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En 2011, une expérimentation préalable d'éco-pâturage caprin (Chèvre des fossés) a été menée dans une zone humide de Mayenne dans le but de contrôler des herbiers de Renouées du Japon. Les premiers résultats ont montré que cette gestion permet de faire baisser les biomasses produites. Les trois années suivantes des expérimentations similaires ont été conduites sur ce site dans des conditions similaires. Comme lors de l'étude préalable, l'expérimentation triennale montre des baisses significatives des pourcentages de recouvrement quel qu'en soit le moment, des hauteurs des tiges et des biomasses sèches en fin du cycle de la Renouée. Elle montre des résultats plus mitigés sur l'augmentation attendue du pourcentage cumulé du recouvrement des autres espèces. Elle ne permet pas de mettre en évidence des bénéfices pour améliorer la richesse spécifique. Dans les parcelles pâturées, il n'y a pas d'augmentation du nombre d'espèces que ce soit à l'intérieur des taches de Renouée ou dans les placettes sans Renouée. Enfin cette gestion ne fait pas diminuer significativement la densité de tiges observée en fin de cycle de la Renouée.

Considerable attention has recently been focused on the potential involvement of DNA methylation in regulating gene expression in cnidarians. Much of this work has been centered on corals, in the context of changes in methylation perhaps facilitating adaptation to higher seawater temperatures and other stressful conditions. Although first proposed more than 30 years ago, the possibility that DNA methylation systems function in protecting animal genomes against the harmful effects of transposon activity has largely been ignored since that time. Here, we show that transposons are specifically targeted by the DNA methylation system in cnidarians, and that the youngest transposons (i.e., those most likely to be active) are most highly methylated. Transposons in longer and highly active genes were preferentially methylated and, as transposons aged, methylation levels declined, reducing the potentially harmful side effects of CpG methylation. In Cnidaria and a range of other invertebrates, correlation between the overall extent of methylation and transposon content was strongly supported. Present transposon burden is the dominant factor in determining overall level of genomic methylation in a range of animals that diverged in or before the early Cambrian, suggesting that genome defense represents the ancestral role of CpG methylation., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Coral reefs are the epitome of species diversity, yet the number of described scleractinian coral species, the framework-builders of coral reefs, remains moderate by comparison. DNA sequencing studies are rapidly challenging this notion by exposing a wealth of undescribed diversity, but the evolutionary and ecological significance of this diversity remains largely unclear. Here, we present an annotated genome for one of the most ubiquitous corals in the Indo-Pacific (Pachyseris speciosa) and uncover, through a comprehensive genomic and phenotypic assessment, that it comprises morphologically indistinguishable but ecologically divergent lineages. Demographic modeling based on whole-genome resequencing indicated that morphological crypsis (across micro- and macromorphological traits) was due to ancient morphological stasis rather than recent divergence. Although the lineages occur sympatrically across shallow and mesophotic habitats, extensive genotyping using a rapid molecular assay revealed differentiation of their ecological distributions. Leveraging "common garden" conditions facilitated by the overlapping distributions, we assessed physiological and quantitative skeletal traits and demonstrated concurrent phenotypic differentiation. Lastly, spawning observations of genotyped colonies highlighted the potential role of temporal reproductive isolation in the limited admixture, with consistent genomic signatures in genes related to morphogenesis and reproduction. Overall, our findings demonstrate the presence of ecologically and phenotypically divergent coral species without substantial morphological differentiation and provide new leads into the potential mechanisms facilitating such divergence. More broadly, they indicate that our current taxonomic framework for reef-building corals may be scratching the surface of the ecologically relevant diversity on coral reefs, consequently limiting our ability to protect or restore this diversity effectively., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

A candidate antimicrobial peptide (AmAMP1) was identified by searching the whole genome sequence of Acropora millepora for short (<125AA) cysteine-rich predicted proteins with an N-terminal signal peptide but lacking clear homologs in the SwissProt database. It resembled but was not closely related to damicornin, the only other known AMP from a coral, and was shown to be active against both Gram-negative and Gram-positive bacteria. These proteins define a family of AMPs present in corals and their close relatives, the Corallimorpharia, and are synthesised as preproproteins in which the C-terminal mature peptide contains a conserved arrangement of six cysteine residues. Consistent with the idea of a common origin for AMPs and toxins, this Cys motif is shared between the coral AMPs and the Shk neurotoxins of sea anemones. AmAMP1 is expressed at late stages of coral development, in ectodermal cells that resemble the "ganglion neurons" of Hydra, in which it has recently been demonstrated that a distinct AMP known as NDA-1 is expressed., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Genetic signatures caused by demographic and adaptive processes during past climatic shifts can inform predictions of species' responses to anthropogenic climate change. To identify these signatures in Acropora tenuis , a reef-building coral threatened by global warming, we first assembled the genome from long reads and then used shallow whole-genome resequencing of 150 colonies from the central inshore Great Barrier Reef to inform population genomic analyses. We identify population structure in the host that reflects a Pleistocene split, whereas photosymbiont differences between reefs most likely reflect contemporary (Holocene) conditions. Signatures of selection in the host were associated with genes linked to diverse processes including osmotic regulation, skeletal development, and the establishment and maintenance of symbiosis. Our results suggest that adaptation to post-glacial climate change in A. tenuis has involved selection on many genes, while differences in symbiont specificity between reefs appear to be unrelated to host population structure., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Corals and the reef ecosystems that they support are in global decline due to increasing anthropogenic pressures such as climate change 1 . However, effective reef conservation strategies are hampered by a limited mechanistic understanding of coral biology and the functional roles of the diverse microbial communities that underpin coral health 2,3 . Here, we present an integrated genomic characterization of the coral species Porites lutea and its microbial partners. High-quality genomes were recovered from P. lutea, as well as a metagenome-assembled Cladocopium C15 (the dinoflagellate symbiont) and 52 bacterial and archaeal populations. Comparative genomic analysis revealed that many of the bacterial and archaeal genomes encode motifs that may be involved in maintaining association with the coral host and in supplying fixed carbon, B-vitamins and amino acids to their eukaryotic partners. Furthermore, mechanisms for ammonia, urea, nitrate, dimethylsulfoniopropionate and taurine transformation were identified that interlink members of the holobiont and may be important for nutrient acquisition and retention in oligotrophic waters. Our findings demonstrate the critical and diverse roles that microorganisms play within the coral holobiont and underscore the need to consider all of the components of the holobiont if we are to effectively inform reef conservation strategies.

