Bathymetric evolution of black corals through deep time.

Deep-sea lineages are generally thought to arise from shallow-water ancestors, but this hypothesis is based on a relatively small number of taxonomic groups. Anthozoans, which include corals and sea anemones, are significant contributors to the faunal diversity of the deep sea, but the timing and mechanisms of their invasion into this biome remain elusive. Here, we reconstruct a fully resolved, time-calibrated phylogeny of 83 species in the order Antipatharia (black coral) to investigate their bathymetric evolutionary history. Our reconstruction indicates that extant black coral lineages first diversified in continental slope depths (∼250-3000 m) during the early Silurian (∼437 millions of years ago (Ma)) and subsequently radiated into, and diversified within, both continental shelf (less than 250 m) and abyssal (greater than 3000 m) habitats. Ancestral state reconstruction analysis suggests that the appearance of morphological features that enhanced the ability of black corals to acquire nutrients coincided with their invasion of novel depths. Our findings have important conservation implications for anthozoan lineages, as the loss of 'source' slope lineages could threaten millions of years of evolutionary history and confound future invasion events, thereby warranting protection.

An Environmental DNA Primer for Microbial and Restoration Ecology.

Environmental DNA (eDNA) sequencing-DNA collected from the environment from living cells or shed DNA-was first developed for working with microbes and has greatly benefitted microbial ecologists for decades since. These tools have only become increasingly powerful with the advent of metabarcoding and metagenomics. Most new studies that examine diverse assemblages of bacteria, archaea, protists, fungi, and viruses lean heavily into eDNA using these newer technologies, as the necessary sequencing technology and bioinformatic tools have become increasingly affordable and user friendly. However, eDNA methods are rapidly evolving, and sometimes it can feel overwhelming to simply keep up with the basics. In this review, we provide a starting point for microbial ecologists who are new to DNA-based methods by detailing the eDNA methods that are most pertinent, including study design, sample collection and storage, selecting the right sequencing technology, lab protocols, equipment, and a few bioinformatic tools. Furthermore, we focus on how eDNA work can benefit restoration and what modifications are needed when working in this subfield.

Phylogenomics, Origin, and Diversification of Anthozoans (Phylum Cnidaria).

Anthozoan cnidarians (corals and sea anemones) include some of the world's most important foundation species, capable of building massive reef complexes that support entire ecosystems. Although previous molecular phylogenetic analyses have revealed widespread homoplasy of the morphological characters traditionally used to define orders and families of anthozoans, analyses using mitochondrial genes or rDNA have failed to resolve many key nodes in the phylogeny. With a fully resolved, time-calibrated phylogeny for 234 species constructed from hundreds of ultraconserved elements and exon loci, we explore the evolutionary origins of the major clades of Anthozoa and some of their salient morphological features. The phylogeny supports reciprocally monophyletic Hexacorallia and Octocorallia, with Ceriantharia as the earliest diverging hexacorals; two reciprocally monophyletic clades of Octocorallia; and monophyly of all hexacoral orders with the exception of the enigmatic sea anemone Relicanthus daphneae. Divergence dating analyses place Anthozoa in the Cryogenian to Tonian periods (648-894 Ma), older than has been suggested by previous studies. Ancestral state reconstructions indicate that the ancestral anthozoan was a solitary polyp that had bilateral symmetry and lacked a skeleton. Colonial growth forms and the ability to precipitate calcium carbonate evolved in the Ediacaran (578 Ma) and Cambrian (503 Ma) respectively; these hallmarks of reef-building species have subsequently arisen multiple times independently in different orders. Anthozoans formed associations with photosymbionts by the Devonian (383 Ma), and photosymbioses have been gained and lost repeatedly in all orders. Together, these results have profound implications for the interpretation of the Precambrian environment and the early evolution of metazoans.[Bilateral symmetry; coloniality; coral; early metazoans; exon capture; Hexacorallia; Octocorallia photosymbiosis; sea anemone; ultraconserved elements.].

A Global eDNA Comparison of Freshwater Bacterioplankton Assemblages Focusing on Large-River Floodplain Lakes of Brazil.

