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

Aim: Biogeographical barriers restrict the movement of individuals, resulting in population divergence, genetic differentiation, endemism and speciation. Yet, some barriers demonstrate unequal effect across species depending on species dispersal, which manifests in varying genetic structure. We test the hypotheses that the genetic structure of four coastal mangrove species would reflect differences in dispersal potential across the Malay Peninsula, a major biogeographical barrier in the Indo-West Pacific region. Location: East and west coasts of the Malay Peninsula. Taxon Mangrove trees Avicennia alba, Sonneratia alba, Bruguiera gymnorhiza and Rhizophora mucronata. Methods: For each species, we characterized genetic structure and gene flow using 7–12 species-specific nuclear microsatellite markers. We tested for east–west genetic differentiation across the peninsula, a stepping-stone migration pattern, and assessed the proportion of recent dispersal and direction of historical migration along the Malacca Strait. Results: Significant east–west genetic differentiation across the peninsula was observed in A. alba, S. alba and B. gymnorhiza, and the effect was most pronounced for the two species with lower dispersal potential (A. alba, S. alba). In contrast, the two species with higher dispersal potential (B. gymnorhiza and R. mucronata) exhibited much higher proportion of recent inter-population migration along the Malacca Strait. The signature of historical colonization from refugia in the Andaman Sea (north-to-south migration along the Malacca Strait) predominated for A. alba and S. alba. Historical south–north migration predominated for R. mucronata and B. gymnorhiza. Main conclusions: This study implicated dispersal potential as a cause of varying mangrove species genetic structure across a biogeographical barrier. The Malay Peninsula functions as a filter to gene flow rather than a barrier. The genetic structure in mangrove species with a higher dispersal potential is more congruent with contemporary gene flow while that of species with a lower dispersal potential reflects historical processes. Our findings hint at the role of dispersal potential as a predictor of gene flow in mangroves

High genetic diversity in a potentially vulnerable tropical tree species despite extreme habitat loss

10.1371/journal.pone.0082632PLoS ONE812-POLN

Frequency of different allele frequency classes.

<p>Frequency of different allele frequency classes.</p

Sample size (N) per locus, size range of alleles, total number of alleles detected, observed (H_o) and expected (H_e) heterozygosity, genotyping error rate, percent missing data, percent null alleles, and inbreeding co-efficient values (F_IS).

<p> Bold indicates significant null alleles.</p

Allele frequencies for each locus.

<p>Alleles present in very low numbers have the frequency presented above the allele if the bar too small to be easily visualized. All potential allele sizes within the captured range (assuming normal dinucleotide repeat units) are included in the x-axis; blanks indicate that this allele size was not captured. A dot below the allele indicates an unusual size (1 bp difference from nearest allele). ‘a’ indicates a private allele in the adult age class, ‘s’ indicates a private allele in the seedling cohort.</p

Comparisons of genetic diversity, reproductive, and spatial genetic structure indices among Singapore <i>K. malaccensis</i> cohorts with reference to Malaysian populations [34], [35].

<p>_e, mean expected heterozygosity; R, mean allelic richness; F_IS, mean inbreeding co-efficient excluding locus Km071 (frequency null alleles ∼0.30); r (0–10 m), average relatedness (r, Queller & Goodnight 1989) for the 0–10 m distance class; S_p, spatial genetic structure intensity (approximate 95% confidence intervals); M, M-values for adult cohort (M_a), and for the seedling plus sapling cohorts combined (M_s); t_m, outcrossing rate and t_m-t_s, biparental inbreeding rates (standard deviations in parentheses). ^a and ^b indicate significant differences between age classes (p<0.05). H</p><p>²seven loci; ³six loci, ⁴4 loci and 9 adults.¹ eight loci; </p

Map of Singapore’s remaining primary forest fragments within a secondary forest and urban matrix.

<p>Dark green – primary forest; Light green – secondary forest; red dots – adult <i>K. malaccensis</i> individuals.</p

Allelic richness accumulation curves for each locus.

<p>Rarefaction curves were produced in the R statistical environment <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0082632#pone.0082632-R1" target="_blank">[69]</a>.</p

Diverse associations among coral host haplotypes and algal endosymbionts may drive adaptation at geographically peripheral and ecologically marginal locations

To understand the evolutionary history and local adaptation of marginal, subtropical populations of a common reef-building coral (genus Pocillopora) and their Symbiodinium endosymbionts

Genetic diversity and connectivity in a brooding reef coral at the limit of its distribution

Remote populations are predicted to be vulnerable owing to their isolation from potential source reefs, and usually low population size and associated increased extinction risk. We investigated genetic diversity, population subdivision and connectivity in the brooding reef coral Seriatopora hystrix at the limits of its Eastern Australian (EA) distribution and three sites in the southern Great Barrier Reef (GBR). Over the approximately 1270 km survey range, high levels of population subdivision were detected (global FST = 0.224), with the greatest range in pairwise FST values observed among the three southernmost locations: Lord Howe Island, Elizabeth Reef and Middleton Reef. Flinders Reef, located between the GBR and the more southerly offshore reefs, was highly isolated and showed the signature of a recent bottleneck. High pairwise FST values and the presence of multiple genetic clusters indicate that EA subtropical coral populations have been historically isolated from each other and the GBR. One putative first-generation migrant was detected from the GBR into the EA subtropics. Occasional long-distance dispersal is supported by changes in species composition at these high-latitude reefs and the occurrence of new species records over the past three decades. While subtropical populations exhibited significantly lower allelic richness than their GBR counterparts, genetic diversity was still moderately high. Furthermore, subtropical populations were not inbred and had a considerable number of private alleles. The results suggest that these high-latitude S. hystrix populations are supplemented by infrequent long-distance migrants from the GBR and may have adequate population sizes to maintain viability and resist severe losses of genetic diversity