Genetic consequence of restricted habitat and population decline in endangered Isoetes sinensis (Isoetaceae)

• Background and Aims: Isoetes sinensis (Isoeteaceae) is a critically endangered aquatic quillwort in eastern China. Rapid decline of extant population size and local population extinction have occurred in recent years and have raised great concerns among conservationists. • Methods: Amplified fragment length polymorphisms (AFLPs) were used to investigate the genetic variation and population structure of seven extant populations of the species. • Key Results: Eight primer combinations produced a total of 343 unambiguous bands of which 210 (61·2 %) were polymorphic. Isoetes sinensis exhibited a high level of intra-population genetic diversity (H E) = 0·118; hs = 0·147; I = 0·192; P = 35·2 %). The genetic variation within each of the populations was not positively correlated with their size, suggesting recent population decline, which is well in accordance with field data of demographic surveys. Moreover, a high degree of genetic differentiation (FST = 0·535; G ST = 0·608; θB = 0·607) was detected among populations and no correlation was found between geographical and genetic distance, suggesting that populations were in disequilibrium of migration-drift. Genetic drift played a more important role than gene flow in the current population genetic structure of I. sinensis because migration of I. sinensis is predominantly water-mediated and habitat range was highly influenced by environment changes. • Conclusions: Genetic information obtained in the present study provides useful baseline data for formulating conservation strategies. Conservation management, including both reinforcement for in situ populations and ex situ conservation programmes should be carefully designed to avoid the potential risk of outbreeding depression by admixture of individuals from different regions. However, translocation within the same regional population should be considered as a measure of genetic enhancement to rehabilitate local populations. An ex situ conservation strategy for conserving all extant populations to maximize genomic representation of the species is also recommended. © The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.