Population Dynamics And Persistence Of Vallisneria Spinulosa In Lakes Of The Middle-lower Reaches Of The Yangtze River Revealed By Molecular Markers

Vallisneria L. are common and dominant submerged species in lakes in the middle-lower reaches of the Yangtze River, which are of ecological importance as structuring components in these shallow lakes. The field investigations showed that V. spinulosa was the dominant species in these lakes, V. natans was very common in this region; V. spinulosa and V. natans widely co-exist in these lakes. Phylogenetic analyses indicated that the co-existence of V. spinulosa and V. natans in lakes in the middle-lower reaches of the Yangtze River were not the results of sympatric speciation. Field investigations and glasshouse experiment suggested different reproductive strategy of V. spinulosa and V. natans. With abilities of tuber production and strong clonal growth, V. spinulosa shows competitive advantage over V. natans. The differences of dispersal and competitive abilities, caused by trade-offs of resource allocation between sexual reproduction and clonal propagation, maybe determine the pattern of competitive coexistence of V. spinulosa and V. natans. Genetic diversity and population genetic structure of V. spinulosa in the middle-lower reaches of the Yangtze River were investigated using allozymes and microsatellite loci. Vallisneria spinulosa maintained high levels of genetic variation both at the species and at the population level. Partitioning of genetic diversity revealed a surprisingly low population differentiation as compared to other hydrophilous angiosperms. Historically, extensive hydrologic connectivity among populations might have facilitated long-distance gene flow and resulted in the pattern of genetic variation revealed in this study, and also played great roles in population dynamics and population persistence of V. spinulosa in this region. With prolonged clonal growth, V. spinulosa might exhibit a lowered susceptibility to habitat loss and fragmentation caused by human activities in the middle-lower reaches of the Yangtze River, and could maintain high genetic diversity and low genetic differentiation among isolated populations.