Tertiary Origin and Pleistocene Diversification of Dragon Blood Tree (Dracaena cambodiana-Asparagaceae) Populations in the Asian Tropical Forests

Abstract

BackgroundThe origin of extraordinarily rich biodiversity in tropical forests is often attributed to evolution under stable climatic conditions over a long period or to climatic fluctuations during the recent Quaternary period. Here, we test these two hypotheses using Dracaena cambodiana, a plant species distributed in paleotropical forests.MethodsWe analyzed nucleotide sequence data of two chloroplast DNA (cpDNA: atpB-rbcL and trnD-trnT) regions and genotype data of six nuclear microsatellites from 15 populations (140 and 363 individuals, respectively) distributed in Indochina Peninsular and Hainan Island to infer the patterns of genetic diversity and phylogeographic structure. The population bottleneck and genetic drift were estimated based upon nuclear microsatellites data using the software programs BOTTLENECK and 2MOD. The lineage divergence times and past population dynamics based on cpDNA data were estimated using coalescent-based isolation-with-migration (IMa) and BEAST software programs.ResultsA significant phylogeographic structure (N ST = 0.876, G ST = 0.796, F ST-SSR = 0.329, R ST = 0.449; N ST>G ST, R ST>F ST-SSR, P<0.05) and genetic differentiation among populations were detected. Bottleneck analyses and Bayesian skyline plot suggested recent population reduction. The cpDNA haplotype network revealed the ancestral populations from the southern Indochina region expanded to northward. The most recent ancestor divergence time of D. cambodiana dated back to the Tertiary era and rapid diversification of terminal lineages corresponded to the Quaternary period.ConclusionsThe results indicated that the present distribution of genetic diversity in D. cambodiana was an outcome of Tertiary dispersal and rapid divergence during the Quaternary period under limited gene flow influenced by the uplift of Himalayan-Tibetan Plateau and Quaternary climatic fluctuations respectively. Evolutionary processes, such as extinction-recolonization during the Pleistocene may have contributed to the fast diversification in D. cambodiana.

What We Know and What We Do Not Know about Dragon Trees?

“…A complete plastome was elaborated for D. cambodiana [48]. This species was also studied as to its haplotypes diversification based on nucleotide sequence data of two chloroplast DNA (cpDNA: atpB-rbcL and trnD-trnT) regions and genotype data of six nuclear microsatellites from 15 populations [49].…”

“…Asian group members contain five arborescent species. D. cambodiana is native in S and W of Hainan island, in Guangxi and Yunnan provinces (all in southern China), in Thailand, Laos, Cambodia, Vietnam, and E India [49,66,67]. D. cochinchinensis grows in Yunnan and Guangxi provinces in China, in Vietnam, and Laos [68,69].…”

“…D. cambodiana is usually found in escarpments of island-like limestone mountains [49]. However, it has also been documented growing on granite along the coast with low rainfall, dry heat, and soil with weak water storage capacity as well as along streams in the mountains far from the sea [203], which suggests that D. cambodiana can grow in ecologically diverse habitats.…”

“…In Hainan Island, the mean geographic distance between current D. cambodiana populations can be as much as 90.89 km, which might lead to a decrease in gene flow and an increase in the probability of divergent natural selection [11]. Among populations, a significant phylogeographic structure and genetic differentiation were detected, and bottleneck analyses suggest a recent population reduction [49]. It is also predicted that such a long-lived species with a narrow genetic base will not be able to adapt to new selection pressures that are caused by changes in environmental and climate conditions [11].…”

Population genetic structure of the endemic rosewoods Dalbergia cochinchinensis and D. oliveri at a regional scale reflects the Indochinese landscape and life‐history traits

“…The population structure of forest-associated species within central Indochina is less well studied (Blair et al, 2013;Fuchs, Ericson, & Pasquet, 2008;Morgan et al, 2011), and particularly Cambodia is underrepresented in the sampling. A few studies assess population structure of plants or trees in the region although most are limited to the local scale (Pakkad, Kanetani, & Elliot, 2014;Senakun, Changtragoon, Pramual, & Prathepha, 2011;Wattanakulpakin, Iamtham, Grubbs, & Volkaert, 2015;Zhao & Zhang, 2015;Zhao et al, 2013).…”