413 publications from this institution
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
move about 66% of above-ground production2. Given the large allocation to below-ground structures, this may be no more than about 33% of total production, about r/3 to ‘12 of the rates in marine communities. In both marine and terrestrial systems, herbivory is generally greater in tropical than in temperate areas, but the highest rates of herbivory on tropical coral reefs can be ten to IO0 times greater than the highest rates in tropical forestst,s. Most herbivory in terrestrial systems is due to insects and vertebrate homeotherms4,5. Insects are largely absent from marine systems, and most herbivory is due to vertebrate ectotherms (fishes1 and a diverse array of invertebrates that are present all year and rarely undergo diapause (sea urchins, gastropods, polychaetes and a variety of marine crustaceansP. Because virtually all marine herbivores are ectotherms, changes in temperature may affect herbivory rates more in marine than in terrestrial systems’. With decreasing temperature, herbivory decreases in marine systems, but may increase in terrestrial communities because of the increased energy demands that low temperatures place on vertebrate homeothemrs. Terrestrial herbivores cope with the large amounts of relatively indigestible cellulose, hemicellulose and lignin that occur in terrestrial plants by f I ) timing their life cycles such that the feeding stages cooccur with the seasonal flush of new, high-quality leaves; (2) sucking
As corals decline and macroalgae proliferate on coral reefs, coral-macroalgal competition becomes more frequent and ecologically important. Whether corals are damaged by these interactions depends on susceptibility of the coral and traits of macroalgal competitors. Investigating changes in gene expression of corals and their intracellular symbiotic algae, Symbiodinium, in response to contact with different macroalgae provides insight into the biological processes and cellular pathways affected by competition with macroalgae. We evaluated the gene expression profiles of coral and Symbiodinium genes from two confamilial corals, Acropora millepora and Montipora digitata, after 6 h and 48 h of contact with four common macroalgae that differ in their allelopathic potency to corals. Contacts with macroalgae affected different biological pathways in the more susceptible (A. millepora) versus the more resistant (M. digitata) coral. Genes of coral hosts and of their associated Symbiodinium also responded in species-specific and time-specific ways to each macroalga. Changes in number and expression intensity of affected genes were greater after 6 h compared to 48 h of contact and were greater following contact with Chlorodesmis fastigiata and Amphiroa crassa than following contact with Galaxaura filamentosa or Turbinaria conoides. We documented a divergence in transcriptional responses between two confamilial corals and their associated Symbiodinium, as well as a diversity of dynamic responses within each coral species with respect to the species of macroalgal competitor and the duration of exposure to that competitor. These responses included early initiation of immune processes by Montipora, which is more resistant to damage after long-term macroalgal contact. Activation of the immune response by corals that better resist algal competition is consistent with the hypothesis that some macroalgal effects on corals may be mediated by microbial pathogens.
Genetic variation in tolerance for seaweed chemical defenses among populations of marine herbivores is poorly described, either because few marine studies have addressed the issue or because the feeding preferences of populations of marine herbivores rarely differentiate. We address this using the polyphagous amphipod Ampithoe longimana (Crustacea), which commonly consumes, and lives on, terpene-rich brown seaweeds in the tropical genus Dictyota. Previous work demonstrated that in areas where the amphipod and seaweeds overlap geographically, these chemically deterrent seaweeds provide the amphipod with spatial refuges from predation by omnivorous fishes that avoid consuming Dictyota. However, the amphipod's distribution extends northward of the seaweed's distribution, making this benefit of association unavailable to more northerly populations of amphipods. On average, populations sympatric with Dictyota have stronger feeding preference for Dictyota species and greater fitness when raised on Dictyota than do populations that are outside Dictyota's geographic endpoint. These results are consistent with the hypothesis that in areas where the amphipods co-exist with Dictyota, selection favors amphipods that tolerate Dictyota's chemical defenses and thereby access its enemy-free space. Amphipods allopatric with Dictyota are unable to tolerate Dictyota's chemical defenses, either because of selection, drift, or some mix of both forces. A trade-off between preference for Dictyota and for the chemically distinct seaweed Hypnea musciformis is suggested by the finding that populations with high preference for Dictyota tended to have lower preference for Hypnea. However, this population-level pattern appears to be the result of independent evolution and not a genetic trade-off: an analysis of full-sib families within a single population detected heritable variation in preferences for Dictyota and suggested this for Hypnea (although the latter was not statistically significant), yet no family-level covariation was detected. Phylogeographic analysis of mitocondrial DNA and nuclear sequences indicates a strong historical break between populations sympatric with Dictyota and populations more than 500 km beyond Dictyota's geographic endpoint. The historical separation of these most northerly populations could have allowed a random accumulation of alleles to effectively degrade tolerance for Dictyota, although selection may also be responsible for the degradation.
