The transcriptome of the venom duct of the Atlantic piscivorous cone species Chelyconus ermineus (Born, 1778) was determined. The venom repertoire of this species includes at least 378 conotoxin precursors, which could be ascribed to 33 known and 22 new (unassigned) protein superfamilies, respectively. Most abundant superfamilies were T, W, O1, M, O2, and Z, accounting for 57% of all detected diversity. A total of three individuals were sequenced showing considerable intraspecific variation: each individual had many exclusive conotoxin precursors, and only 20% of all inferred mature peptides were common to all individuals. Three different regions (distal, medium, and proximal with respect to the venom bulb) of the venom duct were analyzed independently. Diversity (in terms of number of distinct members) of conotoxin precursor superfamilies increased toward the distal region whereas transcripts detected toward the proximal region showed higher expression levels. Only the superfamilies A and I3 showed statistically significant differential expression across regions of the venom duct. Sequences belonging to the alpha (motor cabal) and kappa (lightning-strike cabal) subfamilies of the superfamily A were mainly detected in the proximal region of the venom duct. The mature peptides of the alpha subfamily had the α4/4 cysteine spacing pattern, which has been shown to selectively target muscle nicotinic-acetylcholine receptors, ultimately producing paralysis. This function is performed by mature peptides having a α3/5 cysteine spacing pattern in piscivorous cone species from the Indo-Pacific region, thereby supporting a convergent evolution of piscivory in cones.

BackgroundDue to their great species and ecological diversity as well as their capacity to produce hundreds of different toxins, cone snails are of interest to evolutionary biologists, pharmacologists and amateur naturalists alike. Taxonomic identification of cone snails still relies mostly on the shape, color, and banding patterns of the shell. However, these phenotypic traits are prone to homoplasy. Therefore, the consistent use of genetic data for species delimitation and phylogenetic inference in this apparently hyperdiverse group is largely wanting. Here, we reconstruct the phylogeny of the cones endemic to Cabo Verde archipelago, a well-known radiation of the group, using mitochondrial (mt) genomes.ResultsThe reconstructed phylogeny grouped the analyzed species into two main clades, one including Kalloconus from West Africa sister to Trovaoconus from Cabo Verde and the other with a paraphyletic Lautoconus due to the sister group relationship of Africonus from Cabo Verde and Lautoconus ventricosus from Mediterranean Sea and neighboring Atlantic Ocean to the exclusion of Lautoconus endemic to Senegal (plus Lautoconus guanche from Mauritania, Morocco, and Canary Islands). Within Trovaoconus, up to three main lineages could be distinguished. The clade of Africonus included four main lineages (named I to IV), each further subdivided into two monophyletic groups. The reconstructed phylogeny allowed inferring the evolution of the radula in the studied lineages as well as biogeographic patterns. The number of cone species endemic to Cabo Verde was revised under the light of sequence divergence data and the inferred phylogenetic relationships.ConclusionsThe sequence divergence between continental members of the genus Kalloconus and island endemics ascribed to the genus Trovaoconus is low, prompting for synonymization of the latter. The genus Lautoconus is paraphyletic. Lautoconus ventricosus is the closest living sister group of genus Africonus. Diversification of Africonus was in allopatry due to the direct development nature of their larvae and mainly triggered by eustatic sea level changes during the Miocene-Pliocene. Our study confirms the diversity of cone endemic to Cabo Verde but significantly reduces the number of valid species. Applying a sequence divergence threshold, the number of valid species within the sampled Africonus is reduced to half.Electronic supplementary materialThe online version of this article (10.1186/s12862-017-1069-x) contains supplementary material, which is available to authorized users.

The great morphological and ecological diversity within the superfamily Trochoidea s.l. (Gastropoda: Vetigastropoda) has in the past hindered the reconstruction of a robust phylogeny for the group based on morphology. Moreover, previous molecular phylogenies disagreed on the monophyly and internal relationships of Trochoidea s.l., as well as on its relative phylogenetic position within Vetigastropoda. In order to further resolve the trochoidean and vetigastropod phylogenetic trees, we considerably increased the representation of trochoidean families for which no previous mitochondrial (mt) genomes were available: the complete mt genome of Cittarium pica (Tegulidae) and the nearly complete mt genomes of Tectus virgatus (Tegulidae), Gibbula umbilicaris (Trochidae), and Margarites vorticiferus (Margaritidae) were sequenced. In addition, the nucleotide sequences of all protein coding and rRNA genes of Clanculus margaritarius (Trochidae) and of Calliostoma zizyphinum (Calliostomatidae) were derived from transcriptomic sequence data. The reconstructed phylogenetic trees using probabilistic methods and Neomphalina as outgroup recovered with maximal support a Trochoidea sensu Hickman & McLean, 1990 clade that included superfamilies Angarioidea and Phasianelloidea deeply nested within superfamily Trochoidea sensu Williams (2012). The families Trochidae and Calliostomatidae were the sister group to the remaining trochoidean lineages. Of these, the family Margaritidae was sister to a clade including Phasianelloidea + Angarioidea and Turbinidae + Tegulidae, this latter family being paraphyletic (Cittarium and Tectus need to be assigned to a new family). Gene order within newly determined mt genomes was very stable (with only few rearrangements restricted to tRNA genes) and conformed to the vetigastropod and gastropod consensus genome organizations.

