MORPHOLOGICAL INTEGRATION IN THE SADDLE-BACK TAMARIN (SAGUINUS-FUSCICOLLIS) CRANIUM

Quantitative genetic theory predicts that functionally and developmentally related characters will be morphologically integrated and tend to be inherited together. Furthermore, coinheritance and environmental integration of functionally related characters may be important in facilitating adaptive evolution. The hypothesis that functionally and developmentally related features of the cranium are phenotypically, genetically, and environmentally integrated in the saddle-back tamarin (Saguinus fuscicollis) cranium is tested. Thirty-nine craniofacial measurements were taken on 209 animals from the Oak Ridge Associated Universities' Marmoset Research Center. Heritabilities and phenotypic, genetic, and environmental correlations were calculated using maximum likelihood methods after the data were corrected for sex and specified environmental effects. The correlation matrices were compared to a series of theoretical intertrait connectivities representing expected patterns of morphological integration using Mantel's test. The patterns of phenotypic, genetic, and environmental correlation among craniofacial traits matched patterns predicted on the basis of developmental and functional relationships among cranial traits. The similarity between functional and developmental integration and correlation was largely due to the relatively high correlations among cranial vault traits and among oral traits. Both genetic and environmental correlation among developmentally and functionally related characters may enhance the rate of evolutionary change.