Mitochondrial genome sequencing of a vermivorous cone snail Conus quercinus supports the correlative analysis between phylogenetic relationships and dietary types of Conus species.

Complete mitochondrial genome (mitogenome) sequence of a worm-hunting cone snail, Conus quercinus, was reported in this study. Its mitogenome, the longest one (16,460 bp) among reported Conus specie, is composed of 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes and one D-loop region. The mitochondrial gene arrangement is highly-conserved and identical to other reported. However, the D-loop region of C. quercinus is the longest (943 bp) with the higher A+T content (71.3%) and a long AT tandem repeat stretch (68 bp). Subsequent phylogenetic analysis demonstrated that three different dietary types (vermivorous, molluscivorous and piscivorous) of cone snails are clustered separately, suggesting that the phylogenetics of cone snails is related to their dietary types. In conclusion, our current work improves our understanding of the mitogenomic structure and evolutionary status of the vermivorous C. quercinus, which support the putative hypothesis that the Conus ancestor was vermivorous.

Bioactive Compounds Isolated from Neglected Predatory Marine Gastropods.

A diverse range of predatory marine gastropods produce toxins, yet most of these molecules remain uncharacterized. Conus species have received the most attention from researchers, leading to several conopeptides reaching clinical trials. This review aims to summarize what is known about bioactive compounds isolated from species of neglected marine gastropods, especially in the Turridae, Terebridae, Babyloniidae, Muricidae, Buccinidae, Colubrariidae, Nassariidae, Cassidae, and Ranellidae families. Multiple species have been reported to contain bioactive compounds with potential toxic activity, but most of these compounds have not been characterized or even clearly identified. The bioactive properties and potential applications of echotoxins and related porins from the Ranellidae family are discussed in more detail. Finally, the review concludes with a call for research on understudied species.

Cone Snails: A Big Store of Conotoxins for Novel Drug Discovery.

Marine drugs have developed rapidly in recent decades. Cone snails, a group of more than 700 species, have always been one of the focuses for new drug discovery. These venomous snails capture prey using a diverse array of unique bioactive neurotoxins, usually named as conotoxins or conopeptides. These conotoxins have proven to be valuable pharmacological probes and potential drugs due to their high specificity and affinity to ion channels, receptors, and transporters in the nervous systems of target prey and humans. Several research groups, including ours, have examined the venom gland of cone snails using a combination of transcriptomic and proteomic sequencing, and revealed the existence of hundreds of conotoxin transcripts and thousands of conopeptides in each Conus species. Over 2000 nucleotide and 8000 peptide sequences of conotoxins have been published, and the number is still increasing quickly. However, more than 98% of these sequences still lack 3D structural and functional information. With the rapid development of genomics and bioinformatics in recent years, functional predictions and investigations on conotoxins are making great progress in promoting the discovery of novel drugs. For example, ω-MVIIA was approved by the U.S. Food and Drug Administration in 2004 to treat chronic pain, and nine more conotoxins are at various stages of preclinical or clinical evaluation. In short, the genus Conus, the big family of cone snails, has become an important genetic resource for conotoxin identification and drug development.

Divergence of the Venom Exogene Repertoire in Two Sister Species of Turriconus.

The genus Conus comprises approximately 700 species of venomous marine cone snails that are highly efficient predators of worms, snails, and fish. In evolutionary terms, cone snails are relatively young with the earliest fossil records occurring in the Lower Eocene, 55 Ma. The rapid radiation of cone snail species has been accompanied by remarkably high rates of toxin diversification. To shed light on the molecular mechanisms that accompany speciation, we investigated the toxin repertoire of two sister species, Conus andremenezi and Conus praecellens, that were until recently considered a single variable species. A total of 196 and 250 toxin sequences were identified in the venom gland transcriptomes of C. andremenezi and C. praecellens belonging to 25 and 29 putative toxin gene superfamilies, respectively. Comparative analysis with closely (Conus tribblei and Conus lenavati) and more distantly related species (Conus geographus) suggests that speciation is associated with significant diversification of individual toxin genes (exogenes) whereas the expression pattern of toxin gene superfamilies within lineages remains largely conserved. Thus, changes within individual toxin sequences can serve as a sensitive indicator for recent speciation whereas changes in the expression pattern of gene superfamilies are likely to reflect more dramatic differences in a species' interaction with its prey, predators, and competitors.

