Synthesis of a Borylated Ibuprofen Derivative through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions.

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most common drugs used to manage and treat pain and inflammation. In 2016, a new class of boron functionalized NSAIDs (bora-NSAIDs) was synthesized under mild conditions via the copper-catalyzed regioselective boracarboxylation of vinyl arenes using carbon dioxide (CO2 balloon) and a diboron reductant at room temperature. This original method was performed primarily in a glovebox or with a vacuum gas manifold (Schlenk line) under rigorous air-free and moisture-free conditions, which often led to irreproducible reaction outcomes due to trace impurities. The present protocol describes a simpler and more convenient benchtop method for synthesizing a representative bora-NSAID, bora-ibuprofen. A Suzuki-Miyaura cross-coupling reaction between 1-bromo-4-isobutylbenzene and vinylboronic acid pinacol ester produces 4-isobutylstyrene. The styrene is subsequently boracarboxylated regioselectively to provide bora-ibuprofen, an α-aryl-ß-boryl-propionic acid, with good yield on a multi-gram scale. This procedure allows for the broader utilization of copper-catalyzed boracarboxylation in synthetic laboratories, enabling further research on bora-NSAIDs and other unique boron-functionalized drug-like molecules.

Mercury isotopic evidence for the importance of particles as a source of mercury to marine organisms.

The origin of methylmercury in pelagic fish remains unclear, with many unanswered questions regarding the production and degradation of this neurotoxin in the water column. We used mercury (Hg) stable isotope ratios of marine particles and biota to elucidate the cycling of methylmercury prior to incorporation into the marine food web. The Hg isotopic composition of particles, zooplankton, and fish reveals preferential methylation of Hg within small (< 53 µm) marine particles in the upper 400 m of the North Pacific Ocean. Mass-dependent Hg isotope ratios (δ202Hg) recorded in small particles overlap with previously estimated δ202Hg values for methylmercury sources to Pacific and Atlantic Ocean food webs. Particulate compound specific isotope analysis of amino acids (CSIA-AA) yield δ15N values that indicate more-significant microbial decomposition in small particles compared to larger particles. CSIA-AA and Hg isotope data also suggest that large particles (> 53 µm) collected in the equatorial ocean are distinct from small particles and resemble fecal pellets. Additional evidence for Hg methylation within small particles is provided by a statistical mixing model of even mass-independent (Δ200Hg and Δ204Hg) isotope values, which demonstrates that Hg within near-surface marine organisms (0-150 m) originates from a combination of rainfall and marine particles. In contrast, in meso- and upper bathypelagic organisms (200-1,400 m), the majority of Hg originates from marine particles with little input from wet deposition. The occurrence of methylation within marine particles is supported further by a correlation between Δ200Hg and Δ199Hg values, demonstrating greater overlap in the Hg isotopic composition of marine organisms with marine particles than with total gaseous Hg or wet deposition.

Isotopic composition of the eastern gray whale epidermis indicates contribution of prey outside Arctic feeding grounds.

Eastern gray whales' distribution range and plasticity in feeding behavior complicates the understanding of critical life-history such as pregnancy and lactation. Our goal was to determine if females who experienced gestation, gave birth, and lactated their calves, assimilated a high proportion of benthic amphipods from the Bering Sea, which are considered the species' main prey. We used Bayesian stable isotope mixing models to estimate the probability of contribution of food items sampled along the species' distributional range, using isotopic data on amphipods from the Bering Sea, mysids from Vancouver Island, and amphipods and polychaetes from Ojo de Liebre Lagoon. We sampled epidermal tissue from lactating females (n = 25) and calves (n = 34) and analyzed their carbon and nitrogen isotopic composition. Model outcome indicated that benthic amphipods from the Bering Sea were not the primary food for the eastern gray whale. Each mother performed a different feeding strategy, and prey from Vancouver Island were generally as important as that from the Bering Sea. Moreover, model results indicate a constant use of Ojo de Liebre Lagoon as a feeding ground. Our results appear to agree with previous studies that report continuous feeding by females to satisfy certain physiological requirements (e.g., fatty acids omega-6) during migration and breeding time. Future investigations of the isotopic composition of all those prey items that could be assimilated by the eastern gray whale emerge as critical. Both historical and recent information, that would provide insights in the species feeding ecology under past and present environmental conditions, should be considered as equally important to establish conservation and management plans.