With its network of lotic and lentic habitats that shift during changes in seasonal connection, the tropical and subtropical large-river systems represent possibly the most dynamic of all aquatic environments. Pelagic water samples were collected from Brazilian floodplain lakes (total n = 58) in four flood-pulsed systems (Amazon [n = 21], Araguaia [n = 14], Paraná [n = 15], and Pantanal [n = 8]) in 2011-2012 and sequenced via 454 for bacterial environmental DNA using 16S amplicons; additional abiotic field and laboratory measurements were collected for the assayed lakes. We report here a global comparison of the bacterioplankton makeup of freshwater systems, focusing on a comparison of Brazilian lakes with similar freshwater systems across the globe. The results indicate a surprising similarity at higher taxonomic levels of the bacterioplankton in Brazilian freshwater with global sites. However, substantial novel diversity at the family level was also observed for the Brazilian freshwater systems. Brazilian freshwater bacterioplankton richness was relatively average globally. Ordination results indicate that Brazilian bacterioplankton composition is unique from other areas of the globe. Using Brazil-only ordinations, floodplain system differentiation most strongly correlated with dissolved oxygen, pH, and phosphate. Our data on Brazilian freshwater systems in combination with analysis of a collection of freshwater environmental samples from across the globe offers the first regional picture of bacterioplankton diversity in these important freshwater systems.

A RNA-seq approach to identify putative toxins from acrorhagi in aggressive and non-aggressive Anthopleura elegantissima polyps.

BACKGROUND: The use of venom in intraspecific aggression is uncommon and venom-transmitting structures specifically used for intraspecific competition are found in few lineages of venomous taxa. Next-generation transcriptome sequencing allows robust characterization of venom diversity and exploration of functionally unique tissues. Using a tissue-specific RNA-seq approach, we investigate the venom composition and gene ontology diversity of acrorhagi, specialized structures used in intraspecific competition, in aggressive and non-aggressive polyps of the aggregating sea anemone Anthopleura elegantissima (Cnidaria: Anthozoa: Hexacorallia: Actiniaria: Actiniidae). RESULTS: Collectively, we generated approximately 450,000 transcripts from acrorhagi of aggressive and non-aggressive polyps. For both transcriptomes we identified 65 candidate sea anemone toxin genes, representing phospholipase A2s, cytolysins, neurotoxins, and acrorhagins. When compared to previously characterized sea anemone toxin assemblages, each transcriptome revealed greater within-species sequence divergence across all toxin types. The transcriptome of the aggressive polyp had a higher abundance of type II voltage gated potassium channel toxins/Kunitz-type protease inhibitors and type II acrorhagins. Using toxin-like proteins from other venomous taxa, we also identified 612 candidate toxin-like transcripts with signaling regions, potentially unidentified secretory toxin-like proteins. Among these, metallopeptidases and cysteine rich (CRISP) candidate transcripts were in high abundance. Furthermore, our gene ontology analyses identified a high prevalence of genes associated with "blood coagulation" and "positive regulation of apoptosis", as well as "nucleoside: sodium symporter activity" and "ion channel binding". The resulting assemblage of expressed genes may represent synergistic proteins associated with toxins or proteins related to the morphology and behavior exhibited by the aggressive polyp. CONCLUSION: We implement a multifaceted approach to investigate the assemblage of expressed genes specifically within acrorhagi, specialized structures used only for intraspecific competition. By combining differential expression, phylogenetic, and gene ontology analyses, we identify several candidate toxins and other potentially important proteins in acrorhagi of A. elegantissima. Although not all of the toxins identified are used in intraspecific competition, our analysis highlights some candidates that may play a vital role in intraspecific competition. Our findings provide a framework for further investigation into components of venom used exclusively for intraspecific competition in acrorhagi-bearing sea anemones and potentially other venomous animals.

Environmental DNA Isolation, Validation, and Preservation Methods.