Ocean acidification threatens to disrupt interactions between organisms throughout marine ecosystems. The diversity of reef-building organisms decreases as seawater CO2 increases along natural gradients, yet soft-bodied animals, such as sea anemones, are often resilient. We sequenced the polyA-enriched transcriptome of adult sea anemone Anemonia viridis and its dinoflagellate symbiont sampled along a natural CO2 gradient in Italy to assess stress levels in these organisms. We found that about 3.1% of the anemone transcripts, but <1% of the Symbiodinium sp. transcripts were differentially expressed. Processes enriched at high seawater CO2 were linked to cellular stress and inflammation, including significant up-regulation of protective cellular functions and down-regulation of metabolic pathways. Transposable elements were differentially expressed at high seawater CO2, with an extreme up-regulation (> 100-fold) of the BEL-family of long terminal repeat retrotransposons. Seawater acidified by CO2 generated a significant stress reaction in A. viridis, but no bleaching was observed and Symbiodinium sp. appeared to be less affected. These observed changes indicate the mechanisms by which A. viridis acclimate to survive chronic exposure to ocean acidification conditions. We conclude that many organisms that are common in acidified conditions may nevertheless incur costs due to hypercapnia and/or lowered carbonate saturation states., Competing Interests: The authors have declared that no competing interests exist.

Reef-building corals and some other cnidarians form symbiotic relationships with members of the dinoflagellate family Symbiodinaceae. As Symbiodinaceae is a highly diverse taxon, the physiological interactions between its members and their hosts are assumed to differ between associations. The presence of different symbiont types is known to affect expression levels of specific host genes, but knowledge of the effects on the transcriptome more broadly remains limited. In the present study, transcriptome profiling was conducted on the tropical corallimorpharian, Ricordea yuma, following the establishment of symbiosis with either the 'homologous' symbiont Symbiodinium goreaui (also known as Cladocopium goreaui ; ITS2 type C1) or 'heterologous' symbionts (predominantly S. trenchii , which is also known as Durusdinium trenchii ; ITS2 type D1a) isolated from a different corallimorpharian host ( Rhodactis indosinensis ). Transcriptomic analyses showed that genes encoding host glycogen biosynthesis pathway components are more highly induced during colonization by the homologous symbiont than by the heterologous symbiont. Similar patterns were also observed for several other genes thought to facilitate symbiotic nutrient exchange, including those involved in lipid translocation/storage and metabolite transport. The gene expression results presented here imply that colonization by homologous or heterologous Symbiodinium types may have very different metabolic consequences for the Ricordea host, supporting the notion that even though some cnidarians may be able to form novel symbioses after bleaching, the metabolic performance of these may be compromised.This article has an associated First Person interview with the first author of the paper., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

Neuropeptides play critical roles in cnidarian development. However, although they are known to play key roles in settlement and metamorphosis, their temporal and spatial developmental expression has not previously been characterized in any coral. We here describe Acropora millepora LWamide and RFamide and their developmental expression from the time of their first appearance, using in situ hybridization and FMRFamide immunohistochemistry. AmRFamide transcripts first appear in the ectoderm toward the oral end of the planula larva following blastopore closure. This oral bias becomes less apparent as the planula develops. The cell bodies of AmRFamide-expressing cells are centrally located in the ectoderm, with narrow projections to the mesoglea and to the cell surface. As the planula approaches settlement, AmRFamide expression disappears and is undetectable in the newly settled polyp. Expressing cells then gradually reappear as the polyp develops, becoming particularly abundant on the tentacles. AmLWamide transcripts first appear in ectodermal cells of the developing planula, with minimal expression at its two ends. The cell bodies of expressing cells lie just above the mesoglea, in a position distinct from those of AmRFamide-expressing cells, and have a narrow projection extending across the ectoderm to its surface. AmLWamide-expressing cells persist for most of the planula stage, disappearing shortly before settlement, but later than AmRFamide-expressing cells. As is the case with AmRFamide, expressing cells are absent from the polyp immediately after settlement, reappearing later on its oral side. AmLWamide expression lags that of AmRFamide in both its disappearance and reappearance. Antibodies to FMRFamide stain cells in a pattern similar to that of the transcripts, but also cells in areas where there is no expression revealed by in situ hybridization, most notably at the aboral end of the planula and in the adult polyp. Adult polyps have numerous staining cells on the tentacles and oral discs, as well as an immunoreactive nerve ring around the mouth. There are scattered staining cells in the coenosarc between polyps and staining cells are abundant in the mesenterial filaments. The above results are discussed in the context of our knowledge of the behavior of coral planulae at the time of their settlement and metamorphosis. Corals are facing multiple environmental threats, and these results both highlight the need for, and bring us a step closer to, a mechanistic understanding of a process that is critical to their survival., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Despite the biological and economic significance of scleractinian reef-building corals, the lack of large molecular datasets for a representative range of species limits understanding of many aspects of their biology. Within the Scleractinia, based on molecular evidence, it is generally recognised that there are two major clades, Complexa and Robusta, but the genomic bases of significant differences between them remain unclear., Results: Draft genome assemblies and annotations were generated for three coral species: Galaxea fascicularis (Complexa), Fungia sp., and Goniastrea aspera (Robusta). Whilst phylogenetic analyses strongly support a deep split between Complexa and Robusta, synteny analyses reveal a high level of gene order conservation between all corals, but not between corals and sea anemones or between sea anemones. HOX-related gene clusters are, however, well preserved across all of these combinations. Differences between species are apparent in the distribution and numbers of protein domains and an apparent correlation between number of HSP20 proteins and stress tolerance. Uniquely amongst animals, a complete histidine biosynthesis pathway is present in robust corals but not in complex corals or sea anemones. This pathway appears to be ancestral, and its retention in the robust coral lineage has important implications for coral nutrition and symbiosis., Conclusions: The availability of three new coral genomes enabled recognition of a de novo histidine biosynthesis pathway in robust corals which is only the second identified biosynthetic difference between corals. These datasets provide a platform for understanding many aspects of coral biology, particularly the interactions of corals with their endosymbionts.

[This corrects the article DOI: 10.1038/s42003-018-0098-3.].

Symbiosis between dinoflagellates of the genus Symbiodinium and reef-building corals forms the trophic foundation of the world's coral reef ecosystems. Here we present the first draft genome of Symbiodinium goreaui (Clade C, type C1: 1.03 Gbp), one of the most ubiquitous endosymbionts associated with corals, and an improved draft genome of Symbiodinium kawagutii (Clade F, strain CS-156: 1.05 Gbp) to further elucidate genomic signatures of this symbiosis. Comparative analysis of four available Symbiodinium genomes against other dinoflagellate genomes led to the identification of 2460 nuclear gene families (containing 5% of Symbiodinium genes) that show evidence of positive selection, including genes involved in photosynthesis, transmembrane ion transport, synthesis and modification of amino acids and glycoproteins, and stress response. Further, we identify extensive sets of genes for meiosis and response to light stress. These draft genomes provide a foundational resource for advancing our understanding of  Symbiodinium biology and the coral-algal symbiosis., Competing Interests: The authors declare no competing interests.

