Genetic diversity of phalaris arundinacea populations in relation to river regulation in the Merkys basin, Lithuania

During the 1950s–1960s, the Merkys river basin, the largest protected area of Lithuania, underwent severe anthropogenic regulations. Within the Baltic States, the genetic diversity of Phalaris arundinacea populations is unknown and how they might be affected by anthropogenic activities such as river regulation. The objectives of this study were to compare molecular parameters (SSRs or microsatellite loci) within and among populations from natural river fragments with populations from regulated river parts. Study populations have greater genetic diversity within, rather than among, populations. The upstream portion of the Merkys basin populations had lower genetic diversity compared with further downstream. The mean number of polymorphic SSR loci was lower for populations from regulated parts of the river basin compared with natural ones. Main principle coordinate analysis revealed populations of regulated rivers at marginal positions. Bayesian clustering showed that current populations are admixtures of 3 distinct genetic groups, based on STRUCTURE analysis (K = 3 groupings) in geographic subdivisions of (a) downstream populations (Varėnė, Verseka, Upper Grūda, Lower Grūda, Upper Merkys, Lower Merkys), (b) upstream populations (Upper Šalčia, Beržė, Lower Šalčia, Visinčia, Lower Šaltykščia, Nedilė), and (c) the 2 regulated sites in the distinct geographic area of Taurupis and Upper Šaltykščia. P. arundinacea in the Merkys river basin does not all belong to a single, random-mating population encompassing its tributaries or among populations across its geographic scales. In several instances, river regulation might impair the genetic diversity of P. arundinacea populations.