Vicariance and Oceanic Barriers Drive Contemporary Genetic Structure of Widespread Mangrove Species Sonneratia alba J. Sm in the Indo-West Pacific

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.

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, ), R. apiculata (Guo et al, ), Xylocarpus granatum (Tomizawa et al, ) and Sonneratia alba (Wee et al, ), 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 indicates the presence of a common cryptic barrier.…”

A general framework for propagule dispersal in mangroves

“…Studies at such large geographic scales are, however, relatively rare (e.g. Takayama et al , ; Mori et al , ; Li et al , ; Wee et al , ; He et al , ), as they require substantial funding and international collaboration to support sample collection across countries and high‐throughput molecular analyses. Importantly, care should be taken when using depictions or descriptions of large‐scale ocean circulation to explain (often fine‐scale) genetic information.…”

“…Furthermore, as mangroves are coastal vegetation, their present‐day genetic structure often harbours the signature of historical vicariance events and dispersal barriers during glacial periods when sea level was low and land masses were exposed. Prominent examples include the Central American Isthmus (CAI; Cerón‐Souza et al , ), the Malay Peninsula (Yang et al , ; He et al ), and Australasia (Wee et al , ), all of which were land masses that separated populations that were once connected, with the CAI still acting as a strong dispersal barrier to this day. Therefore, molecular tools allow the identification of land and oceanic barriers that are otherwise difficult to discern, when terrestrial barriers have disappeared and must be reconstructed, and because oceanic barriers are not static or absolute.…”

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

“…This genetic break could be recognized as the "cryptic barrier" [12] that might have historically prevented gene flow between South East Asia and Oceania, as shown in Rhizophora stylosa [12], Bruguiera gymnorhiza [14], Sonneratia alba Griff. [47], and Vigna marina (Burm.) Merr.…”