There are increasing concerns that the current rate of climate change might outpace the ability of reef-building corals to adapt to future conditions. Work on model systems has shown that environmentally induced alterations in DNA methylation can lead to phenotypic acclimatization. While DNA methylation has been reported in corals and is thought to associate with phenotypic plasticity, potential mechanisms linked to changes in whole-genome methylation have yet to be elucidated. We show that DNA methylation significantly reduces spurious transcription in the coral Stylophora pistillata . Furthermore, we find that DNA methylation also reduces transcriptional noise by fine-tuning the expression of highly expressed genes. Analysis of DNA methylation patterns of corals subjected to long-term pH stress showed widespread changes in pathways regulating cell cycle and body size. Correspondingly, we found significant increases in cell and polyp sizes that resulted in more porous skeletons, supporting the hypothesis that linear extension rates are maintained under conditions of reduced calcification. These findings suggest an epigenetic component in phenotypic acclimatization that provides corals with an additional mechanism to cope with environmental change.

Anthozoans (e.g., corals, anemones) are an ecologically important and diverse group of marine metazoans that occur from shallow to deep waters worldwide. However, our understanding of the evolutionary relationships among the ~7,500 species within this class is hindered by the lack of phylogenetically informative markers that can be reliably sequenced across a diversity of taxa. We designed and tested 16,306 RNA baits to capture 720 ultraconserved element loci and 1,071 exon loci. Library preparation and target enrichment were performed on 33 taxa from all orders within the class Anthozoa. Following Illumina sequencing and Trinity assembly, we recovered 1,774 of 1,791 targeted loci. The mean number of loci recovered from each species was 638 ± 222, with more loci recovered from octocorals (783 ± 138 loci) than hexacorals (475 ± 187 loci). Parsimony informative sites ranged from 26 to 49% for alignments at differing hierarchical taxonomic levels (e.g., Anthozoa, Octocorallia, Hexacorallia). The per cent of variable sites within each of three genera (Acropora, Alcyonium, and Sinularia) for which multiple species were sequenced ranged from 4.7% to 30%. Maximum-likelihood analyses recovered highly resolved trees with topologies matching those supported by other studies, including the monophyly of the order Scleractinia. Our results demonstrate the utility of this target-enrichment approach to resolve phylogenetic relationships from relatively old to recent divergences. Redesigning the baits with improved affinities to capture loci within each subclass will provide a valuable toolset to address systematic questions, further our understanding of the timing of diversifications and help resolve long-standing controversial relationships in the class Anthozoa., (© 2017 John Wiley & Sons Ltd.)

Cnidarians harbor a variety of small regulatory RNAs that include microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs), but detailed information is limited. Here, we report the identification and expression of novel miRNAs and putative piRNAs, as well as their genomic loci, in the symbiotic sea anemone Anemonia viridis. We generated a draft assembly of the A. viridis genome with putative size of 313 Mb that appeared to be composed of about 36% repeats, including known transposable elements. We detected approximately equal fractions of DNA transposons and retrotransposons. Deep sequencing of small RNA libraries constructed from A. viridis adults sampled at a natural CO2 gradient off Vulcano Island, Italy, identified 70 distinct miRNAs. Eight were homologous to previously reported miRNAs in cnidarians, whereas 62 appeared novel. Nine miRNAs were recognized as differentially expressed along the natural seawater pH gradient. We found a highly abundant and diverse population of piRNAs, with a substantial fraction showing ping-pong signatures. We identified nearly 22% putative piRNAs potentially targeting transposable elements within the A. viridis genome. The A. viridis genome appeared similar in size to that of other hexacorals with a very high divergence of transposable elements resembling that of the sea anemone genus Exaiptasia. The genome encodes and expresses a high number of small regulatory RNAs, which include novel miRNAs and piRNAs. Differentially expressed small RNAs along the seawater pH gradient indicated regulatory gene responses to environmental stressors., (© The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Bacterial communities colonize epithelial surfaces of most animals. Several factors, including the innate immune system, mucus composition, and diet, have been identified as determinants of host-associated bacterial communities. Here we show that the early branching metazoan Hydra is able to modify bacterial quorum-sensing signals. We identified a eukaryotic mechanism that enables Hydra to specifically modify long-chain 3-oxo-homoserine lactones into their 3-hydroxy-HSL counterparts. Expression data revealed that Hydra 's main bacterial colonizer, Curvibacter sp., responds differentially to N -(3-hydroxydodecanoyl)-l-homoserine lactone (3OHC12-HSL) and N -(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL). Investigating the impacts of the different N -acyl-HSLs on host colonization elucidated that 3OHC12-HSL allows and 3OC12-HSL represses host colonization of Curvibacter sp. These results show that an animal manipulates bacterial quorum-sensing signals and that this modification leads to a phenotypic switch in the bacterial colonizers. This mechanism may enable the host to manipulate the gene expression and thereby the behavior of its bacterial colonizers., Competing Interests: The authors declare no conflict of interest.

The Pacific whiteleg shrimp, Litopenaeus vannamei, is the most farmed aquaculture species worldwide with global production exceeding 3 million tonnes annually. Litopenaeus vannamei has been the focus of many selective breeding programs aiming to improve growth and disease resistance. However, these have been based primarily on phenotypic measurements and omit potential gains by integrating genetic selection into existing breeding programs. Such integration of genetic information has been hindered by the limited available genomic resources, background genetic parameters and knowledge on the genetic architecture of commercial traits for L. vannamei. This study describes the development of a comprehensive set of genomic gene-based resources including the identification and validation of 234,452 putative single nucleotide polymorphisms in-silico, of which 8,967 high value SNPs were incorporated into a commercially available Illumina Infinium ShrimpLD-24 v1.0 genotyping array. A framework genetic linkage map was constructed and combined with locus ordering by disequilibrium methodology to generate an integrated genetic map containing 4,817 SNPs, which spanned a total of 4552.5 cM and covered an estimated 98.12% of the genome. These gene-based genomic resources will not only be valuable for identifying regions underlying important L. vannamei traits, but also as a foundational resource in comparative and genome assembly activities.

Protecting genome integrity against transposable elements is achieved by intricate molecular mechanisms involving PIWI proteins, their associated small RNAs (piRNAs), and epigenetic modifiers such as DNA methylation. Eusocial bees, in particular the Western honeybee, Apis mellifera, have one of the lowest contents of transposable elements in the animal kingdom, and, unlike other animals with a functional DNA methylation system, appear not to methylate their transposons. This raises the question of whether the PIWI machinery has been retained in this species. Using comparative genomics, mass spectrometry, and expressional profiling, we present seminal evidence that the piRNA system is conserved in honeybees. We show that honey bee piRNAs contain a 2'-O-methyl modification at the 3' end, and have a bias towards a 5' terminal U, which are signature features of their biogenesis. Both piRNA repertoire and expression levels are greater in reproductive individuals than in sterile workers. Haploid males, where the detrimental effects of transposons are dominant, have the greatest piRNA levels, but surprisingly, the highest expression of transposons. These results show that even in a transposon-depleted species, the piRNA system is required to guard the vulnerable haploid genome and reproductive castes against transposon-associated genomic instability. This also suggests that dosage plays an important role in the regulation of transposons and piRNAs expression in haplo-diploid systems., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Phytoplankton-bacteria interactions drive the surface ocean sulfur cycle and local climatic processes through the production and exchange of a key compound: dimethylsulfoniopropionate (DMSP). Despite their large-scale implications, these interactions remain unquantified at the cellular-scale. Here we use secondary-ion mass spectrometry to provide the first visualization of DMSP at sub-cellular levels, tracking the fate of a stable sulfur isotope ( 34 S) from its incorporation by microalgae as inorganic sulfate to its biosynthesis and exudation as DMSP, and finally its uptake and degradation by bacteria. Our results identify for the first time the storage locations of DMSP in microalgae, with high enrichments present in vacuoles, cytoplasm and chloroplasts. In addition, we quantify DMSP incorporation at the single-cell level, with DMSP-degrading bacteria containing seven times more 34 S than the control strain. This study provides an unprecedented methodology to label, retain, and image small diffusible molecules, which can be transposable to other symbiotic systems.

