Gene flow in populations of the endangered aquatic fern Ceratopteris pteridoides in China as revealed by ISSR markers

The levels and pattern of the genetic variation within and among populations of the endangered fern Ceratopteris pteridoides (Hook.) Hieron in China were investigated using inter-simple sequence repeat (ISSR) markers. Thirteen ISSR primers used in the study amplified 125 reproducible bands with 56 (PPB = 44.8%) being polymorphic, indicating a relative low level of genetic diversity at the species level. Genetic diversity varied greatly among populations with the PPB values ranging from 14.4% to 32%. The coefficient of genetic differentiation between populations (Gst) was 0.297, indicating low level of genetic variation between C. pteridoides populations. AMOVA analysis also revealed a low level of genetic differentiation among the five populations. Of the total genetic diversity, 26.17% was attributable to among-population diversity. The UPGMA cluster of all samples showed that individuals from the same population occasionally failed to cluster in one distinct group indicating extensive inter-population gene flow among the remaining populations of C. pteridoides in China. A Mantel test showed no significant correlation between genetic distance and geographic distance (r = 0.44, P = 0.91) suggesting that gene flow was not restricted geographically. A number of ways including clonal growth, genetic drift and inbreeding, the extensive hydrologic connectivity among populations, which facilitated long-distance gene flow, might have affected the genetic profiles of C. pteridoides.