The ability of an animal to detect and respond to changes in the environment is crucial to its survival. However, two elements of sensorimotor control – the time required to respond to a stimulus (responsiveness) and the precision of stimulus detection and response production (resolution) – are inherently limited by a competition for space in peripheral nerves and muscles. These limitations only become more acute as animal size increases. In this paper, we investigated whether the physiology of giraffes has found unique solutions for maintaining sensorimotor performance in order to compensate for their extreme size. To examine responsiveness, we quantified three major sources of delay: nerve conduction delay, muscle electromechanical delay and force generation delay. To examine resolution, we quantified the number and size distribution of nerve fibers in the sciatic nerve. Rather than possessing a particularly unique sensorimotor system, we found that our measurements in giraffes were broadly comparable to size-dependent trends seen across other terrestrial mammals. Consequently, both giraffes and other large animals must contend with greater sensorimotor delays and lower innervation density in comparison to smaller animals. Because of their unconventional leg length, giraffes may experience even longer delays compared with other animals of the same mass when sensing distal stimuli. While there are certainly advantages to being tall, there appear to be challenges as well – our results suggest that giraffes are less able to precisely and accurately sense and respond to stimuli using feedback alone, particularly when moving quickly.
↵* These authors contributed equally to this work
This work was supported by Aarhus University, The Danish Research Council and Aarhus Universityhospital, Skejby; by a Simon Fraser University Graduate Research Travel Award, a Simon Fraser University Travel and Minor Research Award, an American Society of Mammalogists Grant-in-Aid of Research and a Society for Integrative and Comparative Biology Grant in Aid of Research to H.L.M.; by a Company of Biologists Travelling Fellowship to S.M.O.; and by a Michael Smith Foundation for Health Research Scholar Award, a Canadian Institutes of Health Research New Investigator Award and a Natural Sciences and Engineering Research Council of Canada Discovery Grant to J.M.D.
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