Mangroves, the only woody halophytes living at the confluence of land and sea, have been heavily used traditionally for food, timber, fuel and medicine, and presently occupy about 181 000 km2 of tropical and subtropical coastline. Over the past 50 years, approximately one-third of the world's mangrove forests have been lost, but most data show very variable loss rates and there is considerable margin of error in most estimates. Mangroves are a valuable ecological and economic resource, being important nursery grounds and breeding sites for birds, fish, crustaceans, shellfish, reptiles and mammals; a renewable source of wood; accumulation sites for sediment, contaminants, carbon and nutrients; and offer protection against coastal erosion. The destruction of mangroves is usually positively related to human population density. Major reasons for destruction are urban development, aquaculture, mining and overexploitation for timber, fish, crustaceans and shellfish. Over the next 25 years, unrestricted clear felling, aquaculture, and overexploitation of fisheries will be the greatest threats, with lesser problems being alteration of hydrology, pollution and global warming. Loss of biodiversity is, and will continue to be, a severe problem as even pristine mangroves are species-poor compared with other tropical ecosystems. The future is not entirely bleak. The number of rehabilitation and restoration projects is increasing worldwide with some countries showing increases in mangrove area. The intensity of coastal aquaculture appears to have levelled off in some parts of the world. Some commercial projects and economic models indicate that mangroves can be used as a sustainable resource, especially for wood. The brightest note is that the rate of population growth is projected to slow during the next 50 years, with a gradual decline thereafter to the end of the century. Mangrove forests will continue to be exploited at current rates to 2025, unless they are seen as a valuable resource to be managed on a sustainable basis. After 2025, the future of mangroves will depend on technological and ecological advances in multi-species silviculture, genetics, and forestry modelling, but the greatest hope for their future is for a reduction in human population growth.

Phylogeographic forces driving evolution of sea-dispersed plants are often influenced by regional and species characteristics, although not yet deciphered at a large spatial scale for many taxa like the mangrove species. This study aimed to assess geographic distribution of genetic variation of this widespread mangrove in the Indo-West Pacific region and identify the phylogeographic factors influencing its present-day distribution. Analysis of five chloroplast DNA fragments' sequences from 37 populations revealed low genetic diversity at the population level and strong genetic structure of in this region. The estimated divergence times between the major genetic lineages indicated that glacial level changes during the Pleistocene epoch induced strong genetic differentiation across the Indian and Pacific Oceans. In comparison to the strong genetic break imposed by the Sunda Shelf toward splitting the lineages of the Indian and Pacific Oceans, the genetic differentiation between Indo-Malesia and Australasia was not so prominent. Long-distance dispersal ability of propagules helped the species to attain transoceanic distribution not only across South East Asia and Australia, but also across the Indian Ocean to East Africa. However, oceanic circulation pattern in the South China Sea was found to act as a barrier creating further intraoceanic genetic differentiation. Overall, phylogeographic analysis in this study revealed that glacial vicariance had profound influence on population differentiation in and caused low genetic diversity except for the refugia populations near the equator which might have persisted through glacial maxima. With increasing loss of suitable habitats due to anthropogenic activities, these findings therefore emphasize the urgent need for conservation actions for all populations throughout the distribution range of.© 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

Vivipary with precocious seedlings in mangrove plants was thought to be a hindrance to long-range dispersal. To examine the extent of seedling dispersal across oceans, we investigated the phylogeny and genetic structure among East Asiatic populations of Kandelia candel based on organelle DNAs. In total, three, 28 and seven haplotypes of the chloroplast DNA (cpDNA) atpB-rbcL spacer, cpDNA trnL-trnF spacer, and mitochondrial DNA (mtDNA) internal transcribed spacer (ITS) were identified, respectively, from 202 individuals. Three data sets suggested consistent phylogenies recovering two differentiated lineages corresponding to geographical regions, i.e. northern South-China-Sea + East-China-Sea region and southern South-China-Sea region (Sarawak). Phylogenetically, the Sarawak population was closely related to the Ranong population of western Peninsula Malaysia instead of other South-China-Sea populations, indicating its possible origin from the Indian Ocean Rim. No geographical subdivision was detected within the northern geographical region. An analysis of molecular variance (AMOVA) revealed low levels of genetic differentiation between and within mainland and island populations (phiCT = 0.015, phiSC = 0.037), indicating conspicuous long-distance seedling dispersal across oceans. Significant linkage disequilibrium excluded the possibility of recurrent homoplasious mutations as the major force causing phylogenetic discrepancy between mtDNA and the trnL-trnF spacer within the northern region. Instead, relative ages of alleles contributed to non-random chlorotype-mitotype associations and tree inconsistency. Widespread distribution and random associations (chi2 = 0.822, P = 0.189) of eight hypothetical ancestral cytotypes indicated the panmixis of populations of the northern geographical region as a whole. In contrast, rare and recently evolved alleles were restricted to marginal populations, revealing some preferential directional migration.