Molecular and morphometric data suggest the presence of a neglected species in the marine gastropod family Conidae.

Knowledge concerning the taxonomic diversity of marine organisms is crucial for understanding processes associated with species diversification in geographic areas that are devoid of obvious barriers to dispersal. The marine gastropod family Conidae contains many species complexes due to lack of clear morphological distinctiveness and existence of morphological intergradations among described species. Conus flavidus Lamarck, 1810 and Conus frigidus Reeve, 1848 are currently recognized as distinct taxa, but are often difficult to distinguish by morphological characters and include several synonyms, including Conus peasei Brazier, 1877. C. peasei was originally described by Pease in 1861 (as Conus neglectus) based on slight morphological differences of a population of C. flavidus from Hawaii that distinguished it from C. flavidus from elsewhere. To evaluate the systematics of this group and specifically test the hypothesis of synonymy of C. peasei with C. flavidus, we examined molecular and morphometric data from specimens of C. flavidus, C. frigidus and C. peasei (i.e., C. flavidus from Hawaii). Multiple clades that contain individuals from particular geographic regions are apparent in gene trees constructed from sequences of a mitochondrial gene region. In particular, sequences of C. peasei cluster together separately from sequences of C. flavidus and C. frigidus. Although individuals of C. peasei, C. flavidus and C. frigidus each contain a unique set of alleles for a nuclear locus, a conotoxin gene, alleles of C. peasei are more similar to those of C. flavidus. In addition, sequences of a region of a second nuclear gene are identical among C. peasei and C. flavidus though they are distinct from sequences of C. frigidus. Morphometric data revealed that shells of C. peasei are distinct in some aspects, but are more similar to those of C. flavidus than to those of C. frigidus. Taken together, these results suggest that C. peasei represents a distinct species. Moreover, based on the contradictory relationships inferred from the mitochondrial and nuclear sequences (as well as morphometric data), C. peasei may have originated through past hybridization among the ancestral lineages that gave rise to C. flavidus and C. frigidus.

Beyond Conus: Phylogenetic relationships of Conidae based on complete mitochondrial genomes.

Understanding how the extraordinary taxonomic and ecological diversity of cone snails (Caenogastropoda: Conidae) evolved requires a statistically robust phylogenetic framework, which thus far is not available. While recent molecular phylogenies have been able to distinguish several deep lineages within the family Conidae, including the genera Profundiconus, Californiconus, Conasprella, and Conus (and within this one, several subgenera), phylogenetic relationships among these genera remain elusive. Moreover, the possibility that additional deep lineages may exist within the family is open. Here, we reconstructed with probabilistic methods a molecular phylogeny of Conidae using the newly sequenced complete or nearly complete mitochondrial (mt) genomes of the following nine species that represent all main Conidae lineages and potentially new ones: Profundiconus teramachii, Californiconus californicus, Conasprella wakayamaensis, Lilliconus sagei, Pseudolilliconus traillii, Conus (Kalloconus) venulatus, Conus (Lautoconus) ventricosus, Conus (Lautoconus) hybridus, and Conus (Eugeniconus) nobilis. To test the monophyly of the family, we also sequenced the nearly complete mt genomes of the following three species representing closely related conoidean families: Benthomangelia sp. (Mangeliidae), Tomopleura sp. (Borsoniidae), and Glyphostoma sp. (Clathurellidae). All newly sequenced conoidean mt genomes shared a relatively constant gene order with rearrangements limited to tRNA genes. The reconstructed phylogeny recovered with high statistical support the monophyly of Conidae and phylogenetic relationships within the family. The genus Profundiconus was placed as sister to the remaining genera. Within these, a clade including Californiconus and Lilliconus+Pseudolilliconus was the sister group of Conasprella to the exclusion of Conus. The phylogeny included a new lineage whose relative phylogenetic position was unknown (Lilliconus) and uncovered thus far hidden diversity within the family (Pseudolilliconus). Moreover, reconstructed phylogenetic relationships allowed inferring that the peculiar diet of Californiconus based on worms, mollusks, crustaceans and fish is derived, and reinforce the hypothesis that the ancestor of Conidae was a worm hunter. A chronogram was reconstructed under an uncorrelated relaxed molecular clock, which dated the origin of the family shortly after the Cretaceous-Tertiary boundary (about 59million years ago) and the divergence among main lineages during the Paleocene and the Eocene (56-30million years ago).