Worms and other marine invertebrates living in soft sediments commonly produce brominated natural products that have been hypothesized to function as defenses against consumers, but this hypothesis has not been tested directly. When 16 species of worms from a Georgia mud flat were fed to two sympatric fishes ( Fundulus heteroclitus , Leiostomus xanthurus ) and a crab ( Callinectes similis ), 15 species (94×;) were palatable to all three predators. Only the hemichordate Saccoglossus kowalevskii was unpalatable to both fishes, but even it was readily consumed by the crab. Bioassay‐guided chemical investigations demonstrated that Saccoglossus kowalevskii was rejected by fishes because it contained 2,3,4‐tribromopyrrole at 0.2×; of worm dry mass. This is the first direct test of brominated worm metabolites as defenses against sympatric consumers. The deterrence of 2,3,4‐tribromopyrrole in S. kowalevskii may explain why densities of this worm increase 40‐fold during seasons when predation is high and densities of palatable worms decline sharply. To more broadly examine the effects of brominated metabolites on worm palatability, we collected from North Carolina, Georgia, and Florida 14 species reported to produce brominated metabolites. These species were fed to sympatric consumers to assess palatability and also analyzed for brominated metabolites by gas chromatography mass spectrometry (GC/MS). Nine of the fourteen species contained brominated metabolites, but only two were unpalatable. In a final test, five additional brominated metabolites produced by marine worms were added to palatable foods at natural concentrations and at up to 20× natural concentrations. None deterred feeding at natural concentrations, one was deterrent at 5−15× natural concentration, and four had no effect at even 20× natural concentration. Thus, while one worm was defended by a brominated compound, most worms containing brominated metabolites were palatable, and brominated natural products seldom functioned as chemical defenses against consumers.
Chemical cues constitute much of the language of life in the sea. Our understanding of biotic interactions and their effects on marine ecosystems will advance more rapidly if this language is studied and understood. Here, I review how chemical cues regulate critical aspects of the behavior of marine organisms from bacteria to phytoplankton to benthic invertebrates and water column fishes. These chemically mediated interactions strongly affect population structure, community organization, and ecosystem function. Chemical cues determine foraging strategies, feeding choices, commensal associations, selection of mates and habitats, competitive interactions, and transfer of energy and nutrients within and among ecosystems. In numerous cases, the indirect effects of chemical signals on behavior have as much or more effect on community structure and function as the direct effects of consumers and pathogens. Chemical cues are critical for understanding marine systems, but their omnipresence and impact are inadequately recognized.
Why corals dominate tropical reefs but are rare or absent on temperate reefs is one of the more intriguing global-scale questions in marine ecology. Restriction of corals from temperate reefs has been suggested to be due to low temperature, competition with seaweeds, and synergistic interactions of physical and biological factors. However, most studies addressing these hypotheses have been non-experimental and conducted on tropical corals and reefs near the extremes of their distribution rather than in temperate habitats using corals that are physiologically suited to temperate environments. Some corals occur only in temperate regions, but their ecology is largely unstudied. In an attempt to understand how temperate corals function at latitudes where corals are relatively rare and where reefs tend to be dominated by seaweeds, we examined responses of the temperate coral Oculina arbuscula to competition with seaweeds on reefs in North Carolina (USA). We asked how competitive interactions were affected by levels of grazing, nutrients, or interactions of these factors. Sampling of 12 reef habitats ranging from 1 m deep, inshore sites to 25 m deep, offshore sites demonstrated a strong negative relationship between percentage cover of seaweeds and density of Oculina colonies. Seaweeds dominated well-lit habitats (shallow inshore reefs or deep offshore reefs with clear waters), while coral was significantly more abundant in low-light habitats where seaweeds were rare (deep inshore habitats or nearshore reefs with turbid waters). This general among-site pattern also occurred within an individual site as one moved from shallow, well-lit waters to deeper, darker waters. Corals transplanted into seaweed-dominated areas grew well if seaweed canopies were removed but grew poorly, or not at all, if canopies were left intact. Seaweeds also significantly inhibited recruitment of O. arbuscula. At a turbid inshore reef, recruitment was high at a depth of 6 m where seaweeds were rare, but very low at a depth of 1 m where seaweeds were abundant. Removal of seaweeds from shallow plots increased recruitment about 12-fold to levels that did not differ significantly from those at 6 m. In grazer-exclusion cages on offshore reefs, Oculina