Benzannulation and Hydrocarboxylation Methods for the Synthesis of a Neopentylene-Fused Analogue of Ibuprofen.

Neopentylene ring fusions (ring-fused 4,4-dimethylcyclopentane polycycles) are found in many natural products, but they are largely absent from synthetic compound libraries and focused medicinal chemistry research. Here is reported a synthetic approach to one of the few non-natural product-based target compounds from medicinal chemistry that includes a neopentylene ring fusion: an analogue of ibuprofen referred to herein as "neoprofen". The approach features ring-opening fragmentation reactions of dimedone derivatives coupled with transition metal-catalyzed benzannulation and hydrocarboxylation methods.

Water column structure influences long-distance latitudinal migration patterns and habitat use of bumphead sunfish Mola alexandrini in the Pacific Ocean.

Satellite-tracking of adult bumphead sunfish, Mola alexandrini, revealed long-distance latitudinal migration patterns covering thousands of kilometers. Horizontal and vertical movements of four bumphead sunfish off Taiwan were recorded with pop-up satellite archival tags in 2019-2020. Two individuals moved northward and traveled to Okinawa Island and Kyushu, Japan and two moved southwards; crossing the equator, to Papua New Guinea and New Caledonia. During daytime, bumphead sunfish descended below the thermocline and ascended to mixed layer depths (MLD) during nighttime. The N-S migrants, however, demonstrated different habitat utilization patterns. Instead of using prevailing currents, the northward movements of sunfish cohorts exhibited extensive use of mesoscale eddies. Fish in anticyclonic eddies usually occupied deeper habitats whereas those in cyclonic eddies used near-surface habitats. On northward excursions, fish spent most of their time in regions with high dissolved oxygen concentrations. Southward movement patterns were associated with major currents and thermal stratification of the water column. In highly stratified regions, fish stayed below the thermocline and frequently ascended to MLD during daytime either to warm muscles or repay oxygen debts. These results for bumphead sunfish present important insights into different habitat use patterns and the ability to undergo long-distance migrations over varying spatial-temporal scales and features.

Isotope data from amino acids indicate Darwin's ground sloth was not an herbivore.

Fossil sloths are regarded as obligate herbivores for reasons including peculiarities of their craniodental morphology and that all living sloths feed exclusively on plants. We challenge this view based on isotopic analyses of nitrogen of specific amino acids, which show that Darwin's ground sloth Mylodon darwinii was an opportunistic omnivore. This direct evidence of omnivory in an ancient sloth requires reevaluation of the ecological structure of South American Cenozoic mammalian communities, as sloths represented a major component of these ecosystems across the past 34 Myr. Furthermore, by analyzing modern mammals with known diets, we provide a basis for reliable interpretation of nitrogen isotopes of amino acids of fossils. We argue that a widely used equation to determine trophic position is unnecessary, and that the relative isotopic values of the amino acids glutamate and phenylalanine alone permit reliable reconstructions of trophic positions of extant and extinct mammals.

Amino acid δ13C and δ15N analyses reveal distinct species-specific patterns of trophic plasticity in a marine symbiosis.