No abstract

The transcriptomes of the venom glands of two individuals of the magician’s cone, Pionoconus magus, from Okinawa (Japan) were sequenced, assembled, and annotated. In addition, RNA-seq raw reads available at the SRA database from one additional specimen of P. magus from the Philippines were also assembled and annotated. The total numbers of identified conotoxin precursors and hormones per specimen were 118, 112, and 93. The three individuals shared only five identical sequences whereas the two specimens from Okinawa had 30 sequences in common. The total number of distinct conotoxin precursors and hormones for P. magus was 275, and were assigned to 53 conotoxin precursor and hormone superfamilies, two of which were new based on their divergent signal region. The superfamilies that had the highest number of precursors were M (42), O1 (34), T (27), A (18), O2 (17), and F (13), accounting for 55% of the total diversity. The D superfamily, previously thought to be exclusive of vermivorous cones was found in P. magus and contained a highly divergent mature region. Similarly, the A superfamily alpha 4/3 was found in P. magus despite the fact that it was previously postulated to be almost exclusive of the genus Rhombiconus. Differential expression analyses of P. magus compared to Chelyconus ermineus, the only fish-hunting cone from the Atlantic Ocean revealed that M and A2 superfamilies appeared to be more expressed in the former whereas the O2 superfamily was more expressed in the latter.

Understanding the relative role of different evolutionary processes leading to the extraordinary morphological, ecological and species diversity of cone snails requires a robust phylogeny, which thus far has been elusive. Here, we constructed a mitochondrial (mt) genome data set, which included four newly sequenced mt genomes, 25 publicly available mt genomes and 24 data sets with all mt protein-coding and rRNA genes assembled from venom gland transcriptomes. In total, we analysed 42 different species representing 27 genera of cone snails, that is, about one third of the generic diversity of the group. In addition, we used the RNA-Seq reads to assemble 21 nuclear genes, which were concatenated in a nuclear data set. Finally, a combined data set including mt and nuclear genes was also constructed. The three data matrices were analysed with probabilistic methods, site-homogeneous and site-heterogeneous models, and with protein-coding genes both at the amino acid and nucleotide levels.Diet specialization, radular morphology and the type of protoconch (paucispiral or multispiral indicating lecithotrophic or planktonic larvae, respectively) as well as conotoxin diversity were mapped onto the reconstructed mt phylogeny, and a chronogram dating mayor cladogenetic events within the group was also reconstructed. K E Y W O R D SConidae, conotoxins, mitogenome, phylogenomics, transcriptomics | 211 ABALDE Et AL. ORCID Manuel J. Tenoriohttps://orcid.org/0000-0003-4088-4958Rafael Zardoya https://orcid.org/0000-0001-6212-9502

The transcriptomes of the venom glands of 13 closely related species of vermivorous cones endemic to West Africa from genera Africonus and Varioconus were sequenced and venom repertoires compared within a phylogenetic framework using one Kalloconus species as outgroup. The total number of conotoxin precursors per species varied between 108 and 221. Individuals of the same species shared about one-fourth of the total conotoxin precursors. The number of common sequences was drastically reduced in the pairwise comparisons between closely related species, and the phylogenetical signal was totally eroded at the inter-generic level (no sequence was identified as shared derived), due to the intrinsic high variability of these secreted peptides. A common set of four conotoxin precursor superfamilies (T, O1, O2 and M) was expanded in all studied cone species, and thus, they are considered the basic venom toolkit for hunting and defense in the West African vermivorous cone snails. Maximum-likelihood ancestral character reconstructions inferred shared conotoxin precursors preferentially at internal nodes close to the tips of the phylogeny (between individuals and between closely related species) as well as in the common ancestor of Varioconus . Besides the common toolkit, the two genera showed significantly distinct catalogues of conotoxin precursors in terms of type of superfamilies present and the abundance of members per superfamily, but had similar relative expression levels indicating functional convergence. Differential expression comparisons between vermivorous and piscivorous cones highlighted the importance of the A and S superfamilies for fish hunting and defense.

Background Venoms are deadly weapons to subdue prey or deter predators that have evolved independently in many animal lineages. The genomes of venomous animals are essential to understand the evolutionary mechanisms involved in the origin and diversification of venoms. Results Here, we report the chromosome-level genome of the venomous Mediterranean cone snail, Lautoconus ventricosus (Caenogastropoda: Conidae). The total size of the assembly is 3.59 Gb; it has high contiguity (N50 = 93.53 Mb) and 86.6 Mb of the genome assembled into the 35 largest scaffolds or pseudochromosomes. On the basis of venom gland transcriptomes, we annotated 262 complete genes encoding conotoxin precursors, hormones, and other venom-related proteins. These genes were scattered in the different pseudochromosomes and located within repetitive regions. The genes encoding conotoxin precursors were normally structured into 3 exons, which did not necessarily coincide with the 3 structural domains of the corresponding proteins. Additionally, we found evidence in the L. ventricosus genome for a past whole-genome duplication event by means of conserved gene synteny with the Pomacea canaliculata genome, the only one available at the chromosome level within Caenogastropoda. The whole-genome duplication event was further confirmed by the presence of a duplicated hox gene cluster. Key genes for gastropod biology including those encoding proteins related to development, shell formation, and sex were located in the genome. Conclusions The new high-quality L. ventricosus genome should become a reference for assembling and analyzing new gastropod genomes and will contribute to future evolutionary genomic studies among venomous animals.