Contaminants disrupt aquatic food webs via decreased consumer efficiency

Changes in consumer-resource dynamics due to environmental stressors can alter energy flows or key interactions within food webs, with potential for cascading effects at population, community, and ecosystem levels. We conducted a meta-analysis to quantify the direction and magnitude of changes in consumption rates following exposure of consumer-resource pairs within freshwater-brackish and marine systems to anthropogenic CO₂, heavy metals, microplastics, oil, pesticides, or pharmaceuticals. Across all contaminants, exposure generally decreased consumption rates, likely due to reduced consumer mobility or search efficiency. These negative effects on consumers appeared to outweigh co-occurring reductions in prey vigilance or antipredator behaviors following contaminant exposure. Consumption was particularly dampened in freshwater-brackish systems, for consumers with sedentary prey, and for lower-trophic-level consumers. This synthesis indicates that energy flow up the food web, toward larger - often ecologically and economically prized - taxa may be dampened as aquatic contaminant loads increase.

Would Antarctic Marine Benthos Survive Alien Species Invasions? What Chemical Ecology May Tell Us

Many Antarctic marine benthic macroinvertebrates are chemically protected against predation by marine natural products of different types. Antarctic potential predators mostly include sea stars (macropredators) and amphipod crustaceans (micropredators) living in the same areas (sympatric). Recently, alien species (allopatric) have been reported to reach the Antarctic coasts, while deep-water crabs are suggested to be more often present in shallower waters. We decided to investigate the effect of the chemical defenses of 29 representative Antarctic marine benthic macroinvertebrates from seven different phyla against predation by using non-native allopatric generalist predators as a proxy for potential alien species. The Antarctic species tested included 14 Porifera, two Cnidaria, two Annelida, one Nemertea, two Bryozooa, three Echinodermata, and five Chordata (Tunicata). Most of these Antarctic marine benthic macroinvertebrates were chemically protected against an allopatric generalist amphipod but not against an allopatric generalist crab from temperate waters. Therefore, both a possible recolonization of large crabs from deep waters or an invasion of non-native generalist crab species could potentially alter the fundamental nature of these communities forever since chemical defenses would not be effective against them. This, together with the increasing temperatures that elevate the probability of alien species surviving, is a huge threat to Antarctic marine benthos.

Experimental evidence of antimicrobial activity in Antarctic seaweeds: ecological role and antibiotic potential

Seaweeds contain a wide range of secondary metabolites which serve multiple functions, including chemical and ecological mediation with microorganisms. Moreover, owing to their diverse bioactivity, including their antibiotic properties, they show potential for human use. Nonetheless, the chemical ecology of seaweeds is not equally understood across different regions; for example, Antarctic seaweeds are among the lesser studied groups. With the aim of improving our current understanding of the chemical ecology and potential bioactivity of Antarctic seaweeds, we performed a screening of antibiotic activity using crude extracts from 22 Antarctic macroalgae species. Extractions were performed separating lipophilic and hydrophilic fractions at natural concentrations. Antimicrobial activity assays were performed using the disk diffusion method against seven Antarctic bacteria and seven human pathogenic surrogates. Our results showed that red seaweeds (especially Delisea pulchra) inhibited a larger number of microorganisms compared with brown seaweeds, and that lipophilic fractions were more active than hydrophilic ones. Both types of bacteria tested (Gram negative and Gram positive) were inhibited, especially by butanolic fractions, suggesting a trend of non-specific chemical defence. However, Gram-negative bacteria and one pathogenic fungus showed greater resistance. Our study contributes to the evidence of antimicrobial chemical interactions between Antarctic seaweeds and sympatric microorganisms, as well as the potential of seaweed extracts for pharmacological applications.

Diverse traits of aquatic plants cannot individually explain their consumption by the generalist gastropod Biomphalairia glabrata

Several experimental studies on aquatic plants have reported the prevalence of chemical defense mechanism against herbivory, as opposed to structural, life-forms or other traits. Here, our laboratory feeding experiments and integrative analysis explored the relationship among palatability (fresh or reconstituted plants used as artificial diet) and various chemical/nutritional traits (i.e., contents of dry mass, ash, nitrogen, protein, and phenols) of diverse aquatic plants and their susceptibility to consumption by the generalist gastropod Biomphalaria glabrata. Biomphalaria glabrata consumed all of the assayed aquatic plants in a hierarchical yet generalized way, with the consumption of fresh plants, their reconstituted forms and defensive properties of lipophilic extracts not being significantly correlated with plant physical or chemical traits to determine the feeding preference of the gastropod. Our results do not reveal a prevalence for a specific plant attribute contributing to herbivory. Instead, they indicate that the susceptibility of aquatic plants to generalist consumers is probably related to a combination of their chemical and physical properties, resulting in moderate grazing rates by generalist consumers.

