Anthopleura and the phylogeny of Actinioidea (Cnidaria: Anthozoa: Actiniaria)

Sea anemone (Anthozoa, Actiniaria) diversity in Mo'orea (French Polynesia)

Sea anemones (Order Actiniaria) are a diverse group of marine invertebrates ubiquitous across marine ecosystems. Despite their wide distribution and success, a knowledge gap persists in our understanding of their diversity within tropical systems, owed to sampling bias of larger and more charismatic species overshadowing cryptic lineages. This study aims to delineate the sea anemone diversity in Mo'orea (French Polynesia) with the use of a dataset from the Mo'orea Biocode's "BioBlitz" initiative, which prioritized the sampling of more cryptic and understudied taxa. Implementing a target enrichment approach, we integrate 71 newly sequenced samples into an expansive phylogenetic framework and contextualize Mo'orea's diversity within global distribution patterns of sea anemones. Our analysis corroborates the presence of several previously documented sea anemones in French Polynesia and identifies for the first time the occurrence of members of genera Andvakia and Aiptasiomorpha. This research unveils the diverse sea anemone ecosystem in Mo'orea, spotlighting the area's ecological significance and emphasizing the need for continued exploration. Our methodology, encompassing a broad BLAST search coupled with phylogenetic analysis, proved to be a practical and effective approach for overcoming the limitations posed by the lack of comprehensive sequence data for sea anemones. We discuss the merits and limitations of current molecular methodologies and stress the importance of further research into lesser-studied marine organisms like sea anemones. Our work sets a precedent for future phylogenetic studies stemming from BioBlitz endeavors.

Fluorescent proteins generate a genetic color polymorphism and counteract oxidative stress in intertidal sea anemones

Fluorescent proteins (FPs) are ubiquitous tools in research, yet their endogenous functions in nature are poorly understood. In this work, we describe a combination of functions for FPs in a clade of intertidal sea anemones whose FPs control a genetic color polymorphism together with the ability to combat oxidative stress. Focusing on the underlying genetics of a fluorescent green "Neon" color morph, we show that allelic differences in a single FP gene generate its strong and vibrant color, by increasing both molecular brightness and FP gene expression level. Natural variation in FP sequences also produces differences in antioxidant capacity. We demonstrate that these FPs are strong antioxidants that can protect live cells against oxidative stress. Finally, based on structural modeling of the responsible amino acids, we propose a model for FP antioxidant function that is driven by molecular surface charge. Together, our findings shed light on the multifaceted functions that can co-occur within a single FP and provide a framework for studying the evolution of fluorescence as it balances spectral and physiological functions in nature.

An Overview of Julia-lythgoe Olefination

Julia-Lythgoe olefination (or simply Julia olefination) is an olefination process between phenyl sulfones and aldehydes (or ketones) to give alkenes after alcohol functionalization and reductive elimination using sodium amalgam or SmI2. It is mainly used to synthesize E-alkenes and is a key step in numerous total syntheses of many natural products. This review exclusively deals with the Julia-Lythgoe olefination and concentrates mainly on the applications of this reaction in natural product synthesis covering literature up to 2021.

Spatial Distribution and Biochemical Characterization of Serine Peptidase Inhibitors in the Venom of the Brazilian Sea Anemone Anthopleura cascaia Using Mass Spectrometry Imaging

Sea anemones are known to produce a diverse array of toxins with different cysteine-rich peptide scaffolds in their venoms. The serine peptidase inhibitors, specifically Kunitz inhibitors, are an important toxin family that is believed to function as defensive peptides, as well as prevent proteolysis of other secreted anemone toxins. In this study, we isolated three serine peptidase inhibitors named Anthopleura cascaia peptide inhibitors I, II, and III (ACPI-I, ACPI-II, and ACPI-III) from the venom of the endemic Brazilian sea anemone A. cascaia. The venom was fractionated using RP-HPLC, and the inhibitory activity of these fractions against trypsin was determined and found to range from 59% to 93%. The spatial distribution of the anemone peptides throughout A. cascaia was observed using mass spectrometry imaging. The inhibitory peptides were found to be present in the tentacles, pedal disc, and mesenterial filaments. We suggest that the three inhibitors observed during this study belong to the venom Kunitz toxin family on the basis of their similarity to PI-actitoxin-aeq3a-like and the identification of amino acid residues that correspond to a serine peptidase binding site. Our findings expand our understanding of the diversity of toxins present in sea anemone venom and shed light on their potential role in protecting other venom components from proteolysis.

