Heritability of Brain Size and Surface Features in Rhesus Macaques (Macaca mulatta)

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Abstract
The extent of heritability for overall brain size and regional cortical surface features such as sulcus lengths is important for demonstrating a genetic component to the observed phenotypic differences among individuals and for evaluating the potential for evolutionary change in response to selection. Although the genetics of brain size has been extensively considered, the detailed morphology of the cortical surface has not previously been subjected to genetic analysis. We estimated the heritability of brain size and cortical sulcus lengths using 438 endocranial casts taken from skeletons of rhesus macaques (Macaca mulatta) from the Cayo Santiago population. Estimates were obtained both by mother-offspring regression and symmetric-differences-squared (SDS) methods. Brain size, measured as cranial capacity, was highly and significantly heritable in this population, confirming results of previous studies with laboratory mice. Overall, cortical sulcus lengths were also heritable, with 35% of the sulci significantly heritable at the 5% level in the mother-offspring analysis. The average mother-offspring heritability estimate, 0.31, was the same as the average heritability obtained previously from a series of 56 cranial metric characters. The SDS analyses generally corresponded to the findings based on mother-offspring regressions, although the significance test appeared more conservative. Both gross and detailed morphology of the brain are heritable.