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Heterobranchs are a fascinating group of marine mollusks that are recognized as an important source of bioactive natural products. Often, these molecules, which are either selected from the diet or de novo biosynthesized by the mollusks, play a fundamental role for their survival being utilized as defensive chemicals against predators. A summary of...
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... most interesting nitrogen-containing compounds that have been characterized in recent years in our lab are undoubtedly phidianidines A (1) and B (2) (Figure 1), two bromoindole alkaloids isolated from a South China Sea collection of the aeolid nudibranch Phidiana militaris [17]. Phidianidines contain the first reported 1,2,4-oxadiazole system in a marine natural product. ...
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... and significant pharmacological properties have been evidenced for this class of compounds [31][32][33]. An additional member of tambjamine family, tambjamine K (3), was isolated from the Azorean nudibranch Tambja ceutae [34] along with previously reported related metabolites, tetrapyrrole (4) [35] and tambjamines A (5) and B (6) [36] (Figure 1). The same metabolites were also detected in the bryozoan Bugula dentata, prey of the mollusks, strongly indicating the dietary origin of these alkaloids in the mollusks. ...
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... are peculiar chlorinated phenyl-pyrrolyloxazoles first described from the sponge Phorbas aff clathrata [39][40][41] and later isolated by us from the Indo-Pacific dorid nudibranch Aldisa andersoni [42]. So, it is quite probable that in the mollusks they could derive from a diet based on Phorbas sponges. A. andersoni was found to contain two new phorbazoles, 9-chloro-phorbazole D (7) and N1-methyl-phorbazole A (8), together with previously described phorbazoles A (9), B (10), and D (11) [39,40] (Figure 1). However, phorbazoles were found to be present mainly and selectively in the external part of the mollusk, more exposed to predation, suggesting their involvement in chemical defense. ...
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... thuridillins are a small group of unique diterpenoids occurring in sacoglossans of the genus Thuridilla. First members to be isolated were thuridillin A (100), thuridillin B (101), and thuridillin C (102) (Figure 10) from two Mediterranean Thuridilla hopei collections from Ionian [101] and Tyrrhenian Sea [102]. Thuridillins were assumed to be derived from a dietary algal precursor [103] the structure of which was closely related to 100−102. ...
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... terminal structural motif could easily generate reactive aldehyde functional groups that are responsible for different biological activities due to the ability to link the free amino groups of putative receptors. Additional members of thuridillin class, thuridillin D (103), thuridillin E (104), and thuridillin F (105) (Figure 10), were isolated along with compound 100 from an Australian collection of Thuridilla splendens [104]. The partial relative configuration of thuridillin D (103) was also determined by a detailed NMR study including a series of experiments to accurately measure JH-H and JH-C coupling constants and NOESY data as well as by conformational analyses [104]. ...
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... partial relative configuration of thuridillin D (103) was also determined by a detailed NMR study including a series of experiments to accurately measure JH-H and JH-C coupling constants and NOESY data as well as by conformational analyses [104]. A subsequent reinvestigation of Mediterranean T. hopei resulted in the isolation of three thuridillin-derived aldehyde metabolites, nor-thuridillonal (106), dihydro-nor-thuridillonal (107) and deacetyldihydro-nor-thuridillonal (108) (Figure 10), co-occurring with previously described thuridillins 100−102 [105]. The main aldehyde 106 was assayed for the feeding-deterrence in the food palatability test with the shrimp Palaemon elegans and resulted to be active at a concentration of 5.0 mg/mL [105]. ...
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... it seemed possible that this animal lacks chemical defense, acting like a Batesian mimic that gains protection from predation through its visual similarity to species that possesses defensive chemical weapons. Instead, the chemical investigation of F. fontandraui collected along Portuguese coasts led to the isolation of the feeding deterrent furanosesquiterpenoid tavacpallescensin (109) (Figure 11), which is most likely derived from sponges of the genus Dysidea upon which the nudibranch feeds [111]. Even in the absence of MDFs, compound 109 ( Figure 11) turned out to be accumulated at very high concentrations in the mantle rim of F. fontandraui, considerably exceeding the threshold value of concentration showing a significant feeding deterrent against the generalist shrimp P. elegans. ...
