Microenvironmental correlates of phenotypic variation in Capsella bursa-pastoris (Cruciferae)

The majority of papers dealing with environmental correlates of phenotypic variability are concerned with macrogeographical structuring of the investigated species. However, a possible major component of phenotypic differentiation in some taxa is small-scale variability in the microenvironment. The statistical methods usually employed for such studies seems to be restricted to a few standardized sets of procedure, often assuming linearity and additivity of effects among variates. In this paper we studied small-scale geographical differentiation of phenotypes of Capsella bursa-pastoris (Cruciferae), a species characterized by an apparent extreme degree of phenetic specialization that could be due to fixation of alternative alleles in small local demes. We use nonparametric multivariate procedures to test the relationships between phenotypic principal components, geographic distance, and a number of microenvironmental parameters. A concept recently applied to population genetics, that of biological boundaries, is used here in relation to phenetic variation to assess its association with geographical mapping of the populations studied. Key words: Capsella, Mantel test, phenotypic boundaries, biotic parameters, principal components analysis.