Epidendrum radicans - genetic data of 4 regional populations

Colonization is a fundamental ecological process that is important for the
persistence of species, particularly when a changing environment
necessitates range shifts. Vacant habitats available for colonization
often arise from landscape disturbance. Colonization and population
expansion processes can be inferred by examining the levels and spatial
distribution of genetic variation of plant populations with known
disturbance histories. Samples (N = 690) of the terrestrial orchid,
Epidendrum radicans, were collected from five lava flow sites on the
slopes of Volcán Arenal in Costa Rica that last experienced major
eruptions in 1968 and 1992. Individuals were also sampled (N = 188) from
four regional populations. Samples were characterized using 15 nuclear
genetic markers and analyzed using population genetics statistics. Genetic
diversity within sites was moderate (He = 0.092 – 0.192). Contrary to
expectation, diversity tended to be lower on the older lava flows (0.131
versus 0.172) which may reflect their more sheltered topography that
restricted pollen/seed immigration, and/or greater intra- and
interspecific competition. Genetic diversity measures indicate that the
lava flows were colonized by numerous individuals that likely originated
from multiple sources while spatial genetic structure (SGS) statistics
indicate that most recruitment in the study sites subsequent to
colonization resulted from in situ reproduction and localized seed
deposition. Younger sites had significantly greater SGS over larger
distances which reflects fewer reproductive events, and less spatial and
temporal overlap of seed shadows relative to the older sites. Clones were
also generally larger on the older sites (≤ 8m versus ≤ 3m).