The Study On Species’ Biology Of Scirpus×Mariqueter And Its Genetic Structure In China

Scirpus x mariqueter Tang&F.T. Wang [=Bolboschoenus planiculmis (F. Schmidt) T. Koyama] is a pioneer species that confined to the brackish habitats of the inter-tidal zone of Yangtze estuary and Hangzhou bay. Studies on clarifying the dubious taxonomic status of Scirpus x mariqueter Tang&F.T. Wang [=Bolboschoenus planiculmis (F. Schmidt) T. Koyama], population genetic structure and breeding system were carried. This report is composed of four parts. Firstly, AFLP markers were applied for hybrid detection of S. x mariqueter. Secondly, the phylogenetic relationship of S. x mariqueter and related taxa were analysed based on internal transcribed spacers (ITS) sequences of nrDNA. Thirdly, the patterns of distribution of genetic variation in S.×mariqueter were studied and the effects of heterogeneous environments on the genetic structure were explored. Finally, breeding experiments were conducted to understand the sexual breeding system of S. x mariqueter and S. planiculmis [=Bolboschoenus planiculmis (F. Schmidt) T. V. Egorova] respectively and their relationships.1) AFLP was used to infer the relationship between S. x mariqueter and its putative progenitors, S. planiculmis and S. triqueter L.[=Schoenoplectus triqueter (L.) Palla]. In phylogenetic analyses, the genetic distance between S.×mariqueter and S. triqueter (0.41±0.026) was much higher than that between S.×mariqueter and S. planiculmis (0.09±0.013), and that samples of S. x mariqueter and those of S. planiculmis did not form a monophyletic group, while the S. triqueter formed a distinct monophyletic group. However, we also detected an apparent clustering of individuals of S. x mariqueter and S. planiculmis separately. Our results disprove the hybrid origin of S.×mariqueter and rather suggest that it is more closely related to S. planiculmis. This result eliminates the validity of the new intergeneric hybrid, x Bolboschoenoplectus mariqueter (Tang&F.T. Wang) Tatanov.2) The ITS sequences were analysed for S.×mariqueter and relatated taxa together from different continents. The main results were:(1) The same ITS sequences of B. planiculmis (F. Schmidt) T.V. Egorova were obtained from Eastern-Asian, Europe and Australia;(2) B. planiculmis and B. maritimus are distinguished from each other at one mutation site;(3) B. yagara contained two groups. The samples of B. yagara (China) and B. laticarpus (Europe) shared the same sequences, while the samples of B. yagara (Europe) grouped together with B. Jluviatilis;(4) Three S. x mariqueter specific polymorphic sites are detected and samples of this species formed a subcluster. The results suggested that S.×mariqueter is a distinct taxon from the species of above Bolboschoenus.3) The distribution of genetic variation is determinded by the mating processes, ecological factors and the pattern of gene flow. AFLP analyses were performed for641individuals from14discrete subpopulations collected across the entire distributional range of S. x mariqueter in China and the results showed that:(1) S. x mariqueter exhibited a moderate level of population genetic diversity (PLP:49.3～66.8%; Ht=0.2101, Hw=0.1773; hs:0.1312～0.1771), as compared to the gene diversity from AFLP analyses of other species in the hydrochorous system. The main factor responsibles for this moderate value was the plant’s mixed breeding system (both sexual and asexual).(2) All individuals of S. x mariqueter were sticked to13genetic groups according to FLOCK analyses. Large amount of migrants among populations and long distant dispersal was also detected (>100km) by assignment tests.(3) No significant isolation by distance (IBD) was revealed by Mantel tests among samples from Yangtze estuary and Hangzhou bay (R2=0.0404, P=0.065). Minimum Spanning Tree (MST) also indicated that there are many exchanges among subpopulations, and the Nanhui is a key region for the connectivity of the metapopulation system.(4) However, different calculation approaches of FST consistently revealed a relatively higher genetic differentiation among subpopulations under the open environments. The results indicated that the local adaption occurred in the heterogeneous environments. Further more, it suggested that selection weakened the effectiveness of dispersal events.(5) In addition, we also investigated the effects of disturbance on Shannon-Weiner’s diversity, and found that more genetic groups were contained under the middle level of disturbance.4) Two conclusions were summarised from the fecundity tests:first, both S.×mariqueter and B. planiculmis were self-compatible, although flowers of the species are protogynous; second, the hybrids could be obtained from cross-breeding between S. x mariqueter and B. planiculmis. Furthermore, microsatellite (SSR) primers were developed and applied to verify the hybrids. The results demonstrated the previous conclusions that S. x mariqueter and B. planiculmis are very closely related taxa.