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School of Biological Sciences

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Start date: 1980 × End date: 1999 ×

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Susceptibility of invertebrate larvae to predators: how common are post-capture larval defenses?

1999-12-30 , Bullard, Stephan G. , Lindquist, Niels Lyle , Hay, Mark E.

Predation is believed to be a major source of mortality for larvae of benthic invertebrates, but the palatability of larvae commonly found in the water column has rarely been assessed. Larval palatability assays were conducted by collecting live invertebrate larvae from a temperate field site and offering them to a suite of common predators (the fishes Lagodon rhomboides, Leiostomus xanthurus, and Monacanthus hispidus and the hard coral Oculina arbuscula). By crushing larvae that were rejected intact and re-offering them to predators, it was possible to distinguish between defenses based on morphological and chemical characteristics of the larvae. Additionally, abundance data were collected for taxonomic groups of larvae at our sampling location. The majority of invertebrate larvae were palatable to consumers. Most predators readily consumed polychaete larvae, barnacle nauplii, bivalve veligers, shrimp zoeae, crab megalopae, phoronid actinotrochs, and hemichordate tornaria (which together accounted for 65% of meroplankton abundance), suggesting that these larvae lacked effective morphological or chemical defenses. Against at least 1 fish predator, a significant number of gastropod veligers, barnacle cyprids, crab zoeae, and stomatopod larvae (which accounted for 34% of meroplankton abundance) appeared to be morphologically defended. Larvae from these groups tended to be rejected whole, but were consumed by fishes once they were crushed. A significant number of nemertean pilidia, asteroid bipinnaria, and cnidarian planulae (which accounted for only 0.2% of meroplankton abundance) were rejected both whole and crushed, suggesting that some species or individuals within these taxa may be chemically defended. Thus, the majority of larvae from this assemblage of temperate meroplankton lacked physical or chemical defenses against potential predators (3 fishes and 1 cnidarian). Among the remaining larvae, physical resistance to predators was much more common than chemical resistance.

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Genetic and biochemical characterization of the interrelationships between prion and cytokeletal proteins in saccharomyces cerevisiae

1999-12 , Bailleul, Peggy Annick

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Mutualism and coral persistence: the role of herbivore resistance to algal chemical defense

1999-09 , Stachowicz, John J. , Hay, Mark E.

Because seaweeds uncontrolled by herbivores can overgrow and kill corals, competition can exclude corals from temperate latitudes where herbivores generally fail to control seaweed biomass. In this study, we show that the coral Oculina arbuscula persists on reefs in temperate North Carolina where seaweeds are common by harboring the omnivorous crab Mithrax forceps, which removes seaweeds and invertebrates growing on or near the coral. In the field, corals from which crabs are experimentally removed develop a dense cover of epibionts, exhibiting reduced growth and increased mortality relative to corals with crabs, which remain epibiont-free. This crab is unusual in that it readily consumes all local seaweeds in laboratory choice assays and is not deterred by chemical defenses that suppress feeding by local fishes, sea urchins, and other crabs. This allows Mithrax to defend corals from overgrowth by chemically noxious seaweeds like Dictyota and Sargassum that are avoided by most local herbivores. However, further field manipulations under reduced light conditions demonstrate that the outcome of the crab–coral interaction is context-dependent: crabs only benefit corals in well-lit areas where seaweeds are abundant. Field observations and tethering experiments show that, by living in association with Oculina, Mithrax gains a refuge from predation. Additionally, crabs grow faster when associated with live corals than with structurally equivalent dead corals, apparently because they are able to consume lipid-rich coral mucus. This mucus provides a dietary supplement that may help corals attract and retain low-mobility symbionts such as Mithrax, securing for the coral long-term and predictable protection against competitors. Structurally complex but competitively inferior organisms, like some corals and coralline algae, provide the biogenic habitat complexity upon which many other species depend. Because these sessile organisms may be dependent on symbionts to remove superior competitors, mutualisms can play an important, but currently underappreciated, role in structuring marine communities where biotic interactions are intense. In this study, the mutualism between Oculina and Mithrax promotes the persistence of both species in habitats from which they might otherwise be excluded by competition and predation.

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Marine bacterial isolates utilize unique mercury resistance mechanisms

1999-08 , Reyes, Nikolle Susanne

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Biogeochemical cycling of metals in redox-stratified marine environments : role of anaerobic microorganisms

1999-12 , Lowe, Kristine L.