Can Cephalopods Vomit? Hypothesis Based on a Review of Circumstantial Evidence and Preliminary Experimental Observations

In representative species of all vertebrate classes, the oral ejection of upper digestive tract contents by vomiting or regurgitation is used to void food contaminated with toxins or containing indigestible material not voidable in the feces. Vomiting or regurgitation has been reported in a number of invertebrate marine species (Exaiptasia diaphana, Cancer productus, and Pleurobranchaea californica), prompting consideration of whether cephalopods have this capability. This "hypothesis and theory" paper reviews four lines of supporting evidence: (1) the mollusk P. californica sharing some digestive tract morphological and innervation similarities with Octopus vulgaris is able to vomit or regurgitate with the mechanisms well characterized, providing an example of motor program switching; (2) a rationale for vomiting or regurgitation in cephalopods based upon the potential requirement to void indigestible material, which may cause damage and ejection of toxin contaminated food; (3) anecdotal reports (including from the literature) of vomiting- or regurgitation-like behavior in several species of cephalopod (Sepia officinalis, Sepioteuthis sepioidea, O. vulgaris, and Enteroctopus dofleini); and (4) anatomical and physiological studies indicating that ejection of gastric/crop contents via the buccal cavity is a theoretical possibility by retroperistalsis in the upper digestive tract (esophagus, crop, and stomach). We have not identified any publications refuting our hypothesis, so a balanced review is not possible. Overall, the evidence presented is circumstantial, so experiments adapting current methodology (e.g., research community survey, in vitro studies of motility, and analysis of indigestible gut contents and feces) are described to obtain additional evidence to either support or refute our hypothesis. We recognize the possibility that further research may not support the hypothesis; therefore, we consider how cephalopods may protect themselves against ingestion of toxic food by external chemodetection prior to ingestion and digestive gland detoxification post-ingestion. Reviewing the evidence for the hypothesis has identified a number of gaps in knowledge of the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestible food residues, pH of digestive secretions, sensory innervation, and digestive gland detoxification mechanisms) of the digestive tract as well as a paucity of recent studies on the role of epithelial chemoreceptors in prey identification and food intake.

Toxins or medicines? Phytoplankton diets mediate host and parasite fitness in a freshwater system

Diets must satisfy the everyday metabolic requirements of organisms and can also serve as medicines to combat disease. Currently, the medicinal role of diets is much better understood in terrestrial than in aquatic ecosystems. This is surprising because phytoplankton species synthesize secondary metabolites with known antimicrobial properties. Here, we investigated the medicinal properties of phytoplankton (including toxin-producing cyanobacteria) against parasites of the dominant freshwater herbivore, Daphnia. We fed Daphnia dentifera on green algae and toxic cyanobacteria diets known to vary in their nutritional quality and toxin production, and an additional diet of Microcystis with added pure microcystin-LR. We then exposed Daphnia to fungal and bacterial parasites. Anabaena, Microcystis and Chlorella diets prevented infection of Daphnia by the fungal parasite Metschnikowia, while Nodularia toxins increased offspring production by infected hosts. In contrast to their medicinal effects against Metschnikowia, toxic phytoplankton generally decreased the fitness of Daphnia infected with the bacterial parasite, Pasteuria. We also measured the amount of toxin produced by phytoplankton over time. Concentrations of anatoxin-a produced by Anabaena increased in the presence of Metschnikowia, suggesting parasite-induced toxin production. Our research illustrates that phytoplankton can serve as toxins or medicines for their consumers, depending upon the identity of their parasites.

Impact of herbivory and competition on lake ecosystem structure: underwater experimental manipulation

Two basic ecological relationships, herbivory and competition, distinctively influence terrestrial ecosystem characteristics, such as plant cover, species richness and species composition. We conducted a cage experiment under natural conditions in an aquatic ecosystem to test the impacts of two treatments combined in a factorial manner: (i) a pulse treatment – removal of dominant competitors among primary producers (macroalgae Chara sp. and Vaucheria sp.), and (ii) a press treatment – preventing herbivore (fish, crayfish) access to caged plots. The plots were sampled once before the treatments were established and four more times within two years. Both treatments had a significantly positive impact on macrophyte cover and species richness and changed the macrophyte species composition. The effect of the macroalgae removal was immediate with the highest species richness occurrence during the first post-treatment monitoring, but the positive effect vanished with time. In contrast, preventing herbivore access had a gradual but long-lasting effect and reached a more steady-state over time. Two of the most common species showed contrasting responses, the palatable Potamogeton pectinatus was most supported by caging, while the distasteful Myriophyllum spicatum preferred open plots. Our findings may be applicable during the revitalisation of aquatic ecosystems that aims to increase macrophyte biodiversity.

Sponge chemical defenses are a possible mechanism for increasing sponge abundance on reefs in Zanzibar

Coral reefs are experiencing increasing anthropogenic impacts that result in substantial declines of reef-building corals and a change of community structure towards other benthic invertebrates or macroalgae. Reefs around Zanzibar are exposed to untreated sewage and runoff from the main city Stonetown. At many of these sites, sponge cover has increased over the last years. Sponges are one of the top spatial competitors on reefs worldwide. Their success is, in part, dependent on their strong chemical defenses against predators, microbial attacks and other sessile benthic competitors. This is the first study that investigates the bioactive properties of sponge species in the Western Indian Ocean region. Crude extracts of the ten most dominant sponge species were assessed for their chemical defenses against 35 bacterial strains (nine known as marine pathogens) using disc diffusion assays and general cytotoxic activities were assessed with brine shrimp lethality assays. The three chemically most active sponge species were additionally tested for their allelopathic properties against the scleractinian coral competitor Porites sp.. The antimicrobial assays revealed that all tested sponge extracts had strong antimicrobial properties and that the majority (80%) of the tested sponges were equally defended against pathogenic and environmental bacterial strains. Additionally, seven out of ten sponge species exhibited cytotoxic activities in the brine shrimp assay. Moreover, we could also show that the three most bioactive sponge species were able to decrease the photosynthetic performance of the coral symbionts and thus were likely to impair the coral physiology.