Endosymbioses between dinoflagellate algae ( Symbiodinium sp.) and scleractinian coral species form the foundation of coral reef ecosystems. The coral symbiosis is highly susceptible to elevated temperatures, resulting in coral bleaching, where the algal symbiont is released from host cells. This experiment aimed to determine the transcriptional changes in cultured Symbiodinium , to better understand the response of cellular mechanisms under future temperature conditions. Cultures were exposed to elevated temperatures (average 31°C) or control conditions (24.5°C) for a period of 28 days. Whole transcriptome sequencing of Symbiodinium cells on days 4, 19, and 28 were used to identify differentially expressed genes under thermal stress. A large number of genes representing 37.01% of the transcriptome (∼23,654 unique genes, FDR < 0.05) with differential expression were detected at no less than one of the time points. Consistent with previous studies of Symbiodinium gene expression, fold changes across the transcriptome were low, with 92.49% differentially expressed genes at ≤2-fold change. The transcriptional response included differential expression of genes encoding stress response components such as the antioxidant network and molecular chaperones, cellular components such as core photosynthesis machinery, integral light-harvesting protein complexes and enzymes such as fatty acid desaturases. Differential expression of genes encoding glyoxylate cycle enzymes were also found, representing the first report of this in Symbiodinium . As photosynthate transfer from Symbiodinium to coral hosts provides up to 90% of a coral's daily energy requirements, the implications of altered metabolic processes from exposure to thermal stress found in this study on coral- Symbiodinium associations are unknown and should be considered when assessing the stability of the symbiotic relationship under future climate conditions.

Corallimorpharians (coral-like anemones) have a close phylogenetic relationship with scleractinians (hard corals) and can potentially provide novel perspectives on the evolution of biomineralization within the anthozoan subclass Hexacorallia. A survey of the transcriptomes of three representative corallimorpharians led to the identification of homologs of some skeletal organic matrix proteins (SOMPs) previously considered to be restricted to corals.Carbonic anhydrases (CAs), which are ubiquitous proteins involved in CO2 trafficking, are involved in both coral calcification and photosynthesis by endosymbiotic Symbiodinium (zooxanthellae). These multiple roles are assumed to place increased demands on the CA repertoire and have presumably driven the elaboration of the complex CA repertoires typical of corals (note that "corals" are defined here as reef-building Scleractinia). Comparison of the CA inventories of corallimorpharians with those of corals reveals that corals have specifically expanded the secreted and membrane-associated type CAs, whereas similar complexity is observed in the two groups with respect to other CA types.Comparison of the CA complement of the nonsymbiotic corallimorph Corynactis australis with that of Ricordea yuma, a corallimorph which normally hosts Symbiodinium, reveals similar numbers and distribution of CA types and suggests that an expansion of the CA repertoire has been necessary to enable calcification but may not be a requirement to enable symbiosis. Consistent with this idea, preliminary analysis suggests that the CA complexity of zooxanthellate and nonzooxanthellate sea anemones is similar.The comparisons above suggest that although there are relatively few new genes in the skeletal organic matrix of corals (which controls the skeleton deposition process), the evolution of calcification required an expanded repertoire of secreted and membrane-associated CAs., (© The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Shelled pteropods play key roles in the global carbon cycle and food webs of various ecosystems. Their thin external shell is sensitive to small changes in pH, and shell dissolution has already been observed in areas where aragonite saturation state is ~1. A decline in pteropod abundance has the potential to disrupt trophic networks and directly impact commercial fisheries. Therefore, it is crucial to understand how pteropods will be affected by global environmental change, particularly ocean acidification. In this study, physiological and molecular approaches were used to investigate the response of the Mediterranean pteropod, Heliconoides inflatus, to pH values projected for 2100 under a moderate emissions trajectory (RCP6.0). Pteropods were subjected to pH T 7.9 for 3 days, and gene expression levels, calcification and respiration rates were measured relative to pH T 8.1 controls. Gross calcification decreased markedly under low pH conditions, while genes potentially involved in calcification were up-regulated, reflecting the inability of pteropods to maintain calcification rates. Gene expression data imply that under low pH conditions, both metabolic processes and protein synthesis may be compromised, while genes involved in acid-base regulation were up-regulated. A large number of genes related to nervous system structure and function were also up-regulated in the low pH treatment, including a GABA A receptor subunit. This observation is particularly interesting because GABA A receptor disturbances, leading to altered behavior, have been documented in several other marine animals after exposure to elevated CO 2 . The up-regulation of many genes involved in nervous system function suggests that exposure to low pH could have major effects on pteropod behavior. This study illustrates the power of combining physiological and molecular approaches. It also reveals the importance of behavioral analyses in studies aimed at understanding the impacts of low pH on marine animals., (© 2016 John Wiley & Sons Ltd.)

Calcification is one of the most distinctive traits of scleractinian corals. Their hard skeletons form the substratum of reef ecosystems and confer on corals their remarkable diversity of shapes. Corallimorpharians are non-calcifying, close relatives of scleractinian corals, and the evolutionary relationship between these two groups is key to understanding the evolution of calcification in the coral lineage. One pivotal question is whether scleractinians are a monophyletic group, paraphyly being an alternative possibility if corallimorpharians are corals that have lost their ability to calcify, as is implied by the "naked-coral" hypothesis. Despite major efforts, relationships between scleractinians and corallimorpharians remain equivocal and controversial. Although the complete mitochondrial genomes of a range of scleractinians and corallimorpharians have been obtained, heterogeneity in composition and evolutionary rates means that mitochondrial sequences are insufficient to understand the relationship between these two groups. To overcome these limitations, transcriptome data were generated for three representative corallimorpharians. These were used in combination with sequences available for a representative range of scleractinians to identify 291 orthologous single copy protein-coding nuclear markers. Unlike the mitochondrial sequences, these nuclear markers do not display any distinct compositional bias in their nucleotide or amino-acid sequences. A range of phylogenomic approaches congruently reveal a topology consistent with scleractinian monophyly and corallimorpharians as the sister clade of scleractinians., Competing Interests: The authors declare there are no competing interests.

