Genetic diversity and occupation strategy of Egeria najas (Hydrocharitaceae) in different habitats along the Upper Paraná River corridor

Egeria najas is a submerged aquatic macrophyte native to South America, with high propagation in reservoirs and natural lakes, whose reproductive strategy is little known. Understanding the genetic diversity of macrophyte populations can provide important information about this species' dispersion and colonization strategies, and support management actions. We aimed to genetically characterize populations of E. najas that colonize reservoirs and natural aquatic habitats (in a floodplain) in the Upper Paraná River basin, using the molecular markers ITS and trnL-trnF. The results showed the absence of genetic variation for the nuclear marker ITS and 13 distinct haplotypes for trnL-trnF. One of these haplotypes occurred in all habitats and 11 are unique haplotypes, of which 5 occurred in the Itaipu Reservoir and 6 in the floodplain. The null genetic diversity for the nuclear marker and the genetic homogeneity of the studied populations indicates that the reproduction of E. najas is mostly vegetative. The source of chloroplast marker haplotype variability may be somatic mutations. The connectivity among aquatic environments associated with river flow favors the transport of aquatic macrophyte propagules to different habitats. In the case of E. najas, whose vegetative propagules regenerate easily, the frequency of migrations supports the low genetic variability observed in populations of the Upper Paraná. In addition, the ability to occupy new habitats and recolonize disturbed ones strongly indicates that E. najas populations follow the metapopulation dynamics.