Barrier to Gene Flow of Grey Mangrove Avicennia marina Populations in the Malay Peninsula as Revealed From Nuclear Microsatellites and Chloroplast Haplotypes

Abstract

Contemporary mangrove forest areas took shape historically and their genetic connectivity depends on sea-faring propagules, subsequent settlement, and persistence in suitable environments. Mangrove species world-wide may experience genetic breaks caused by major land barriers or opposing ocean currents influencing their population genetic structure. For Malay Peninsula, several aquatic species showed strong genetic differentiation between East and West coast regions due to the Sunda shelf flooding since the Last Glacial Maximum. In this study genetic diversity and structure of Avicennia marina populations in Malay Peninsula were assessed using nuclear microsatellite markers and chloroplast sequences. Even though all populations showed identical morphological features of A. marina, three evolutionary significant units were obtained with nuclear and cytoplasmic markers. Avicennia marina along a 586 km stretch of the West coast differed strongly from populations along an 80 km stretch of the East coast featuring chloroplast capture of Avicennia alba in an introgressive A. marina. Over and above this expected East-West division, an intra-regional subdivision was detected among A. marina populations in the narrowest region of the Strait of Malacca. The latter genetic break was supported by an amova, structure, and barrier analysis whereas RST > FST indicated an evolutionary signal of long-lasting divergence. Two different haplotypes along the Western coast showed phylogeographic relationship with either a northern or a putative southern lineage, thereby assuming two Avicennia sources facing each other during Holocene occupation with prolonged separation in the Strait of Malacca. Migrate-n model testing supported a northward unidirectional stepping-stone migration route, although with an unclear directionality at the genetic break position, most likely due to weak oceanic currents. Low levels of genetic diversity and southward connectivity was detected for East coast Avicennia populations. We compared the fine-scale spatial genetic structure (FSGS) of Avicennia populations along the exposed coast in the East vs. the sheltered coast in the West. A majority of transects from both coastlines revealed no within-site kinship-based FSGS, although the remoteness of the open sea is important for Avicennia patches to maintain a neighborhood. The results provide new insights for mangrove researchers and managers for future in-depth ecological-genetic-based species conservation efforts in Malay Peninsula.

Assessment of the Genetic Diversity and Population Structure of Rhizophora mucronata along Coastal Areas in Thailand

“…Our results showed that the genetic diversity of R. mucronata was moderate (I = 0.573, Ho = 0.619, He = 0.391, Table 2 ). The same result has been found in previous mangrove studies, such as Avicennia marina worldwide [ 77 ], A. marina in the Malay Peninsula [ 60 ], and Kandelia obovata in China [ 78 ]. In addition, low genetic diversity of Rhizophora species was detected in several studies carried out in Japan, Brazil, Mexico, Southeast Asia, and the Indo-West Pacific region [ 14 , 31 , 32 , 61 , 70 , 79 , 80 ].…”

“…In addition, in a genetic study of R. apiculata using SNP markers, it was reported that the Gulf of Thailand population separated from the Andaman population [ 21 ]. Moreover, several studies have reported high differentiation between mangrove populations on both sides of the Malay Peninsula, including Ceriops tagal [ 54 , 55 ], Bruguiera gymnorrhiza [ 56 , 57 ], Excoecaria agallocha [ 58 ], Sonneratia alba [ 57 , 59 ], Avicennia marina [ 60 ], and Avicennia alba [ 57 ]. Meanwhile, our results showed that the Malay Peninsula has a minimal effect on the R. mucronata species.…”

Studies on genetic diversity, gene flow and landscape genetic in Avicennia marina: Spatial PCA, Random Forest, and phylogeography approaches

“…These results are in accord to the present study findings. Different studies have reported both long-range connection of mangrove trees in relation to ocean currents and direction, especially along same coastlines, and also the occurrence of a stepping-stone model of migration between estuaries [ 36 , 37 ]. The present study aligns with several studies throughout the world, which shows that.…”

When nature needs a helping hand: Different levels of human intervention for mangrove (re-)establishment

“…While many terrestrial forest restoration programs incorporate genetic information to strengthen the resistance and resilience of forest ecosystems to environmental changes, restoration programs for marine ecosystems-including mangrove forests-have rarely 10.3389/ffgc.2022.784322 done so, partly due to a lack of empirical data on genetic diversity and structure of the studied ecosystem, or to the complexity and costs of genetic/genomic approaches (Coleman et al, 2020). To the best of our knowledge, no mangrove (re-)establishment program have thus far considered genetic information in their planning phase (only in the monitoring phase; e.g., Granado et al, 2018), despite the increase in knowledge about genetic variation in mangrove ecosystems gained over the last two decades (e.g., Dodd et al, 2002;Triest, 2008;Wee et al, 2015;Hodel et al, 2018;Azman et al, 2020;Mantiquilla et al, 2021;Triest et al, 2021).…”