Oceanic currents, not land masses, maintain the genetic structure of the mangrove Rhizophora mucronata Lam. (Rhizophoraceae) in Southeast Asia

Abstract

Aim Mangroves are intertidal plants with sea-dispersed propagules, hence their population structure can offer valuable insights into the biogeographical processes driving population subdivision in coastal species. In this study, we used molecular markers and ocean circulation simulations to examine the effects of ocean currents and land masses on the genetic structure of the major mangrove species Rhizophora mucronata. Location Southeast Asia.Methods We assessed the genetic structure of 13 R. mucronata populations from continental Southeast Asia and Sumatra using 10 microsatellite loci. We first examined the relative effects of geographical distance and land mass (the Malay Peninsula) in shaping the genetic structure of R. mucronata in Southeast Asia. We then characterized the genetic structure of R. mucronata and compared it to the simulated ocean circulation patterns within our study region. ResultsDespite the low genetic diversity, significant genetic structuring was detected across R. mucronata populations. Contrary to observations on other mangrove species, genetic differentiation in R. mucronata was not found across the coasts of the Malay Peninsula, nor was it correlated with geographical distance. Instead, the most distinct genetic discontinuity was found at the boundary between the Andaman Sea and the Malacca Strait, and this can be explained by the prevailing ocean currents in this region.Main conclusions Our study presents novel evidence that the genetic structure of R. mucronata is maintained by ocean current-facilitated propagule dispersal.

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

“…Notably, on top of EIO-SCS divergence, our data also supported further subdivision of population structuring within the EIO and SCS. These subdivisions were not detected in a previous study by Yang et al (2017) [11], and highlighted the potential importance of oceanic barriers in restricting gene flow (see also [7]). …”

“…Nevertheless, gene flow was detected between these two lineages, suggesting that recent post-glaciation contact counteracted the strong effects of vicariance. It is interesting to note that the phylogeographic pattern observed here differed from that of R. mucronata, for which a genetic continuity was detected at the boundary between the Andaman Sea and the Malacca Strait [7]. In S. alba, the boundary was pushed further south into the Malacca Strait.…”

“…The SCS populations (east coast Malay Peninsula) were represented by MA3, TH3, VIE, MA4, PH1 and PH2. In the predictor matrix, population pairs from different coasts were coded 1 (high expected genetic differentiation), while population pairs from the same coast were coded 0 (low expected genetic differentiation) [7,36]. A Mantel R statistic based on Pearson's product-moment correlation between the pairwise genetic distance matrix and the predictor matrix was performed with 999 permutations using the package "vegan" [37] implemented in the R statistical platform.…”

“…[4] but between the edge of the Andaman Sea and the Strait of Malacca in Rhizophora mucronata Lam. [7,8]. This discordance reflects the contribution of taxon-specific traits to the fine-scaled genetic structure, e.g., the unexpected location of the genetic divide in R. mucronata was attributed to its high capabilities in long distance dispersal and the importance of ocean currents in driving it.…”

Isolation by resistance across a complex coral reef seascape

“…This 'isolation by resistance' (IBR) pattern may be particularly evident when an organism's reproductive strategy involves a sedentary adult phase and a pelagic larval stage that is subject to prevailing currents. Complex ocean circulation can represent significant barriers to dispersal and can produce patterns of genetic structure that are often difficult to interpret; however, incorporating oceanographic mechanisms into the analyses of population genetic data has placed confounding patterns of genetic patchiness into more ecologically relevant contexts [18][19][20][21][22].…”