P2.104 Thursday, Jan. 5 Limb growth, locomotor development, and life history in lagomorphs FELLMANN, C.D.*; YOUNG, J.W.; Ashland University; Northeastern Ohio Medical University email@example.com
Young mammals must often navigate in the same niche as adults despite a number of growth-related limits to locomotor performance. As such, juveniles are expected to exhibit compensatory mechanisms that allow them to offset such limitations, increasing their chance of reaching sexual maturity. In a set of classic studies, Carrier (1983, 1995) found that in young hares, limb joint mechanical advantage and long bone cross-sectional dimensions scale with negative allometry, whereas bone mineral density increases with age. Together, these “compensatory” growth trajectories facilitate increased force output during jumping, allowing juvenile hares to achieve adult-like escape velocities at just 30% of adult mass. Here, we tested whether similar trends could be found among cottontail rabbits, a less precocial group of Lagomorphs. Cottontail rabbits leave the nest at three weeks, rather than at birth as in hares, and use darting locomotor maneuvers, rather than sprinting, to evade predators. Using microCT and 3D morphometrics, we documented ontogenetic changes in bone geometry, density, and limb joint mechanical advantage. Our results indicate that, like jackrabbits, 1) immature rabbits have significantly lower limb bone mineral density, 2) increased humeral and femoral bending strength, and 3) increased mechanical advantage at the elbow, knee, and ankle. These results show that immature rabbits, like the jackrabbits in Carrier’s studies, exhibit patterns of post-cranial growth which likely facilitate predator evasion early in ontogeny, suggesting that ontogenetic compensation for growth-related limits on locomotor performance may be common across the Lagomorpha. Research supported by NEOMED.