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... the chemical investigation of F. fontandraui collected along Portuguese coasts led to the isolation of the feeding deterrent furanosesquiterpenoid tavacpallescensin (109) (Figure 11), which is most likely derived from sponges of the genus Dysidea upon which the nudibranch feeds [111]. Even in the absence of MDFs, compound 109 ( Figure 11) turned out to be accumulated at very high concentrations in the mantle rim of F. fontandraui, considerably exceeding the threshold value of concentration showing a significant feeding deterrent against the generalist shrimp P. elegans. This finding demonstrated that H. fontandraui is chemically defended, much as other aposematic blue-colored species within a Müllerian mimetic circle, and does not represent a Batesian mimic. ...
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... Gavagnin et al. / Chem. J. Mold., 2019, 14(2) Supporting that Müllerian mimicry does not involve visual mimicry only, but may also employ aposematic chemosensory signals, the toxic and feeding deterrent 16-membered macrolide latrunculin A (110) (Figure 11) was found in the mantle rim of five different nudibranch species from Australian coasts [112]. In this view, compound 110 can be detected also by potential predators devoid of well-developed visual systems. ...
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... particular, Dorisprismatica (= Glossodoris) atromarginata was found to contain the furanospongianes spongiatrioltriacetate (111) and spongiatrioldiacetate (112) especially accumulated in the MDFs, while spongiatriol (113) was distributed in the mantle and viscera of the nudibranch. Instead, the border of the mantle (which includes the MDFs) of Goniobranchus (= Chromodoris) sinensis, which includes the MDFs, contained a 1:3 mixture of compounds aplyroseol-2 (114), and its corresponding dialdehyde (115) (Figure 11). From the MDFs of an unidentified Hypselodoris species of the genus Hypselodoris was isolated compound 116, (+)-tetradehydrofurospongin-1 (Figure 11). ...
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... the border of the mantle (which includes the MDFs) of Goniobranchus (= Chromodoris) sinensis, which includes the MDFs, contained a 1:3 mixture of compounds aplyroseol-2 (114), and its corresponding dialdehyde (115) (Figure 11). From the MDFs of an unidentified Hypselodoris species of the genus Hypselodoris was isolated compound 116, (+)-tetradehydrofurospongin-1 (Figure 11). In the MDFs of Hypselodoris infucata and Hypselodoris (= Risbecia) tryoni (Garrett, 1873) was only found compound 117, (-)-furodysinin. ...
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... the MDFs of Hypselodoris infucata and Hypselodoris (= Risbecia) tryoni (Garrett, 1873) was only found compound 117, (-)-furodysinin. Along with 117, nakafuran-9 (118) (Figure 11) was also found in the MDFs of Ceratosoma gracillimum. Overall, only distasteful compounds were found to be accumulated in the MDFs at extremely high concentrations. ...
Citations
... They mainly prey on a high variety of marine sessile organisms, from algae to sponges, cnidarians, bryozoans and tunicates, and very often take up the chemical compounds of the food for their own defence. These "stolen" compounds have become of high interest for pharmacists in finding new drug leads for medical applications [6][7][8][9][10]. However, they are also of high interest because of various unique biological phenomena. ...
Background
The soft-bodied cladobranch sea slugs represent roughly half of the biodiversity of marine nudibranch molluscs on the planet. Despite their global distribution from shallow waters to the deep sea, from tropical into polar seas, and their important role in marine ecosystems and for humans (as targets for drug discovery), the evolutionary history of cladobranch sea slugs is not yet fully understood.
Results
To enlarge the current knowledge on the phylogenetic relationships, we generated new transcriptome data for 19 species of cladobranch sea slugs and two additional outgroup taxa ( Berthella plumula and Polycera quadrilineata ). We complemented our taxon sampling with previously published transcriptome data, resulting in a final data set covering 56 species from all but one accepted cladobranch superfamilies. We assembled all transcriptomes using six different assemblers, selecting those assemblies that provided the largest amount of potentially phylogenetically informative sites. Quality-driven compilation of data sets resulted in four different supermatrices: two with full coverage of genes per species (446 and 335 single-copy protein-coding genes, respectively) and two with a less stringent coverage (667 genes with 98.9% partition coverage and 1767 genes with 86% partition coverage, respectively). We used these supermatrices to infer statistically robust maximum-likelihood trees. All analyses, irrespective of the data set, indicate maximal statistical support for all major splits and phylogenetic relationships at the family level. Besides the questionable position of Noumeaella rubrofasciata , rendering the Facelinidae as polyphyletic, the only notable discordance between the inferred trees is the position of Embletonia pulchra . Extensive testing using Four-cluster Likelihood Mapping, Approximately Unbiased tests, and Quartet Scores revealed that its position is not due to any informative phylogenetic signal, but caused by confounding signal.
