Gonçalo Calado

Modelling growth of Ruppia cirrhosa

The main objectives of this work were to synthesise information on the autoecology of Ruppia cirrhosa Petagna (Grande) in a mathematical model and to use the model to simulate its growth, production and harvest. Model parameters were allowed to vary as a result of acclimation, following experimental data reported in the literature. Biomass data from Santo Andre lagoon (SW Portugal) were used to calibrate the model. Validation was carried out with independent data sets from Santo Andre lagoon and from Tancada lagoon (NE Spain). Model simulations show a reasonable agreement with observed data with a similar biomass temporal dynamics and peaks. Self-shading appears to be an important self-regulating mechanism of biomass growth and production. The results obtained predict an annual net primary production of 361 g DW m 2 well within the estimates based on harvesting techniques (295‐589 g DW m 2 ). Model results suggest that controlled harvesting of macrophyte biomass may be carried out without affecting macrophyte real net production, through the reduction of light limitation under the plant canopy.

Coloration and Defense in the Nudibranch Gastropod Hypselodoris fontandraui

The striking color patterns of chromodorid (and other) nudibranchs appear to be indicative of aposematism. In Müllerian mimicry, all the mimic species have a defense mechanism. It has been proposed that a group of blue, white, and yellow Mediterranean and northeastern Atlantic species of the genus Hypselodoris form a Müllerian mimetic circle. One of these, H. fontandraui, lacks the mantle dermal formations (repugnatorial glands) that are typically found in other members of this circle and are reservoirs of feeding deterrent compounds. It therefore seemed possible that this animal lacks chemical defense and acts like a Batesian mimic. Within this study, we found that this nudibranch contains the furanosesquiterpenoid tavacpallescensin, most probably derived from sponges of the genus Dysidea, upon which it probably feeds. The metabolite concentrations were measured from samples of the mantle rim, other external parts, and internal organs. Concentrations were about 4 times higher in the mantle rim than in the other external parts, and more than 20 times higher in the mantle rim than in the internal organs, considerably exceeding the threshold value of concentration showing the maximum dose effect as feeding deterrent against the crustacean Palaemon elegans. In conclusion, the reported data clearly demonstrate that H. fontandraui is chemically defended in much the same way as its aposematic, co-occurring, and blue-colored congeners within the Müllerian mimetic circle and is not a Batesian mimic.

A new cytotoxic tambjamine alkaloid from the Azorean nudibranch Tambja ceutae

The chemical investigation of Azorean nudibranch mollusk Tambja ceutae led us to isolate a new member of the tambjamine family, tambjamine K (1). The bryozoan Bugula dentata, prey of the nudibranch, was also analyzed and found to contain compound 1 in very small amounts together with known blue pigment 2 and tambjamines A (3) and B (4). The structure of tambjamine 1 was elucidated by the interpretation of the spectroscopic data as well as by the comparison with related compounds. Compounds 1 and 2 possess antiproliferative activity, in particular, tambjamine K (1) displayed high cytotoxicity against both tumor and non-tumor mammalian cells.

Can molluscs biosynthesize typical sponge metabolites? The case of the nudibranch Doriopsilla areolata

Abstract The first study on the biosynthesis of terpenoid metabolites in the porostome nudibranch Doriopsilla areolata is described herein. The de novo origin of two different groups of bi- and tri-cyclic sesquiterpenes, exhibiting opposite A/B ring junctions, has been clearly demonstrated by in vivo incorporation of labeled mevalonate. Surprisingly, metabolites of both series have been previously reported to co-occur in a sponge of genus Dysidea , that could be included in the diet of the nudibranch.

Chemical studies of porostome nudibranchs: comparative and ecological aspects

Summary. Three porostome nudibranchs, Dendrodoris krebsii from Mexico, Doriopsilla albopunctata from California and Doriopsilla areolata from Portugal, have been chemically investigated. The presence of sesquiterpenes of the drimane class in these molluscs has been confirmed. In addition, these species have shown to contain sesquiterpenes of ent-pallescensin-A (or pallescensin-A) series, co-occurring with drimane metabolites. Most of these sesquiterpenes are typical sponge metabolites, suggesting a dietary origin in the molluscs, even though de novo biosynthesis, rigorously demonstrated for some Dendrodoris molluscs, may occur.

