Department of Theoretical Biology, University of Vienna
Friday Morning, 301D
Phenotypic variation is a central quantitative concept in evolutionary biology and ecology. Since phenotypic variation results from variation in developmental processes, it is also key to any connection between developmental and evolutionary biology. It is relatively simple to measures the variance of a single phenotypic trait, but a biologically meaningful quantification of phenotypic variation for multiple traits is surprisingly difficult. I suggest one criterion (affine invariance) for biological meaningfulness and demonstrate quantifications of phenotypic variation that fulfill this criterion. I apply these statistics to study phenotypic variation in postnatal cranial development of humans. Variation of cranial shape decreases until about 7 years of age and increases again thereafter. Decreasing variance results from developmental canalization, i.e., targeted growth compensating environmental perturbations of development. Interestingly, not all cranial shape features are equally canalized. For example, the size of the face relative to the cranial base is highly canalized, whereas the overall length relative to the height of the cranium does not appear to be canalized throughout postnatal development. These different developmental dynamics likely are important determinants of phenotypic evolution and are also relevant for orthodontic treatment.