Effects of hydrological connection and human disturbance on genetic variation of submerged Vallisneria natans populations in four lakes in China

With the increase in the need for flood prevention and lake resource used by humans,the construction of floodgates and sluices has changed the hydrological connection between rivers and lakes,and between adjacent lakes.In river-disconnected lakes,exploitation and use of lake resources have resulted in water quality decline and mechanical disturbance intensification to a different degree.Of the large number of river-disconnected lakes in the middle-lower reaches of the Changjiang(Yangtze)River,the Futou Lake,and the Xiliang Lake lie close together and are,historically,directly connected,and so do Liangzi Lake and Baoan Lake.The extent of human disturbance is severe in the Futou Lake and the Baoan Lake,but relatively mild in the Xiliang Lake and Liangzi Lake.The freshwater rosette-forming submerged plant Vallisneria natans is one of the dominant species in the four lakes.Using microsatellite markers,we studied the genetic variation of V.natans subpopulations in lakes with different intensities of human disturbance and historical direct hydrological connections.Our results showed that human disturbance decreased plant density and clonal growth in V.natans,but might increase genetic and clonal diversity at a subpopulation level and enhance gene flow among subpopulations by sexual propagule movement.Under similar climatic conditions,different intensities of disturbance seem to have such a high selective potential to differentiate genetically adjacent lake populations that they outperform the forces of gene flow through historical direct hydrological interconnection,which tends to produce genetic homogeneity.Our findings imply that human disturbance has a profound eff ect on the evolutionary process of natural populations of submerged plants.Moreover,increased subpopulation genetic diversity can enhance resistance and resilience to environmental disturbances.To a certain degree,we could expect that disturbed populations have the possibility of restoring spontaneously if humans cease to perturb natural ecosystems in the future.