Conclusions
Our data matrices and the inferred trees can serve as a solid foundation for future work on the taxonomy and evolutionary history of Cladobranchia. The placement of E. pulchra , however, proves challenging, even with large data sets and various optimization strategies. Moreover, quartet mapping results show that confounding signal present in the data is sufficient to explain the inferred position of E. pulchra , again leaving its phylogenetic position as an enigma.
... Polypropionates from sacoglossans have been reported to be used as sunscreens in several species [412,461]. These compounds are de novo biosynthesized by the slugs, and their biosynthesis is affected by UVR [462,463]. Elysia species possess γ-pyrone propionates, such as phototridachiapyrone J (172) in the Atlantic E. patagonica [412], and tridachiahydropyrone (173) and phototridachiahydropyrone (174) in the Caribbean Elysia crispata [78,317]. Phototridachiahydropyrone (174) seems to originate from a rearrangement mechanism during the photochemical electrocyclic formation of tridachiahydropyrone (173) under prolonged UVR exposition [464]. ...
The natural products of heterobranch molluscs display a huge variability both in structure
and in their bioactivity. Despite the considerable lack of information, it can be observed from the recent literature that this group of animals possesses an astonishing arsenal of molecules from different origins that provide the molluscs with potent chemicals that are ecologically and pharmacologically relevant. In this review, we analyze the bioactivity of more than 450 compounds from ca. 400 species of heterobranch molluscs that are useful for the snails to protect themselves in different ways and/or that may be useful to us because of their pharmacological activities. Their ecological activities include predator avoidance, toxicity, antimicrobials, antifouling, trail-following and alarm pheromones, sunscreens and UV protection, tissue regeneration, and others. The most studied ecological activity is predation avoidance, followed by toxicity. Their pharmacological activities consist of cytotoxicity and antitumoral activity; antibiotic, antiparasitic, antiviral, and anti-inflammatory activity; and activity against neurodegenerative diseases and others. The most studied pharmacological activities are cytotoxicity and anticancer activities, followed by antibiotic activity. Overall, it can be observed that heterobranch molluscs are extremely interesting in regard to the study of marine natural products in terms of both chemical ecology and biotechnology studies, providing many leads for further detailed research in these fields in the near future.
... In this context, the family Onchidiidae, living in the intertidal flats of tropical and temperate coasts encountering high fluctuation of abiotic parameters, are of special interest. So far only polypropionate esters, cholesterol, stearic acid, ethylhexylglycerins such as chimyl alcohol, and batyl alcohol have been reported from these pulmonate slugs [17][18][19] . ...
... Compounds that were found in both species also included a diverse mixture of polypropionate esters as the most common and prominent chemical features. Polypropionates are reported from various Onchidiidae, including Onchidium reevesii 17 , partly described under the former name Onchidium struma (nomen nudum) 40 , various unidentified Onchidium species 18,19,41 , and also P. verruculata 42 . Polypropionates with different carbon skeleton were also described from genus Siphonaria (Gastropoda: Tectipleura) such as Siphonaria baconi Reeve, 1856 (now accepted as Siphonaria zelandica Quoy and Gaimard, 1833) 43 , and Siphonaria diemenensis Quoy and Gaimard, 1833 44 . ...
... However, the diversity and contribution of these metabolites with respect to each species was not reported before. Onchitriol and Ilikonapyrone compounds are polypropionates whose skeletons contain 32 carbon atoms, two γ-pyrone rings, and several hydroxy groups 19 . They were previously isolated from P. verruculata (as Onchidium verruculatum) 42 , and also from other members assigned to the genus Onchidium (as Onchidium sp., Onchidium sp.1, and Onchidium sp.2) 18,41 . ...
