Genetic Diversity Of Three Species Of Aquatic Macrophytes In Six Chinese Lakes

Aquatic macrophytes are important components of plant communities in wetland ecosystems, many cosmopolitan species have adapted to greatly different environments. In Lake Erhai and Caohai, which locate in Yunnan-Guizhou Plateau on the second step of terrain ladders in China, and in Lake Liangzihu, Honghu, Taihu and Weishan, which belong to the third step, leaf samples of three aquatic species [emergent Typha latifolia L. rooted floating-leaved Nymphoides peltatum (Gmel.) O. Kuntze and submerged Potamogeton lucens L.] were collected. The genetic diversity and genetic variation of the aquatic macrophytes were analyzed by ISSR molecular marker technique in this study The results were as follows:1. One hundred and one samples of T. latifolia were collected from 5 lakes (Liangzihu, Honghu, Taihu, Weishanhu and Caohai). From 100 ISSR primers, we selected 13 primers amplified polymorphic and reproducible bands. Totally 204 bands were amplified using these primers, and among them 184 bands were polymorphic. Thus, percentage of polymorphic bands was 90.20%. The genetic diversity index (H) was 0.2330 and the Shannon diversity index (Ⅰ) was 0.3649. Coefficient of genetic differentiation (Gst) was 0.3195. Typha Latifolia studied had relatively high genetic diversities, comparing with previous studies on T. Latifolia in East Asia and eastern North America.Gene flow (Nm) was 1.0650. Clustering analysis and principal component analysis showed that populations of Lake Weishanhu and Taihu and those of Lake Liangzi and Honghu respectively had a close genetic relationship. However, the Lake Caohai had closer genetic relationships with Lake Liangzihu and Honghu than Lake Taihu and Weishanhu.2. One hundred and forty-seven samples of N. peltatum were collected from 5 lakes (Liangzihu, Honghu, Taihu, Caohai and Erhai). From 100 ISSR primers, we selected 11 primers amplified polymorphic and reproducible bands. Totally 219 bands were amplified using these primers, and among them all bands was polymorphic. Thus, percentage of polymorphic bands was 100%. The genetic diversity index (H) was 0.2118 and the Shannon diversity index (I) was 0.3480. Nymphoides peltatum studied had relatively high genetic diversities, comparing with previous studies on N._ Peltatum in Lake Kasumigaura of Japan, Lake Erhai and Lake Zhijiang. Coefficient of genetic differentiation (Gst) was 0.1849. Gene flow (Nm) was 2.2037. Clustering analysis and principal component analysis showed that populations of Lake Caohai and Erhai and those of Lake Liangzi and Honghu respectively had a close genetic relationship However, the Lake Taihu population clustered relatively distant from the other 4 lakes.3. One hundred and seventeen samples of P. lucens were collected from 4 lakes (Honghu, Taihu,Weishanhu and Caohai). From 100 ISSR primers, we selected 11 primers amplified polymorphic and reproducible bands. Totally 202 bands were amplified using these primers, and among them all bands was polymorphic. Thus, percentage of polymorphic bands was 100%. The genetic diversity index (H) was 0.2500 and the Shannon diversity index (I) was 0.3927. Potamogeton lucens studied had relatively high genetic diversities, comparing with previous studies on P. malaianus Miq. in Lake Honghu and P. pectinatus L in Yangtze River. Coefficient of genetic differentiation (Gst) was 0.2868. Gene flow (Nm) was 1.2436. Clustering analysis and principal component analysis showed that populations of Lake Honghu and Taihu and those of Lake Weishanhu and Caohai respectively had a close genetic relationship.Our results showed that the three aquatic species studied had relatively high genetic diversities. Among the six lakes, the genetic diversity of the species studied in populations of Lake Liangzihu,Taihu and Weishanhu was relatively higher than that of Lake Erhai, Honghu and Caohai. Comparing the populations in the three lakes from which samples of all of the species studied were collected, the genetic diversity ranked as follows:Lake Taihu> Lake Honghu> Lake Caohai. Possible explanations include that (1) eutrophication in Lake Taihu has very long history and evolution process; (2) river-lake isolation by embankments since 1950 has reduced gene flow, thus lowering genetic diversity of the aquatic species; and (3) Lake Caohai had experienced many times dry upFor the three aquatic species, coefficients of genetic differentiation were less than 0.3200. Namely, the genetic variation among populations was lower than that within populations. Gene flow among populations was more than 1, which showed that gene flow between populations was very frequent. The frequent gene flow among populations could be one of the reasons for the smaller genetic differentiation among populations than within populations.For T. latifolia and N. peltatum, populations with close geographic distances had relatively close genetic relationships, while for P. lucens populations of Lake Weishanhu and Caohai had a relatively close genetic relationship, regardless of a large geographic distance between them. The results indicated that genetic relationships among populations of the aquatic species may be not only related to geographic distances, but also other factors such as hydrographic connectivity, selction pressure of environments, life form and breeding system contribute to the genetic relatedness.