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A substantial proportion of the world's living species, including one-third of the reef-building corals, are threatened with extinction and in pressing need of conservation action. In order to reduce biodiversity loss, it is important to consider species' contribution to evolutionary diversity along with their risk of extinction for the purpose of setting conservation priorities. Here I reconstruct the most comprehensive tree of life for the order Scleractinia (1,293 species) that includes all 837 living reef species, and employ a composite measure of phylogenetic distinctiveness and extinction risk to identify the most endangered lineages that would not be given top priority on the basis of risk alone. The preservation of these lineages, not just the threatened species, is vital for safeguarding evolutionary diversity. Tests for phylogeny-associated patterns show that corals facing elevated extinction risk are not clustered on the tree, but species that are susceptible, resistant or resilient to impacts such as bleaching and disease tend to be close relatives. Intensification of these threats or extirpation of the endangered lineages could therefore result in disproportionate pruning of the coral tree of life.

Urban coral reefs are regarded as marginal communities that live under localized conditions considered detrimental for coral survival, such as high sediment load. They are also impacted by global environmental changes, especially increases in sea surface temperatures. These conditions can cause sub-optimal performance and may lead to dissociation of the mutualistic symbiosis between the coral host and its endosymbionts (Symbiodiniaceae), which provide the majority of the coral’s daily energy budget. While recent studies have explored gene transcriptional responses to extreme conditions using cultured cells of Symbiodiniaceae, it is generally unknown how their responses manifest in hospite. Here, we investigate differential gene expression of endosymbionts hosted by the common reef-building coral Pocillopora acuta, following separate and combined exposures to two major environmental stressors: heat and sediment. We report that Durusdinium largely dominate the Symbiodiniaceae population in P. acuta, which suggests that the observed differential gene expression patterns are mainly responses from this known stress-tolerant endosymbiont genus. Differentially expressed genes were detected in response to heat, and to combined heat and sediment. These genes are associated with various biological processes including apoptosis, cell proliferation, cell–extracellular matrix adhesion, DNA damage repair, lipid catabolism, and lipid homeostasis. Our study provides valuable insights regarding the role of gene regulation by the endosymbiotic dinoflagellates to help maintain health and function of the coral host, which ultimately contributes to the persistence of P. acuta in Singapore’s highly urbanized reefs.

Comprising approximately 7500 living species of various corals and sea anemones, Anthozoa ranks among the most ecologically and economically valuable marine taxa. However, the taxonomy and systematics of anthozoans remain in flux as several facets of their biology (e.g. cryptic speciation, hybridisation and introgression, morphological plasticity and convergence) confound taxonomists even today. Rapid advancements in molecular sequencing and analyses have made available vast quantities of genomic data on an increasing number of species across the anthozoan tree of life. While whole genome assemblies are expected to result in the most robust phylogenetic trees, reduced-representation techniques such as genome skimming, RAD-seq, phylotranscriptomics and hybrid capture have led to well-supported inferences at various taxonomic levels and may still be favoured at this stage due to the high cost associated with even a single genome assembly. Here, we examine the different genotyping and analytical approaches used in anthozoan phylogeny reconstructions, their applicability across different divergences, and the coverage of studies among anthozoan clades to date. Based on our review of 82 phylogenomic studies, we describe the suitability of methods employed relative to their aims, highlight the imbalanced coverage of taxonomic groups studied and assess immediate and long-term needs where consolidation and streamlining of approaches would further advance the field. Overall, we find that Scleractinia (Anthozoa) is the most phylogenetically sampled group and studies on Octocorallia (Anthozoa) and its subclades are emerging. Nevertheless, we emphasise the need for more phylotranscriptomic, hybrid capture and whole genome sequencing across all anthozoans to increase topological support and generate more precise divergence time estimates. The enhanced phylogenetic understanding of Anthozoa is expected to provide insights into the evolution of genes and adaptations to environmental stressors amidst the current climate and mass extinction crises.

Despite their recognized importance in terrestrial and aquatic ecosystems, marine fungi, especially those associated with host organisms, remain poorly studied. Corals contain diverse communities of microbes that play important roles in adapting to disturbance and promoting host health, but studies on coral-associated fungal communities are conspicuous by their absence. Here, we comprehensively characterized the fungal communities and diversity associated with 97 unrelated coral colonies of Pocillopora acuta from nine islands in Singapore. We depleted coral DNA prior to PCR amplification of the fungal barcoding region (ITS1) to minimize issues of preferential host DNA amplification. This approach produced over a hundred times greater proportion of reads that were of fungal origin (75%) than previous studies, allowing us to more precisely characterize the associated fungal communities. We found no spatial structuring of fungal communities based upon sampling location, and provide evidence that suggests coral-associated fungi are more than just pathogens within their hosts. Many have been putatively identified as saprotrophs that are likely involved in making nutrients available for their host, and others may be possible symbiotrophs. Characterization of host-associated fungal communities provides valuable understanding—including information on the coral holobiont and how it functions—on a frequently overlooked, yet important microbial group.

The evolution rates of mtDNA in early metazoans hold important implications for DNA barcoding. Here, we present a comprehensive analysis of intra- and interspecific COI variabilities in Porifera and Cnidaria (separately as Anthozoa, Hydrozoa, and Scyphozoa) using a data set of 619 sequences from 224 species. We found variation within and between species to be much lower in Porifera and Anthozoa compared to Medusozoa (Hydrozoa and Scyphozoa), which has divergences similar to typical metazoans. Given that recent evidence has shown that fungi also exhibit limited COI divergence, slow-evolving mtDNA is likely to be plesiomorphic for the Metazoa. Higher rates of evolution could have originated independently in Medusozoa and Bilateria or been acquired in the Cnidaria + Bilateria clade and lost in the Anthozoa. Low identification success and substantial overlap between intra- and interspecific COI distances render the Anthozoa unsuitable for DNA barcoding. Caution is also advised for Porifera and Hydrozoa because of relatively low identification success rates as even threshold divergence that maximizes the “barcoding gap” does not improve identification success.

