Analysis of rDNA reveals a high genetic diversity of Halophila major in the Wallacea region

Abstract

The genus Halophila shows the highest species diversity within the seagrass genera. Southeast Asian countries where several boundary lines exist were considered as the origin of seagrasses. We hypothesize that the boundary lines, such as Wallace’s and Lydekker’s Lines, may act as marine geographic barriers to the population structure of Halophila major. Seagrass samples were collected at three islands in Vietnamese waters and analyzed by the molecular maker ITS. These sequences were compared with published ITS sequences from seagrasses collected in the whole region of interest. In this study, we reveal the haplotype and nucleotide diversity, linking population genetics, phylogeography, phylogenetics and estimation of relative divergence times of H. major and other members of the Halophila genus. The morphological characters show variation. The results of the ITS marker analysis reveal smaller groups of H. major from Myanmar, Shoalwater Bay (Australia) and Okinawa (Japan) with high supporting values. The remaining groups including Sri Lanka, Viet Nam, the Philippines, Thailand, Malaysia, Indonesia, Two Peoples Bay (Australia) and Tokushima (Japan) showed low supporting values. The Wallacea region shows the highest haplotype and also nucleotide diversity. Non-significant differences were found among regions, but significant differences were presented among populations. The relative divergence times between some members of section Halophila were estimated 2.15–6.64 Mya.

Morphological variation and haplotype diversity of \(\textit{Halimeda macroloba}\) and \(\textit{H. opuntia}\) (Chlorophyta: Halimedaceae) from Southern Vietnam

“…Arina et al, [1] also depicted two morphotypes of H. bonerensis from Malaysia based on the morphology of utricle and medullary filaments. Morphotype was also reported in our previous studies in marine plants such as Halophila ovalis [29] and Halophila major [30].…”

Current advances in seagrass research: A review from Viet Nam

“…For region 3, numerous geographically suitable areas (e.g., lagoons, bays, islands, islets, atolls, and reefs) can be identified along the coast providing a diversity of habitats for the occurrence of seagrasses. The seagrass distribution of region 3 is the most well-studied among the four regions with a total area of 3,109 ha (Cao, 2011;Cao et al, 2019;Nguyen et al, 2021a;Nguyen et al, 2021b). Recently, Nguyen et al (2021a) showed that the seagrass distribution at Phu Quoc Island (i.e., the biggest island of Viet Nam) was about 7,579 ha and is considered the biggest seagrass bed in Viet Nam (region 4).…”

“…Among families, both Penaeidae and Portunidae were the dominant groups. For the diversity of zoobenthos, 203 species including 92 species of mollusk, 51 Hb, Hu, Rm, Zj (Cao et al, 2014;Cao et al (2020a) 3 8 3,109 Hb, Hd, Ho, Hma Hmi, Hsp, Ea, Th, Tc, Cr, Cs, Hu, Hp, Si, Rm (Nguyen et al, 2021b), (Cao et al, 2019;Cao et al, 2020b;Nguyen et al, 2021a) 4 9 7,609 Hb, Hd, Ho, Hma "Hmi", Hsp, Ea, Th, Cr, Cs, Hu, Hp, Si (Do et al, 2020), (Nguyen et al, 2021b), (Nguyen et al, species of crustacean, 49 species of polychaeta, and other species of Echinodermata were found (Nguyen, 2013). Biodiversity of marine organisms in seagrass beds along the coast of region 3 also showed variation.…”

“…Recently, Nguyen et al (2021a) reported that the main characteristic between H. ovalis and H. major is that distance between the intra-marginal veins and the lamina margin of H. ovalis is much wider than H. major, and the intra-marginal veins of H. ovalis is easily recognized by naked eyes, and other parameters including leaf width, leaf length, number of cross-veins, number of branching cross-veins, space between cross-veins, and the angle between cross veins and midveins did not show significant differences between two species. For different habitat types, H. ovalis grows in lagoons that experience large salinity differences between the dry and the rainy seasons, low water velocity, and weak wave action, whereas H. major is found in the offshore islands (Nguyen et al, 2021b). "Halophila major SL type" collected from Nha Trang Bay showed morphological characters consistent with H. major; however, Nguyen et al (2021a) suggested that this population may be the cross-hybridization between H. ovalis and H. major.…”

“…Halophila major, the sister species of H. ovalis, was reported in offshore islands in Viet Nam. By using rDNA marker (ITS1-5.8S-ITS2), Nguyen et al (2021b) depicted the haplotype network of H. major in the world (Figure 5). There are two haplotypes in southern Viet Nam, one of them is common to those from the Philippines.…”