Compound-specific isotope analyses (CSIA) and multivariate "isotope fingerprinting" track biosynthetic sources and reveal trophic interactions in food webs. However, CSIA have not been widely applied in the study of marine symbioses. Here, we exposed a reef coral (Montipora capitata) in symbiosis with Symbiodiniaceae algae to experimental treatments (autotrophy, mixotrophy, heterotrophy) to test for trophic shifts and amino acid (AA) sources using paired bulk (δ13C, δ15N) and AA-CSIA (δ13CAA, δ15NAA). Treatments did not influence carbon or nitrogen trophic proxies, thereby not supporting nutritional plasticity. Instead, hosts and symbionts consistently overlapped in essential- and nonessential-δ13CAA (11 of 13 amino acids) and trophic- and source-δ15NAA values (9 of 13 amino acids). Host and symbiont trophic-δ15NAA values positively correlated with a plankton end-member, indicative of trophic connections and dietary sources for trophic-AA nitrogen. However, mass balance of AA-trophic positions (TPGlx-Phe) revealed heterotrophic influences to be highly variable (1-41% heterotrophy). Linear discriminant analysis using M. capitata mean-normalized essential-δ13CAA with previously published values (Pocillopora meandrina) showed similar nutrition isotope fingerprints (Symbiodiniaceae vs. plankton) but revealed species-specific trophic strategies. Montipora capitata and Symbiodiniaceae shared identical AA-fingerprints, whereas P. meandrina was assigned to either symbiont or plankton nutrition. Thus, M. capitata was 100% reliant on symbionts for essential-δ13CAA and demonstrated autotrophic fidelity and contrasts with trophic plasticity reported in P. meandrina. While M. capitata AA may originate from host and/or symbiont biosynthesis, AA carbon is Symbiodiniaceae-derived. Together, AA-CSIA/isotope fingerprinting advances the study of coral trophic plasticity and are powerful tools in the study of marine symbioses.

Abyssal deposit feeders are secondary consumers of detritus and rely on nutrition derived from microbial communities in their guts.

Trophic ecology of detrital-based food webs is still poorly understood. Abyssal plains depend entirely on detritus and are among the most understudied ecosystems, with deposit feeders dominating megafaunal communities. We used compound-specific stable isotope ratios of amino acids (CSIA-AA) to estimate the trophic position of three abundant species of deposit feeders collected from the abyssal plain of the Northeast Pacific (Station M; ~ 4000 m depth), and compared it to the trophic position of their gut contents and the surrounding sediments. Our results suggest that detritus forms the base of the food web and gut contents of deposit feeders have a trophic position consistent with primary consumers and are largely composed of a living biomass of heterotrophic prokaryotes. Subsequently, deposit feeders are a trophic level above their gut contents making them secondary consumers of detritus on the abyssal plain. Based on δ13C values of essential amino acids, we found that gut contents of deposit feeders are distinct from the surrounding surface detritus and form a unique food source, which was assimilated by the deposit feeders primarily in periods of low food supply. Overall, our results show that the guts of deposit feeders constitute hotspots of organic matter on the abyssal plain that occupy one trophic level above detritus, increasing the food-chain length in this detritus-based ecosystem.

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota.

Mercury isotopic compositions of amphipods and snailfish from deep-sea trenches reveal information on the sources and transformations of mercury in the deep oceans. Evidence for methyl-mercury subjected to photochemical degradation in the photic zone is provided by odd-mass independent isotope values (Δ199Hg) in amphipods from the Kermadec Trench, which average 1.57‰ (±0.14, n = 12, SD), and amphipods from the Mariana Trench, which average 1.49‰ (±0.28, n = 13). These values are close to the average value of 1.48‰ (±0.34, n = 10) for methyl-mercury in fish that feed at ∼500-m depth in the central Pacific Ocean. Evidence for variable contributions of mercury from rainfall is provided by even-mass independent isotope values (Δ200Hg) in amphipods that average 0.03‰ (±0.02, n = 12) for the Kermadec and 0.07‰ (±0.01, n = 13) for the Mariana Trench compared to the rainfall average of 0.13 (±0.05, n = 8) in the central Pacific. Mass-dependent isotope values (δ202Hg) are elevated in amphipods from the Kermadec Trench (0.91 ±0.22‰, n = 12) compared to the Mariana Trench (0.26 ±0.23‰, n = 13), suggesting a higher level of microbial demethylation of the methyl-mercury pool before incorporation into the base of the foodweb. Our study suggests that mercury in the marine foodweb at ∼500 m, which is predominantly anthropogenic, is transported to deep-sea trenches primarily in carrion, and then incorporated into hadal (6,000-11,000-m) food webs. Anthropogenic Hg added to the surface ocean is, therefore, expected to be rapidly transported to the deepest reaches of the oceans.