Human injuries and fatalities due to venomous marine snails of the family Conidae.

OBJECTIVE: This paper provides the first compilation in more than 30 years of human injuries and fatalities from envenomation by marine gastropod molluscs of the predominantly tropical family Conidae. It seeks to apply recent advances in knowledge of the physiological effects of conopeptides and molecular genetics to improve our understanding of the human responses to stings by species that normally use their venom peptides to paralyze and overcome prey such as polychaete worms, other gastropod molluscs, and fishes. RESULTS: A database has been constructed for the 139 cases accepted as reliably reporting each human injury. It includes data on the species responsible, the time and place where the stinging occurred and the sting site on the victim's body, the time-course of clinical effects, treatment carried out, if any, and outcome. Members of the hyperdiverse genus Conus caused all the injuries, except for 2 cases involving species from the recently separated genus Conasprella. Death occurred in 36 cases, 57 cases presented with serious symptoms but recovered completely, and in 44 cases victims were only minimally affected. A few cases are listed as tentative because the information in the reports was limited or unverifiable. Many cases have undoubtedly gone unreported and been forgotten. No cases are known for the period between the date of the first reliable report in the 17th century, and the mid-19th century. Knowledge of conopeptide molecular structure and function has recently burgeoned, permitting initial exploration of relationships between the symptoms and outcomes of human injuries and modes of action of these mainly small, very toxic neuroactive peptides. These relationships are reviewed here, especially in regard to the severe and fatal cases, with the aim of making recent knowledge accessible to clinicians and others involved in treating the effects of human stings, which continue to be reported. CONCLUSIONS: Conus geographus, a specialized predator of fishes, which it paralyzes with its venom and swallows whole, is the most dangerous species to humans. It accounts for about half of the known human envenomations and almost all the fatalities. Children succumb more often to C. geographus stings than adults and stings by larger snails are lethal more often than stings from smaller snails, regardless of the victim's age. Other piscivorous Conus species have stung humans, but with nonlethal results. A few species that normally prey on other gastropods have also seriously injured humans, but most of the fatalities reported have not been confirmed. Most species of Conidae prey only on marine worms; 18 of these species are known to have stung humans, with generally mild effects. Research on the treatment of Conus stings has lagged behind that on the application of conopeptides in pharmacological research and in the development of new pharmaceuticals. However, improved communication and availability of medical aid in remote tropical areas has likely contributed to reducing the mortality rate during the last half century.

Effects of conopeptide-containing venom from seven species of Conidae gastropoda on the chick biventer-cervicis nerve-muscle assessed using the ConoServer database.