Background: Research into various aspects of coral biology has greatly increased in recent years due to anthropogenic threats to coral health including pollution, ocean warming and acidification. However, knowledge of coral early development has lagged. The present paper describes the embryonic development of two previously uncharacterized robust corals, Favia lizardensis (a massive brain coral) and Ctenactis echinata (a solitary coral) and compares it to that of the previously characterized complex coral, Acropora millepora, both morphologically and in terms of the expression of a set of key developmental genes., Results: Illumina sequencing of mixed age embryos was carried out, resulting in embryonic transcriptomes consisting of 40605 contigs for C.echinata (N50 = 1080 bp) and 48536 contigs for F.lizardensis (N50 = 1496 bp). The transcriptomes have been annotated against Swiss-Prot and were sufficiently complete to enable the identification of orthologs of many key genes controlling development in bilaterians. Developmental series of images of whole mounts and sections reveal that the early stages of both species contain a blastocoel, consistent with their membership of the robust clade. In situ hybridization was used to examine the expression of the developmentally important genes brachyury, chordin and forkhead. The expression of brachyury and forkhead was consistent with that previously reported for Acropora and allowed us to confirm that the pseudo-blastopore sometimes seen in robust corals such as Favia spp. is not directly associated with gastrulation. C.echinata chordin expression, however, differed from that seen in the other two corals., Conclusions: Embryonic transcriptomes were assembled for the brain coral Favia lizardensis and the solitary coral Ctenactis echinata. Both species have a blastocoel in their early developmental stages, consistent with their phylogenetic position as members of the robust clade. Expression of the key developmental genes brachyury, chordin and forkhead was investigated, allowing comparison to that of their orthologs in Acropora, Nematostella and bilaterians and demonstrating that even within the Anthozoa there are significant differences in expression patterns.

Background: Apoptotic cell death is a defining and ubiquitous characteristic of metazoans, but its evolutionary origins are unclear. Although Caenorhabditis and Drosophila played key roles in establishing the molecular bases of apoptosis, it is now clear that cell death pathways of these animals do not reflect ancestral characteristics. Conversely, recent work suggests that the apoptotic networks of cnidarians may be complex and vertebrate-like, hence characterization of the apoptotic complement of representatives of the basal cnidarian class Anthozoa will help us to understand the evolution of the vertebrate apoptotic network., Results: We describe the Bcl-2 and caspase protein repertoires of the coral Acropora millepora, making use of the comprehensive transcriptomic data available for this species. Molecular phylogenetics indicates that some Acropora proteins are orthologs of specific mammalian pro-apoptotic Bcl-2 family members, but the relationships of other Bcl-2 and caspases are unclear. The pro- or anti-apoptotic activities of coral Bcl-2 proteins were investigated by expression in mammalian cells, and the results imply functional conservation of the effector/anti-apoptotic machinery despite limited sequence conservation in the anti-apoptotic Bcl-2 proteins. A novel caspase type ("Caspase-X"), containing both inactive and active caspase domains, was identified in Acropora and appears to be restricted to corals. When expressed in mammalian cells, full-length caspase-X caused loss of viability, and a truncated version containing only the active domain was more effective in inducing cell death, suggesting that the inactive domain might modulate activity in the full-length protein. Structure prediction suggests that the active and inactive caspase domains in caspase-X are likely to interact, resulting in a structure resembling that of the active domain in procaspase-8 and the inactive caspase domain in the mammalian c-FLIP anti-apoptotic factor., Conclusions: The data presented here confirm that many of the basic mechanisms involved in both the intrinsic and extrinsic apoptotic pathways were in place in the common ancestor of cnidarians and bilaterians. With the identification of most or all of the repertoires of coral Bcl-2 and caspases, our results not only provide new perspectives on the evolution of apoptotic pathways, but also a framework for future experimental studies towards a complete understanding of coral bleaching mechanisms, in which apoptotic cell death might be involved.

The cellular mechanisms employed by some organisms to produce contrasting morphological and reproductive phenotypes from the same genome remains one of the key unresolved issues in biology. Honeybees (Apis mellifera) use differential feeding and a haplodiploid sex determination system to generate three distinct organismal outcomes from the same genome. Here we investigate the honeybee female and male caste-specific microRNA and transcriptomic molecular signatures during a critical time of larval development. Both previously undetected and novel miRNAs have been discovered, expanding the inventory of these genomic regulators in invertebrates. We show significant differences in the microRNA and transcriptional profiles of diploid females relative to haploid drone males as well as between reproductively distinct females (queens and workers). Queens and drones show gene enrichment in physio-metabolic pathways, whereas workers show enrichment in processes associated with neuronal development, cell signalling and caste biased structural differences. Interestingly, predicted miRNA targets are primarily associated with non-physio-metabolic genes, especially neuronal targets, suggesting a mechanistic disjunction from DNA methylation that regulates physio-metabolic processes. Accordingly, miRNA targets are under-represented in methylated genes. Our data show how a common set of genetic elements are differentially harnessed by an organism, which may provide the remarkable level of developmental flexibility required.

The evolutionary success of reef-building corals is often attributed to their symbiotic relationship with photosynthetic dinoflagellates of the genus Symbiodinium, but metabolic interactions between the partners and the molecular bases of light-enhanced calcification (LEC) are not well understood. Here, the metabolic bases of the interaction between the coral Acropora millepora and its dinoflagellate symbiont were investigated by comparing gene expression levels under light and dark conditions at the whole transcriptome level. Among the 497 differentially expressed genes identified, a suite of genes involved in cholesterol transport was found to be upregulated under light conditions, confirming the significance of this compound in the coral symbiosis. Although ion transporters likely to have roles in calcification were not differentially expressed in this study, expression levels of many genes associated with skeletal organic matrix composition and organization were higher in light conditions. This implies that the rate of organic matrix synthesis is one factor limiting calcification at night. Thus, LEC during the day is likely to be a consequence of increases in both matrix synthesis and the supply of precursor molecules as a result of photosynthetic activity., (© 2015 John Wiley & Sons Ltd.)

Background: Bisulphite sequencing enables the detection of cytosine methylation. The sequence of the methylation states of cytosines on any given read forms a methylation pattern that carries substantially more information than merely studying the average methylation level at individual positions. In order to understand better the complexity of DNA methylation landscapes in biological samples, it is important to study the diversity of these methylation patterns. However, the accurate quantification of methylation patterns is subject to sequencing errors and spurious signals due to incomplete bisulphite conversion of cytosines., Results: A statistical model is developed which accounts for the distribution of DNA methylation patterns at any given locus. The model incorporates the effects of sequencing errors and spurious reads, and enables estimation of the true underlying distribution of methylation patterns., Conclusions: Calculation of the estimated distribution over methylation patterns is implemented in the R Bioconductor package MPFE. Source code and documentation of the package are also available for download at http://bioconductor.org/packages/3.0/bioc/html/MPFE.html .

