Predicting endemism from population structure of a widespread species: Case study in Centaurea maculosa Lam. (Asteraceae)

Amounts of genetic variability, genetic differentiation among taxa and popu lations, and population sizes were studied in five populations of Centaurea maculosa ssp. maculosa (a widespread taxon), all six populations of C. cor ymbosa (a narrowly endemic species), and the single population of C. maculo sa ssp. albida Seventeen isozyme loci were studied, of which nine were poly morphic. Results suggest that C. corymbosa and C, maculosa ssp, albida are likely derived from C. maculosa ssp. maculosa because the former represent a sample of tbe diversity of the latter, The percentage of polymorphic loci and Nei's genetic diversity were positively and significantly correlated w ith population size over all populations, but not within each taxon. Popula tions of both the widespread C. maculosa ssp. maculosa and the rare C. cory mbosa were strongly differentiated: overall, F-ST values were 0.26 and 0.34 , respectively. Differentiation among populations of different taxa was of the same order of magnitude as that observed among populations within taxa. Nevertheless, significant differentiation among the three taxa was found b y a hierarchical analysis of variance on allele frequencies. We suggest tha t bottlenecks or founder effects associated with colonization events and ec ological specialization in some populations of C. maculosa ssp. maculosa ha ve led to new taxa such as C. corymbosa and C. maculosa ssp. albida This ma y be a direct consequence of the particularly strong differentiation among populations of the widespread C, maculosa ssp. maculosa Our study highlight s the utility of considering closely related widespread taxa in order to un derstand the population biology and evolution of rare species, as well as t o design proper management programs.