Intraspecific and intrafamilial variation in primate forearm muscle architecture

Abstract

Recent studies have examined locomotion and postural correlates of primate forearm muscle architecture. However, these have done so using relatively small sample sizes – usually one or two specimens per species, and relatively few species per genus and family. Thus, little is known about intraspecific variation in forearm muscle fiber architecture in primates, and whether there are notable differences in these variables between closely related taxa. The current study addresses these deficits by assessing both qualitative (presence/absence of specific muscles) and quantitative (physiological cross‐sectional area [PCSA], fascicle length [FL] and muscle mass [MM]) differences in forearm muscle architecture of larger intraspecific and samples with greater coverage of specific primate families than had been included in previous work. Namely, we studied 30 callitrichid specimens from 11 species, 15 lemurid specimens from 7 species and 9 cebids from two species ‐ a total sample size of 54 specimens from 20 species. Within species, FL varied the greatest among architectural variables and MM varied the least. We also found that there is great variation in both the extent of separation and fusion of flexor digitorum superficialis and profundus, and in the extent of accessory extensors in most species of callitrichids and Saimiri, but no variation in the gross forearm muscle architecture within lemurids. More than a quarter of the callitrichid specimens had forearm muscle configurations that deviate from their standard published description, suggesting that blanket characterizations of anatomical configurations at the genus or family level may obscure potentially important intra‐ and inter‐specific trends.Support or Funding InformationNational Science Foundation: IOS‐15‐57125, BCS‐14‐40599