First record of a sea anemone of genus Bunodosoma with two oral discs: a clue to asexual reproduction?

Different reproductive strategies (both sexual and asexual) that may occur in individuals of the same species may explain the success of sea anemones (Cnidaria:Actiniaria) in colonizing different ecosystems around the planet. Here we provide the first record of a Bunodosoma specimen with two oral discs and discuss the possibility of asexual reproduction in this genus. One individual of Bunodosoma cangicum was found in Carneiros beach (Pernambuco state, Brazil) with two fully individualized oral discs but with column and pedal disc still connected. Our finding may represent a clue to longitudinal fission in Bunodosoma. Yet, despite the number of different studies carried out so far, the absence of data regarding asexual reproduction in Bunodosoma suggests that it might be rare in this genus, occurring only in sporadic cases such as recovery from injury.

Population genomics for symbiotic anthozoans: can reduced representation approaches be used for taxa without reference genomes?

Population genetic studies of symbiotic anthozoans have been historically challenging because their endosymbioses with dinoflagellates have impeded marker development. Genomic approaches like reduced representation sequencing alleviate marker development issues but produce anonymous loci, and without a reference genome, it is unknown which organism is contributing to the observed patterns. Alternative methods such as bait-capture sequencing targeting Ultra-Conserved Elements are now possible but costly. Thus, RADseq remains attractive, but how useful are these methods for symbiotic anthozoan taxa without a reference genome to separate anthozoan from algal sequences? We explore this through a case-study using a double-digest RADseq dataset for the sea anemone Bartholomea annulata. We assembled a holobiont dataset (3854 loci) for 101 individuals, then used a reference genome to create an aposymbiotic dataset (1402 loci). For both datasets, we investigated population structure and used coalescent simulations to estimate demography and population parameters. We demonstrate complete overlap in the spatial patterns of genetic diversity, demographic histories, and population parameter estimates for holobiont and aposymbiotic datasets. We hypothesize that the unique combination of anthozoan biology, diversity of the endosymbionts, and the manner in which assembly programs identify orthologous loci alleviates the need for reference genomes in some circumstances. We explore this hypothesis by assembling an additional 21 datasets using the assembly programs pyRAD and Stacks. We conclude that RADseq methods are more tractable for symbiotic anthozoans without reference genomes than previously realized.

Comparison of sequence-capture and ddRAD approaches in resolving species and populations in hexacorallian anthozoans

Genome-level sequencing is the next step in understanding species-level relationships within Anthozoa (soft corals, anemones, stony corals, and their kin) as morphological and PCR-directed (single-locus) sequencing methods often fall short of differentiating species. The sea anemone genus Metridium is a common northern temperate sea anemone whose species are difficult to differentiate using morphology alone. Here we use Metridium as a case study to confirm the low level of information available in six loci for species differentiation commonly sequenced for Actiniaria and explore and compare the efficacy of ddRAD and sequence-capture methods in species-level systematics and biogeographic studies. We produce phylogenetic trees from concatenated datasets and perform DAPC and STRUCTURE analyses using SNP data. The six conventional loci are not able to consistently differentiate species within Metridium. The sequence-capture dataset resulted in high support and resolution for both current species and relationships between geographic areas. The ddRAD datasets displayed ambiguity among species, and support between major geographic groupings was not as high as the sequence-capture datasets. The level of resolution and support resulting from the sequence-capture data, combined with the ability to add additional individuals and expand beyond the genus Metridium over time, emphasizes the utility of sequence-capture methods for both systematics and future biogeographic studies within anthozoans. We discuss the strengths and weaknesses of the genomic approaches in light of our findings and suggest potential implications for the biogeography of Metridium based on our sampling.