Tracing gestation and lactation in free ranging gray whales using the stable isotopic composition of epidermis layers.

The isotopic composition of baleen whales' epidermis structural layers can give information about dietary change over time. This study investigated if epidermis layers integrated isotopic values that record physiological changes from gestation to lactation. Epidermis tissues (n = 43) were collected from free ranging lactating female gray whale and calves during the beginning of three breeding seasons. Modelling of δ13C and δ15N values show intra- and inter-individual differences based on epidermal layers, age class and year of sampling. The isotopic composition of mother-calf pairs is correlated, and the estimates of the maximum mother-to-calf isotopic difference was ~1.4‰ for δ13C and between 1 and 1.5‰ for δ15N values. Change in δ15N values among epidermal layers in calves was associated with the transition from fetus to consumption of maternal milk. It is here proposed when lactation influences calf epidermis, δ15N values decrease consistently from the outermost to the innermost layer. However, if a calf was born only few days before collection, epidermis integrates more variable δ15N patterns because gestation still affects the isotopic composition of the layers. The possibility of calculating mother-to-calf nitrogen isotope fractionation, and the regularity of changes between calf layer δ15N values, allowed results of an isotopic clock model to predict the age of each calf when sampled with its mother. This model has the potential to be a straightforward method to estimate the beginning of lactation, therefore calf birth date when direct observations are not feasible. The non-lethal remote collection of epidermis appears to be an effective tool for the study of the physiology of reproduction of baleen whales. The parallel study of the three epidermal structural layers highlighted the importance of considering the unique mother-calf pair physiological status at the time of sampling time when stable isotope results are interpreted.

Divergent symbiont communities determine the physiology and nutrition of a reef coral across a light-availability gradient.

Reef corals are mixotrophic organisms relying on symbiont-derived photoautotrophy and water column heterotrophy. Coral endosymbionts (Family: Symbiodiniaceae), while typically considered mutualists, display a range of species-specific and environmentally mediated opportunism in their interactions with coral hosts, potentially requiring corals to rely more on heterotrophy to avoid declines in performance. To test the influence of symbiont communities on coral physiology (tissue biomass, symbiont density, photopigmentation) and nutrition (δ13C, δ15N), we sampled Montipora capitata colonies dominated by a specialist symbiont Cladocopium spp. or a putative opportunist Durusdinium glynnii (hereafter, C- or D-colonies) from Kane'ohe Bay, Hawai'i, across gradients in photosynthetically active radiation (PAR) during summer and winter. We report for the first time that isotope values of reef corals are influenced by Symbiodiniaceae communities, indicative of different autotrophic capacities among symbiont species. D-colonies had on average 56% higher symbiont densities, but lower photopigments per symbiont cell and consistently lower δ13C values in host and symbiont tissues; this pattern in isotope values is consistent with lower symbiont carbon assimilation and translocation to the host. Neither C- nor D-colonies showed signs of greater heterotrophy or nutritional plasticity; instead changes in δ13C values were driven by PAR availability and photoacclimation attributes that differed between symbiont communities. Together, these results reveal Symbiodiniaceae functional diversity produces distinct holobionts with different capacities for autotrophic nutrition, and energy tradeoffs from associating with opportunist symbionts are not met with increased heterotrophy.

Trophic Ecology of the Tropical Pacific Sponge Mycale grandis Inferred from Amino Acid Compound-Specific Isotopic Analyses.