Environmental DNA (eDNA) workflows contain many familiar molecular-lab techniques, but also employ several unique methodologies. When working with eDNA, it is essential to avoid contamination from the point of collection through preservation and select a meaningful negative control. As eDNA can be obtained from a variety of samples and habitats (e.g., soil, water, air, or tissue), protocols will vary depending on usage. Samples may require additional steps to dilute, block, or remove inhibitors or physically break up samples or filters. Thereafter, standard DNA isolation techniques (kit-based or phenol:chloroform:isoamyl [PCI]) are employed. Once DNA is extracted, it is typically quantified using a fluorometer. Yields vary greatly, but are important to know prior to amplification of the gene(s) of interest. Long-term storage of both the sampled material and the extracted DNA is encouraged, as it provides a backup for spilled/contaminated samples, lost data, reanalysis, and future studies using newer technology. Storage in a freezer is often ideal; however, some storage buffers (e.g., Longmires) require that filters or swabs are kept at room temperature to prevent precipitation of buffer-related solutes. These baseline methods for eDNA isolation, validation, and preservation are detailed in this protocol chapter. In addition, we outline a cost-effective, homebrew extraction protocol optimized to extract eDNA.

Complete mitochondrial genomes of the black corals Alternatipathesmirabilis Opresko & Molodtsova, 2021 and Parantipatheslarix (Esper, 1788) (Cnidaria, Anthozoa, Hexacorallia, Antipatharia, Schizopathidae).

We describe the complete mitogenomes of the black corals Alternatipathesmirabilis Opresko & Molodtsova, 2021 and Parantipatheslarix (Esper, 1790) (Cnidaria, Anthozoa, Hexacorallia, Antipatharia, Schizopathidae). The analysed specimens include the holotype of Alternatipathesmirabilis, collected from Derickson Seamount (North Pacific Ocean; Gulf of Alaska) at 4,685 m depth and a potential topotype of Parantipatheslarix, collected from Secca dei Candelieri (Mediterranean Sea; Tyrrhenian Sea; Salerno Gulf; Italy) at 131 m depth. We also assemble, annotate and make available nine additional black coral mitogenomes that were included in a recent phylogeny (Quattrini et al. 2023b), but not made easily accessible on GenBank. This is the first study to present and compare two mitogenomes from the same species of black coral (Stauropathesarctica (Lütken, 1871)) and, thus, place minimum boundaries on the expected level of intraspecific variation at the mitogenome level. We also compare interspecific variation at the mitogenome-level across five different specimens of Parantipathes Brook, 1889 (representing at least two different species) from the NE Atlantic and Mediterranean Sea.

Transcriptomics of a Greenlandic Snailfish Reveals Exceptionally High Expression of Antifreeze Protein Transcripts.

Polar fishes have evolved antifreeze proteins (AFPs) that allow them to survive in subzero temperatures. We performed deep transcriptomic sequencing on a postlarval/juvenile variegated snailfish, Liparis gibbus (Actinopterygii: Scorpaeniformes: Cottoidei: Liparidae), living in an iceberg habitat (-2°C) in Eastern Greenland and report detection of highly expressed transcripts that code for putative AFPs from 2 gene families, Type I and LS-12-like proteins (putative Type IV AFPs). The transcripts encoding both proteins have expression levels among the top <1% of expressed genes in the fish. The Type I AFP sequence is different from a reported Type I AFP from the same species, possibly expressed from a different genetic locus. While prior findings from related adult sculpins suggest that LS-12-like/Type IV AFPs may not have a role in antifreeze protection, our finding of very high relative gene expression of the LS-12-like gene suggests that highly active transcription of the gene is important to the fish in the iceberg habitat and raises the possibility that weak or combinatorial antifreeze activity could be beneficial. These findings highlight the physiological importance of antifreeze proteins to the survival of fishes living in polar habitats.

New genus and species of black coral from the SW Pacific and Antarctica (Cnidaria: Anthozoa: Antipatharia: Schizopathidae).

A new genus, Diplopathes, in the family Schizopathidae, and three new species are described from the Southwest Pacific and Antarctic region based on morphological data. The new genus superficially resembles Telopathes in being branched and having simple, bilateral pinnules, but differs in having strictly alternately arranged pinnules, and in having small polyps 4 mm or less in transverse diameter. Mitochondrial DNA placed Diplopathes and Telopathes in separate clades within the Schizopathidae, thus supporting the significance of seemingly subtle anatomical differences. The new species are: D. antarctica, with sparse branching, pinnules of up to 7 cm long, and polypar spines up to 0.045 mm tall; D. multipinnata, with dense branching, pinnules up to 3 cm long, and polypar spines up to 0.1 mm tall; and D. tuatoruensis, with very sparse branching, pinnules up to 10 cm long, and polypar spines up to 0.1 mm. Interestingly, the three new species do not form a monophyletic clade based on mitochondrial DNA. We propose and discuss two hypotheses to explain the results of the phylogenetic reconstruction, including that molecular and physical change are uncoupled or that we have uncovered another example of morphological convergence in unrelated species.

