The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)


An evaluation of integration in the hybrid baboon cranium

TERRENCE B. RITZMAN1,2 and REBECCA R. ACKERMANN1.

1Department of Archaeology, University of Cape Town, 2School of Human Evolution and Social Change, Arizona State University

April 14, 2016 11:00, Imperial Ballroom B Add to calendar

Studies in many mammal groups have shown that hybrid populations are highly variable and possess a range of phenotypic traits, including those resembling either parent population, intermediate traits, and traits outside the range of either parent population. Hybrid baboon crania have also been shown to be highly variable, both in size and shape, and transgressive. Underlying causes for this variation – particularly for shape variation – are currently not fully understood. This study tests the hypothesis that hybridization changes the magnitude and/or pattern of morphological integration, with the prediction that the hybrids will exhibit lower levels of integration than (and different patterns from) parents. This hypothesis was tested using a dataset of 32 three-dimensional landmarks from Papio cynocephalus (n=45, P. anubis (n=195), and their F1 hybrids (n=75). These landmarks were converted into 25 linear distances, which were subsequently analyzed; geometric morphometric analyses were also performed. To quantify levels integration, variance-covariance matrices were compared. Patterns of integration were assessed by examining axes of shape from Procrustes superimposed principal components analyses. Results indicate that, as predicted, the hybrids have significantly lower levels of integration than their parents (p<0.001); clear differences in patterns of integration are also evident, and this ‘dis-integration’ may explain the increased morphological variance observed in these hybrids. These results suggest that hybridization disrupts previously evolved patterns of integration, resulting in distinctive patterns of covariation in the cranium, and thereby providing novel variation upon which selection can subsequently act.

Funding: Claude Leon Foundation Post-Doctoral Fellowship, National Research Foundation of South Africa, DST/NRF Centre of Excellence in Palaeosciences (COE-Pal)