recruitment varied significantly between sites and years. Almost no recruitment was observed at a well-lit, plant-dominated site while recruitment was higher, to very high, at a turbid site with few seaweeds. At this turbid site, recruitment was facilitated by grazing but could not be related to grazer effects on seaweeds. Facilitation was apparently due to consumers removing barnacles, which dominated this low-light site if grazers were excluded. Cage exclusion of larger herbivores at two offshore sites (primarily fishes) and one inshore site (fishes and urchins) had no significant effect on coral growth. At the well-lit inshore site, herbivores had a large effect on the species composition of the seaweed community, but little effect on the total abundance of seaweeds. Large grazers caused palatable red seaweeds to be replaced by similar amounts of unpalatable brown seaweeds. Therefore, herbivory alone had little impact on total seaweed abundance and the levels of seaweed competition affecting co-occurring O. arbuscula. In contrast, when we conducted a factorial experiment manipulating both herbivory and nutrient levels, exclusion cages significantly reduced coral growth. In this experiment, nutrient addition had no effect on brown seaweeds but significantly increased the percentage cover of red seaweeds in exclusion cages. Nutrient addition also tended to suppress coral growth in herbivore-exclusion cages where red seaweeds were stimulated, but to increase coral growth in open cages where herbivores had removed the red seaweeds.
Coral diversity positively affects corals, but these benefits have limits and are threatened by ongoing species loss.
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 207:243-253 (2000) - doi:10.3354/meps207243 Activated chemical defenses in tropical versus temperate seaweeds Giancarlo L. Cetrulo1,*, Mark E. Hay2,** 1University of North Carolina at Chapel Hill, Institute of Marine Sciences, 3431 Arendell St., Morehead City, North Carolina 28557, USA 2School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA *Present address: SEA Laboratory, 1021 N. Harbor Dr., Redondo Beach, California 90266, USA **Corresponding author. E-mail: mark.hay@biology.gatech.edu ABSTRACT: Chemical defenses that are rapidly activated in response to injury have been reported in numerous species of vascular plants, but activated chemical defense has been demonstrated for only 1 genus of seaweed. To investigate the frequency of potential activated chemical defenses in seaweeds and to determine if there are geographic differences in the frequency of theses, we conducted urchin and fish feeding assays using chemical extracts from 42 species of temperate or tropical seaweeds that were damaged immediately before extraction in organic solvents (= the potentially activated extract) or placed in organic solvents before they were damaged (= the non-activated extract). Seven species exhibited changes in palatability consistent with activated defenses while 4 species became more, rather than less, palatable if they were damaged 30 s before extraction. Frequency of activation did not vary geographically. Seventeen percent of tropical species (4 of 24) and 17% of temperate species (3 of 18) exhibited changes in palatability that were consistent with activation of chemical defenses. Thin-layer chromatography of lipid-soluble extracts indicated that damaging the thallus prior to extraction caused noticeable chemical changes in 70% of the species evaluated. Investigations of algal chemical defenses thus need to consider the effects of injury during herbivore attacks and the effects of extraction methodology on the types of, and concentrations of, metabolites discovered in seaweeds. KEY WORDS: Activated chemical defenses · Fish · Marine · Plant-herbivore interaction · Sea urchin · Seaweed Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 207. Online publication date: November 22, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.
Results of regression analyses testing for relationships between mean effect size and experimental duration.
The palatable plants investigated in this study gained significant protection from herbivores by associating with abundant competitors that were less susceptible to herbivory. When herbivores were excluded, palatable species associated with unpalatable ones grew at only 14%-19% of the rate of palatable plants separated from unpalatable ones. When herbivores were present, however, palatable species appeared to depend completely on unpalatable competitors to provide microsites of reduced herbivory to prevent grazers from causing local extinction of the preferred species. For the species studied here, the cost of being associated with a larger, unpalatable competitor was much less than the cost of increased consumption in the absence of that competitor. Under these conditions, one competitor can have a strong positive effect on another. Associational defenses can provide an unappreciated mechanism for maintaining species richness within communities that are dominated by one or a few major species. In this community, increases in the abundance of common late-successional competitors led to increases, not decreases, in the abundance and number of other species and to retention, not exclusion, of early-successional species.