Corals play a key role in ocean ecosystems and carbonate balance, but their molecular response to ocean acidification remains unclear. The only previous whole-transcriptome study (Moya et al. Molecular Ecology, 2012; 21, 2440) documented extensive disruption of gene expression, particularly of genes encoding skeletal organic matrix proteins, in juvenile corals (Acropora millepora) after short-term (3 d) exposure to elevated pCO2 . In this study, whole-transcriptome analysis was used to compare the effects of such 'acute' (3 d) exposure to elevated pCO2 with a longer ('prolonged'; 9 d) period of exposure beginning immediately post-fertilization. Far fewer genes were differentially expressed under the 9-d treatment, and although the transcriptome data implied wholesale disruption of metabolism and calcification genes in the acute treatment experiment, expression of most genes was at control levels after prolonged treatment. There was little overlap between the genes responding to the acute and prolonged treatments, but heat shock proteins (HSPs) and heat shock factors (HSFs) were over-represented amongst the genes responding to both treatments. Amongst these was an HSP70 gene previously shown to be involved in acclimation to thermal stress in a field population of another acroporid coral. The most obvious feature of the molecular response in the 9-d treatment experiment was the upregulation of five distinct Bcl-2 family members, the majority predicted to be anti-apoptotic. This suggests that an important component of the longer term response to elevated CO2 is suppression of apoptosis. It therefore appears that juvenile A. millepora have the capacity to rapidly acclimate to elevated pCO2 , a process mediated by upregulation of specific HSPs and a suite of Bcl-2 family members., (© 2014 John Wiley & Sons Ltd.)

The relationship between Scleractinia and Corallimorpharia, Orders within Anthozoa distinguished by the presence of an aragonite skeleton in the former, is controversial. Although classically considered distinct groups, some phylogenetic analyses have placed the Corallimorpharia within a larger Scleractinia/Corallimorpharia clade, leading to the suggestion that the Corallimorpharia are "naked corals" that arose via skeleton loss during the Cretaceous from a Scleractinian ancestor. Scleractinian paraphyly is, however, contradicted by a number of recent phylogenetic studies based on mt nucleotide (nt) sequence data. Whereas the "naked coral" hypothesis was based on analysis of the sequences of proteins encoded by a relatively small number of mt genomes, here a much-expanded dataset was used to reinvestigate hexacorallian phylogeny. The initial observation was that, whereas analyses based on nt data support scleractinian monophyly, those based on amino acid (aa) data support the "naked coral" hypothesis, irrespective of the method and with very strong support. To better understand the bases of these contrasting results, the effects of systematic errors were examined. Compared to other hexacorallians, the mt genomes of "Robust" corals have a higher (A+T) content, codon usage is far more constrained, and the proteins that they encode have a markedly higher phenylalanine content, leading us to suggest that mt DNA repair may be impaired in this lineage. Thus the "naked coral" topology could be caused by high levels of saturation in these mitochondrial sequences, long-branch effects or model violations. The equivocal results of these extensive analyses highlight the fundamental problems of basing coral phylogeny on mitochondrial sequence data.

Word match counts have traditionally been proposed as an alignment-free measure of similarity for biological sequences. The D(2) statistic, which simply counts the number of exact word matches between two sequences, is a useful test bed for developing rigorous mathematical results, which can then be extended to more biologically useful measures. The distributional properties of the D(2) statistic under the null hypothesis of identically and independently distributed letters have been studied extensively, but no comprehensive study of the D(2) distribution for biologically more realistic higher-order Markovian sequences exists. Here we derive exact formulas for the mean and variance of the D(2) statistic for Markovian sequences of any order, and demonstrate through Monte Carlo simulations that the entire distribution is accurately characterized by a Pólya-Aeppli distribution for sequence lengths of biological interest. The approach is novel in that Markovian dependency is defined for sequences with periodic boundary conditions, and this enables exact analytic formulas for the mean and variance to be derived. We also carry out a preliminary comparison between the approximate D(2) distribution computed with the theoretical mean and variance under a Markovian hypothesis and an empirical D(2) distribution from the human genome.

Pearl oysters are not only farmed for their gemstone quality pearls worldwide, but they are also becoming important model organisms for investigating genetic mechanisms of biomineralisation. Despite their economic and scientific significance, limited genomic resources are available for this important group of bivalves, hampering investigations into identifying genes that regulate important pearl quality traits and unique biological characteristics (i.e. biomineralisation). The silver-lipped pearl oyster, Pinctada maxima, is one species where there is interest in understanding genes that regulate commercially important pearl traits, but presently, there is a dearth of genomic information. The objective of this study was to develop and validate a large number of type I genome-wide single nucleotide polymorphisms (SNPs) for P. maxima suitable for high-throughput genotyping. In addition, sequence annotations and Gene Ontology terms were assigned to a large mantle tissue 454 expressed sequence tag assembly (96,794 contigs) and information on known bivalve biomineralisation genes was incorporated into SNP discovery. The SNP discovery effort resulted in the de novo identification of 172,625 SNPs, of which 9,108 were identified as high value [minor allele frequency (MAF)≥ 0.15, read depth  ≥ 8]. Validation of 2,782 of these SNPs using Illumina iSelect Infinium genotyping technology returned some of the highest assay conversion (86.6 %) and validation (59.9 %; mean MAF 0.28) rates observed in aquaculture species to date. Genomic resources presented here will be pivotal to future research investigating the biological mechanisms behind biomineralisation and will form a strong foundation for genetic selective breeding programs in the P. maxima pearling industry.

Globally, reef-building corals are the most prolific producers of dimethylsulphoniopropionate (DMSP), a central molecule in the marine sulphur cycle and precursor of the climate-active gas dimethylsulphide. At present, DMSP production by corals is attributed entirely to their algal endosymbiont, Symbiodinium. Combining chemical, genomic and molecular approaches, we show that coral juveniles produce DMSP in the absence of algal symbionts. DMSP levels increased up to 54% over time in newly settled coral juveniles lacking algal endosymbionts, and further increases, up to 76%, were recorded when juveniles were subjected to thermal stress. We uncovered coral orthologues of two algal genes recently identified in DMSP biosynthesis, strongly indicating that corals possess the enzymatic machinery necessary for DMSP production. Our results overturn the paradigm that photosynthetic organisms are the sole biological source of DMSP, and highlight the double jeopardy represented by worldwide declining coral cover, as the potential to alleviate thermal stress through coral-produced DMSP declines correspondingly.

Background: As a step towards understanding coral immunity we present the first whole transcriptome analysis of the acute responses of Acropora millepora to challenge with the bacterial cell wall derivative MDP and the viral mimic poly I:C, defined immunogens provoking distinct but well characterised responses in higher animals., Results: These experiments reveal similarities with the responses both of arthropods and mammals, as well as coral-specific effects. The most surprising finding was that MDP specifically induced three members of the GiMAP gene family, which has been implicated in immunity in mammals but is absent from Drosophila and Caenorhabditis. Like their mammalian homologs, GiMAP genes are arranged in a tandem cluster in the coral genome., Conclusions: A phylogenomic survey of this gene family implies ancient origins, multiple independent losses and lineage-specific expansions during animal evolution. Whilst functional convergence cannot be ruled out, GiMAP expression in corals may reflect an ancestral role in immunity, perhaps in phagolysosomal processing.

