Scratching beneath the surface: Quantification of muscle architecture and myosin heavy chain content in the forelimbs of black-tailed prairie dogs (Cynomys, Rodentia).

Black-tailed prairie dogs (Cynomys ludovicianus) excavate burrow systems for a variety of reasons, including social organization and predator avoidance. As such, they have evolved a suite of musculoskeletal traits in their forelimbs that are employed for scratch-digging (i.e., digging motion performed by alternating power and recovery strokes). However, the degree to which their muscular anatomy has become modified in response to the selective pressures of their semi-fossorial lifestyle is unknown. To better understand the functional capacities of their forelimb musculature, dissections of C. ludovicianus (N = 9) were conducted to quantify limb mechanical advantage, muscle architectural properties, and myosin heavy chain (MHC) isoform content. Compared with previous data from other ground squirrels, forelimb muscle mass distribution in black-tailed prairie dogs is broadly similar with a large investment of scapular and shoulder muscle mass that accounts for two-thirds of the total forelimb muscle mass. The majority of muscles have long fascicles with correspondingly high fascicle length-to-muscle length (L