Intraspecific geographic-morphological variation patterns in Fucus distichus and F. evanescens

The intraspecific patterns of morphometric variation were examined in Fucus distichus L. and F. evanescens C.Ag., using samples gathered from 49 sites spread across the North Atlantic. Ten characters were measured on each plant. The data were subjected to bivariate regression analyses, canonical correlation analysis and nested analysis of variance (ANOVA). It was shown that the combined effects of the three environmental variables measured for each site (latitude, longitude and exposure) could only explain 23 and 15% respectively of the intraspecific morphometric variation. Inter-individual, within-site differences accounted for a further 62 and 53%. The remaining variation appears to be expressed on a geographic scale of tens of kilometres at most. Thus, the species seem to take the form of fine-scale phenotypic mosaics, superimposed on weak major clines. Such a pattern has not previously been described for any macroalga, although it is known in some angiosperms.