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Dynamics and Thermodynamics of β-Hairpin Assembly: Insights from Various Simulation Techniques

1999-12 , Kolinski, Andrzej , Ilkowski, Bartosz , Skolnick, Jeffrey

Small peptides that might have some features of globular proteins can provide important insights into the protein folding problem. Two simulation methods, Monte Carlo Dynamics (MCD), based on the Metropolis sampling scheme, and Entropy Sampling Monte Carlo (ESMC), were applied in a study of a high-resolution lattice model of the C-terminal fragment of the B1 domain of protein G. The results provide a detailed description of folding dynamics and thermodynamics and agree with recent experimental findings (Munoz et al., 1997. Nature. 390:196–197). In particular, it was found that the folding is cooperative and has features of an all-or-none transition. Hairpin assembly is usually initiated by turn formation; however, hydrophobic collapse, followed by the system rearrangement, was also observed. The denatured state exhibits a substantial amount of fluctuating helical conformations, despite the strong b-type secondary structure propensities encoded in the sequence.

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Extensive bloom of a N₂-fixing diatom/cyanobacterial association in the tropical Atlantic Ocean

1999-08-20 , Carpenter, Edward J. , Montoya, Joseph P. , Burns, James , Mulholland, Margaret R. , Subramaniam, Ajit , Capone, Douglas G.

We encountered an extensive bloom of the colonial diatom Hemiaulus hauckii along a 2500 km cruise track off the NE coast of South America in autumn 1996. Each diatom cell contained the heterocystous, N₂-fixing cyanobacterial endosymbiont Richelia intracellularis. Surface Richelia heterocyst (and filament) densities increased from <100 to >10⁶ heterocyst l⁻¹ in the bloom. Total abundance ranged from 10⁶ heterocyst m⁻² outside the bloom to over 10¹⁰ heterocyst m⁻² within the bloom. Rates of primary production averaged 1.2 g C m⁻² d⁻¹, higher than typical for oligotrophic open ocean waters. N₂ fixation during the bloom by the Richelia/Hemiaulus association added an average of 45 mg N m⁻² d⁻¹, to the water column. The relative importance of NH₄⁺ uptake over the course of the bloom increased from 0 to 42% of total N uptake by the Hemiaulus/Richelia association. N2 fixation by Richelia exceeded estimates of 'new' N flux via NO₃ diffusion from deep water and, together with additional N₂ fixation by the cyanobacterium Trichodesmium, could supply about 25% of the total N demand through the water column during the bloom. Suspended particles and zooplankton collected within the bloom were depleted in ¹⁵N, reflecting the dominant contribution of N₂ fixation to the planktonic N budget. The bloom was spatially extensive, as revealed by satellite imagery, and is calculated to have contributed about 0.5 Tg N to the euphotic zone. Such blooms may represent an important and previously unrecognized source of new N to support primary production in nutrient-poor tropical waters. Furthermore, this bloom demonstrates that heterocystous cyanobacteria can also make quantitatively important contributions of N in oceanic water column environments.

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Genetic analysis of the cellular control of [PSI] prion

1999-12 , Zink, Amy Darlene

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Reduced mobility is associated with compensatory feeding and increased diet breadth of marine crabs

1999-11-03 , Stachowicz, John J. , Hay, Mark E.

Direct effects of predation have been widely recognized as important in affecting prey population dynamics and evolution. However, less attention has been devoted to the consequences of indirect effects of predators on prey behavior. For example, to avoid predation many animals restrict their activities to physical refugia and adopt low-mobility lifestyles, yet the consequences of these anti-predator behaviors for foraging and diet selection are relatively unknown. In this study we examine the relationships between mobility, feeding preferences, and compensatory feeding for 3 species of marine decapod crabs feeding on seaweeds in North Carolina, USA. Low mobility and high site fidelity of crabs were associated with a broad, non-selective diet and compensatory feeding. The majid Mithrax forceps exhibited the lowest mobility, highest site fidelity, and least selective diet of the 3 species, whereas another majid Libinia dubia was intermediate in both mobility and selectivity, and the xanthid Panopeus herbstii had the greatest mobility and narrowest diet. Of these 3 crabs, only M. forceps compensated for low food quality by increasing consumption rates in single food-species feeding assays. This may be because M. forceps is resistant to (or tolerant of) seaweed chemical defenses, while other crab species are not. The ability to consume, and presumably subsist on, a wide variety of potential foods including those defended from more mobile consumers may facilitate a low-mobility lifestyle, allowing the crab to minimize movement and reduce exposure to predators. Low mobility and high site-fidelity may thus facilitate the formation and use of associational refuges with sessile benthic organisms that are resistant to predators; these associations can have important community and ecosystem-wide consequences.

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A microbially-driven Fenton reaction for oxidative dechlorination of pentachlorophenol by shewanella putrefaciens

1999-08 , McKinzi, Adonia

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