88 - Morphological Analysis of Carpals and Prepollex in Daubentonia Madagascariensis to Demonstrate Locomotive Adaptations

Poster Board Number: 88
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Abstract Body : Daubentonia madagascariensis, the Aye-Aye, is a Madagascan primate with many unique phenotypic adaptations. Daubentonia is most renowned for its derived manus, featuring a spindly ossified third digit articulating at a ball-and-socket metacarpophalangeal joint, used for arboreal percussive hunting. Daubentonia has a digit lateral to its pollex, known either as a “prepollex,” or, more preferentially, a “pseudothumb”. The pseudothumb was initially assumed to enhance grasping mobility impaired by hyperspecialized digits. In contrast, more recent literature suggests that the specialized carpals of Daubentonia are adapted for ambulatory needs. Kivell, Schmitt, and Wunderlich (2010) suggested that Daubentonia must utilize unique mechanisms to offset heavy pressures on its hands and feet during arboreal quadrupedal locomotion. Another recent study, Hartstone-Rose et al. (2019) described the ontogeny of the wrist skeleton in Daubentonia, but did not consider the newborn stage, prior to engaging in locomotor behavior.

This study used 3D reconstructions of the manus and associated soft tissue of a newborn Daubentonia based on diffusible iodine contrast-enhanced computed tomography (diceCT) scans, analyzed using 3DSlicer software. We isolated the cartilage precursors of carpal elements. We collected several volumetric measures, including those for the carpals and the pseudothumb. Newborn structures were compared to the skeletal structures of adult Daubentonia. We found that growth of the prepollex was more pronounced (8.4-fold growth) than that of the other carpals like the scaphoid (5.3-fold growth). We also identified a consistent pairing of sesamoid bones at each digit’s metacarpophalangeal joint in the adult Daubentonia. These data suggest that Daubentonia’s carpals may be especially sensitive to epigenetic modeling, with biomechanical stresses and strains being primary stimuli for osteogenic responses. Morphological and quantitative analyses of the radiocarpal joint and its kinematics are frequently underrepresented in the scientific literature. Therefore, these results suggest that more study would prove instrumental in identifying in vivo biomechanical trade-offs of primate locomotion.