal, circumferential, oblique, and radial) based on centerline orientation relative to the longitudinal axis and periosteal surface of the bone. Ontogenetic trends in the proportion of canal categories for each bone were assessed using beta regression with a logit link function. Our results show that canal orientation is not random in the sampled bones. Contrary to predictions, vascular canal orientation is predominately longitudinal. Moreover, we did not find significant ontogenetic trends in the proportions of vascular canal categories in forelimb or hindlimb bones. The results from the glaucous-winged gull suggest that factors other than locomotion contribute to vascular canal orientation in avian bone.