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

/ML) ratios, whereas aside from the main carpal and digital flexors/extensors, selected intrinsic shoulder flexors/extensors, and the smallest elbow extensors, most muscles have low physiological cross-sectional area to muscle mass (PCSA/MM) ratios. Notably, only the massive m. pectoralis superficialis was considered to be a high power muscle by its architectural properties, although several muscles are modified for large joint torque or torque range, including m. latissimus dorsi and a well-developed m. triceps brachii long head. Mechanical advantage is correspondingly greatest at the shoulder joint, intermediate at the elbow joint, and low at the carpal joint. Lastly, muscle composition is fast-contracting by moderate expression of fast MHC-2B and low expression of slow MHC-1. That said, %MHC isoform content shows a predominance of fast MHC-2A as predicted, which progressively increases distally throughout the forelimb. These findings collectively suggest that C. ludovicianus is less specialized among burrowing rodents as hypothesized. Its forelimb musculoskeletal properties are likely constrained by a preference for medium soil types and cooperative social behavior, and may further represent a trade-off between terrestrial locomotor behavior and digging function. Nonetheless, the modifications observed are comparible with other semi-fossorial members of the Marmotini tribe with respect to distinctive traits for scratch-digging. Future work is needed to quantify muscle properties in additional genera (e.g., Tamias, Spermophilus) to better assess selection for burrowing in ground squirrels.