Contrasting modes of mitochondrial genome evolution in sister taxa of wood-eating marine bivalves (Teredinidae and Xylophagaidae).

The bivalve families Teredinidae and Xylophagaidae include voracious consumers of wood in shallow and deep-water marine environments, respectively. The taxa are sister clades whose members consume wood as food with the aid of intracellular cellulolytic endosymbionts housed in their gills. This combination of adaptations is found in no other group of animals and was likely present in the common ancestor of both families. Despite these commonalities, the two families have followed dramatically different evolutionary paths with respect to anatomy, life history and distribution. Here we present 42 new mitochondrial genome sequences from Teredinidae and Xylophagaidae and show that distinct trajectories have also occurred in the evolution and organization of their mitochondrial genomes. Teredinidae display significantly greater rates of amino acid substitution but absolute conservation of protein-coding gene order, whereas Xylophagaidae display significantly less amino acid change but have undergone numerous and diverse changes in genome organization since their divergence from a common ancestor. As with many bivalves, these mitochondrial genomes encode two ribosomal RNAs, 12 protein coding genes, and 22 tRNAs; atp8 was not detected. We further show that their phylogeny, as inferred from amino acid sequences of 12 concatenated mitochondrial protein-coding genes, is largely congruent with those inferred from their nuclear genomes based on 18S and 28S ribosomal RNA sequences. Our results provide a robust phylogenetic framework to explore the tempo and mode of mitochondrial genome evolution and offer directions for future phylogenetic and taxonomic studies of wood-boring bivalves.

Description of two new genera and two new species of antipatharian corals in the family Aphanipathidae (Cnidaria: Anthozoa: Antipatharia).

Two new genera and two new species of black corals are recognized in the family Aphanipathidae. The new genus Anozopathes, with the species A. hawaiiensis sp. nov. and A. palauensis, sp. nov. is characterized by a sparsely and irregularly branched corallum with relatively long branches which can be straight, curved or crooked. The genus Aphanostichopathes, with the type species Cirripathes paucispina Brook, is characterized by an unbranched corallum with a long, curved stem with loose distal coils. Mitochondrial DNA data (nad5-IGR-nad1 for Anozopathes and cox3-cox1 for Aphanostichopathes) indicate that both taxa are related to the genera Aphanipathes, Phanopathes and Acanthopathes in the family Aphanipathidae, and morphologically they both share the characteristic of having spines with distinct conical tubercles. The two new species of Anozopathes are separated primarily by differences in colony growth form and in the size and shape of the skeletal spines. Species of Aphanostichopathes are separated primarily by differences in the size and shape of the spines and by size and density of the tubercles on the surface of the spines.

Morphological and molecular description of a new genus and species of black coral (Cnidaria: Anthozoa: Hexacorallia: Antipatharia: Antipathidae: Blastopathes) from Papua New Guinea.

Blastopathes medusa gen. nov., sp. nov., is described from Kimbe Bay, Papua New Guinea, based on morphological and molecular data. Blastopathes, assigned to the Antipathidae, is a large, mythology-inspiring black coral characterized by clusters of elongate stem-like branches that extend out at their base and then curve upward. Colonies are not pinnulate and contain single branches, which could represent new branch cluster formations. Morphological and molecular (mitochondrial DNA and targeted capture of nuclear loci) evidence supporting the establishment of a new genus is discussed. This is the first study to utilize the target capture of ultraconserved elements (UCEs) and exonic loci to elucidate phylogenetic relationships among black corals and to identify and place a new genus and species.

Ultra-gentle soft robotic fingers induce minimal transcriptomic response in a fragile marine animal.

Tessler et al. demonstrate that a 'soft' robot causes less stress to a jellyfish while handling compared to a traditional 'hard' robot.

Palaeoclimate ocean conditions shaped the evolution of corals and their skeletons through deep time.

