Orthogonal projections and bootstrap resampling procedures in the study ofinfraspecific variation

The effect of an increase in quantitative continuous characters resulting f rom indeterminate growth upon the analysis of population differentiation wa s investigated using, as an example, a set of continuous characters measure d as distance variables in 10 populations of a rodent species. The data bef ore and after correction for allometric size effects using orthogonal proje ctions were analyzed with a parametric bootstrap resampling procedure appli ed to canonical variate analysis. The variance component of the distance me asures attributable to indeterminate growth within the populations was foun d to be substantial, although the ordination of the populations was not aff ected, as evidenced by the relative and absolute positions of the centroids . The covariance pattern of the distance variables used to infer the nature of the morphological differences was strongly influenced by indeterminate growth. The uncorrected data produced a misleading picture of morphological differentiation by indicating that groups of populations differed in size. However, the data corrected for allometric effects clearly demonstrated th at populations differed morphologically both in size and shape. These resul ts are discussed in terms of the analysis of morphological differentiation among populations and the definition of infraspecific geographic units.