Grazer responses to variable macroalgal resource conditions facilitate habitat structuring

Consumer responses to altered resource conditions can vary depending on dietary preference, resource characteristics and secondary resource features such as shelter. These can have cascading effects, especially if the consumed resource impacts on overall ecological functioning. In this study, we assessed the dietary composition of grazer communities following seasonal changes in the characteristics of their staple food-source (macroalgae). This was conducted in the living stromatolite pools growing along the coast of South Africa. Stable isotope mixing models suggested that following macroalgal bleaching in summer, metazoan consumers shifted their diet from predominantly macroalgae to a generalist composition. This has important implications for the integrity of the stromatolite matrix and its layered deposition. Where previously in winter stromatolite microalgae comprised a minor component of metazoan consumer diets, in summer, following a change in the resource conditions of macroalgae, microalgae featured more prominently in grazer diets. This seasonal grazing pressure on stromatolite-related resources probably promotes the pattern of annual layering observed in the stromatolite accretion. It also demonstrates a mechanism whereby grazer dietary shifts following a change in their preferred food resource can affect the ecosystem structure of their environment, specifically the stromatolite layering process which responds to microalgal growth or grazing conditions.

Experimental evidence of chemical defence mechanisms in Antarctic bryozoans

Bryozoans are among the most abundant and diverse members of the Antarctic benthos, however the role of bioactive metabolites in ecological interactions has been scarcely studied. To extend our knowledge about the chemical ecology of Antarctic bryozoans, crude ether extracts (EE) and butanol extracts (BE) obtained from two Antarctic common species (Cornucopina pectogemma and Nematoflustra flagellata), were tested for antibacterial and repellent activities. The extracts were screened for quorum quenching and antibacterial activities against four Antarctic bacterial strains (Bacillus aquimaris, Micrococcus sp., Oceanobacillus sp. and Paracoccus sp.). The Antarctic amphipod Cheirimedon femoratus and the sea star Odontaster validus were selected as sympatric predators to perform anti-predatory and substrate preference assays. No quorum quenching activity was detected in any of the extracts, while all EE exhibited growth inhibition towards at least one bacterium strain. Although the species were not repellent against the sea star, they caused repellence to the amphipods in both extracts, suggesting that defence activities against predation derive from both lipophilic and hydrophilic metabolites. In the substrate preference assays, one EE and one BE deriving from different specimens of the species C. pectogemma were active. This study reveals intraspecific variability of chemical defences and supports the fact that chemically mediated interactions are common in Antarctic bryozoans as means of protection against fouling and predation.

Identification and Characterization of a 25 kDa Protein That Is Indispensable for the Efficient Saccharification of Eisenia bicyclis in the Digestive Fluid of Aplysia kurodai

The digestive fluid of the sea hare Aplysia kurodai can liberate approximately 2.5 mg of glucose from 10 mg of dried Eisenia bicyclis powder. Although laminaran, a major storage polysaccharide in E. bicyclis, is easily digested to glucose by the synergistic action of the 110 and 210 kDa A. kurodai β-glucosidases (BGLs), glucose is not liberated from E. bicyclis by direct incubation with these BGLs. To clarify this discrepancy, we searched for an Eisenia hydrolysis enhancing protein (EHEP) in the digestive fluid of A. kurodai. A novel 25 kDa protein that enhances E. bicyclis saccharification by β-glucosidases was purified to a homogeneous state from the digestive fluid of A. kurodai, and its cDNA was cloned from total cDNAs reverse-transcribed from hepatopancreas total RNA. The E. bicyclis extract strongly inhibited BGLs, suggesting some compound within this brown alga functioned as a feeding deterrent. However, when E. bicyclis was incubated with BGLs in the presence of EHEP, glucose production was markedly increased. As E. bicyclis is rich in phlorotannin, which are only found in brown algae, our study suggested that these compounds are the main BGL inhibitors in E. bicyclis extract. EHEP protects BGLs from phlorotannin inhibition by binding to phlorotannins and forming an insoluble complex with phloroglucinol and phlorotannins. These findings indicated that EHEP plays a key role in the saccharification of brown seaweeds containing phlorotannins in the digestive fluid of A. kurodai. This is the first report of EHEP as a phlorotannin-binding protein that protects BGLs from inhibition.

New Cytotoxic Cembranoid from Indonesian Soft Coral Sarcophyton sp

CONTEXT

Sarcophyton is a soft coral species that contains various secondary metabolites with cytotoxic activity. The production of cytotoxic compounds in soft corals is suggested as their allelochemical to win space competition. Therefore, if a particular soft coral species dominates a reef area, it may suggest to contain interesting bioactive compounds.

