Abstract
Xylocarpus granatum J. Koenig is one of the most widespread core component species of mangrove forests in the Indo-West Pacific (IWP) region, and as such is suitable for examining how genetic structure is generated across spatiotemporal scales. We evaluated the genetic structure of this species using maternally inherited chloroplast (cp) and bi-parentally inherited nuclear DNA markers, with samples collected across the species range. Both cp and nuclear DNA showed generally similar patterns, revealing three genetic groups in the Indian Ocean, South China Sea (with Palau), and Oceania, respectively. The genetic diversity of the Oceania group was significantly lower, and the level of population differentiation within the Oceania group was significantly higher, than in the South China Sea group. These results revealed that in addition to the Malay Peninsula—a common land barrier for mangroves—there is a genetic barrier in an oceanic region of the West Pacific that prevents gene flow among populations. Moreover, demographic inference suggested that these patterns were generated in relation to sea level changes during the last glacial period and the emergence of Sahul Shelf which lied northwest of Australia. We propose that the three genetic groups should be considered independent conservation units, and that the Oceania group has a higher conservation priority.
Highlights
Mangrove is a unique forest ecosystem that connects different habitats: land, freshwater, and ocean
We need to be cautious about uncertainties in the approximate Bayesian computation (ABC). Inferences, such as the generation time of species, overlapping of generations, and wide 95% CI of inferred parameters in the assumed model [16], the present results suggest that genetic differentiation caused by a genetic barrier between the South China Sea and Oceania was generated by episodes of eustatic change in sea levels in relation to ice ages over the past several hundred thousand years
A clear genetic structure was detected within the distribution range of one of the most widespread and core component species of mangrove forests in the Indo-West Pacific (IWP)
Summary
Mangrove is a unique forest ecosystem that connects different habitats: land, freshwater, and ocean. Despite the wide distribution range of mangrove forests, the number of component species is relatively small compared with other tropical forest habitats [6]. 30–40 species are recognized as core mangrove component species [1,2] Even though this may be a small number, most species are widespread, enabling mangrove forests to be distributed globally across the tropics. Core groups of mangroves, such as Avicennia spp., Rhizhophora spp., Bruguiera spp., and Xylocarpus spp., are found across different continents and oceanic regions [1,3]. Each group is an important component of mangrove ecosystems, and contributes to forest formation and succession processes. By dispersing buoyant propagules via ocean currents, mangrove species have established wide distribution ranges spanning over continents
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