Meeting Abstract
P3.129 Thursday, Jan. 6 Preliminary Study of Anti-fatigue Failure Mechanisms in the Trochilid Skeleton FAJARDO, R.J.*; SCHMITZ, J.E.; RIPLOG-PETERSON, S.; O’CONNOR, P.M.; UTHSCSA, San Antonio; UTHSCSA, San Antonio; AZ Sonoran Desert Mus.; Ohio Univ. fajardor@uthscsa.edu
Wing stroke frequency in medium-sized hummingbirds (e.g., Selasphorus rufus) is ~52 Hz during feeding flight. This level of cyclic loading translates into approximately 106 cycles every 3-4 days,. Mammalian models of cyclic loading demonstrate that bone fatigue failure can be achieved with as little as five minutes of moderate impact, high frequency loading imposed over six weeks. The intense dynamics of hummingbird flight suggest that these taxa employ strategies to prevent fatigue failure of wing skeletal elements. Anti-fatigue mechanisms may include alteration of tissue mineral density (TMD) or targeted remodeling to repair microdamage. We examined both parameters in two trochilid species, S. rufus and Calypte anna, using an intraindividual (fore- vs. hind limb) comparative approach. Humerus to femur comparisons were utilized as hind limbs are used primarily for perching (quasi-static loading). Quantitative backscattered electron imaging and microCT analyses indicated that TMD in the humerus and femur were similar. Osteocyte density did not differ between the elements, and an analysis of tartrate-resistant acid phosphatase positive cells indicated that osteoclasts were generally scarce, suggesting that remodeling is not enhanced in the forelimb. The data presented herein suggest that traits of material composition and bone turnover are similar in the humerus and femur. Thus, typical fatigue-failure prevention mechanisms of low tissue density (crack prevention) and increased remodeling (crack repair) do not appear to be present in the wing skeleton. Other analyses of anti-fatigue mechanisms and wing loading are necessary to better characterize bone functional responses in this extreme loading situation.