The impact of ocean acidification (OA) on coral calcification, a subject of intense current interest, is poorly understood in part because of the presence of symbionts in adult corals. Early life history stages of Acropora spp. provide an opportunity to study the effects of elevated CO(2) on coral calcification without the complication of symbiont metabolism. Therefore, we used the Illumina RNAseq approach to study the effects of acute exposure to elevated CO(2) on gene expression in primary polyps of Acropora millepora, using as reference a novel comprehensive transcriptome assembly developed for this study. Gene ontology analysis of this whole transcriptome data set indicated that CO(2) -driven acidification strongly suppressed metabolism but enhanced extracellular organic matrix synthesis, whereas targeted analyses revealed complex effects on genes implicated in calcification. Unexpectedly, expression of most ion transport proteins was unaffected, while many membrane-associated or secreted carbonic anhydrases were expressed at lower levels. The most dramatic effect of CO(2) -driven acidification, however, was on genes encoding candidate and known components of the skeletal organic matrix that controls CaCO(3) deposition. The skeletal organic matrix effects included elevated expression of adult-type galaxins and some secreted acidic proteins, but down-regulation of other galaxins, secreted acidic proteins, SCRiPs and other coral-specific genes, suggesting specialized roles for the members of these protein families and complex impacts of OA on mineral deposition. This study is the first exhaustive exploration of the transcriptomic response of a scleractinian coral to acidification and provides an unbiased perspective on its effects during the early stages of calcification., (© 2012 Blackwell Publishing Ltd.)

Insects are the most diverse group of animals on the planet, comprising over 90% of all metazoan life forms, and have adapted to a wide diversity of ecosystems in nearly all environments. They have evolved highly sensitive chemical senses that are central to their interaction with their environment and to communication between individuals. Understanding the molecular bases of insect olfaction is therefore of great importance from both a basic and applied perspective. Odorant binding proteins (OBPs) are some of most abundant proteins found in insect olfactory organs, where they are the first component of the olfactory transduction cascade, carrying odorant molecules to the olfactory receptors. We carried out a search for OBPs in the genome of the parasitoid wasp Nasonia vitripennis and identified 90 sequences encoding putative OBPs. This is the largest OBP family so far reported in insects. We report unique features of the N. vitripennis OBPs, including the presence and evolutionary origin of a new subfamily of double-domain OBPs (consisting of two concatenated OBP domains), the loss of conserved cysteine residues and the expression of pseudogenes. This study also demonstrates the extremely dynamic evolution of the insect OBP family: (i) the number of different OBPs can vary greatly between species; (ii) the sequences are highly diverse, sometimes as a result of positive selection pressure with even the canonical cysteines being lost; (iii) new lineage specific domain arrangements can arise, such as the double domain OBP subfamily of wasps and mosquitoes.

Background: A successful metamorphosis from a planktonic larva to a settled polyp, which under favorable conditions will establish a future colony, is critical for the survival of corals. However, in contrast to the situation in other animals, e.g., frogs and insects, little is known about the molecular basis of coral metamorphosis. We have begun to redress this situation with previous microarray studies, but there is still a great deal to learn. In the present paper we have utilized a different technology, subtractive hybridization, to characterize genes differentially expressed across this developmental transition and to compare the success of this method to microarray., Methodology/principal Findings: Suppressive subtractive hybridization (SSH) was used to identify two pools of transcripts from the coral, Acropora millepora. One is enriched for transcripts expressed at higher levels at the pre-settlement stage, and the other for transcripts expressed at higher levels at the post-settlement stage. Virtual northern blots were used to demonstrate the efficacy of the subtractive hybridization technique. Both pools contain transcripts coding for proteins in various functional classes but transcriptional regulatory proteins were represented more frequently in the post-settlement pool. Approximately 18% of the transcripts showed no significant similarity to any other sequence on the public databases. Transcripts of particular interest were further characterized by in situ hybridization, which showed that many are regulated spatially as well as temporally. Notably, many transcripts exhibit axially restricted expression patterns that correlate with the pool from which they were isolated. Several transcripts are expressed in patterns consistent with a role in calcification., Conclusions: We have characterized over 200 transcripts that are differentially expressed between the planula larva and post-settlement polyp of the coral, Acropora millepora. Sequence, putative function, and in some cases temporal and spatial expression are reported.

Members of the universal stress protein (USP) family were originally identified in stressed bacteria on the basis of a shared domain, which has since been reported in a phylogenetically diverse range of prokaryotes, fungi, protists, and plants. Although not previously characterized in metazoans, here we report that USP genes are distributed in animal genomes in a unique pattern that reflects frequent independent losses and independent expansions. Multiple USP loci are present in urochordates as well as all Cnidaria and Lophotrochozoa examined, but none were detected in any of the available ecdysozoan or non-urochordate deuterostome genome data. The vast majority of the metazoan USPs are short, single-domain proteins and are phylogenetically distinct from the prokaryotic, plant, protist, and fungal members of the protein family. Whereas most of the metazoan USP genes contain introns, with few exceptions those in the cnidarian Hydra are intronless and cluster together in phylogenetic analyses. Expression patterns were determined for several cnidarian USPs, including two genes belonging to the intronless clade, and these imply diverse functions. The apparent paradox of implied diversity of roles despite high overall levels of sequence (and implied structural) similarity parallels the situation in bacteria. The absence of USP genes in ecdysozoans and most deuterostomes may be a consequence of functional redundancy or specialization in taxon-specific roles.

To identify fast-evolving genes in reef-building corals, we performed direct comparative sequence analysis with expressed sequence tag (EST) datasets from two acroporid species: Acropora palmata from the Caribbean Sea and A. millepora from the Great Barrier Reef in Australia. Comparison of 589 independent sequences from 1,421 A. palmata contigs, with 10,247 A. millepora contigs resulted in the identification of 196 putative homologues. Most of the homologous pairs demonstrated high amino acid similarities (over 90%). Comparisons of putative homologues showing low amino acid similarities (under 90%) among the Acropora species to the near complete datasets from two other cnidarians (Hydra magnipapillata and Nematostella vectensis) implied that some were non-orthologous. Within 86 homologous pairs, 39 exhibited dN/dS ratios significantly less than 1, suggesting that these genes are under purifying selection associated with functional constraints. Eight independent genes showed dN/dS ratios exceeding 1, while three deviated significantly from 1, suggesting that these genes may play important roles in the adaptive evolution of Acropora. Our results also indicated that CEL-III lectin was under positive selection, consistent with a possible role in immunity or symbiont recognition. Further studies are needed to clarify the possible functions of the genes under positive selection to provide insight into the evolutionary process of corals.

