Meeting Abstract

67.3  Monday, Jan. 6 08:30  Ontogeny of locomotor performance in Eastern cottontail rabbits: II. Hindlimb joint work during acceleration YOUNG, J. W.*; RUSSO, G. A.; ROSE, J. A.; BUTCHER, M. T.; SMITH, G. A.; NEOMED; NEOMED; Youngstown State Univ.; Youngstown State Univ; Univ. of Akron jwyoung@neomed.edu

Due to small size and ecological inexperience, juvenile animals are often under greater predation risk than adults. Although previous studies of several taxa have identified specific musculoskeletal growth trajectories that may alleviate juvenile risk by improving locomotor performance, few have measured age-related changes in performance, particularly in mammals. We used high-speed video and force platforms to quantify how growing cottontail rabbits (Sylvilagus floridanus), a species that experiences high predation at early ages, modulate hindlimb mechanics during acceleration. We collected 38 trials from a cross-sectional series of six wild-caught rabbits (mass: 0.23-1.3kg; age based on published growth curves: 37-184d). Overall, accelerations ranged from -0.6 to 8.6ms^-2, corresponding to a -0.57 to 0.95 ms^-1 change in velocity during stance. Increasing acceleration was associated with linear increases in total hindlimb joint work (R²=0.76, p<0.001), and was primarily powered by increases in hip (R²=0.67, p<0.001) and ankle work (R²=0.80, p<0.001). Although measured accelerations slightly increased with age (R²=0.16, p=0.01) this effect disappeared when the youngest (and slowest) individual was removed from the dataset (R²=0.07, p=0.15). Moreover, multiple regressions showed that age, controlling for acceleration and mass, was not significantly associated with either total limb work or individual joint work (all p>0.05), suggesting similar capacities for power output in juveniles and adults. When combined with the results of previous morphological studies, our findings support the hypothesis that musculoskeletal growth in rabbits is optimized to increase performance at early ages. Supported by NSF IOS 1146916, 1146851 and 1147044.