Molluscan diversity in the North Atlantic Ocean: new records of opisthobranch gastropods from the Archipelago of the Azores

New findings of opisthobranch gastropods are reported to the Azores resulting from fieldwork undertaken in the islands of Faial and Sao Jorge (Central Group, Azores) during August 2007. Intertidal and subtidal areas down to 35 metres deep were sampled. Forty-four species were collected and eight are new records to the Azores, namely Chelidonura africana, Odontoglaja sabadiega, Aplysia juliana, Elysia flava, Thuridilla picta, Doris sticta, Catriona maua and Taringa armata . This increases the diversity of opisthobranchs in the archipelago to 141 species. Our results provide further support for the closer affinity of the Azorean marine diversity with the eastern Atlantic/Mediterranean Sea biota (75% of species) but they also show a biogeographic bound with the Caribbean province (25% of common species).

Light and electron microscopy study of the salivary glands of the carnivorous opisthobranch Philinopsis depicta (Mollusca, Gastropoda)

Cephalaspideans are a group of opisthobranch gastropods that comprises carnivorous and herbivorous species, allowing an investigation of the relationship between these diets and the morphofunctional features of the salivary glands. In this study, the salivary glands of the carnivorous cephalaspidean Philinopsis depicta were observed by light and electron microscopy. The secretory epithelium of these ribbon-shaped glands is formed by ciliated cells, granular cells and cells with apical vacuole. In ciliated cells the nucleus and most cytoplasmic organelles are located in the wider apical region and a very thin stalk reaches the base of the epithelium. These cells possess significant amounts of glycogen. Granular cells are packed with electron-dense secretory granules and also contain several cisternae of rough endoplasmic reticulum and Golgi stacks. The other type of secretory cell is mainly characterized by the presence of a large apical vacuole containing secretion. These cells possess high amounts of rough endoplasmic reticulum cisternae and several Golgi stacks. Vesicles with peripheral electron-dense material are also abundant, and seem to fuse to form the apical vacuole. The available data point out to a significant difference between the salivary glands of carnivorous and herbivorous cephalaspidean opisthobranchs, with an intensification of protein secretion in carnivorous species.

Turning the game around: toxicity in a nudibranch-sponge predator–prey association

Escalation theory proposes enemy-related selection as the most relevant factor of natural selection among individual organisms. When hazardous to predators, prey might be considered enemies that influence predator evolution. Opisthobranch molluscs that prey on chemically defended prey are an interesting study case on this subject. Predation on chemically defended species paved the way for opisthobranchs to enter in an arms race, developing means to detoxify and/or excrete harmful compounds, which led to the sequestration of those compounds and their self-defensive use, an escalation of defenses. Here we aim to understand whether the opisthobranch predator is better protected than its chemically defended prey, using as predator–prey model, a nudibranch (Hypselodoriscantabrica) and the sponge it preys upon (Dysidea fragilis), and from which it obtains deterrent chemical compounds. Specimens of both species were collected on the Portuguese coast, and their crude extracts were analyzed and used in palatability tests. Nudibranchs revealed a higher natural concentration of crude extract, probably due to a progressive accumulation of the compounds. Both predator and prey extracts revealed similar mixtures of deterrent metabolites (furanosesquiterpenes). Palatability tests revealed a more effective deterrence in the nudibranch extracts because significant rejection rates were observed at lower concentrations than those necessary for the sponge extracts to have the same effect. We concluded that the predator is chemically better protected than its prey, which suggests that its acquisition of chemical defenses reveals a defensive escalation.

With a little help from DNA barcoding: investigating the diversity of Gastropoda from the Portuguese coast

The Gastropoda is one of the best studied classes of marine invertebrates. Yet, most species have been delimited based on morphology only. The application of DNA barcodes has shown to be greatly useful to help delimiting species. Therefore, sequences of the cytochrome c oxidase I gene from 108 specimens of 34 morpho-species were used to investigate the molecular diversity within the gastropods from the Portuguese coast. To the above dataset, we added available COI-5P sequences of taxonomically close species, in a total of 58 morpho-species examined. There was a good match between ours and sequences from independent studies, in public repositories. We found 32 concordant (91.4%) out of the 35 Barcode Index Numbers (BINs) generated from our sequences. The application of a ranking system to the barcodes yield over 70% with top taxonomic congruence, while 14.2% of the species barcodes had insufficient data. In the majority of the cases, there was a good concordance between morphological identification and DNA barcodes. Nonetheless, the discordance between morphological and molecular data is a reminder that even the comparatively well-known European marine gastropods can benefit from being probed using the DNA barcode approach. Discordant cases should be reviewed with more integrative studies.

On the occurrence of the Caribbean sea slug Thuridilla mazda in the eastern Atlantic Ocean

The Caribbean gastropod species Thuridilla mazda was collected for the first time in eastern Atlantic shores, namely on the island of Sao Miguel, archipelago of the Azores. This new record raises the total number of opisthobranch species known in the Azores to 144 and shows the potential importance of the Gulf Stream for dispersal of Caribbean species across the North Atlantic and its putative impact on the marine colonization of the Azores.