Many sponges host abundant and active microbial communities that may play a role in the uptake of dissolved organic matter (DOM) by the sponge holobiont, although the mechanism of DOM uptake and metabolism is uncertain. Bulk and compound-specific isotopic analysis of whole sponge, isolated sponge cells, and isolated symbiotic microbial cells of the shallow water tropical Pacific sponge Mycale grandis were used to elucidate the trophic relationships between the host sponge and its associated microbial community. δ15N and δ13C values of amino acids in M. grandis isolated sponge cells are not different from those of its bacterial symbionts. Consequently, there is no difference in trophic position of the sponge and its symbiotic microbes indicating that M. grandis sponge cell isolates do not display amino acid isotopic characteristics typical of metazoan feeding. Furthermore, both the isolated microbial and sponge cell fractions were characterized by a similarly high ΣV value-a measure of bacterial-re-synthesis of organic matter calculated from the sum of variance among individual δ15N values of trophic amino acids. These high ΣV values observed in the sponge suggest that M. grandis is not reliant on translocated photosynthate from photosymbionts or feeding on water column picoplankton, but obtains nutrition through the uptake of amino acids of bacterial origin. Our results suggest that direct assimilation of bacterially synthesized amino acids from its symbionts, either in a manner similar to translocation observed in the coral holobiont or through phagotrophic feeding, is an important if not primary pathway of amino acid acquisition for M. grandis.

Differences in the trophic ecology of micronekton driven by diel vertical migration.

Many species of micronekton perform diel vertical migrations (DVMs), which ultimately contributes to carbon export to the deep sea. However, not all micronekton species perform DVM, and the nonmigrators, which are often understudied, have different energetic requirements that might be reflected in their trophic ecology. We analyze bulk tissue and whole animal stable nitrogen isotopic compositions (δ 15N values) of micronekton species collected seasonally between 0 and 1250 m depth to explore differences in the trophic ecology of vertically migrating and nonmigrating micronekton in the central North Pacific. Nonmigrating species exhibit depth-related increases in δ 15N values mirroring their main prey, zooplankton. Higher variance in δ 15N values of bathypelagic species points to the increasing reliance of deeper dwelling micronekton on microbially reworked, very small suspended particles. Migrators have higher δ 15N values than nonmigrators inhabiting the epipelagic zone, suggesting the consumption of material during the day at depth, not only at night when they migrate closer to the surface. Migrating species also appear to eat larger prey and exhibit a higher range of variation in δ 15N values seasonally than nonmigrators, likely because of their higher energy needs. The dependence on material at depth enriched in 15N relative to surface particles is higher in migratory fish that ascend only to the lower epipelagic zone. Our results confirm that stark differences in the food habits and dietary sources of micronekton species are driven by vertical migrations.

Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery.

Ocean warming and the increased prevalence of coral bleaching events threaten coral reefs. However, the biology of corals during and following bleaching events under field conditions is poorly understood. We examined bleaching and postbleaching recovery in Montipora capitata and Porites compressa corals that either bleached or did not bleach during a 2014 bleaching event at three reef locations in Kane'ohe Bay, O'ahu, Hawai'i. We measured changes in chlorophylls, tissue biomass, and nutritional plasticity using stable isotopes (δ 13C, δ 15N). Coral traits showed significant variation among periods, sites, bleaching conditions, and their interactions. Bleached colonies of both species had lower chlorophyll and total biomass, and while M. capitata chlorophyll and biomass recovered 3 months later, P. compressa chlorophyll recovery was location dependent and total biomass of previously bleached colonies remained low. Biomass energy reserves were not affected by bleaching, instead M. capitata proteins and P. compressa biomass energy and lipids declined over time and P. compressa lipids were site specific during bleaching recovery. Stable isotope analyses did not indicate increased heterotrophic nutrition in bleached colonies of either species, during or after thermal stress. Instead, mass balance calculations revealed that variations in δ 13C values reflect biomass compositional change (i.e., protein : lipid : carbohydrate ratios). Observed δ 15N values reflected spatiotemporal variability in nitrogen sources in both species and bleaching effects on symbiont nitrogen demand in P. compressa. These results highlight the dynamic responses of corals to natural bleaching and recovery and identify the need to consider the influence of biomass composition in the interpretation of isotopic values in corals.

Rapid nickel(ii)-promoted cysteine S-arylation with arylboronic acids.