BACKGROUND: Conotoxins in the venom of marine gastropods (genus Conus, family Conidae) have been incriminated in fatal human stingings. Conotoxins are peptides (conopeptides) which target specific classes of ion channels and block receptors involved in neuromuscular transmission. Some conopeptides also block receptors involved in neuropathic pain and one such peptide with an analgesic potency greater than that of morphine is marketed for clinical use. OBJECTIVES: To determine the effects of venom from seven species of Conidae, Conus arenatus, Conus coronatus, Conus ebraeus, Conus lividus, Conus miles, Conus rattus, and Conus textile, collected in the inter-tidal zone of the Indian Ocean, East Africa, on the chick biventer-cervicis nervemuscle preparation and to assess the effects using data on conopeptide content in venom of the species examined reported in the literature and the ConoServer database. RESULTS: Only venom extracts from C. arenatus and C. textile, blocked twitch responses and produced depolarization and contracture of slow fibers of the stimulated chick nerve-muscle preparation. This is the first study showing that venom from C. arenatus is a potent inhibitor of neuromuscular transmission. However, in the case of C. textile, a species associated with fatal human stingings, the inhibitor activity was ~ 3-fold greater. These results are consistent with the occurrence of specific α-conopeptides, namely α-4/6-CtxTxID in C. textile and α-CtxArIB in C. arenatus targeting acetylcholine receptors at the neuromuscular junction. Information extractable from the ConoServer database was of limited value for evaluation of our findings since all the species examined contain numerous conopeptides, the majority of which have not been characterized pharmacologically or for which even the gene superfamily is unknown. Venom from C. textile, C. arenatus, C. coronatus, C. ebraeus, and C. rattus produced an initial facilitation of the twitch response similar to that produced by neostigmine. Venom from C. lividus and C. miles had no effect on twitch responses and did not depolarize slow fibers even at high concentrations. CONCLUSIONS: Using the chick biventer-cervicis nerve-muscle preparation, which contains both twitch and slow muscle fibers, a neuromuscular blocking and muscle depolarizing action could be demonstrated in venom extracts from C. textile, a Conus species associated with fatal human stingings, and C. arenatus. The results are consistent with the known presence of specific α-conopeptides in these species targeting nAChRs. Venom from C. coronatus, C. ebraeus, C. rattus, C. lividus, and C. miles, although purported to contained numerous conopeptides belonging to a variety of pharmacological classes, were either inactive on the preparation or caused only a minor potentiation of the twitch response. Although the ConoServer database provides valuable global data on conopeptide structure, occurrence and properties, it lacks specific information on receptor targets and affinities.

High-throughput identification of novel conotoxins from the Chinese tubular cone snail (Conus betulinus) by multi-transcriptome sequencing.

BACKGROUND: The venom of predatory marine cone snails mainly contains a diverse array of unique bioactive peptides commonly referred to as conopeptides or conotoxins. These peptides have proven to be valuable pharmacological probes and potential drugs because of their high specificity and affinity to important ion channels, receptors and transporters of the nervous system. Most previous studies have focused specifically on the conopeptides from piscivorous and molluscivorous cone snails, but little attention has been devoted to the dominant vermivorous species. RESULTS: The vermivorous Chinese tubular cone snail, Conus betulinus, is the dominant Conus species inhabiting the South China Sea. The transcriptomes of venom ducts and venom bulbs from a variety of specimens of this species were sequenced using both next-generation sequencing and traditional Sanger sequencing technologies, resulting in the identification of a total of 215 distinct conopeptides. Among these, 183 were novel conopeptides, including nine new superfamilies. It appeared that most of the identified conopeptides were synthesized in the venom duct, while a handful of conopeptides were identified only in the venom bulb and at very low levels. CONCLUSIONS: We identified 215 unique putative conopeptide transcripts from the combination of five transcriptomes and one EST sequencing dataset. Variation in conopeptides from different specimens of C. betulinus was observed, which suggested the presence of intraspecific variability in toxin production at the genetic level. These novel conopeptides provide a potentially fertile resource for the development of new pharmaceuticals, and a pathway for the discovery of new conotoxins.

Characterization of the complete mitochondrial genome of Conus tribblei Walls, 1977.

The genus Conus sensu lato consists of 500-700 species. However, the mitochondrial genomes of only few species have been fully sequenced and reported so far. In this study, the complete mitochondrial genome of Conus tribblei, a member of the poorly known subgenus Splinoconus is sequenced with the mean coverage of 604×. The mitochondrial genome is 15 570 bp long and consists of genes encoding for 13 respiratory chain proteins, 22 tRNA and 2 rRNA. The gene organization is highly conserved among the Conus species. The longest intergenic region between tRNA-Phe and cytochrome c oxidase subunit III (cox3), which in C. tribblei is 169 bp long and contains a 112 bp long segment of inverted repeat, represents the putative control region. The control regions of Conus species exhibited variability in the length and position of the inverted repeats. Therefore, this region may have the potential to be used as a genetic marker for species discrimination.

The complete mitochondrial genome of Conus tulipa (Neogastropoda: Conidae).