AIMS

This research aimed to characterize the cytotoxic compounds in dominant soft coral species (Sarcophyton sp.) on the reef at the Western side of Mahengetang Island, Indonesia.

SUBJECTS AND METHODS

Isolation of cytotoxic compounds through ethanol extracts had been done with preparative high-performance liquid chromatography and bioassay-guided fractionation by MCF-7 (breast) cancer cell lines. The structures of each cytotoxic compounds were elucidated on the basis of mass and nuclear magnetic resonance spectroscopic studies.

RESULTS

Elucidation through all compounds found a new cembranoid, namely, 2-hydroxy-crassocolide E (1), alongside with 5 known cembranoids; sarcophytoxide (2), sarcrassin E (3), 3,7,11-cembreriene-2,15-diol (4), 11,12-epoxy-Sarcophytol A (5), and sarcophytol A (6). All of these cembranoids were showed to inhibit the growth of MCF-7 (breast) cancer, with 50% inhibition of tumor cell lines growth lower than 30 mg/L.

CONCLUSIONS

Results of this study suggest that a soft coral species which dominate a reef area is a potential source for various bioactive compounds.

SUMMARY

Elucidation of cytotoxic compounds from Sarcophyton sp. that dominate the reef at Mahengetang Island Indonesia revealed a new compound (2-hydroxy-crassocolide E) alongside with 5 known cembranoid compounds. Abbreviations Used: SCUBA: Self-contained underwater breathing apparatus; HPLC: High performance liquid chromatography; NMR: Nuclear magnetic resonance; IT-TOF: Ion trap-time of flight; MTT: 3-(4,5-dimethylthiazol-2-yl)-2; 5-diphenyltetrazolinon bromide; DEPT: Distortionless enhancement by polarisation transfer; COSY: Correlation spectroscopy; HMBC: Heteronuclear multiplebond correlation; NOE: Nuclear overhauser effect; IG50: 50% inhibition growth.

Chemical mediation as a structuring element in marine gastropod predator-prey interactions

Some diterpenoid compounds protect the sacoglossansElysiasp. andCyerce nigricansfrom their carnivorous predator the dorid nudibranch,Gymnodorissp., unlike chemically unprotected gastropods that are consumed by this voracious nudibranch (photo Philippe Bourseiller).

Biochemical Mechanisms for Geographical Adaptations to Novel Toxin Exposures in Butterflyfish

Some species of butterflyfish have had preyed upon corals for millions of years, yet the mechanism of butterflyfish specialized coral feeding strategy remains poorly understood. Certain butterflyfish have the ability to feed on allelochemically rich soft corals, e.g. Sinularia maxima. Cytochrome P450 (CYP) is the predominant enzyme system responsible for the detoxification of dietary allelochemicals. CYP2-like and CYP3A-like content have been associated with butterflyfish that preferentially consumes allelochemically rich soft corals. To investigate the role of butterflyfish CYP2 and CYP3A enzymes in dietary preference, we conducted oral feeding experiments using homogenates of S. maxima and a toxin isolated from the coral in four species of butterflyfish with different feeding strategies. After oral exposure to the S. maxima toxin 5-episinulaptolide (5ESL), which is not normally encountered in the Hawaiian butterflyfish diet, an endemic specialist, Chaetodon multicinctus experienced 100% mortality compared to a generalist, Chaetodon auriga, which had significantly more (3–6 fold higher) CYP3A-like basal content and catalytic activity. The specialist, Chaetodon unimaculatus, which preferentially feed on S. maxima in Guam, but not in Hawaii, had 100% survival, a significant induction of 8–12 fold CYP3A-like content, and an increased ability (2-fold) to metabolize 5ESL over other species. Computer modeling data of CYP3A4 with 5ESL were consistent with microsomal transformation of 5ESL to a C15-16 epoxide from livers of C. unimaculatus. Epoxide formation correlated with CYP3A-like content, catalytic activity, induction, and NADPH-dependent metabolism of 5ESL. These results suggest a potentially important role for the CYP3A family in butterflyfish-coral diet selection through allelochemical detoxification.

Natural products mediating ecological interactions in Antarctic benthic communities: a mini-review of the known molecules

Out of the many bioactive compounds described from the oceans, only a small fraction have been studied for their ecological significance. Similarly, most chemically mediated interactions are not well understood, because the molecules involved remain unrevealed. In Antarctica, this gap in knowledge is even more acute in comparison to tropical or temperate regions, even though polar organisms are also prolific producers of chemical defenses, and pharmacologically relevant products are being reported from the Southern Ocean. The extreme and unique marine environments surrounding Antarctica along with the numerous unusual interactions taking place in benthic communities are expected to select for novel functional secondary metabolites. There is an urgent need to comprehend the evolutionary role of marine derived substances in general, and particularly at the Poles, since molecules of keystone significance are vital in species survival, and therefore, in structuring the communities. Here we provide a mini-review on the identified marine natural products proven to have an ecological function in Antarctic ecosystems. This report recapitulates some of the bibliography from original Antarctic reviews, and updates the new literature in the field from 2009 to the present.

