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1. Previously, the Yangtze River connected thousands of shallow lakes which together formed a potamo-lacustrine system capable of sustaining a rich variety of submerged macrophytes. 2. Potamogeton malaianus is one of the dominant submerged macrophytes in many lakes of this area. Genetic variation and population structure of P. malaianus populations from ten lakes in the potamo-lacustrine system were assessed using inter-simple sequence repeat markers. 3. Twelve primer combinations produced a total of 166 unambiguous bands of which 117 (70.5%) were polymorphic. Potamogeton malaianus exhibited a moderate level of population genetic diversity ( PP = 70.5%, HE = 0.163 and I = 0.255), as compared with that of plants in the same habitat and range. The main factors responsible for this moderate value were the plant’s mixed breeding system (both sexual and asexual) and the hydrological connectivity among habitats. 4. F statistics, calculated using different approaches, consistently revealed a moderate genetic differentiation among populations, contributing about 20% of total genetic diversity. An estimate of gene flow (using FST) suggested that gene flow played a more important role than genetic drift in the current population genetic structure of P. malaianus ( Nm = 1.131). 5. The genetic diversity of P. malaianus did not increase downstream. A high level of linkage–disequilibrium at the whole population level suggested that metapopulation processes may affect genetic structure. The migration pattern of P. malaianus was best explained by a two-dimensional stepping stone model, indicating that bird-mediated dispersal could greatly influence gene movements among lakes. [ABSTRACT FROM AUTHOR]

Abstract: Vallisneria natans and Vallisneria spinulosa are two morphologically very similar and sympatrically dominant submerged macrophytes in lakes of the middle–lower reaches of the Yangtze River. Genetic variation was compared based on a total of 196 individuals from six V. natans populations and 201 individuals from seven V. spinulosa populations. Using eight ISSR primers, a total of 139 and 129 DNA fragments were generated with 121 being polymorphic in V. natans and 99 in V. spinulosa. The two species maintained higher genetic variation both at the species and population levels in comparison with other aquatic macrophytes. A higher level of genetic diversity among populations was found in V. natans than in V. spinulosa: the percentage of polymorphic loci (PPL) in V. natans was 52–62% vs. 38–47% in V. spinulosa; gene diversity (H) was 0.21 in V. natans vs. 0.17 in V. spinulosa. Both an analysis of molecular variance (AMOVA) and F-estimation (F ST ) showed that most of the total genetic variation resided within populations of both species (AMOVA: 85% and 80%; F ST : 0.132 and 0.202), indicating low genetic differentiation between populations. Principal coordinates analysis (PCA) indicated evident gene flow between populations of both species. The outcrossing reproductive mode and pervasive gene flow might have played important roles in maintaining high genetic diversity and in shaping low population differentiation of the two Vallisneria species, while the extent of clonal growth might account for the different levels of population divergence between them. [Copyright &y& Elsevier]