1Anatomy and Neurobiology, University of Kentucky, Lexington, 2Department of Physical Therapy, Duquesne University, 3School of Physical Therapy, Slippery Rock University, 4Department of Anthropology, University of Pittsburgh, 5Division of Psychiatry and Behavioral Sciences, Emory University, 6Center for Translational Social Neuroscience, Emory University, 7Yerkes National Primate Research Center, Emory University
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Vibrissae (whiskers) are specialized sensory hairs that respond to mechanical stimuli such as tension and displacement. Typically, vibrissae on mammals are organized into discrete rows and are sometimes associated with intrinsic muscles, which form a sling around the vibrissa capsule and protract vibrissae. In primates, intrinsic muscles are documented in tarsiers and some, but not all, strepsirrhines. Some mammals that present with both intrinsic muscles and highly organized vibrissae can move those vibrissae in a fast, rhythmic, repetitive pattern called whisking. Whisking mammals such as rodents have a higher proportion of fast twitch (type-II) muscle fibers relative to slow twitch (type-I) fibers. It is unknown if primates with organized vibrissae and intrinsic muscles can whisk. To address this question we compared the internal (proportion of type-I and type-II muscle fibers) and external (length) vibrissa morphology of five prosimians and three non-primate mammals. Micrographs of specimens prepared using fiber-type immunohistochemistry were used to evaluate the proportion of type-I and II muscle fibers. Like previous researchers, we found that among our non-primate sample, whisking animals have the highest proportion of type-II fibers, while type-I fibers are more ubiquitous in non-whisking mammals. Fiber typing results suggest that prosimians probably do not whisk as they have a high proportion of type-1 fibers. Moreover, prosimians have shorter vibrissae than most non-primate mammals (P<0.05). Despite these differences, the anatomical evidence suggests most prosimians can protract their vibrissae and that these hairs do play an important role in navigating through low light conditions.
Grant support: NIH MH082282; Samuel and Emma Winters Foundation