Meeting Abstract
An animal’s ability to maintain a vertical clinging or grasping posture against gravity is constrained for species without claws or adhesive pads. These animals must in theory use cheiridial anatomy, body geometry, and muscles to generate enough force normal to the vertical support to avoid slipping or rotating away from the substrate. Available models predict changes in posture and grip to maintain position based on body mass, substrate diameter, and locomotor mode, yet little empirical data exist to test these models. Within primates, strepsirrhines are an ideal group to study as species span a range of body masses and include species of many locomotor modes with some specialized for vertical clinging and leaping. Eight species with a range of body masses (150-4000g) and locomotor modes were prompted to vertically cling or grasp on three substrates of increasing diameter. Individuals were filmed by two videocameras in order to calculate limb joint angles in three dimensions. These data indicate that there is a differentiation in the functional role between the forelimb and hindlimb. The forelimb joint angles are similar between species, where mean elbow angles for all species on all substrates is 77°, with a minimum mean of 61.1° and maximum mean of 90.8°. In contrast, hindlimb joint angles are more complex. Hindlimb angles differ between species, with locomotor mode explaining much of the variance. Variance in knee angles for all species on all substrates was high, with a mean of 65.8° and a minimum mean of 17.5° and a maximum mean of 101.6°. These results support previous notions of the different functional role of the fore- and hindlimb in primates and may play a role in the unusual hindlimb-dominant weight support pattern in strepsirrhines.