1. Mangrove species richness declines dramatically from a maximum in the Indo‐West Pacific (IWP) to a minimum in the Caribbean and Western Atlantic. Explaining this ‘anomalous’ biogeographic pattern has been a focus of discussion for most of this century.2. Two hypotheses have been put forward to explain the mangrove biodiversity anomaly. The ‘centre‐of‐origin hypothesis’ asserts that all mangrove taxa originated in the IWP and subsequently dispersed to other parts of the world. The ‘vicariance hypothesis’ asserts that mangrove taxa evolved around the Tethys Sea during the Late Cretaceous, and regional species diversity resulted from in situ diversification after continental drift.3. Five lines of evidence are used to test between these two hypotheses. First, we review the mangrove fossil record. Second, we compare modern and fossil distributions of mangroves and eight genera of gastropods that show high fidelity to the mangrove environment. Third, we describe species‐area relationships of mangroves and associated gastropods with respect to area of available habitat. Fourth, we analyse patterns of nestedness of individual plant and gastropod communities in mangrove forests. Fifth, we analyse patterns of nestedness of individual plant and gastropod species.4. All five lines of evidence support the vicariance hypothesis. The first occurrences in the fossil record of most mangrove genera and many genera of gastropods associated with mangrove forests appear around the Tethys Sea from the Late Cretaceous through the Early Tertiary. Globally, species richness in any given mangrove forest is tightly correlated with available area. Patterns of nestedness at the community and species‐level both point towards three independent regions of diversification of mangrove ecosystems: South‐east Asia, the Caribbean and Eastern Pacific, and the Indian Ocean region.

Mangroves are ecologically important forest communities in tropical and subtropical coasts, the effective management of which requires understanding of their phylogeographic patterns. However, these patterns often vary among different species, even among ecologically similar taxa or congeneric species. Here, we investigated the levels and patterns of genetic variation within Lumnitzera consisting of two species (L. racemosa and L. littorea) with nearly sympatric ranges across the Indo-West Pacific (IWP) region by sequencing three chloroplast DNA regions (for both species) and genotyping 11 nuclear microsatellite loci (for L. littorea). Consistent with findings in studies on other mangrove species, we found that both L. racemosa and L. littorea showed relatively high genetic variation among populations but low genetic variation within populations. Haplotype network and genetic clustering analyses indicated two well-differentiated clades in both L. racemosa and L. littorea. The relationship between geographic and genetic distances and divergence time estimates of the haplotypes indicated that limited dispersal ability of the propagules, emergence of land barriers during ancient sea-level changes, and contemporary oceanic circulation pattern in the IWP influenced the current population structure of the two species. However, the position of genetic break was found to vary between the two species: in L. racemosa, strong divergence was observed between populations from the Indian Ocean and the Pacific Ocean possibly due to land barrier effect of the Malay Peninsula; in L. littorea, the phylogeographic pattern was created by a more eastward genetic break along the biogeographic barrier identified as the Huxley’s line. Overall, our findings strongly supported previous hypothesis of mangrove species divergence and revealed that the two Lumnitzera species have different phylogeographic patterns despite their close genetic relationship and similar current geographic distribution. The findings also provided references for the management of Lumnitzera mangroves, especially for the threatened L. littorea.