Marine invertebrate xenobiotic-activated nuclear receptors: their application as sensor elements in high-throughput bioassays for marine bioactive compounds

Developing high-throughput assays to screen marine extracts for bioactive compounds presents both conceptual and technical challenges. One major challenge is to develop assays that have well-grounded ecological and evolutionary rationales. In this review we propose that a specific group of ligand-activated transcription factors are particularly well-suited to act as sensors in such bioassays. More specifically, xenobiotic-activated nuclear receptors (XANRs) regulate transcription of genes involved in xenobiotic detoxification. XANR ligand-binding domains (LBDs) may adaptively evolve to bind those bioactive, and potentially toxic, compounds to which organisms are normally exposed to through their specific diets. A brief overview of the function and taxonomic distribution of both vertebrate and invertebrate XANRs is first provided. Proof-of-concept experiments are then described which confirm that a filter-feeding marine invertebrate XANR LBD is activated by marine bioactive compounds. We speculate that increasing access to marine invertebrate genome sequence data, in combination with the expression of functional recombinant marine invertebrate XANR LBDs, will facilitate the generation of high-throughput bioassays/biosensors of widely differing specificities, but all based on activation of XANR LBDs. Such assays may find application in screening marine extracts for bioactive compounds that could act as drug lead compounds.

Defensive metabolites from Antarctic invertebrates: does energetic content interfere with feeding repellence?

Many bioactive products from benthic invertebrates mediating ecological interactions have proved to reduce predation, but their mechanisms of action, and their molecular identities, are usually unknown. It was suggested, yet scarcely investigated, that nutritional quality interferes with defensive metabolites. This means that antifeedants would be less effective when combined with energetically rich prey, and that higher amounts of defensive compounds would be needed for predator avoidance. We evaluated the effects of five types of repellents obtained from Antarctic invertebrates, in combination with diets of different energetic values. The compounds came from soft corals, ascidians and hexactinellid sponges; they included wax esters, alkaloids, a meroterpenoid, a steroid, and the recently described organic acid, glassponsine. Feeding repellency was tested through preference assays by preparing diets (alginate pearls) combining different energetic content and inorganic material. Experimental diets contained various concentrations of each repellent product, and were offered along with control compound-free pearls, to the Antarctic omnivore amphipod Cheirimedon femoratus. Meridianin alkaloids were the most active repellents, and wax esters were the least active when combined with foods of distinct energetic content. Our data show that levels of repellency vary for each compound, and that they perform differently when mixed with distinct assay foods. The natural products that interacted the most with energetic content were those occurring in nature at higher concentrations. The bioactivity of the remaining metabolites tested was found to depend on a threshold concentration, enough to elicit feeding repellence, independently from nutritional quality.

Biogeographic and phylogenetic effects on feeding resistance of generalist herbivores toward plant chemical defenses

Many terrestrial and most marine herbivores have generalist diets, yet the role that evolutionary history plays in their foraging behaviors is poorly documented. On tropical hard-bottom reefs, generalist fishes and sea urchins readily consume seaweeds that produce lipophilic secondary metabolites. In contrast, herbivores on temperate reefs less commonly encounter seaweeds with analogous metabolites. This biogeographic pattern suggests that tropical herbivores should evolve greater feeding resistance to lipophilic defenses relative to temperate herbivores, but tests of this biogeographic pattern are rare. We offered lipophilic extracts from nine subtropical seaweeds at two concentrations to sea urchins (four subtropical and three cold-temperate populations) and quantified urchin feeding resistance. Patterns of feeding resistance toward lipophilic defenses were more similar within genera than across genera of urchins, indicating a substantial role for phylogenetic history in the feeding ecology of these generalist herbivores. The biogeographic origin of urchins also influenced feeding resistance, as subtropical species displayed greater feeding resistance than did temperate species. Similarly, a subtropical population of Arbacia punctulata had greater feeding resistance for Dictyota and Stypopodium extracts relative to temperate A. punctulata. We conclude that evolutionary history plays a more central role in the foraging ecology of generalist herbivores than is currently appreciated.

A pharm-ecological perspective of terrestrial and aquatic plant-herbivore interactions

We describe some recent themes in the nutritional and chemical ecology of herbivores and the importance of a broad pharmacological view of plant nutrients and chemical defenses that we integrate as "Pharm-ecology". The central role that dose, concentration, and response to plant components (nutrients and secondary metabolites) play in herbivore foraging behavior argues for broader application of approaches derived from pharmacology to both terrestrial and aquatic plant-herbivore systems. We describe how concepts of pharmacokinetics and pharmacodynamics are used to better understand the foraging phenotype of herbivores relative to nutrient and secondary metabolites in food. Implementing these concepts into the field remains a challenge, but new modeling approaches that emphasize tradeoffs and the properties of individual animals show promise. Throughout, we highlight similarities and differences between the historic and future applications of pharm-ecological concepts in understanding the ecology and evolution of terrestrial and aquatic interactions between herbivores and plants. We offer several pharm-ecology related questions and hypotheses that could strengthen our understanding of the nutritional and chemical factors that modulate foraging behavior of herbivores across terrestrial and aquatic systems.

