Bayu Adjie

Genetic differentiation and phylogeography of partially sympatric species complex Rhizophora mucronata Lam. and R. stylosa Griff. using SSR markers

BackgroundMangrove forests are ecologically important but globally threatened intertidal plant communities. Effective mangrove conservation requires the determination of species identity, management units, and genetic structure. Here, we investigate the genetic distinctiveness and genetic structure of an iconic but yet taxonomically confusing species complex Rhizophora mucronata and R. stylosa across their distributional range, by employing a suite of 20 informative nuclear SSR markers.ResultsOur results demonstrated the general genetic distinctiveness of R. mucronata and R. stylosa, and potential hybridization or introgression between them. We investigated the population genetics of each species without the putative hybrids, and found strong genetic structure between oceanic regions in both R. mucronata and R. stylosa. In R. mucronata, a strong divergence was detected between populations from the Indian Ocean region (Indian Ocean and Andaman Sea) and the Pacific Ocean region (Malacca Strait, South China Sea and Northwest Pacific Ocean). In R. stylosa, the genetic break was located more eastward, between populations from South and East China Sea and populations from the Southwest Pacific Ocean. The location of these genetic breaks coincided with the boundaries of oceanic currents, thus suggesting that oceanic circulation patterns might have acted as a cryptic barrier to gene flow.ConclusionsOur findings have important implications on the conservation of mangroves, especially relating to replanting efforts and the definition of evolutionary significant units in Rhizophora species. We outlined the genetic structure and identified geographical areas that require further investigations for both R. mucronata and R. stylosa. These results serve as the foundation for the conservation genetics of R. mucronata and R. stylosa and highlighted the need to recognize the genetic distinctiveness of closely-related species, determine their respective genetic structure, and avoid artificially promoting hybridization in mangrove restoration programmes.

Development and characterization of 15 polymorphic microsatellite loci in Sonneratia alba (Lythraceae) using next-generation sequencing

A set of 15 new microsatellite loci was developed and characterized for the widespread mangrove tree species Sonneratia alba (Lythraceae) by using next-generation sequencing. Forty-eight S. alba samples from seven populations in the Indo-West Pacific region were genotyped; all loci were polymorphic, with the number of alleles ranging from three to eight. The mean observed heterozygosity per locus was 0.21 for a population from Sabah, Malaysia. No null allele or significant linkage disequilibrium was detected, indicating the robustness of the markers. Only one locus (SA103) showed deviation from Hardy–Weinberg equilibrium. As characterization of these microsatellite loci was done with samples covering most of the species’ distribution range, the markers can be applied to genetic diversity studies over the broad geographical range of the species.

Isolation and characterization of 14 microsatellite markers for Rhizophora mucronata (Rhizophoraceae) and their potential use in range-wide population studies

A set of 14 new microsatellite markers was developed for mangrove species Rhizophora mucronata (Rhizophoraceae) by using pyrosequencing. Fifty-six samples from 9 populations of R. mucronata in the Indo-West Pacific region were genotyped; all loci were polymorphic, with the number of alleles ranging from 2 to 9. The mean expected heterozygosity per locus was 0.16 in a population from Sabah, no significant linkage disequilibrium was found among loci, and significant deviation from Hardy–Weinberg equilibrium was found in 3 loci. The polymorphic microsatellite markers with samples covering most of the species’ distribution range can be applied in genetic diversity studies covering a broad geographical range of the species.

Development of 11 polymorphic microsatellite markers for Xylocarpus granatum (Meliaceae) using next-generation sequencing technology

Human impacts have seriously damaged mangroves, and conservation of mangroves will require information on local and regional population genetic structures. Here, we report the development and polymorphism of eleven novel microsatellite markers, developed using next-generation sequencing on 56 samples of widespread mangrove species Xylocarpus granatum (Meliaceae) from nine populations across the Indo-West Pacific region. All loci were found to be polymorphic, with the number of alleles per locus ranging from four to 19. In a population from Sabah (Malaysia), the mean observed and expected heterozygosity per locus was 0.59 and 0.58, respectively. No null allele, significant linkage disequilibrium or deviation from Hardy–Weinberg equilibrium was detected among all loci. The eleven markers developed can be valuable tools to conservation genetics of this species across its distributional range.