Allopatric speciation requiring an unbroken period of geographical isolation has been the standard model of neo-Darwinism. While doubts have been repeatedly raised, strict allopatry without any gene flow remains a plausible mechanism in most cases. To rigorously reject strict allopatry, genomic sequences superimposed on the geological records of a well-delineated geographical barrier are necessary. The Strait of Malacca, narrowly connecting the Pacific and Indian Ocean coasts, serves at different times either as a geographical barrier or a conduit of gene flow for coastal/marine species. We surveyed 1700 plants from 29 populations of 5 common mangrove species by large-scale DNA sequencing and added several whole-genome assemblies. Speciation between the two oceans is driven by cycles of isolation and gene flow due to the fluctuations in sea level leading to the opening/closing of the Strait to ocean currents. Because the time required for speciation in mangroves is longer than the isolation phases, speciation in these mangroves has proceeded through many cycles of mixing-isolation-mixing, or MIM, cycles. the MIM mechanism, by relaxing the condition of no gene flow, can promote speciation in many more geographical features than strict allopatry can. Finally, the MIM mechanism of speciation is also efficient, potentially yielding (> 1) species ather cycles.Mechanisms of species formation have always been a conundrum. Speciation between populations that are fully geographically isolated, or allopatric speciation, has been the standard solution in the last 50 years. Complete geographical isolation with no possibility of gene flow, however, is often untenable and is inefficient in generating the enormous biodiversity. By studying mangroves on the Indo-Malayan coasts, a global hotspot of coastal biodiversity, we were able to combine genomic data with geographical records on the Indo-Pacific Barrier that separates Pacific and Indian Ocean coasts. We discovered a novel mechanism of speciation that we call mixingisolation-mixing (MIM) cycles. By permitting intermittent gene flow during speciation,MIMcycles can potentially generate species at an exponential rate, thus combining speciation and biodiversity in a unified framework.

Comparing with other regions, Asia is mostly dominated by the monsoon climate and tropical plants can be found at the furthest places away from the equator. Understanding the role of monsoon in the dispersal and evolution of tropical plants is helpful for exploring the distribution patterns of vegetation and mechanisms underlying the origin and maintenance of biodiversity in Asia. In summer, there are three types of monsoon in Asia, i.e. East Asia Monsoon, South Asia Monsoon, North-west Pacific Ocean Monsoon. The summer monsoon climate in Asia originated at about 40 Ma, when the early angiosperm evolved and started its diversification in Southeast Asia and South China. It suggested that the monsoon may facilitate the quick speciation and spread of early angiosperm. Monsoon climate facilitates the northward spread of Asia’s tropical plants and some tropical plants can be found even at Yarlung Zangbo River and the boundaries of Guizhou-Guangxi-Yunnan. Such effetcs largely change distribution patterns of zonal vegetation and even causes local vegetation types in some places with unusual topography such as tropical seasonal rainforests, monsoon rainforests, savanna and grassland along dry-hot valley in Southwest China, coastal savanna in West Hainan Island. The three summer monsoons interact at Southwest China and Indo-China Peninsula and these regions are dominated by limestone landscapes and high mountains with big rivers. Some Asia-endemic tropical taxa even formed a diversification and endemism center at this region, which may be a reason for the formation and maintenance of Indo-Burma biodiversity hotspots with global warming, the monsoon may further promote the northward spread of tropical plants and may have fundamental effects on biodiversity and flora evolution in South China.

亚洲是全球季风气候最典型的区域, 也是热带植物分布距离赤道最远的地区。揭示季风对热带植物迁移与进化的影响规律, 有利于深入认识东亚植被分布和生物多样性形成与维持机制。亚洲地区夏季盛行东亚季风、南亚季风和西北太平洋季风。历史上, 季风盛行的时间与早期被子植物在东南亚群岛、华夏古陆起源的时间大致吻合, 季风可能促进了被子植物的快速分化与扩散。季风是热带植物得以向北扩散到我国滇黔桂交界区和雅鲁藏布江河谷的根本原因, 并导致了热带季节性雨林、热带季雨林、干旱河谷稀树灌丛或草原、海南岛西部滨海稀树草原等特殊植被的形成。亚洲的三大夏季风在高山纵横、大河奔流和石灰岩地貌密布的中国西南与中南半岛一带交汇、叠加, 使之成为一些典型热带类群的物种多样与特有种分布中心。这可能是中国-缅甸生物多样性热点地区形成与维持的一个重要原因。随着全球气候变暖, 季风可能促进热带植物的进一步北迁, 增加中国南方植物区系的热带植物成分。