Local adaptation in adult feeding preference and juvenile performance in the generalist herbivore Idotea balthica

Populations can respond to environmental heterogeneity by genetic adaptation to local conditions. Evidence for local adaptation in herbivores with relatively broad host breadth is scarce, either because generalists rarely locally adapt or because fewer studies have tested for local adaptation. The marine isopod Idotea balthica, a small (<3 cm) generalist herbivore common to estuaries of the northwestern Atlantic, is found on multiple macroalgae and sea grasses north of 42°N, while more southerly populations utilize sea grass-dominated and macroalgal-poor habitats. Feeding preference assays revealed a latitudinal shift in preference hierarchy that mirrors this geographic variation in host availability. Northern populations have higher feeding preference for fresh and freeze-dried tissue of the brown macroalga Fucus vesiculosus and consumed more of its water-soluble and lipophilic extracts relative to southern populations. In contrast, southern populations have a relatively higher preference for the green macroalga Ulva linza and sea grass Zostera marina. The rank of hosts in feeding assays exhibited by northern adults (Fucus = Ulva > Zostera) and southern adults (Ulva > Fucus > Zostera) closely mirrored ranking of juvenile growth rates, suggesting that preference and performance are strongly correlated across these macrophytes. Several of our assays included isopods that had parents reared under uniform laboratory conditions, indicating that geographic differences are genetically mediated and unlikely to reflect phenotypic plasticity or maternal effects. Local adaptation in host use traits may be common in broadly distributed, generalist herbivores in marine and terrestrial systems, and will manifest itself as local shifts in the preference ranking of hosts.

Chemo-ecological studies on hexactinellid sponges from the Southern Ocean

Hexactinellids (glass sponges) are an understudied class with syncytial organization and poor procariotic associations, thought to lack defensive secondary metabolites. Poriferans, though, are outstanding sources of bioactive compounds; nonetheless, a growing suspicion suggests that many of these chemicals could be symbiont-derived. In Polar latitudes, sponges are readily invaded by diatoms, which could provide natural products. Hexactinellids are typical of deep waters; but in Antarctica, they dominate the upper shelf providing shelter and food supply to many opportunistic mesograzers and macroinvertebrates, which exert strong ecological pressures on them. Aiming to examine the incidence of defensive activities of hexactinellids against consumption, feeding experiments were conducted using their lipophilic fractions. Antarctic hexactinellid and demosponge extracts were tested against the asteroid Odontaster validus and the amphipod Cheirimedon femoratus as putative sympatric, omnivorous consumers. Hexactinellids yielded greater unpalatable activities towards the amphipod, while no apparent allocation of lipophilic defenses was noted. After chemical analyses on the lipophilic fractions from these Antarctic glass sponges, quite similar profiles were revealed, and no peculiar secondary metabolites, comparable to those characterizing other poriferans, were found. Instead, the lipidic compounds 5α(H)-cholestan-3-one and two glycoceramides were isolated for their particular outspread presence in our samples. The isolated compounds were further assessed in asteroid feeding assays, and their occurrence was evaluated for chemotaxonomical purposes in all the Antarctic samples as well as in glass sponges from other latitudes by NMR and MS. Characteristic sphingolipids are proposed as chemical markers in Hexactinellida, with possible contributions to the classification of this unsettled class.

Parallels between zootherapeutic practices in ethnoveterinary and human complementary medicine in northeastern Brazil

AIM OF THE STUDY

The purpose of this study was to describe the local zootherapeutic practices in ethnoveterinay medicine of semi-arid of NE Brazil (Caatinga biome) and to contribute to future research about the validation of the effects and side effects of these animal products. In this sense, we sought to determine the connections between human and animal ethnopharmacology and their implications for ethnoveterinary medicine in northeastern Brazil.

MATERIALS AND METHODS

In this study we analyze data gathered through fieldwork conducted in the semi-arid of Paraiba State, NE Brazil, where 123 people (98 men and 25 women) provided information on animal species used as medicine, body parts used to prepare the remedies and illnesses to which the remedies were prescribed. The information obtained through semi-structured interviews was complemented by free interviews and informal conversations.

RESULTS

A total of 46 animal species (43 vertebrates and 3 invertebrates) were found to be used to treat 33 different ailments in livestocks and pets and 62 conditions in humans. Interviewees cited a wide range of materials derived from animal bodies (or their metabolic products) that are used as remedies in local EVM, nonetheless, fats (and/or suet) is the most frequently reported natural remedies. EVM practices have close relationships with human complementary and alternative medicine (CAM) and probably evolved based on traditional human medicine practices; as such, the division between EVM and CAM is not always obvious from the viewpoint of the local residents. Descriptions of diseases, symptoms or treatments were often associated with both humans and animals (especially livestock), and 24 animal species (52%) were prescribed to treat similar ailments in both humans and animals based on local knowledge about CAM.

CONCLUSIONS

Our results suggest that traditional knowledge of animal-based medicines in ethnoveterinary practices co-evolved with traditional knowledge of human ethnomedicine. The examination of folk knowledge and animal health practices will give us a better understanding of human interactions with their local environment and aid in formulating appropriate strategies for the validation of traditional remedies and for natural resource conservation.