Phylogenetic Relatedness within the Internally Brooding Sea Anemones from the Arctic-Boreal Region

Phylogenetic analyses based on mitochondrial 16S rDNA, nuclear 28S rDNA, and morphological and ecological traits of Aulactinia, Urticina and Cribrinopsis sea anemones inhabiting the Arctic-boreal region indicate discordances between trees derived from molecular sequences and those based on morphological traits. Nuclear genes were more informative than mitochondrial and morphological datasets. Our findings indicate that 16S rDNA has limited applicability for phylogenetic analyses at lower taxonomic levels and can only be used for distinction of families. Although 28S rDNA allowed for the classification of distinct genera, it could not confirm that species of Urticina and Cribrinopsis, which appeared to be closely related, were correctly separated into two different genera. The nuclear tree revealed inconsistencies between specimens belonging to European Urticina crassicornis and Pacific U. crassicornis; the latter seems to be a different species. In contrast to Pacific U. crassicornis, the specimens collected from different localities in the Barents Sea are on the same tree branch. The same was observed for specimens of Aulactinia stella. Both species brood their young internally. The dispersal of sea anemones with brooding juveniles seems to be less limited than expected and might be sufficient to settle habitats more than a thousand kilometers away.

Origin and evolution of the symbiosis between sea anemones (Cnidaria, Anthozoa, Actiniaria) and hermit crabs, with additional notes on anemone-gastropod associations

The anemone-crab mutualism is ubiquitous in temperate and tropical marine environments. In this symbiosis, one or more anemones live on a shell inhabited by a hermit crab and reciprocal phoretic, trophic, and defensive benefits are exchanged between the partners. Sea anemone-hermit crab symbionts belong to three families: Hormathiidae (Calliactis and Paracalliactis), Sagartiidae (Carcinactis and Verrillactis), and Actiniidae (Stylobates). Hermit crabs establish most partnerships by detaching anemones and placing them on their shell; sea anemones can also mount shells unaided, triggered by a mollusc-derived substance in the periostracum of the shell. At least partial cooperation by the anemones is necessary for successful establishment of the symbiosis. Here, we expand the evolutionary framework for hormathiid symbionts by generating a phylogeny with at least one member of each actiniarian symbiotic genus with hermit crabs using five molecular markers (16S, 12S, 18S, 28S, CO3). We not only corroborated the results from a previous study by finding two origins of hermit crab symbiosis within Hormathiidae, but also found additional origins for hermit crab symbiosis within Actiniaria. We provide for the first time evidence of a close relationship between symbionts Carcinactis dolosa and V. paguri. The ability to secrete chitin by the ectoderm of the column is inferred to be broadly convergent within Actiniaria whereas the secretion of a chitinous carcinoecium by the pedal disc is a distinct but convergent morphological adaptation of several lineages within Actiniaria. Our finding of multiple origins for both the hermit crab and gastropod symbioses suggests that the shell-mounting behavior might only have been the precursor of the hermit crab association among Calliactis spp.

The draft genome of Actinia tenebrosa reveals insights into toxin evolution

Sea anemones have a wide array of toxic compounds (peptide toxins found in their venom) which have potential uses as therapeutics. To date, the majority of studies characterizing toxins in sea anemones have been restricted to species from the superfamily, Actinioidea. No highly complete draft genomes are currently available for this superfamily, however, highlighting our limited understanding of the genes encoding toxins in this important group. Here we have sequenced, assembled, and annotated a draft genome for Actinia tenebrosa. The genome is estimated to be approximately 255 megabases, with 31,556 protein-coding genes. Quality metrics revealed that this draft genome matches the quality and completeness of other model cnidarian genomes, including Nematostella, Hydra, and Acropora. Phylogenomic analyses revealed strong conservation of the Cnidaria and Hexacorallia core-gene set. However, we found that lineage-specific gene families have undergone significant expansion events compared with shared gene families. Enrichment analysis performed for both gene ontologies, and protein domains revealed that genes encoding toxins contribute to a significant proportion of the lineage-specific genes and gene families. The results make clear that the draft genome of A. tenebrosa will provide insight into the evolution of toxins and lineage-specific genes, and provide an important resource for the discovery of novel biological compounds.