The knowledge of relationships between taxa is essential to understand and explain the chemical diversity of the respective groups. Here, twelve individuals of the panpulmonate slug Peronia persiae from two localities in Persian Gulf, and one animal of P. verruculata from Bangka Island, Indonesia, were analyzed in a phylogenetic and chemotaxonomic framework. Based on the ABGD test and haplotype networking using COI gene sequences of Peronia specimens, nine well-supported clades were found. Haplotype network analysis highlighted a considerable distance between the specimens of P. persiae and other clades. Metabolomic analysis of both species using tandem mass spectrometry-based GNPS molecular networking revealed a large chemical diversity within Peronia of different clades and localities. While P. persiae from different localities showed a highly similar metabolome, only few identical chemical features were found across the clades. The main common metabolites in both Peronia species were assigned as polypropionate esters of onchitriols and ilikonapyrones, and osmoprotectant amino acid-betaine compounds. On the other hand, the isoflavonoids genistein and daidzein were exclusively detected in P. persiae, while cholesterol and conjugated chenodeoxycholic acids were only found in P. verruculata. Flavonoids, bile acids, and amino acid-betaine compounds were not reported before from Onchidiidae, some are even new for panpulmonates. Our chemical analyses indicate a close chemotaxonomic relation between phylogeographically distant Peronia species.
The genus Elysia comprises about one-third of the species richness in Sacoglossa. However, the species diversity in the genus remains poorly characterized in some areas like the north-eastern Atlantic and Mediterranean waters. To clarify the systematics of this genus and to characterize the species diversity in undersampled regions, we performed an integrative study based on a thorough literature review, molecular and morphological analyses, and species delimitation approaches. We conducted phylogenetic analyses of partial sequences of two mitochondrial genes (COI and 16S) and two nuclear genes (H3, 28S) using Bayesian inference and maximum likelihood methods, which confirmed the presence of five of the recognized European Elysia species: Elysia viridis, E. timida, E. flava, E. margaritae, and E. rubeni. Moreover, a new species (Elysia azorica sp. nov.) was identified in the Azores, and E. gordanae, currently considered a junior synonym of E. margaritae, was recovered as a distinct species. In addition, we consider E. hetta as a junior synonym of E. gordanae, and E. translucens as a taxon inquirendum. Finally, the tropical E. evelinae is recorded along European coasts for the first time. Our results demonstrate the value of integrative approaches in resolving taxonomic uncertainty surrounding polymorphism and unravelling potential cases of cryptic or pseudocryptic species complexes.
Background
Cladobranch sea slugs represent roughly half of the biodiversity of soft-bodied, marine gastropod molluscs (Nudibranchia) on the planet. Despite their global distribution from shallow waters to the deep sea, from tropical into polar seas, and their important role in marine ecosystems and for humans (as bioindicators and providers of medical drug leads), the evolutionary history of cladobranch sea slugs is not yet fully understood. Here, we amplify the current knowledge on the phylogenetic relationships by extending the cladobranch and outgroup taxon sampling using transcriptome data.
Results
We generated new transcriptome data for 19 species of cladobranch sea slugs and two additional outgroup taxa. We complemented our taxon sampling with previously published transcriptome data, resulting in a final supermatrix covering 56 species from all but one accepted cladobranch superfamilies. Transcriptome assembly using six different assemblers, selection of those assemblies providing the largest amount of potentially phylogenetically informative sites, and quality-driven compilation of data sets resulted in three different supermatrices: one with a full coverage of genes per species (446 single-copy protein-coding genes) and two with a less stringent coverage (667 genes with 98.9% partition coverage and 1,767 genes with 86% partition coverage, respectively). We used these supermatrices to infer statistically robust maximum-likelihood trees. All analyses, irrespective of the data set, indicate maximum statistical support for all major splits and phylogenetic relationships on family level. The only discordance between the inferred trees is the position of Embletonia pulchra . Extensive testing using Four-cluster Likelihood Mapping, Approximately Unbiased tests, and Quartet Scores revealed that its position is not due to any informative phylogenetic signal, but caused by confounding signal.
Conclusions
Our data matrices and the inferred trees inferred can serve as a solid foundation for future work on the taxonomy and evolutionary history of Cladobranchia. The correct placement of E. pulchra , however, proves challenging, even with large data sets. Moreover, quartet mapping shows that confounding signal present in the data is sufficient to explain the inferred position of E. pulchra , again leaving its phylogenetic position as an enigma.