The nature of nutrition: a unifying framework

We present a graphical approach, which we believe can help to integrate nutrition into the broader biological sciences, and introduce generality into the applied nutritional sciences. This ‘Geometric Framework’ takes account of the fact that animals need multiple nutrients in changing amounts and balance, and that nutrients come packaged in foods that are often hard to find, dangerous to subdue and costly to process. We then show how the Geometric Framework has been used to understand the links between nutrition and relevant aspects of the biology of individual animals. These aspects include the physiological mechanisms that direct the nutritional interactions of the animal with its environment, and the fitness consequences of these interactions. Having considered the implications of diet for individuals, we show that these effects can translate into the collective behaviour of groups and societies, and in turn ramify throughout food webs to influence the structure of ecosystems.

Cytochrome P450 diversity and induction by gorgonian allelochemicals in the marine gastropod Cyphoma gibbosum

BACKGROUND

Intense consumer pressure strongly affects the structural organization and function of marine ecosystems, while also having a profound effect on the phenotype of both predator and prey. Allelochemicals produced by prey often render their tissues unpalatable or toxic to a majority of potential consumers, yet some marine consumers have evolved resistance to host chemical defenses. A key challenge facing marine ecologists seeking to explain the vast differences in consumer tolerance of dietary allelochemicals is understanding the biochemical and molecular mechanisms underlying diet choice. The ability of marine consumers to tolerate toxin-laden prey may involve the cooperative action of biotransformation enzymes, including the inducible cytochrome P450s (CYPs), which have received little attention in marine invertebrates despite the importance of allelochemicals in their evolution.

RESULTS

Here, we investigated the diversity, transcriptional response, and enzymatic activity of CYPs possibly involved in allelochemical detoxification in the generalist gastropod Cyphoma gibbosum, which feeds exclusively on chemically defended gorgonians. Twelve new genes in CYP family 4 were identified from the digestive gland of C. gibbosum. Laboratory-based feeding studies demonstrated a 2.7- to 5.1-fold induction of Cyphoma CYP4BK and CYP4BL transcripts following dietary exposure to the gorgonian Plexaura homomalla, which contains high concentrations of anti-predatory prostaglandins. Phylogenetic analysis revealed that C. gibbosum CYP4BK and CYP4BL were most closely related to vertebrate CYP4A and CYP4F, which metabolize pathophysiologically important fatty acids, including prostaglandins. Experiments involving heterologous expression of selected allelochemically-responsive C. gibbosum CYP4s indicated a possible role of one or more CYP4BL forms in eicosanoid metabolism. Sequence analysis further demonstrated that Cyphoma CYP4BK/4BL and vertebrate CYP4A/4F forms share identical amino acid residues at key positions within fatty acid substrate recognition sites.

CONCLUSIONS

These results demonstrate differential regulation of CYP transcripts in a marine consumer feeding on an allelochemical-rich diet, and significantly advance our understanding of both the adaptive molecular mechanisms that marine consumers use to cope with environmental chemical pressures and the evolutionary history of allelochemical-metabolizing enzymes in the CYP superfamily.

The role of multixenobiotic transporters in predatory marine molluscs as counter-defense mechanisms against dietary allelochemicals

Multixenobiotic transporters have been extensively studied for their ability to modulate the disposition and toxicity of pharmacological agents, yet their influence in regulating the levels of dietary toxins within marine consumers has only recently been explored. This study presents functional and molecular evidence for multixenobiotic transporter-mediated efflux activity and expression in the generalist gastropod Cyphoma gibbosum, and the specialist nudibranch Tritonia hamnerorum, obligate predators of chemically defended gorgonian corals. Immunochemical analysis revealed that proteins with homology to permeability glycoprotein (P-gp) were highly expressed in T. hamnerorum whole animal homogenates and localized to the apical tips of the gut epithelium, a location consistent with a role in protection against ingested prey toxins. In vivo dye assays with specific inhibitors of efflux transporters demonstrated the activity of P-gp and multidrug resistance-associated protein (MRP) families of ABC transporters in T. hamnerorum. In addition, we identified eight partial cDNA sequences encoding two ABCB and two ABCC proteins from each molluscan species. Digestive gland transcripts of C. gibbosum MRP-1, which have homology to vertebrate glutathione-conjugate transporters, were constitutively expressed regardless of gorgonian diet. This constitutive expression may reflect the ubiquitous presence of high affinity substrates for C. gibbosum glutathione transferases in gorgonian tissues likely necessitating export by MRPs. Our results suggest that differences in multixenobiotic transporter expression patterns and activity in molluscan predators may stem from the divergent foraging strategies of each consumer.