The complete mitogenome sequence of the cone snail Conus tulipa (Linnaeus, 1758) has been sequenced by next-generation sequencing method. The assembled mitogenome is 16,599 bp in length, including 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The overall base composition of C. tulipa is 28.7% A, 15.2% C, 18.4% G and 37.7% T. It shows 81.1% identity to the cone snail C. consors, 78.5% to C. borgesi and 77.5% to C. textile. Using the 13 protein-coding genes and 2 ribosomal RNA genes of C. tulipa in this study, together with 18 other closely species, we constructed the species phylogenetic tree to verify the accuracy and utility of new determined mitogenome sequence. The complete mitogenome of the C. tulipa provides an essential and important DNA molecular data for further phylogeography and evolutionary analysis for cone snail phylogeny.

Cone shell envenomation: epidemiology, pharmacology and medical care.

The marine environment presents much danger, specifically in regards to the numerous venomous inhabitants within tropical and subtropical waters. The toxins from one such group of venomous marine snails, commonly referred to as 'cone snails', have been well documented in causing human fatalities. Yet information regarding medical treatment for cone snail envenomation is limited and poorly accessible. To correct this, medical and scientific expertise and literary review on Conus provide a basic and comprehensive directive focused on the medical treatment and post-mortem investigative analysis of cone snail envenomation. We emphasize what we expect to be the most lethal feeding group of Conus and provide a brief background to the epidemiology of their stings. We describe the venom apparatus of Conus and its utility of rapid venom delivery. We have compiled the documented incidences of Conus envenomation to offer thorough reference of known signs and symptoms - this too drawing on personal experiences in the field. We have also made available a brief background to the biochemistry and pharmacology of Conus venoms to highlight their complex nature.

Comparison of the Venom Peptides and Their Expression in Closely Related Conus Species: Insights into Adaptive Post-speciation Evolution of Conus Exogenomes.

Genes that encode products with exogenous targets, which comprise an organism's "exogenome," typically exhibit high rates of evolution. The genes encoding the venom peptides (conotoxins or conopeptides) in Conus sensu lato exemplify this class of genes. Their rapid diversification has been established and is believed to be linked to the high speciation rate in this genus. However, the molecular mechanisms that underlie venom peptide diversification and ultimately emergence of new species remain poorly understood. In this study, the sequences and expression levels of conotoxins from several specimens of two closely related worm-hunting species, Conus tribblei and Conus lenavati, were compared through transcriptome analysis. Majority of the identified putative conopeptides were novel, and their diversity, even in each specimen, was remarkably high suggesting a wide range of prey targets for these species. Comparison of the interspecific expression patterns of conopeptides at the superfamily level resulted in the discovery of both conserved as well as species-specific expression patterns, indicating divergence in the regulatory network affecting conotoxin gene expression. Comparison of the transcriptomes of the individual snails revealed that each specimen produces a distinct set of highly expressed conopeptides, reflecting the capability of individual snails to fine-tune the composition of their venoms. These observations reflect the role of sequence divergence and divergence in the control of expression for specific conopeptides in the evolution of the exogenome and hence venom composition in Conus.

Glowing seashells: diversity of fossilized coloration patterns on coral reef-associated cone snail (Gastropoda: Conidae) shells from the Neogene of the Dominican Republic.

The biology of modern Conidae (cone snails)--which includes the hyperdiverse genus Conus--has been intensively studied, but the fossil record of the clade remains poorly understood, particularly within an evolutionary framework. Here, ultraviolet light is used to reveal and characterize the original shell coloration patterns of 28 species of cone snails from three Neogene coral reef-associated deposits from the Cibao Valley, northern Dominican Republic. These fossils come from the upper Miocene Cercado Fm. and lower Pliocene Gurabo Fm., and range in age from about 6.6-4.8 Ma. Comparison of the revealed coloration patterns with those of extant species allow the taxa to be assigned to three genera of cone snails (Profundiconus, Conasprella, and Conus) and at least nine subgenera. Thirteen members of these phylogenetically diverse reef faunas are described as new species. These include: Profundiconus? hennigi, Conasprella (Ximeniconus) ageri, Conus anningae, Conus lyelli, Conus (Atlanticonus?) franklinae, Conus (Stephanoconus) gouldi, Conus (Stephanoconus) bellacoensis, Conus (Ductoconus) cashi, Conus (Dauciconus) garrisoni, Conus (Dauciconus?) zambaensis, Conus (Spuriconus?) kaesleri, Conus (Spuriconus?) lombardii, and Conus (Lautoconus?) carlottae. Each of the three reef deposits contain a minimum of 14-16 cone snail species, levels of diversity that are similar to modern Indo-Pacific reef systems. Finally, most of the 28 species can be assigned to modern clades and thus have important implications for understanding the biogeographic and temporal histories of these clades in tropical America.