The Belt and Road Initiative (BRI) of China is sharply catalyzing the evolution of the global economic landscape. In order to cope with these great changes, China needs to take South China Sea Region (SCSR) as its strategic pivot and explore the construction possibility of a strategic integrated economic zone combining China and ASEAN. Based on key indicators, this paper outlines the overall development characteristics of SCSR, analyses the structural characteristics of industry and trade based on the indexes of industrial structure similarity and trade structure coincidence, depicts the spatial network characteristics of the core growth area around SCSR, and discusses the construction prospect of multiple integrated economic zone in SCSR. The results show that: (1) From 2000 to 2017, the main economic indicators of SCSR grew pretty well, the development speed and quality were much higher than the global average level in the same period. (2) Driven by the global industrial transfer stages and spatial paths, SCSR has evolved into four levels, the first level includes Macao, Singapore, and Hong Kong, the second level includes Guangdong, Fujian, Taiwan, Brunei and Malaysia, the third level includes Yunnan, Guangxi, Hainan, Thailand, Indonesia, Philippines and Vietnam, the fourth level includes Myanmar, Laos and Cambodia. (3) The indexes of industrial structure similarity and trade structure coincidence of 11 countries in SCSR keep at a high level, which do not only show the integration trend from the horizontal and vertical dimensions, but also from the upgrading and downgrading states. (4) SCSR has formed nine core growth regions, and the advantage industries and export commodity types between different regions are characterized by convergence and complementarity due to the polarization and diffusion effect of the growth poles. (5) From a long-term perspective, SCSR has had the external and internal conditions for building a multiple integrated economic zone. The 5th round of global industrial transfer and the reconstruction of the global value chain will build a production-consumption network which can match the characteristics of regional resource endowments, while the spatial network will be built by spatial entities such as urban agglomeration and high-speed transportation, and the cooperation policy platform from internal and external conditions will better guarantee the construction of the multiple integrated economic zone as well.

《区域全面经济伙伴关系协定》（RCEP）合作框架正催化全球经济版图格局发生剧烈演变,为应对“百年未有之大变局”,中国需要以“一带一路”倡议为契机,以环南海区域为战略基点,在深入研究区域发展特征的基础上,探讨建设“中国+东南亚”战略性一体化经济区的可能性并付诸实施。本文以环南海区域为重点,结合区域发展重点指标描述了其整体发展特征,利用产业结构相似度指数和贸易结构重合度指数,对环南海区域产业与对外贸易的结构性特征进行了剖析,并刻画了环南海区域核心增长区域的空间网络特征,最后讨论了环南海区域构建多元一体化经济区的前景并提出政策建议。结果表明：① 2000—2017年环南海区域主要发展指标增长态势强劲,发展速度和质量远超全球同期平均水平。② 在全球产业转移周期阶段与空间路径的双重驱动下,环南海区域形成了“澳新港—粤闽台文马—滇桂琼泰印菲越—缅老柬”四大梯级发展格局。③ 环南海区域11个国家间产业结构相似度指数和贸易结构重合度指数均处于较高水平,兼具“横向一体化”和“纵向梯级化”复合特征;产业结构与全球贸易商品结构呈现出“高端化”和“低端化”并举的态势。④ 环南海区域已经形成九大核心增长区域,增长极的极化与扩散效应使得不同区域之间的优势产业和出口商品类型呈现相似性和互补性。⑤ 展望未来,新一轮全球产业转移及其引致的全球价值链重组将构建起深度匹配地区资源禀赋特征的区域一体化生产—消费网络,而城市群、高速交通等空间实体所构建的“点—轴”空间网络和“内—外”开放合作政策平台也将更好保障一体化经济区的构建与发展。

There are a variety of proposed evolutionary and ecological explanations for why some species have more extensive geographical ranges than others. One of the most common explanations is variation in species' dispersal ability. However, the purported relationship between dispersal distance and range size has been subjected to few theoretical investigations, and empirical tests reach conflicting conclusions. We attempt to reconcile the equivocal results of previous studies by reviewing and synthesizing quantitative dispersal data, examining the relationship between average dispersal ability and range size for different spatial scales, regions and taxonomic groups. We use extensive data from marine taxa whose average dispersal varies by seven orders of magnitude. Our results suggest dispersal is not a general determinant of range size, but can play an important role in some circumstances. We also review the mechanistic theories proposed to explain a positive relationship between range size and dispersal and explore their underlying rationales and supporting or refuting evidence. Despite numerous studies assuming a priori that dispersal influences range size, this is the first comprehensive conceptual evaluation of these ideas. Overall, our results indicate that although dispersal can be an important process moderating species' distributions, increased attention should be paid to other processes responsible for range size variation.

Kandelia (Rhizophoraceae) has long been regarded as a monotypic mangrove genus. Recent studies in chromosome number, molecular phylogeography, physiological adaptation, and leaf anatomy, however, reveal that there are two well differentiated sets of geographical populations separated by the South China Sea. These are recognized as two distinct species, Kandelia candel (L.) Druce and Kandelia obovata Sheue, Liu & Yong sp. nov.

The genetic differentiation and structure of Hibiscus tiliaceus, a pantropical plant with sea-drifted seeds, and four allied species were studied using six microsatellite markers. A low level of genetic differentiation was observed among H. tiliaceus populations in the Pacific and Indian Ocean regions, similar to the results of a previous chloroplast DNA (cpDNA) study. Frequent gene flow by long-distance seed dispersal is responsible for species integration of H. tiliaceus in the wide distribution range. On the other hand, highly differentiated populations of H. tiliaceus were detected in West Africa, as well as of Hibiscus pernambucensis in southern Brazil. In the former populations, the African continent may be a geographical barrier that prevents gene flow by sea-drifted seeds. In the latter populations, although there are no known land barriers, the bifurcating South Equatorial Current at the north-eastern horn of Brazil can be a potential barrier to gene flow and may promote the genetic differentiation of these populations. Our results also suggest clear species segregation between H. tiliaceus and H. pernambucensis, which confirms the introgression scenario between these two species that was suggested by a previous cpDNA study. Our results also provide good evidence for recent transatlantic long-distance seed dispersal by sea current. Despite the distinct geographical structure observed in the cpDNA haplotypes, a low level of genetic differentiation was found between Pacific and Atlantic populations of H. pernambucensis, which could be caused by transisthmian gene flow.

Inference of genetic structure and demographic history is fundamental issue in evolutionary biology. We examined the levels and patterns of genetic variation of a widespread mangrove species in the Indo-West Pacific region, Bruguiera gymnorrhiza, using ten nuclear gene regions. Genetic variation of individual populations covering its distribution range was low, but as the entire species it was comparable to other plant species. Genetic differentiation among the investigated populations was high. They could be divided into two genetic clusters: the West and East clusters of the Malay Peninsula. Our results indicated that these two genetic clusters derived from their ancestral population whose effective size of which was much larger compared to the two extant clusters. The point estimate of speciation time between B. gymnorrhiza and Bruguiera sexangula was two times older than that of divergence time between the two clusters. Migration from the West cluster to the East cluster was much higher than the opposite direction but both estimated migration rates were low. The past Sundaland and/or the present Malay Peninsula are likely to prevent gene flow between the West and East clusters and function as a geographical or land barrier.

Glaciation and deglaciation and the accompanying lowering and rising of sea levels during the late Pleistocene are known to have greatly affected land mass configurations in Southeast Asia. The objective of this report is to provide a series of maps that estimate the areas of exposed land in the Indo‐Australian region during periods of the Pleistocene when sea levels were below present day levels.

Patterns of genetic structure are essential for a comprehensive understanding of the evolution and biogeography of a species. Here, we investigated the genetic patterns of one of the most widespread and abundant mangrove species in the Indo-West Pacific, Sonneratia alba J. Sm., in order to gain insights into the ecological and evolutionary drivers of genetic structure in mangroves. We employed 11 nuclear microsatellite loci and two chloroplast regions to genotyped 25 S. alba populations. Our objectives were to (1) assess the level of genetic diversity and its geographic distribution; and (2) determine the genetic structure of the populations. Our results revealed significant genetic differentiation among populations. We detected a major genetic break between Indo-Malesia and Australasia, and further population subdivision within each oceanic region in these two major clusters. The phylogeographic patterns indicated a strong influence of vicariance, oceanic barriers and geographic distance on genetic structure. In addition, we found low genetic diversity and high genetic drift at range edge. This study advances the scope of mangrove biogeography by demonstrating a unique scenario whereby a widespread species has limited dispersal and high genetic divergence among populations.