Genetic variability in tolerance to copper contamination in a herbivorous marine invertebrate

Anthropogenic stresses such as metal contamination can have profound ecological impacts in a wide range of habitats. Reduced survival of organisms in contaminated habitats has the potential to result in the evolution of genotypes tolerant to deleterious contaminants. Local adaptation to contamination requires directional selection, genetic variation in traits relating to tolerance, spatial variability in exposure to the contaminant and limited gene flow between populations. This study assesses variation in tolerance in the herbivorous marine invertebrate Peramphithoe parmerong whose algal diets in Sydney Harbour readily accumulate the metal copper. A quantitative genetics approach (a full-sib, split family design) was used to quantify variation among families in survival on the contaminated diet. A significant genotype-by-environment interaction in offspring survival between the copper contaminated and uncontaminated diet treatments revealed variation in tolerance to copper by P. parmerong. Amphipods that survived 30 days of exposure to copper contaminated diets were slightly smaller and ate less algae than those reared on uncontaminated food. This reflects an additional sub-lethal effect associated with the consumption of contaminated algae. However, there was no evidence of acclimation to contaminated diets, nor a cost of reduced feeding for those genotypes with increased tolerance. This study provides strong evidence for the potential of a marine invertebrate to evolve tolerance to contaminants found in their diet.

Overview of the chemical ecology of benthic marine invertebrates along the western Antarctic peninsula

Thirteen years ago in a review that appeared in the American Zoologist, we presented the first survey of the chemical and ecological bioactivity of Antarctic shallow-water marine invertebrates. In essence, we reported that despite theoretical predictions to the contrary the incidence of chemical defenses among sessile and sluggish Antarctic marine invertebrates was widespread. Since that time we and others have significantly expanded upon the base of knowledge of Antarctic marine invertebrates' chemical ecology, both from the perspective of examining marine invertebrates in new, distinct geographic provinces, as well as broadening the evaluation of the ecological significance of secondary metabolites. Importantly, many of these studies have been framed within established theoretical constructs, particularly the Optimal Defense Theory. In the present article, we review the current knowledge of chemical ecology of benthic marine invertebrates comprising communities along the Western Antarctic Peninsula (WAP), a region of Antarctica that is both physically and biologically distinct from the rest of the continent. Our overview indicates that, similar to other regions of Antarctica, anti-predator chemical defenses are widespread among species occurring along the WAP. In some groups, such as the sponges, the incidence of chemical defenses against predation is comparable to, or even slightly higher than, that found in tropical marine systems. While there is substantial knowledge of the chemical defenses of benthic marine invertebrates against predators, much less is known about chemical anti-foulants. The sole survey conducted to date suggests that secondary metabolites in benthic sponges are likely to be important in the prevention of fouling by benthic diatoms, yet generally lack activity against marine bacteria. Our understanding of the sensory ecology of Antarctic benthic marine invertebrates, despite its great potential, remains in its infancy. For example, along the WAP, community-level non-consumptive effects occur when amphipods chemically sense fish predators and respond by seeking refuge in chemically-defended macroalgae. Such interactions may be important in releasing amphipods from predation pressure and facilitating their unusually high abundances along the WAP. Moreover, recent studies on the sensory biology of the Antarctic keystone sea star Odontaster validus indicate that chemotactile-mediated interactions between conspecifics and other sympatric predatory sea stars may have significant ramifications in structuring community dynamics. Finally, from a global environmental perspective, understanding how chemical ecology structures marine benthic communities along the WAP must increasingly be viewed in the context of the dramatic impacts of rapid climatic change now occurring in this biogeographic region.

Biochemical warfare on the reef: the role of glutathione transferases in consumer tolerance of dietary prostaglandins

BACKGROUND

Despite the profound variation among marine consumers in tolerance for allelochemically-rich foods, few studies have examined the biochemical adaptations underlying diet choice. Here we examine the role of glutathione S-transferases (GSTs) in the detoxification of dietary allelochemicals in the digestive gland of the predatory gastropod Cyphoma gibbosum, a generalist consumer of gorgonian corals. Controlled laboratory feeding experiments were used to investigate the influence of gorgonian diet on Cyphoma GST activity and isoform expression. Gorgonian extracts and semi-purified fractions were also screened to identify inhibitors and possible substrates of Cyphoma GSTs. In addition, we investigated the inhibitory properties of prostaglandins (PGs) structurally similar to antipredatory PGs found in high concentrations in the Caribbean gorgonian Plexaura homomalla.

PRINCIPAL FINDINGS

Cyphoma GST subunit composition was invariant and activity was constitutively high regardless of gorgonian diet. Bioassay-guided fractionation of gorgonian extracts revealed that moderately hydrophobic fractions from all eight gorgonian species examined contained putative GST substrates/inhibitors. LC-MS and NMR spectral analysis of the most inhibitory fraction from P. homomalla subsequently identified prostaglandin A(2) (PGA(2)) as the dominant component. A similar screening of commercially available prostaglandins in series A, E, and F revealed that those prostaglandins most abundant in gorgonian tissues (e.g., PGA(2)) were also the most potent inhibitors. In vivo estimates of PGA(2) concentration in digestive gland tissues calculated from snail grazing rates revealed that Cyphoma GSTs would be saturated with respect to PGA(2) and operating at or near physiological capacity.

SIGNIFICANCE

The high, constitutive activity of Cyphoma GSTs is likely necessitated by the ubiquitous presence of GST substrates and/or inhibitors in this consumer's gorgonian diet. This generalist's GSTs may operate as 'all-purpose' detoxification enzymes, capable of conjugating or sequestering a broad range of lipophilic gorgonian compounds, thereby allowing this predator to exploit a range of chemically-defended prey, resulting in a competitive dietary advantage for this species.