High conopeptide diversity in Conus tribblei revealed through analysis of venom duct transcriptome using two high-throughput sequencing platforms.

The venom of each species of Conus contains different kinds of pharmacologically active peptides which are mostly unique to that species. Collectively, the ~500-700 species of Conus produce a large number of these peptides, perhaps exceeding 140,000 different types in total. To date, however, only a small fraction of this diversity has been characterized via transcriptome sequencing. In addition, the sampling of this chemical diversity has not been uniform across the different lineages in the genus. In this study, we used high-throughput transcriptome sequencing approach to further investigate the diversity of Conus venom peptides. We chose a species, Conus tribblei, as a representative of a poorly studied clade of Conus. Using the Roche 454 and Illumina platforms, we discovered 136 unique and novel putative conopeptides belonging to 30 known gene superfamilies and 6 new conopeptide groups, the greatest diversity so far observed from a transcriptome. Most of the identified peptides exhibited divergence from the known conopeptides, and some contained cysteine frameworks observed for the first time in cone snails. In addition, several enzymes involved in posttranslational modification of conopeptides and also some proteins involved in efficient delivery of the conopeptides to prey were identified as well. Interestingly, a number of conopeptides highly similar to the conopeptides identified in a phylogenetically distant species, the generalist feeder Conus californicus, were observed. The high diversity of conopeptides and the presence of conopeptides similar to those in C. californicus suggest that C. tribblei may have a broad range of prey preferences.

Intraspecific variations in Conus geographus defence-evoked venom and estimation of the human lethal dose.

Conus geographus is the most dangerous cone snail species known, with reported human fatality rates as high as 65%. Crude venom gland extracts have been used to determine animal LD50 and to aid the isolation of several potent paralytic toxins. However, not only is the composition of injected venoms known to differ significantly from that in dissected venom glands, but also to vary according to predatory or defensive stimuli. Therefore, to study the venom that is directly relevant to human envenomation, the defense-evoked venom of several specimens of C. geographus was collected and analyzed by standard LC-MS methods. The molecular composition of individual defense-evoked venom showed significant intraspecific variations, but a core of paralytic conotoxins including α-GI, α-GII, µ-GIIIA, ω-GVIA and ω-GVIIA was always present in large amounts, consistent with the symptomology and high fatality rate in humans. Differences between injected and dissected venoms obtained from the same specimen were also evident. Interestingly, an apparent linear correlation between the dry weight/volume of injected venom and the size of the shell allowed extrapolation to a human lethal dose (0.038-0.029 mg/kg) from an historic fatal case of C. geographus envenomation, which may help in the management of future victims.

When everything converges: integrative taxonomy with shell, DNA and venomic data reveals Conus conco, a new species of cone snails (Gastropoda: Conoidea).

Cone snails have long been studied both by taxonomists for the diversity of their shells and by biochemists for the potential therapeutic applications of their toxins. Phylogenetic approaches have revealed that different lineages of Conus evolved divergent venoms, a property that is exploited to enhance the discovery of new conotoxins, but is rarely used in taxonomy. Specimens belonging to the Indo-West Pacific Conus lividus species complex were analyzed using phenetic and phylogenetic methods based on shell morphology, COI and 28S rRNA gene sequences and venom mRNA expression and protein composition. All methods converged to reveal a new species, C. conco n. sp. (described in Supplementary data), restricted to the Marquesas Islands, where it diverged recently (∼3mya) from C. lividus. The geographical distribution of C. conco and C. lividus and their phylogenetic relationships suggest that the two species diverged in allopatry. Furthermore, the diversity of the transcript sequences and toxin molecular masses suggest that C. conco evolved unique toxins, presumably in response to new selective pressure, such as the availability of new preys and ecological niches. Furthermore, this new species evolved new transcripts giving rise to original toxin structures, probably each carrying specific biological activity.

