Intriguing small-scale spatial distribution of chloropastic and nuclear diversity in the endangered plant Biscutella neustriaca (Brassicaceae)

Abstract

Biscutella neustriaca is an isolated plant taxon with about three thousand known individuals distributed in several fragmented populations. Despite its status as an endangered plant subject to a European LIFE programme for its protection, no conclusive genetic analysis has been performed to help its conservation. We analysed the genetic variability and distribution of nuclear microsatellite markers in a large sample of the population, as well as of the MatK chloroplastic gene in a subsample. We showed, first, that both pollen and seed dispersal, as well as clonal reproduction are strongly limited, and the mating system is obligate outcrossing. Second, we detected two highly divergent chloroplast haplogroups, as well as two completely distinct nuclear gene pools suggesting an ancient isolation between two groups of populations. Intriguingly, a third group of populations appears to combine the nuclear gene pool of one group with the chloroplast haplotype of the other group, suggesting a more recent dramatic colonization and foundation event. Thanks to complementary geological and historical data, we propose a scenario for the evolutionary history of this metapopulation influenced by the dynamics of Seine meanders and human activities. Finally, we give some suggestions for future conservation actions.