S-Arylation of cysteine residues is an increasingly powerful tool for site-specific modification of proteins, providing novel structure and electronic perturbation. The present work demonstrates an operationally-simple cysteine arylation reaction 2-nitro-substituted arylboronic acids, promoted by a simple nickel(ii) salt. The process exhibits strikingly fast reaction rates under physiological conditions in purely aqueous media with excellent selectivity toward cysteine residues. Cysteine arylation of natural proteins and peptides allows attachment of useful reactive handles for stapling, imaging, or further conjugation.

Effects of chemical preservation on bulk and amino acid isotope ratios of zooplankton, fish, and squid tissues.

RATIONALE: It is imperative to understand how chemical preservation alters tissue isotopic compositions before using historical samples in ecological studies. Specifically, although compound-specific isotope analysis of amino acids (CSIA-AA) is becoming a widely used tool, there is little information on how preservation techniques affect amino acid δ15 N values. METHODS: We evaluated the effects of chemical preservatives on bulk tissue δ13 C and δ15 N and amino acid δ15 N values, measured by gas chromatography/isotope ratio mass spectrometry (GC/IRMS), of (a) tuna (Thunnus albacares) and squid (Dosidicus gigas) muscle tissues that were fixed in formaldehyde and stored in ethanol for 2 years and (b) two copepod species, Calanus pacificus and Eucalanus californicus, which were preserved in formaldehyde for 24-25 years. RESULTS: Tissues in formaldehyde-ethanol had higher bulk δ15 N values (+1.4, D. gigas; +1.6‰, T. albacares), higher δ13 C values for D. gigas (+0.5‰), and lower δ13 C values for T. albacares (-0.8‰) than frozen samples. The bulk δ15 N values from copepods were not different those from frozen samples, although the δ13 C values from both species were lower (-1.0‰ for E. californicus and -2.2‰ for C. pacificus) than those from frozen samples. The mean amino acid δ15 N values from chemically preserved tissues were largely within 1‰ of those of frozen tissues, but the phenylalanine δ15 N values were altered to a larger extent (range: 0.5-4.5‰). CONCLUSIONS: The effects of preservation on bulk δ13 C values were variable, where the direction and magnitude of change varied among taxa. The changes in bulk δ15 N values associated with chemical preservation were mostly minimal, suggesting that storage in formaldehyde or ethanol will not affect the interpretation of δ15 N values used in ecological studies. The preservation effects on amino acid δ15 N values were also mostly minimal, mirroring bulk δ15 N trends, which is promising for future CSIA-AA studies of archived specimens. However, there were substantial differences in phenylalanine and valine δ15 N values, which we speculate resulted from interference in the chromatographic resolution of unknown compounds rather than alteration of tissue isotopic composition due to chemical preservation.

Long-term trends in the foraging ecology and habitat use of an endangered species: an isotopic perspective.

Evaluating long-term drivers of foraging ecology and population productivity is crucial for providing ecological baselines and forecasting species responses to future environmental conditions. Here, we examine the trophic ecology and habitat use of North Atlantic leatherback turtles (St. Croix nesting population) and investigate the effects of large-scale oceanographic conditions on leatherback foraging dynamics. We used bulk and compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) to estimate leatherback trophic position (TP) over an 18-year period, compare these estimates with TP estimates from a Pacific leatherback population, and elucidate the pre-nesting habitat use patterns of leatherbacks. Our secondary objective was to use oceanographic indices and nesting information from St. Croix leatherbacks to evaluate relationships between trophic ecology, nesting parameters, and regional environmental conditions measured by the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation. We found no change in leatherback TP over time and no difference in TP between Atlantic and Pacific leatherbacks, indicating that differences in trophic ecology between populations are an unlikely driver of the population dichotomy between Pacific and Atlantic leatherbacks. Isotope data suggested that St. Croix leatherbacks inhabit multiple oceanic regions prior to nesting, although, like their conspecifics in the Pacific, individuals exhibit fidelity to specific foraging regions. Leatherback nesting parameters were weakly related to the NAO, which may suggest that positive NAO phases benefit St. Croix leatherbacks, potentially through increases in resource availability in their foraging areas. Our data contribute to the understanding of leatherback turtle ecology and potential mechanistic drivers of the dichotomy between populations of this protected species.

