title: Significant demographic and fine-scale genetic structure in expanding and senescing populations of the terrestrial orchid Cymbidium goeringii (Orchidaceae).
abstract: OBJECTIVE
  Fine-scale genetic structure (FSGS) in plants is influenced by variation in spatial and temporal demographic processes. To determine how demographic structure and FSGS change with stages of population succession, we studied replicate expanding and senescing populations of the Asian terrestrial orchid Cymbidium goeringii.
  
  
  METHODS
  We used spatial autocorrelation methods (O-ring and kinship statistics) to quantify spatial demographic structure and FSGS in two expanding and two senescing populations, also measuring genetic diversity and inbreeding in each.
  
  
  RESULTS
  All populations exhibited significant aggregation of individuals and FSGS at short spatial scales. In expanding populations, this finding was associated with high recruitment rates, suggesting restricted seed dispersal. In senescing populations, recruitment was minimal, suggesting alternative mechanisms of aggregation, perhaps including spatial associations with mycorrhizal fungi. All populations had significant evidence of genetic bottlenecks, and inbreeding levels were consistently high.
  
  
  CONCLUSIONS
  Our results indicate that different successional stages can generate similar patterns of spatial demographic and genetic structure, but as a consequence of different processes. These results contrast with the only other study of senescence effects on population genetic structure in an herbaceous perennial, which found little to no FSGS in senescing populations. With the exception of populations subject to mass collection by orchid sellers, significant FSGS is characteristic of the 16 terrestrial orchid species examined to date. From a conservation perspective, this result suggests that inference of orchid population history will benefit from analyses of both FSGS and demographic structure in combination with other ecological field data.
authors: Department of Biology, Gyeongsang National University, Jinju, Republic of Korea.
authors: Mi Yoon
authors: MY
authors: Chung
authors: John D
authors: JD
authors: Nason
authors: Myong Gi
authors: MG
authors: Chung
mesh_terms: D014644:Genetic Variation; D005843:Geography; D029595:Orchidaceae / Q000235:genetics* / Q000254:growth & development*; D010802:Phylogeny; D011157:Population Dynamics; D056910:Republic of Korea; D013045:Species Specificity