Effect of habitat fragmentation on genetic structure of terrestrial
orchid Cymbidium faberi in the Qinling Mountains
Abstract
Species dispersal patterns and population genetic structure can be
influenced by large geographical features and habitat fragmentation. The
Qinling Mountains are a major east-west mountain range and they are also
the northernmost habitat of wild Cymbidium faberi in China. However, the
impact of the Qinling Mountains and habitat fragmentation in the areas
on genetic variation of C. faberi at population level is still poorly
understood. Here, genetic analysis of C. faberi in the Qingling
Mountains was conducted based on two chloroplast DNA sequences of 271
samples in 15 locations. Hierarchical analyses of molecular variance
(AMOVA) and mantel test indicated that most of the genetic variance was
within populations, genetic distance between populations was correlated
with the geographical distance but not strong (mantel r = 0.505, P =
0.011). Spatial analysis of molecular variance (SAMOVA) indicated that
the FCT reached the maximum value at K = 2 and then decreased, which
supported a two-group genetic structure. Furthermore, the Extended
Bayesian Skyline Plot revealed that the estimates of effective
population size of C. faberi were under demographic equilibrium in the
past but an apparent decline going from approximately 1 Ma towards the
present. Moreover, we found that the genetic diversity of C. faberi in
fragmented landscape was lower compared to continuous ones. Therefore,
we concluded that the habitat fragmentation has restricted the gene flow
of C. faberi by disrupting seed dispersal. Our findings may provide
helpful references for understanding how humans shape the genetic
structure and the importance of conserving wild orchids.