Access to a pair of ambiphilic phosphine-borane regioisomers by rhodium-catalyzed hydroboration.

Lewis basic substrates, such as vinylphosphines and enamines, can be problematic for transition-metal catalysed hydrofunctionalization reactions due to their propensity to ligate and deactivate transition-metal catalysts as well as form direct Lewis adducts with reaction partners. While exploring rhodium-catalyzed hydroboration of diphenylvinylphosphine with pinacolborane, we found that a high degree of regiocontrol could be achieved without the need to diminish the Lewis basicity of the phosphine by oxidation or prior-protection. At slightly elevated temperature, a high yield of the previously unreported branched regioisomer, 1-pinacolatoborono-1-diphenylphosphinoethane, was achieved with regioselectivity greater than 10 : 1 using [Rh(COD)Cl]2 as the catalyst and AgOTf as a catalytic additive. Inversion of regioselectivity occurred at low temperature and high yield of the linear regioisomer was observed. Subsequent functionalization of the new branched phosphine-boronic ester and its coordination to rhodium were also investigated.

Assessing seasonal changes in animal diets with stable-isotope analysis of amino acids: a migratory boreal songbird switches diet over its annual cycle.

Tools to study seasonal changes in animal diets are needed to address a wide range of ecological questions. This is especially true of migratory animals that experience distinct environments where diets may be substantially different. However, tracking diets of individuals that move vast distances has proven difficult. Compound-specific isotope analysis has emerged as a valuable tool to study diets but has been little used to study dietary changes of migratory animals. Using this technique, we quantify seasonal variation in the annual diet of a migratory songbird (gray-cheeked thrush, Catharus minimus) and test the hypothesis that migrants change their diet in response to the energetic requirements of different periods of the annual cycle. By measuring δ13C and δ15N values of amino acids from feathers grown on the breeding grounds, blood formed during migration and claw grown on the wintering grounds, we found that migration is associated with greater consumption of fruit, compared to the breeding or wintering periods. This was confirmed by the lower trophic position of blood compared to feather and claw, by a decrease in the δ15N value of the source amino acid phenylalanine in blood as a function of days of stopover, and by the positive correlation between δ15N and δ13C values of phenylalanine in blood, and not in feather or claw. This study illustrates how isotopic analysis of amino acids can contribute to understand food webs, seasonal dietary changes and metabolic routing of nutrients in migratory animals.

Light and temperature control the seasonal distribution of thaumarchaeota in the South Atlantic bight.

Mid-summer peaks in the abundance of Thaumarchaeota and nitrite concentration observed on the Georgia, USA, coast could result from in situ activity or advection of populations from another source. We collected data on the distribution of Thaumarchaeota, ammonia-oxidizing betaproteobacteria (AOB), Nitrospina, environmental variables and rates of ammonia oxidation during six cruises in the South Atlantic Bight (SAB) from April to November 2014. These data were used to examine seasonality of nitrification in offshore waters and to test the hypothesis that the bloom was localized to inshore waters. The abundance of Thaumarchaeota marker genes (16S rRNA and amoA) increased at inshore and nearshore stations starting in July and peaked in August at >107 copies L-1. The bloom did not extend onto the mid-shelf, where Thaumarchaeota genes ranged from 103 to 105 copies L-1. Ammonia oxidation rates (AO) were highest at inshore stations during summer (to 840 nmol L-1 d-1) and were always at the limit of detection at mid-shelf stations. Nitrite concentrations were correlated with AO (R = 0.94) and were never elevated at mid-shelf stations. Gene sequences from samples collected at mid-shelf stations generated using Archaea 16S rRNA primers were dominated by Euryarchaeota; sequences from inshore and nearshore stations were dominated by Thaumarchaeota. Thaumarchaeota were also abundant at depth at the shelf-break; however, this population was phylogenetically distinct from the inshore/nearshore population. Our analysis shows that the bloom is confined to inshore waters during summer and suggests that Thaumarchaeota distributions in the SAB are controlled primarily by photoinhibition and secondarily by water temperature.