The Coral Triangle (CT) region of the Indo-Pacific realm harbors an extraordinary number of species, with richness decreasing away from this biodiversity hotspot. Despite multiple competing hypotheses, the dynamics underlying this regional diversity pattern remain poorly understood. Here, we use a time-calibrated evolutionary tree of living reef coral species, their current geographic ranges, and model-based estimates of regional rates of speciation, extinction, and geographic range shifts to show that origination rates within the CT are lower than in surrounding regions, a result inconsistent with the long-standing center of origin hypothesis. Furthermore, endemism of coral species in the CT is low, and the CT endemics are older than relatives found outside this region. Overall, our model results suggest that the high diversity of reef corals in the CT is largely due to range expansions into this region of species that evolved elsewhere. These findings strongly support the notion that geographic range shifts play a critical role in generating species diversity gradients. They also show that preserving the processes that gave rise to the striking diversity of corals in the CT requires protecting not just reefs within the hotspot, but also those in the surrounding areas.

Characterisation of genomic variation among corals can help uncover variants underlying trait differences and contribute towards genotype prioritisation in coastal restoration projects. For example, there is growing interest in identifying resilient genotypes for transplantation, and to better understand the genetic processes that allow some individuals to survive in specific conditions better than others. The coral species Pocillopora acuta is known to survive in a wide range of habitats, from reefs artificial coastal defences, suggesting its potential use as a starter species for ecological engineering efforts involving coral transplantation onto intertidal seawalls. However, the intertidal section of coastal armour is a challenging environment for corals, with conditions during periods of emersion being particularly stressful. Here, we scanned the entire genome of P. acuta corals to identify the regions harbouring single nucleotide polymorphisms (SNPs) and copy number variations (CNVs) that separate intertidal colonies ( n  = 18) from those found in subtidal areas ( n  = 21). Findings revealed 74,391 high quality SNPs distributed across 386 regions of the P. acuta genome. While the majority of the detected SNPs were in non-coding regions, 12% were identified in exons (i.e. coding regions). Functional SNPs that were significantly associated with intertidal colonies were found in overrepresented genomic regions linked to cellular homeostasis, metabolism, and signalling processes, which may represent local environmental adaptation in the intertidal. Interestingly, regions that exhibited CNVs were also associated with metabolic and signalling processes, suggesting P. acuta corals living in the intertidal have a high capacity to perform biological functions critical for survival in extreme environments.

Background DNA metabarcoding applies high-throughput sequencing approaches to generate numerous DNA barcodes from mixed sample pools for mass species identification and community characterisation. To date, however, most metabarcoding studies employ second-generation sequencing platforms like Illumina, which are limited by short read lengths and longer turnaround times. While third-generation platforms such as the MinION (Oxford Nanopore Technologies) can sequence longer reads and even in real-time, application of these platforms for metabarcoding has remained limited possibly due to the relatively high read error rates as well as the paucity of specialised software for processing such reads. Results We show that this is no longer the case by performing nanopore-based, cytochrome c oxidase subunit I (COI) metabarcoding on 34 zooplankton bulk samples, and benchmarking the results against conventional Illumina MiSeq sequencing. Nanopore R10.3 sequencing chemistry and super accurate (SUP) basecalling model reduced raw read error rates to ~ 4%, and consensus calling with amplicon_sorter (without further error correction) generated metabarcodes that were ≤ 1% erroneous. Although Illumina recovered a higher number of molecular operational taxonomic units (MOTUs) than nanopore sequencing (589 vs. 471), we found no significant differences in the zooplankton communities inferred between the sequencing platforms. Importantly, 406 of 444 (91.4%) shared MOTUs between Illumina and nanopore were also found to be free of indel errors, and 85% of the zooplankton richness could be recovered after just 12–15 h of sequencing. Conclusion Our results demonstrate that nanopore sequencing can generate metabarcodes with Illumina-like accuracy, and we are the first study to show that nanopore metabarcodes are almost always indel-free. We also show that nanopore metabarcoding is viable for characterising species-rich communities rapidly, and that the same ecological conclusions can be obtained regardless of the sequencing platform used. Collectively, our study inspires confidence in nanopore sequencing and paves the way for greater utilisation of nanopore technology in various metabarcoding applications.

Evolutionary reconstructions of scleractinian corals have a discrepant proportion of zooxanthellate reef-building species in relation to their azooxanthellate deep-sea counterparts. In particular, the earliest diverging “Basal” lineage remains poorly studied compared to “Robust” and “Complex” corals. The lack of data from corals other than reef-building species impairs a broader understanding of scleractinian evolution. Here, based on complete mitogenomes, the early onset of azooxanthellate corals is explored focusing on one of the most morphologically distinct families, Micrabaciidae. Sequenced on both Illumina and Sanger platforms, mitogenomes of four micrabaciids range from 19,048 to 19,542 bp and have gene content and order similar to the majority of scleractinians. Phylogenies containing all mitochondrial genes confirm the monophyly of Micrabaciidae as a sister group to the rest of Scleractinia. This topology not only corroborates the hypothesis of a solitary and azooxanthellate ancestor for the order, but also agrees with the unique skeletal microstructure previously found in the family. Moreover, the early-diverging position of micrabaciids followed by gardineriids reinforces the previously observed macromorphological similarities between micrabaciids and Corallimorpharia as well as its microstructural differences with Gardineriidae. The fact that both families share features with family Kilbuchophylliidae ultimately points towards a Middle Ordovician origin for Scleractinia.