Two approaches for the selection of Relevant Genetics Units for Conservation (RGUCs) in the narrow European endemic steppe plant Boleum asperum (Brassicaceae).

Several methods based on population biology, biogeography, ecology, and genetics have been traditionally used for
the identification of units for conservation below the species level. We use a combination of two methods based on
population genetic structure estimators and on probabilities of loss of rare alleles to identify the Relevant Genetic
Units for Conservation (RGUCs). The aims were to assess the genetic diversity and population structure of the
endemic steppe plant Boleum asperum (Brassicaceae), and to determine how many and which populations
significantly represent the total genetic diversity and the rarest allelic variation. Despite the high amplified
fragment length polymorphism genetic diversity values detected in B. asperum (hT = 0.744), caused probably by its
hexaploidy and allogamy, moderate spatial genetic differentiation was detected among populations (< 20%) and
geographical ranges (> 13%), suggesting the existence of an ancestral continuous distribution range that was
fragmented into separate ‘islands’ in more recent historical times. Five RGUCs, accounting for the 85.10% of the
total genetic variation and representative of the entire geographical distribution of the species, were selected for
in situ conservation. Ex situ conservation is proposed to complement the preservation of B. asperum. This method
of objective selection of populations may be applied to other candidate taxa for conservation with prior adjustment
of the threshold values of diversity required for effective protection of each particular species.