Coral bleaching is a major threat to coral reefs worldwide and is predicted to intensify with increasing global temperature. This study represents the first investigation of gene expression in an Indo-Pacific coral species undergoing natural bleaching which involved the loss of algal symbionts. Quantitative real-time polymerase chain reaction experiments were conducted to select and evaluate coral internal control genes (ICGs), and to investigate selected coral genes of interest (GOIs) for changes in gene expression in nine colonies of the scleractinian coral Acropora millepora undergoing bleaching at Magnetic Island, Great Barrier Reef, Australia. Among the six ICGs tested, glyceraldehyde 3-phosphate dehydrogenase and the ribosomal protein genes S7 and L9 exhibited the most constant expression levels between samples from healthy-looking colonies and samples from the same colonies when severely bleached a year later. These ICGs were therefore utilised for normalisation of expression data for seven selected GOIs. Of the seven GOIs, homologues of catalase, C-type lectin and chromoprotein genes were significantly up-regulated as a result of bleaching by factors of 1.81, 1.46 and 1.61 (linear mixed models analysis of variance, P < 0.05), respectively. We present these genes as potential coral bleaching response genes. In contrast, three genes, including one putative ICG, showed highly variable levels of expression between coral colonies. Potential variation in microhabitat, gene function unrelated to the stress response and individualised stress responses may influence such differences between colonies and need to be better understood when designing and interpreting future studies of gene expression in natural coral populations.

Recent thought on genome evolution has focused on the creation of new genes and changes in regulatory mechanisms while ignoring the role of selective gene loss in shaping genomes. Using data from two cnidarians, the jellyfish Clytia and the coral Acropora, we examined the relative significance of new 'taxonomically restricted' genes and selectively retained ancestral genes in enabling the evolution of novel traits. Consistent with its more complex life-cycle, the proportion of novel genes identified in Clytia was higher than that in the 'polyp only' cnidarians Nematostella and Hydra, but each of these cnidarians has retained a proportion of ancestral genes not present in the other two. The ubiquity and near-stochastic nature of gene loss can explain the discord between patterns of gene distribution and taxonomy., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Word matches are often used in sequence comparison methods, either as a measure of sequence similarity or in the first search steps of algorithms such as BLAST or BLAT. The D2 statistic is the number of matches of words of k letters between two sequences. Recent advances have been made in the characterization of this statistic and in the approximation of its distribution. Here, these results are extended to the case of approximate word matches. We compute the exact value of the variance of the D2 statistic for the case of a uniform letter distribution, and introduce a method to provide accurate approximations of the variance in the remaining cases. This enables the distribution of D2 to be approximated for typical situations arising in biological research. We apply these results to the identification of cis-regulatory modules, and show that this method detects such sequences with a high accuracy. The ability to approximate the distribution of D2 for both exact and approximate word matches will enable the use of this statistic in a more precise manner for sequence comparison, database searches, and identification of transcription factor binding sites.

Tribolium castaneum is a member of the most species-rich eukaryotic order, a powerful model organism for the study of generalized insect development, and an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved the ability to interact with a diverse chemical environment, as shown by large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes. Development in Tribolium is more representative of other insects than is Drosophila, a fact reflected in gene content and function. For example, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, some being expressed in the growth zone crucial for axial elongation in short-germ development. Systemic RNA interference in T. castaneum functions differently from that in Caenorhabditis elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control.

Small chemosensory proteins (CSPs) belong to a conserved, but poorly understood, protein family found in insects and other arthropods. They exhibit both broad and restricted expression patterns during development. In this paper, we used a combination of genome annotation, transcriptional profiling and RNA interference to unravel the functional significance of a honeybee gene (csp5) belonging to the CSP family. We show that csp5 expression resembles the maternal-zygotic pattern that is characterized by the initiation of transcription in the ovary and the replacement of maternal mRNA with embryonic mRNA. Blocking the embryonic expression of csp5 with double-stranded RNA causes abnormalities in all body parts where csp5 is highly expressed. The treated embryos show a "diffuse", often grotesque morphology, and the head skeleton appears to be severely affected. They are 'unable-to-hatch' and cannot progress to the larval stages. Our findings reveal a novel, essential role for this gene family and suggest that csp5 (unable-to-hatch) is an ectodermal gene involved in embryonic integument formation. Our study confirms the utility of an RNAi approach to functional characterization of novel developmental genes uncovered by the honeybee genome project and provides a starting point for further studies on embryonic integument formation in this insect.

Small chemosensory proteins (CSPs) belong to a conserved, but poorly understood protein family that has been implicated in transporting chemical stimuli within insect sensilla. However, their expression patterns suggest that these molecules are also critical for other functions including early development. Here we used both bioinformatics and experimental approaches to characterize the CSP gene family in a social insect, the Western honey bee Apis mellifera, and then compared its members to CSPs in other arthropods. The number of CSPs in the honey bee genome (six) is similar to that found in the sequenced dipteran species (four-seven), but is much lower than the number of CSPs in the moth or in the beetle (around 20 each). These differences seem to be the result of lineage specific expansions. Our analysis of CSPs in a number of arthropods reveals a conserved gene family found in both Mandibulates and Chelicerates. Expressional profiling in diverse tissues and throughout development reveals broader than expected patterns of expression with none of the CSPs restricted to the antennae and one found only in the queen ovaries and in embryos. We conclude that CSPs are multifunctional context-dependent proteins involved in diverse cellular processes ranging from embryonic development to chemosensory signal transduction. Some CSPs may function in cuticle synthesis, consistent with their evolutionary origins in the arthropods.

Background: The number of k-words shared between two sequences is a simple and efficient alignment-free sequence comparison method. This statistic, D2, has been used for the clustering of EST sequences. Sequence comparison based on D2 is extremely fast, its runtime is proportional to the size of the sequences under scrutiny, whereas alignment-based comparisons have a worst-case run time proportional to the square of the size. Recent studies have tackled the rigorous study of the statistical distribution of D2, and asymptotic regimes have been derived. The distribution of approximate k-word matches has also been studied., Results: We have computed the D2 optimal word size for various sequence lengths, and for both perfect and approximate word matches. Kolmogorov-Smirnov tests show D2 to have a compound Poisson distribution at the optimal word size for small sequence lengths (below 400 letters) and a normal distribution at the optimal word size for large sequence lengths (above 1600 letters). We find that the D2 statistic outperforms BLAST in the comparison of artificially evolved sequences, and performs similarly to other methods based on exact word matches. These results obtained with randomly generated sequences are also valid for sequences derived from human genomic DNA., Conclusion: We have characterized the distribution of the D2 statistic at optimal word sizes. We find that the best trade-off between computational efficiency and accuracy is obtained with exact word matches. Given that our numerical tests have not included sequence shuffling, transposition or splicing, the improvements over existing methods reported here underestimate that expected in real sequences. Because of the linear run time and of the known normal asymptotic behavior, D2-based methods are most appropriate for large genomic sequences.