Outcrossing Rates and Gene Flow in Natural Population of the Endangered Endemic Aquatic Lycophyte Isoetes yunguiensis as Revealed by ISSR Markers

In this study, mating system, genetic diversity, and genetic structure of the endangered endemic aquatic Isoetes yunguiensis in China was investigated using ISSR markers. The results of ISSR analyses showed that the estimate of multilocus outcrossing rate ( t m ) was high at species level ( t m = 0.955), indicating that diploid I . yunguiensis is a predominant outcrossing species. Nine selected ISSR primers used in the study amplified 66 reproducible bands, 41 of which were polymorphic among 37 individuals. High level of genetic diversity was detected at the species level (PPB = 62.12%), whereas, relatively low genetic diversity existed within populations (PPB = 39.39%). Analysis of molecular variance (AMOVA) revealed that 31.99% of the genetic variation was attributable to differences between populations and the rest (68.01%) to variability within populationsof I . yunguiensis. Value of F st (0.320) indicated that genetic differentiation between populations also was significant. These results showed that I . yunguiensis predominantly favors crossing, and has a high level of genetic diversity and highly significant genetic variation between and within populations. Gene flow (Nm) among populations is equal to 1.177. High outcrossing rates may be responsible for the high levels of genetic diversity observed in the I. yunguiensis population. To maintain the current level of genetic diversity for this species, we recommend increasing in situ conservation sites.