The 89th Annual Meeting of the American Association of Physical Anthropologists (2020)

Strain Energy Variation Relates to Food Effects while Strain Orientation Relates to Individual Effects in Robust and Gracile Cebus Morphotypes


1Biology, Mercer University, 2Organismal Biology and Anatomy, University of Chicago

April 18, 2020 , Platinum Ballroom Add to calendar

Laboratory trained Cebus monkeys of both robust and gracile morphotypes were used to record suture strain and muscle activity simultaneously while subjects fed on several different foods with contrasting material properties. This included three gage sites along the sagittal suture (bregma, middle, and lambda) and several EMG recording sites within masseter and temporalis muscles. In this study we sought to explain variance in suture strain energy and orientation during feeding on various item types. Using RStudio (version 1.1.456) a series of mixed effects models were calculated with random factors (Individual and Food Item Type) as well as fixed factors (Chew Side, Chew Cycle Type, and Strain Gage Site). For measures of strain magnitude (Log10Max, Log10Min, and Strain Mode ratio) the food effect explains more variance than the individual effect. For strain orientation data the individual effect explains more variance than the food effect. One interpretation is that food has a greater impact on masticatory strain magnitudes than the individual subject in our experiment. Conversely, strain orientations transduced through the sagittal suture at different strain gage recording sites are explained more by individual effects and not as much by the specific food being consumed. Results show significant variation in strain regimes along the sagittal suture. Strains are laterally directed but strain mode data does not suggest this is strongly in tension. However, for the very robust specimen, many of the chew cycle observations on nuts and nut shells are tensional, especially at the posterior end of the suture.

This research was funded by the NSF HOMINID grant (BCS 0725147).

Slides/Poster (pdf)