Conservation genetics of epiphytic and terrestrial orchids


Photograph of Laelia rubescens (an orchid)We have used terrestrial and epiphytic orchids as model systems to investigate the processes influencing the evolution of fine-scale, spatial genetic structure within populations and how this structure may be altered by various factors, including human-mediated disturbance. As orchid seeds are minute, dust-like, and wind-dispersed, it is has generally been assumed that they would be dispersed over long distances. Despite this long-standing expectation, our papers were among the first to show that orchid populations may exhibit significant fine-scale genetic structure (FSGS): structure that is indicative of seed dispersal that is at least partially restricted about the maternal plant. To date we have studied FSGS in six orchid species, one epiphytic (Laelia; Trapnell et al. 2004) and five terrestrial (Cephalanthera, Cremastra, Cymbidium,Liparis, Orchis; Chung et al. 2004a,b, 2005a,b, 2011, 2014; Chung & Nason 2007). In all cases we have found significant FSGS with the spatial scale of this structure ranging from a fraction of a meter up to a few meters in extent and, in Laelia, in three dimensions. We have shown this structure to be influenced by vegetative reproduction and clonal spread (Chung et al. 2004b), inbreeding (Chung et al. 2004a, 2005a, Chung & Nason 2007), and a population's successional stage (expanding or senescing, Chung et al. 2011). These studies have also contributed to the conservation biology of orchids, investigating the genetic consequences of hybridization of a rare species with a wide-spread congener (Chung et al. 2005b), habitat fragmentation or harvesting of plants by orchid sellers (Chung & Nason 2007; Chung et al. 2014), and how trade-offs between sexual and clonal reproduction impact effective population size (Chung et al. 2004b).