Analysis of genetic population structure and diversity in Mallotus oblongifolius using ISSR and SRAP markers

BACKGROUND: Mallotus oblongifolius, an evergreen shrub endemic to Hainan Island, China, is important both medicinally and economically. Due to its special medicinal significance and the continuing rise of market demand, its populations in the wild have been subject to long-term illegal and unrestrained collection. Hence, an evaluation of genetic variability is essential for the conservation and genetic reserve development of this species. METHODS: Sequence-related amplified polymorphism (SRAP) and inter-simple sequence repeat (ISSR) markers were employed to assess the genetic diversity and genetic structure of 20 natural populations of M. oblongifolius growing in different eco-geographical regions of Hainan Island, China. RESULTS: We revealed a considerable genetic diversity (h = 0.336, I = 0.5057, SRAP markers; h = 0.3068, I = 0.4657, ISSR markers) and weak genetic differentiation (Gst = 0.2764 for SRAP, Gst = 0.2709 for ISSR) with the same gene flow (Nm = 1.3092 for SRAP, Nm = 1.346 for ISSR) among the M. oblongifolius populations. The Mantel Test showed that the distribution of genetic variation among populations could not be explained by the pronounced geographical distances (r = 0.01255, p = 0.5538). All results of the Unweighted Pair Group Method with Arithmetic Mean (UPGMA), Neighbor-joining (NJ), Principal Coordinate Analysis (PCoA) and Bayesian analyses supported a habitat-specific genetic clustering model for M. oblongifolius, indicating a local adaptive divergence for the studied populations. DISCUSSION: We suggested that the habitat fragmentation and specificity for M. oblongifolius populations weakened the natural gene flow and promoted an adaptation to special habitats, which was the main reason for local adaptive divergence among M. oblongifolius.