Genetic Structure and Population Demographic History of a Widespread Mangrove Plant Xylocarpus granatum J. Koenig across the Indo-West Pacific Region

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.

The presence of a cryptic barrier in the West Pacific Ocean suggests the effect of glacial climate changes on a widespread sea‐dispersed plant, Vigna marina (Fabaceae)

“…For widespread sea‐dispersed plants in tropical regions, the influence of glacial climate change has been less expected, due to their extremely high ability for LDD that may easily homogenize populations by sea‐dispersed seeds, and also because the locations of refugia have not been clear for tropical plants. The findings of this study, as well as other recent ones using molecular markers and the ABC approach, provided evidence suggesting the presence of cryptic barriers in the West Pacific (for example, Xylocarpus granatum (Tomizawa et al, ); Sonneratia alba (Wee et al, )) in relation to the LGM. These findings suggest that not only the widespread temperate forest plants, but also the sea‐dispersed tropical plants have been influenced by glacial climate change.…”

“…A clear genetic break in the West Pacific Ocean has also been observed in some other sea-dispersed plants: Rhizophora stylosa (Wee et al, 2015), R. apiculata (Guo et al, 2016), Xylocarpus granatum (Tomizawa et al, 2017) and Sonneratia alba , and in these cases the locations of the genetic breaks roughly corresponded to the one determined for V. marina. The presence of common genetic structure in multiple widespread sea-dispersed species…”

“…It is well kwon that richness of alleles or haplotypes is expected to be higher in refugial areas than areas recolonized after the glacial period (Comps, Gömöry, Letouzey, Thiébaut, & Petit, 2001;Petit et al, 2003). provided evidence suggesting the presence of cryptic barriers in the West Pacific (for example, Xylocarpus granatum (Tomizawa et al, 2017); Sonneratia alba ) in relation to the LGM.…”

Genetic structures across a biogeographical barrier reflect dispersal potential of four Southeast Asian mangrove plant species

“…The current study is particularly timely with respect to the increased research on global phylogeography of mangroves in the past several years (e.g. Guo et al, 2018;Tomizawa et al, 2017;Wee et al, 2017;Yang et al, 2017). Our findings emphasize a lack of congruency in genetic structure across mangrove species at the local scale and calls for caution against a generalized interpretation of their genetic patterns.…”

Global-scale dispersal and connectivity in mangroves

“…Overall, these results may help explain the distribution of mangrove species in the Indian Ocean region, such as R. mucronata (e.g., refs. 45 and 63), A. marina (60), and Xylocarpus granatum J. Koenig (64). Although we did not observe direct connectivity between East African and Australian populations, the directionality of transport via the subtropical gyre ( SI Appendix , Fig.…”