Monitoring Genetic Diversity in Lithuanian Riverine Populations of Stuckenia pectinata Using SSR and ISSR Markers

Sago pondweed (Stuckenia pectinata (L.) Börner) is a genetically and ecologically diverse submerged macrophyte, notable for its versatile reproductive characteristics, with a broad global distribution, excluding only the Arctic and Antarctic regions. This cosmopolitan species remains underexplored genetically in Lithuania compared to some other European regions. The aim of this study was to investigate the state and distribution of genetic diversity across Lithuanian river populations. We analyzed genetic variation in ten riverine populations using both simple sequence repeats (SSRs) and intersimple sequence repeats (ISSR). Genetic distances between genotypes and populations, as revealed by SSR markers, correlated with those determined using ISSR markers, confirming consistency across the two marker systems. STRUCTURE analysis revealed the presence of two distinct genotype pools. Our study demonstrated that the majority of genetic variation resides within populations, with an FST value of 0.212 (SSR) and a ΦPT value of 0.352 (ISSR). These findings suggest high genetic differentiation among populations. The absence of a relationship between genetic diversity and hydrochemical or hydromorphological parameters at plant collection sites suggests that the population structure of this species is shaped primarily by evolutionary and/or demographic mechanisms, rather than by local environmental hydrochemical conditions. Overall, this study revealed high within-population genetic diversity and underlying genetic structure in S. pectinata populations across Lithuanian rivers.