Identifying how past environmental conditions shaped the evolution of corals and their skeletal traits provides a framework for predicting their persistence and that of their non-calcifying relatives under impending global warming and ocean acidification. Here we show that ocean geochemistry, particularly aragonite-calcite seas, drives patterns of morphological evolution in anthozoans (corals, sea anemones) by examining skeletal traits in the context of a robust, time-calibrated phylogeny. The lability of skeletal composition among octocorals suggests a greater ability to adapt to changes in ocean chemistry compared with the homogeneity of the aragonitic skeleton of scleractinian corals. Pulses of diversification in anthozoans follow mass extinctions and reef crises, with sea anemones and proteinaceous corals filling empty niches as tropical reef builders went extinct. Changing environmental conditions will likely diminish aragonitic reef-building scleractinians, but the evolutionary history of the Anthozoa suggests other groups will persist and diversify in their wake.

Ideating iDNA: Lessons and limitations from leeches in legacy collections.

Indirect methods for conducting faunal inventories present great promise, and genomic inventories derived from environmental sources (eDNA) are improving. Invertebrate ingested DNA (iDNA) from terrestrial leeches in the family Haemadipsidae has shown potential for surveying vertebrates and biodiversity monitoring in protected areas. Here we present an initial, and critical, evaluation of the limitations and biases of current iDNA protocols for biodiversity monitoring using both standard and NGS barcoding approaches. Key findings include the need for taxon relevant multi-locus markers and reference databases. In particular, the limitations of available reference databases have profound potential to mislead and bias eDNA and iDNA results if not critically interpreted. Nevertheless, there is great potential for recovery of amplifiable DNA from gut contents of invertebrate museum specimens which may reveal both temporal patterns and cryptic diversity in protected areas with increased efficiency. Our analyses of ingested DNA (iDNA) from both freshly stored and previously collected (legacy) samples of terrestrial leeches successfully identified vertebrates from Myanmar, Australia and Madagascar and indicate the potential to characterize microbial communities, pathogen diversity and interactions at low cost.

Linear Mitochondrial Genome in Anthozoa (Cnidaria): A Case Study in Ceriantharia.

Sequences and structural attributes of mitochondrial genomes have played a critical role in the clarification of relationships among Cnidaria, a key phylum of early-diverging animals. Among the major lineages of Cnidaria, Ceriantharia ("tube anemones") remains one of the most enigmatic in terms of its phylogenetic position. We sequenced the mitochondrial genomes of two ceriantharians to see whether the complete organellar genome would provide more support for the phylogenetic placement of Ceriantharia. For both Isarachnanthus nocturnus and Pachycerianthus magnus, the mitochondrial gene sequences could not be assembled into a single circular genome. Instead, our analyses suggest that both species have mitochondrial genomes consisting of multiple linear fragments. Linear mitogenomes are characteristic of members of Medusozoa, one of the major lineages of Cnidaria, but are unreported for Anthozoa, which includes the Ceriantharia. The inferred number of fragments and variation in gene order between species is much greater within Ceriantharia than among the lineages of Medusozoa. We identify origins of replication for each of the five putative chromosomes of the Isarachnanthus nocturnus mitogenome and for each of the eight putative chromosomes of the Pachycerianthus magnus mitogenome. At 80,923 bp, I. nocturnus now holds the record for the largest animal mitochondrial genome reported to date. The novelty of the mitogenomic structure in Ceriantharia highlights the distinctiveness of this lineage but, because it appears to be both unique to and diverse within Ceriantharia, it is uninformative about the phylogenetic position of Ceriantharia relative to other Anthozoa. The presence of tRNAMet and tRNATrp in both ceriantharian mitogenomes supports a closer relationship between Ceriantharia and Hexacorallia than between Ceriantharia and any other cnidarian lineage, but phylogenetic analysis of the genes contained in the mitogenomes suggests that Ceriantharia is sister to a clade containing Octocorallia + Hexacorallia indicating a possible suppression of tRNATrp in Octocorallia.

Mitogenomics suggests a sister relationship of Relicanthus daphneae (Cnidaria: Anthozoa: Hexacorallia: incerti ordinis) with Actiniaria.

