The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

The functional influence on trait covariance in platyrrhine mandibles


Duke Physician Assistant Program, Duke School of Medicine

March 27, 2015 8:00, Grand Ballroom A/B Add to calendar

Covariance structure has important implications for understanding morphological adaptability. “Functional” models suggest there are two modular units in the mammalian mandible, the alveolus and ramus. I hypothesize that if function influences trait correlation, covariance should differ among primates with diverse diets. The following predictions were tested: 1) trait covariance is greater in the entire mandible, as well as within each functional module, in primate taxa displaying durophagous diets (Cebus apella, Pithecia pithecia) when compared to non-durophagous taxa (Saimiri sciureus, Callicebus torquatus); and 2) alveolar-ramal functional models accurately represent adult primate mandibular covariance.

Geometric morphometric techniques were applied to three-dimensional fixed and sliding semi-landmark data collected on an adult sample of platyrrhine mandibles (n=127). Pair-wise comparisons of covariance magnitudes between dietary groups were conducted using singular value decomposition scores. RV-coefficients were calculated to determine the best modular fit. All significance values are based on permutation tests.

Durophagous primates possess greater magnitudes of overall mandibular covariance compared to non-durophagous primates (p<0.001). However, when the alveolus and ramus were compared independently, only alveolar units displayed differences in covariance magnitudes (p<0.01) amongst dietary groups. This suggests that mandibular trait covariance is influenced by functional demands and the degree of covariance corresponds to that demand. Additionally, some modular units within the mandible (i.e. alveolus) are more susceptible to influence from external forces than others. Lastly, RV-coefficient results did not support the alveolar-ramal functional model. Thus, while function plays a critical role in determining mandibular covariance other factors, such as developmental processes, must also be considered.