Evolution at a different pace: distinctive phylogenetic patterns of cone snails from two ancient oceanic archipelagos.

Ancient oceanic archipelagos of similar geological age are expected to accrue comparable numbers of endemic lineages with identical life history strategies, especially if the islands exhibit analogous habitats. We tested this hypothesis using marine snails of the genus Conus from the Atlantic archipelagos of Cape Verde and Canary Islands. Together with Azores and Madeira, these archipelagos comprise the Macaronesia biogeographic region and differ remarkably in the diversity of this group. More than 50 endemic Conus species have been described from Cape Verde, whereas prior to this study, only two nonendemic species, including a putative species complex, were thought to occur in the Canary Islands. We combined molecular phylogenetic data and geometric morphometrics with bathymetric and paleoclimatic reconstructions to understand the contrasting diversification patterns found in these regions. Our results suggest that species diversity is even lower than previously thought in the Canary Islands, with the putative species complex corresponding to a single species, Conus guanche. One explanation for the enormous disparity in Conus diversity is that the amount of available habitat may differ, or may have differed in the past due to eustatic (global) sea level changes. Historical bathymetric data, however, indicated that sea level fluctuations since the Miocene have had a similar impact on the available habitat area in both Cape Verde and Canary archipelagos and therefore do not explain this disparity. We suggest that recurrent gene flow between the Canary Islands and West Africa, habitat losses due to intense volcanic activity in combination with unsuccessful colonization of new Conus species from more diverse regions, were all determinant in shaping diversity patterns within the Canarian archipelago. Worldwide Conus species diversity follows the well-established pattern of latitudinal increase of species richness from the poles towards the tropics. However, the eastern Atlantic revealed a striking pattern with two main peaks of Conus species richness in the subtropical area and decreasing diversities toward the tropical western African coast. A Random Forests model using 12 oceanographic variables suggested that sea surface temperature is the main determinant of Conus diversity either at continental scales (eastern Atlantic coast) or in a broader context (worldwide). Other factors such as availability of suitable habitat and reduced salinity due to the influx of large rivers in the tropical area also play an important role in shaping Conus diversity patterns in the western coast of Africa.

Application of community phylogenetic approaches to understand gene expression: differential exploration of venom gene space in predatory marine gastropods.

BACKGROUND: Predatory marine gastropods of the genus Conus exhibit substantial variation in venom composition both within and among species. Apart from mechanisms associated with extensive turnover of gene families and rapid evolution of genes that encode venom components ('conotoxins'), the evolution of distinct conotoxin expression patterns is an additional source of variation that may drive interspecific differences in the utilization of species' 'venom gene space'. To determine the evolution of expression patterns of venom genes of Conus species, we evaluated the expression of A-superfamily conotoxin genes of a set of closely related Conus species by comparing recovered transcripts of A-superfamily genes that were previously identified from the genomes of these species. We modified community phylogenetics approaches to incorporate phylogenetic history and disparity of genes and their expression profiles to determine patterns of venom gene space utilization. RESULTS: Less than half of the A-superfamily gene repertoire of these species is expressed, and only a few orthologous genes are coexpressed among species. Species exhibit substantially distinct expression strategies, with some expressing sets of closely related loci ('under-dispersed' expression of available genes) while others express sets of more disparate genes ('over-dispersed' expression). In addition, expressed genes show higher dN/dS values than either unexpressed or ancestral genes; this implies that expression exposes genes to selection and facilitates rapid evolution of these genes. Few recent lineage-specific gene duplicates are expressed simultaneously, suggesting that expression divergence among redundant gene copies may be established shortly after gene duplication. CONCLUSIONS: Our study demonstrates that venom gene space is explored differentially by Conus species, a process that effectively permits the independent and rapid evolution of venoms in these species.