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

Assessing morphological variations in the seagrass genus Halodule (Cymodoceaceae) along the Brazilian coast through genetic analyses

Background

Seagrass meadows are distributed globally and provide critical ecological functions and ecosystem services, but seagrasses are still poorly studied compared with other coastal and marine foundation species. Species taxonomy is uncertain in various seagrass genera, such as the genus Halodule. Until recently, the morphological characteristics of leaves were the major criteria for species identification. In Brazil, three species of Halodule are recognized and separated solely using leaf morphology criteria by some authors; however, the leaves present high variability and plasticity, resulting in great uncertainty about species diversity. A review of seagrass species validation using both morphological and phylogenetic methods is needed. This includes examining the genus Halodule with the aim of better understanding its diversity and spatial distribution and consequently supporting management and conservation goals.

Methods

Plant samples with the morphological forms of H. beaudettei and H. wrightii were collected at five sites across three Brazilian marine ecoregions. Leaf tip format and leaf width and length were compared among all the sites and between the two populations with different leaf tip forms. Molecular diversity and divergence indices and analyses were used to estimate the genetic distance between H. wrightii and H. beaudettei populations. To determine the phylogenetic relationship between the two morphologies, we sequenced two molecular markers, the internal transcribed spacer (ITS) fragment and the rbcL gene, to construct phylogenetic trees using Bayesian inference.

Results

We identified H. beaudettei morphology at two sites in Northeast Brazil, while H. wrightii was found in all the ecoregions in the remaining areas, distinguished by the leaf tip shape that occurred at each site. Leaf width and length varied across the five sites, and leaf length differed between H. wrightii and H. beaudettei, with higher values observed in H. beaudettei. Variations in morphological measurements may be related to habitat conditions at each site studied. No divergence was observed for the DNA sequences of two molecular markers, except for a single base in the ITS region, resulting in the Brazilian specimens merging at a single node in the phylogenetic trees. AMOVA and genetic distance analysis revealed low genetic variation but high structuring within populations. The ITS marker showed insufficient genetic variance to delineate the two morphologies as different species which indicating H. wrightii and H. beaudettei are closely related. A genomic approach is needed to fully resolve this issue. This study represents the first step toward the complete determination of the Halodule genus on the Brazilian coast.

Cytomolecular diversity among Vigna Savi (Leguminosae) subgenera

The genus Vigna (Leguminosae) comprises about 150 species grouped into five subgenera. The present study aimed to improve the understanding of karyotype diversity and evolution in Vigna, using new and previously published data through different cytogenetic and DNA content approaches. In the Vigna subgenera, we observed a random distribution of rDNA patterns. The 35S rDNA varied in position, from terminal to proximal, and in number, ranging from one (V. aconitifolia, V. subg. Ceratotropis) to seven pairs (V. unguiculata subsp. unguiculata, V. subg. Vigna). On the other hand, the number of 5S rDNA was conserved (one or two pairs), except for V. radiata (V. subg. Ceratotropis), which had three pairs. Genome size was relatively conserved within the genus, ranging from 1C = 0.43 to 0.70 pg in V. oblongifolia and V. unguiculata subsp. unguiculata, respectively, both belonging to V. subg. Vigna. However, we observed a positive correlation between DNA content and the number of 35S rDNA sites. In addition, data from chromosome-specific BAC-FISH suggest that the ancestral 35S rDNA locus is conserved on chromosome 6 within Vigna. Considering the rapid diversification in the number and position of rDNA sites, such conservation is surprising and suggests that additional sites may have spread out from this ancestral locus.

Marine Floral Biodiversity, Threats, and Conservation in Vietnam: An Updated Review

Part of the Indo-Chinese peninsula and located on the northwest edge of the Coral Triangle in the South China Sea, the Vietnamese coastal zone is home to a wealthy marine biodiversity associated with the regional geological setting and history, which supports a large number of marine ecosystems along a subtropical to tropical gradient. The diversity of coastal benthic marine primary producers is also a key biological factor supporting marine biological diversity. The present review provides: (1) an updated checklist of the Vietnamese marine flora, (2) a review of molecular-assisted alpha taxonomic efforts, (3) an analysis of marine floral biodiversity spatial distribution nationally and regionally (South China Sea), (4) a review of the impact of anthropogenic and environmental stressors on the Vietnamese marine flora, and (5) the efforts developed in the last decade for its conservation. Based on the studies conducted since 2013 and the nomenclatural changes that occurred during this period, an updated checklist of benthic marine algae and seagrasses consisted in a new total of 878 species, including 439 Rhodophyta, 156 Ochrophyta, 196 Chlorophyta, 87 Cyanobacteria, and 15 phanerogam seagrasses. This update contains 54 new records and 5 new species of macroalgae. The fairly poor number of new records and new species identified in the last 10 years in a "mega-diverse" country can be largely attributed to the limited efforts in exploring algal biodiversity and the limited use of genetic tools, with only 25.4% (15 species) of these new records and species made based on molecular-assisted alpha taxonomy. The South Central Coast supports the highest species diversity of marine algae, which coincides with the largest density of coral reefs along the Vietnamese coast. Vietnam holds in the South China Sea one of the richest marine floras, imputable to the country's geographical, geological, and climatic settings. However, Vietnam marine floral biodiversity is under critical threats examined here, and current efforts are insufficient for its conservation. A methodical molecular-assisted re-examination of Vietnam marine floral biodiversity is urgently needed, complemented with in-depth investigations of the main threats targeting marine flora and vulnerable taxa, and finally, conservation measures should be urgently implemented.

Phylogenomic Insights into the Phylogeography of Halophila baillonii Asch

A molecular genetic approach was used to elucidate the phylogeographic relationships of the clover grass (Halophila baillonii Asch.) from three key regions within its current distributional range. Halophila baillonii is a small seagrass that has historically been only found in a few locations in the Caribbean and Atlantic coast of Brazil. In the past few decades H. baillonii has also been observed in the Eastern Tropical Pacific (ETP). Very little is known about the relationship between the ETP populations and the Caribbean and Atlantic ones. To study their relationship, we used a hybrid capture approach targeting chloroplast loci on samples from Belize, Brazil, and the Pacific coast of Costa Rica. Phylogenetic analyses resolved H. baillonii as monophyletic and placed the samples from Belize and Costa Rica in a clade sister to the Brazilian ones. The results clearly indicate that the ETP samples are very closely related to Belize and that the most likely explanation of its occurrence in the ETP is a recent introduction, possibly as a consequence of the opening of the Panama Canal.

Current advances in seagrass research: A review from Viet Nam

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total C _org stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity.