Abstract Cold waves restrict the distribution of mangroves. This study examined the contribution of PSII heterogeneity and stomatal functioning to sustaining photochemistry and photoprotection in mangroves during a cold wave. We exposed eight populations of Kandelia obovata (cold-tolerant) and, Bruguiera gymnorhiza (cold-susceptible) from different latitudes to 27/20°C (favorable) and 10/3°C (chilling; simulated cold wave) day and night temperatures. Multiple trait responses imply that cold waves affected K. obovata the least. Significant changes in chlorophyll fluorescence transients (photosystem II [PSII]) with a slight decrease in the redox status of P700 (photosystem I [PSI]) imply a greater impact of a cold wave on PSII. During the cold wave, photochemical efficiency of PSII, efficiency of the water-splitting complex, light absorptance, stomatal pore area, cyclic electron flow, nonphotochemical quenching, and number of active PSIIα and PSII QB reducing centers decreased, while light transmittance, night respiration, and inactive PSII QB nonreducing, PSIIβ, and γ centers increased in both species. The population of K. obovata from the coldest latitudinal site (Fujian, China) was least affected by cold wave due to local evolutionary adaptations. Modulation of PSII heterogeneity and stomatal functioning is important to sustaining photochemistry and photoprotection in mangroves to cope with cold waves. Highlights PSII heterogeneity and stomatal functioning support mangroves to cope with cold waves. Local evolutionary adaptations promote the cold tolerance of mangrove populations.
Abstract 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.
Coastal urbanization is a key driver of mangrove loss, yet its global impacts on mangroves have yet to be thoroughly understood. Here we present a fine-scale assessment of the hidden impacts of urbanization on mangroves mediated by climate, and the joint effects of urbanization and climate at the global scale. Surprisingly, both urbanization and climate had positive impacts on mangrove growth and carbon stock in some regions, which is different from the general belief of the adverse impacts from previous research. In total, 27.3% of global mangroves received positive impacts from urbanization regarding their extent and carbon stock, among which 59.5% are indirectly mediated by climate. Moreover, mangroves in subtropical/temperate climate zones experienced more indirect positive impacts from urbanization, which enhances local climate conditions for growth by altering temperature, rainfall and sea levels. These findings suggest the feasibility of facilitating mangrove conservation through effective urban planning to achieve coastal sustainability. Mangroves may indirectly benefit from coastal urbanization in some areas due to more favorable local climatic conditions for growth, according to modeling of urbanization, climate, and mangrove growth causal relationships.
Abstract Aim Mangroves are intertidal plants with sea‐dispersed propagules, hence their population structure can offer valuable insights into the biogeographical processes driving population subdivision in coastal species. In this study, we used molecular markers and ocean circulation simulations to examine the effects of ocean currents and land masses on the genetic structure of the major mangrove species Rhizophora mucronata . Location Southeast Asia. Methods We assessed the genetic structure of 13 R. mucronata populations from continental Southeast Asia and Sumatra using 10 microsatellite loci. We first examined the relative effects of geographical distance and land mass (the Malay Peninsula) in shaping the genetic structure of R. mucronata in Southeast Asia. We then characterized the genetic structure of R. mucronata and compared it to the simulated ocean circulation patterns within our study region. Results Despite the low genetic diversity, significant genetic structuring was detected across R. mucronata populations. Contrary to observations on other mangrove species, genetic differentiation in R. mucronata was not found across the coasts of the Malay Peninsula, nor was it correlated with geographical distance. Instead, the most distinct genetic discontinuity was found at the boundary between the Andaman Sea and the Malacca Strait, and this can be explained by the prevailing ocean currents in this region. Main conclusions Our study presents novel evidence that the genetic structure of R. mucronata is maintained by ocean current‐facilitated propagule dispersal.
Environmental adaption of rubisco in global marine systems Marine environments are responsible for 50% of the net primary fixation of carbon globally. Predominantly, the Calvin Benson Basham cycle fixes carbon with the initial enzyme being Rubisco. Rubisco has been shown to be a significant bottleneck in photosynthesis, due to a slow catalytic rate and promiscuity of the enzyme. Previous Rubisco studies have largely focused on land plants, and little is known about the diversity and abundance of Rubisco within marine environments. Through analysing publicly available metagenomes and metatranscriptomes from the Earth’s seas and oceans; we have begun to paint a picture of the global abundance and variation of Rubisco. On top of this, sequence analysis of Rubisco structures provides evidence for adaption of the large and small subunit to differing environments, highlighting residues that diverge in tropical and polar systems. This study expands our knowledge of the Rubisco sequence space and presents opportunities for future engineering projects in economically important plants. Southeast Asian Mangroves in a Changing World: Insights from Phylogeography, Gene Expression and eDNA Metabarcoding Mangroves are one of the most threatened ecosystems in the world. Understanding the drivers and limitations of gene flow, phylogeography and genetic adaptation is crucial to effectively manage the threats and conserve the long-term evolutionary potential of mangroves. The first part of this talk summarizes key research findings on the biogeography of major mangrove tree species in Southeast Asia and the greater Indo-West Pacific region. In essence, propagule dispersal capabilities, land barriers and ocean currents are drivers of gene flow and underscores the importance of long-distance dispersal in connecting fragmented mangrove populations. The second part of the talk describes our work on abiotic stress response in mangroves, especially at the species range limits. Current understanding of the molecular mechanism underlying stress adaptation points toward diverging strategies in stress response, even among closely related species. These studies will be important in estimating the adaptive potential of mangroves under climate change. The third part of this talk focuses on recent pstudies on the application of environmental DNA (eDNA) as an effective biomonitoring tool in mangroves. Our findings demonstrated the dynamic distribution of fish species, the transient nature of eDNA in tropical waters, and the importance of bioregionalization in designing global studies.
Abstract The demersal brown banded bamboo shark Chiloscyllium punctatum is a major component of sharks landed in Malaysia. However, little is known about their population structure and the effect of high fishing pressure on these weak swimming sharks. Both mitochondrial DNA control region (1072 bp) and NADH dehydrogenase subunit 2 (1044 bp) were used to elucidate the genetic structure and connectivity of C. punctatum among five major areas within the Sundaland region. Our findings revealed (i) strong genetic structure with little present day mixing between the major areas, (ii) high intra-population genetic diversity with unique haplotypes, (iii) significant correlation between genetic differentiation and geographical distance coupled with detectable presence of fine scale geographical barriers (i.e. the South China Sea), (iv) historical directional gene flow from the east coast of Peninsular Malaysia towards the west coast and Borneo, and (v) no detectable genetic differentiation along the coastline of east Peninsular Malaysia. Genetic patterns inferred from the mitochondrial DNA loci were consistent with the strong coastal shelf association in this species, the presence of contemporary barriers shaped by benthic features, and limited current-driven egg dispersal. Fine scale population structure of C. punctatum highlights the need to improve genetic understanding for fishery management and conservation of other small-sized sharks.
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