Abstract
Patterns of genetic structure are essential for a comprehensive understanding of the evolution and biogeography of a species. Here, we investigated the genetic patterns of one of the most widespread and abundant mangrove species in the Indo-West Pacific, Sonneratia alba J. Sm., in order to gain insights into the ecological and evolutionary drivers of genetic structure in mangroves. We employed 11 nuclear microsatellite loci and two chloroplast regions to genotyped 25 S. alba populations. Our objectives were to (1) assess the level of genetic diversity and its geographic distribution; and (2) determine the genetic structure of the populations. Our results revealed significant genetic differentiation among populations. We detected a major genetic break between Indo-Malesia and Australasia, and further population subdivision within each oceanic region in these two major clusters. The phylogeographic patterns indicated a strong influence of vicariance, oceanic barriers and geographic distance on genetic structure. In addition, we found low genetic diversity and high genetic drift at range edge. This study advances the scope of mangrove biogeography by demonstrating a unique scenario whereby a widespread species has limited dispersal and high genetic divergence among populations.
Highlights
Mangroves are widespread, tropical and subtropical coastal plant communities with strong genetic structures that are mainly shaped by their biogeographic history
Our study represents a comprehensive assessment of the global phylogeography of S. alba
By sampling throughout its entire distribution range, we demonstrated that gene flow in this species is highly restricted by genetic barriers and geographic distance despite having a widespread distribution and dispersal by sea
Summary
Tropical and subtropical coastal plant communities with strong genetic structures that are mainly shaped by their biogeographic history. Mangroves from the IWP exhibited phylogeographic congruency across species, whereby populations were genetically differentiated according to three subregions: the EIO, SCS and Northern Australia (NA), suggesting limited gene flow across these subregions [4,5,6]. These phylogeographic congruencies in co-distributed mangroves enabled the identification of geographic factors (e.g., land barriers) that shaped the genetic structure, and provided insights into past dynamics of mangrove forest cover
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