Relicanthus daphneae (formerly Boloceroides daphneae) was first described in 2006 as a giant sea anemone based on morphology. In 2014, its classification was challenged based on molecular data: using five genes, Relicanthus was resolved sister to zoanthideans, but with mixed support. To better understand the evolutionary relationship of Relicanthus with other early-branching metazoans, we present 15 newly-sequenced sea anemone mitochondrial genomes and a mitogenome-based phylogeny including all major cnidarian groups, sponges, and placozoans. Our phylogenetic reconstruction reveals a moderately supported sister relationship between Relicanthus and the Actiniaria. Morphologically, the cnidae of Relicanthus has apical flaps, the only existing synapomorphy for sea anemones. Based on both molecular and morphological results, we propose a third suborder (Helenmonae) within the Actiniaria to accommodate Relicanthus. Although Relicanthus shares the same gene order and content with other available actiniarian mitogenomes, it is clearly distinct at the nucleotide level from anemones within the existing suborders. The phylogenetic position of Relicanthus could reflect its association with the periphery of isolated hydrothermal vents, which, although patchy and ephemeral, harbor unique chemosynthetic communities that provide a relatively stable food source to higher trophic levels over long evolutionary timescales. The ability to colonize the deep sea and the periphery of new vent systems may be facilitated by Relicanthus' large and extremely yolky eggs.

The transcriptome of the Bermuda fireworm Odontosyllis enopla (Annelida: Syllidae): A unique luciferase gene family and putative epitoky-related genes.

The Bermuda fireworm Odontosyllis enopla exhibits an extremely tight circalunar circadian behavior that results in an impressive bioluminescent mating swarm, thought to be due to a conventional luciferase-mediated oxidation of a light-emitting luciferin. In addition, the four eyes become hypertrophied and heavily pigmented, and the nephridial system is modified to store and release gametes and associated secretions. In an effort to elucidate transcripts related to bioluminescence, circadian or circalunar periodicity, as well as epitoky-related changes of the eyes and nephridial system, we examined the transcriptomic profile of three female O. enopla during a bioluminescent swarm in Ferry Reach, Bermuda. Using the well-characterized luciferase gene of the Japanese syllid Odontosyllis undecimdonta as a reference, a complete best-matching luciferase open reading frame (329 amino acids in length) was found in all three individuals analyzed in addition to numerous other paralogous sequences in this new gene family. No photoproteins were detected. We also recovered a predicted homolog of 4-coumarate-CoA ligase (268 amino acids in length) that best matched luciferase of the firefly Luciola with the best predicted template being the crystal structure of luciferase for Photinus pyralis, the common eastern firefly. A wide variety of genes associated with periodicity were recovered including predicted homologs of clock, bmal1, period, and timeless. Several genes corresponding to putative epitoky-related changes of the eyes were recovered including predicted homologs of a phototransduction gene, a retinol dehydrogenase and carotenoid isomerooxygenase as well as a visual perception related retinal rod rhodopsin-sensitive cGMP 3',5'-cyclic phosphodiesterase. Genes correlating to putative epitoky-related changes of the nephridia included predicted homologs of nephrocystin-3 and an egg-release sex peptide receptor.

Universal target-enrichment baits for anthozoan (Cnidaria) phylogenomics: New approaches to long-standing problems.

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.

Comparative transcriptomics reveal developmental turning points during embryogenesis of a hemimetabolous insect, the damselfly Ischnura elegans.

Identifying transcriptional changes during embryogenesis is of crucial importance for unravelling evolutionary, molecular and cellular mechanisms that underpin patterning and morphogenesis. However, comparative studies focusing on early/embryonic stages during insect development are limited to a few taxa. Drosophila melanogaster is the paradigm for insect development, whereas comparative transcriptomic studies of embryonic stages of hemimetabolous insects are completely lacking. We reconstructed the first comparative transcriptome covering the daily embryonic developmental progression of the blue-tailed damselfly Ischnura elegans (Odonata), an ancient hemimetabolous representative. We identified a "core" set of 6,794 transcripts - shared by all embryonic stages - which are mainly involved in anatomical structure development and cellular nitrogen compound metabolic processes. We further used weighted gene co-expression network analysis to identify transcriptional changes during Odonata embryogenesis. Based on these analyses distinct clusters of transcriptional active sequences could be revealed, indicating that embryos at different development stages have their own transcriptomic profile according to the developmental events and leading to sequential reprogramming of metabolic and developmental genes. Interestingly, a major change in transcriptionally active sequences is correlated with katatrepsis (revolution) during mid-embryogenesis, a 180° rotation of the embryo within the egg and specific to hemimetabolous insects.