Controls on zooplankton assemblages in the northeastern Chukchi Sea

Thesis (Ph.D.) University of Alaska Fairbanks, 2016The Chukchi Sea is a broad and shallow marginal sea of the western Arctic Ocean that lies between the Bering Sea and the deeper Amerasian basin. It plays a pivotal role as the only gateway for transporting heat, carbon, nutrients, and plankton from the North Pacific into the Arctic Ocean. I examined the seasonal and inter-annual variability of the zooplankton communities in the northeastern region of the Chukchi Sea as part of a high-resolution multidisciplinary ecosystem study. Specifically, I examined how the physical onset of each open water season influenced the composition, abundance, and biomass of zooplankton assemblages from the 2008 to 2010 field seasons. Copepods in the genus Pseudocalanus are key members of the Chukchi community, and may be undergoing species-level biogeographic shift in response to climate change. I determined the degree of gene flow and population connectivity in the Chukchi Sea through comparative phylogeographic analysis of the Pseudocalanus species complex to the northern Gulf of Alaska and Beaufort Sea. I then investigated the extent to which biogeochemical factors influence these zooplankton assemblages by relating a portion of the seasonal production to concurrent changes in herbivorous mesozooplankton biomass during 2010 and 2011. This work demonstrates just how complex and variable marine ecosystems of the western Arctic are, where multidisciplinary and analytical approaches will become essential in detecting change, especially with the rate of present-day climate perturbations.Chapter 1: Seasonal and interannual variation in the planktonic communities of the northeastern Chukchi Sea during the summer and early fall -- Chapter 2: Phylogeography and connectivity of the Pseudocalanus (Copepoda: Calanoida) species complex in the eastern North Pacific Ocean and the Pacific Arctic Region -- Chapter 3: Community production in the northeastern Chukchi Sea and its relationship to phytoplankton and mesozooplankton biomass, 2010-2011 -- General Conclusions -- References

Electrochemical microsensors for cutaneous surface analysis: Application to the determination of pH and the antioxidant properties of stratum corneum

Potentiometry and cyclic voltammetry were proposed as simple, reliable and non invasive methods for the simultaneous determination of pH and antioxidant properties of skin. Experiments were performed with microelectrodes just deposited on skin surface without any gel or water added. pH was measured by means of the zero current potential of a tungsten W/WO3 sensor. A nerstian response was recorded in pH range 4 to 6 corresponding to the normal skin pH values. The global antioxidant capacity was deduced from the anodic charge passed during the plotting of cyclic voltammograms on platinum or gold microelectrodes. Comparing the half wave or peak potentials of these curves with those recorded for experiments performed in aqueous solution, the main hydrophilic antioxidants species were detected, i.e. ascorbic acid, uric acid and glutathione. This relatively easy-to-use analytical method made it possible to follow in real time the efficiency of topic treatment as well as to study the influence of oxidative stres

Elaboration of integrated microelectrodes for the detection of antioxidant species

(Pt–Pt–Ag/AgCl) and (Au–Pt–Ag/AgCl) electrochemical microcells (ElecCell) were developed for the detection of redox species by cyclic voltammetry. A special emphasis was placed on the SU-8 waferlevel passivation process in order to optimize the electrochemical properties of the different “thin film” metallic layers, i.e. gold or platinum for the working electrode, platinum for the counter electrode and silver/silver chloride for the reference electrode. (Au–Pt–Ag/AgCl) microcells were applied for the detection of antioxidant species such as ascorbic and uric acids in phosphate buffer solution, evidencing high sensitivity but low selectivity. Works were extended to skin analysis, demonstrating that a good electrical contact with the skin hydrolipidic film allowed the effective evaluation of the skin global antioxidant capacity

Exploration of the global antioxidant capacity of the stratum corneum by cyclic voltammetry

Cyclic voltammetry is proposed as a new method for evaluating the antioxidant capacity of skin based on the reducing properties of low molecular weight antioxidants (LMWA). Experiments were performed simply by recording the anodic current at 0.9 V/SCE of a platinum microelectrode placed directly on the epidermis surface without any gel or water. This method ensured a direct, rapid (less than 1 min), reliable (accuracy 12%) and non-invasive measurement of the global antioxidant capacity of the stratum corneum with a high spatiotemporal resolution. At the same time, the pH of the skin surface was determined by recording the cathodic current at 0 V/SCE. Based on an exploratory study involving nine volunteer subjects, the evolution of the amperometric response of the microelectrode with time revealed a periodic modification of the redox properties

New insights on the molecular recognition of imidacloprid with Aplysia californica AChBP: a computational study

The binding of imidacloprid (IMI), the forerunner of neonicotinoid insecticides, with the acetylcholine binding protein (AChBP) from Aplysia californica, the established model for the extracellular domain of insects nicotinic acetylcholine receptors, has been studied with a two-layer ONIOM partition approach (M06-2X/6-311G(d):PM6). Our calculations allow delineating the contributions of the key residues of AChBP for IMI binding. In particular, the importance of Trp147 and Cys190-191, through weak CH...pi interactions and both van der Waals and hydrogen-bond (H-bond) interactions, respectively, are highlighted. Furthermore, H-bonds between hydroxyl groups of both Ser189 and Tyr55 and the IMI nitro group are pointed out. The participation of Ile118, whose main chain NH and carbonyl group are hydrogen-bonded with the IMI pyridinic nitrogen through a water molecule, is characterized. Our simulations also indicate the presence of a significant contribution of this residue through van der Waals interactions. The various trends obtained by the calculations of the pairwise interaction energies are confirmed through a complementary noncovalent interaction (NCI) analysis of selected IMI-AChBP amino acid pairs. Indeed, the contribution of a halogen-bond interaction between IMI and AChBP, recently proposed in the literature, is corroborated by our NCI analysis

Similar Comparative Low and High Doses of Deltamethrin and Acetamiprid Differently Impair the Retrieval of the Proboscis Extension Reflex in the Forager Honey Bee (Apis mellifera)

In the present study, the effects of low (10 ng/bee) and high (100 ng/bee) doses of acetamiprid and deltamethrin insecticides on multi-trial learning and retrieval were evaluated in the honey bee Apis mellifera. After oral application, acetamiprid and deltamethrin at the concentrations used were not able to impair learning sessions. When the retention tests were performed 1 h, 6 h, and 24 h after learning, we found a significant difference between bees after learning sessions when drugs were applied 24 h before learning. Deltamethrin-treated bees were found to be more sensitive at 10 ng/bee and 100 ng/bee doses compared to acetamiprid-treated bees, only with amounts of 100 ng/bee and at 6 h and 24 h delays. When insecticides were applied during learning sessions, none of the tested insecticides was able to impair learning performance at 10 ng/bee or 100 ng/bee but retention performance was altered 24 h after learning sessions. Acetamiprid was the only one to impair retrieval at 10 ng/bee, whereas at 100 ng/bee an impairment of retrieval was found with both insecticides. The present results therefore suggest that acetamiprid and deltamethrin are able to impair retrieval performance in the honey bee Apis mellifera

Pretreatment of the cockroach cercal afferent/giant interneuron synapses with nicotinoids and neonicotinoids differently affects acetylcholine and nicotine-induced ganglionic depolarizations

We have recently demonstrated that neonicotinoid insecticides were able to act as agonists of postsynaptic nicotinic acetylcholine receptors (nAChRs) expressed at the synapse between the cercal nerve XI and the giant interneurons, in the sixth abdominal ganglion. In this work, we demonstrated that nicotinoids such as nornicotine acted as an agonist of nicotinic acetylcholine receptors expressed at cercal afferent/giant interneurons while cotinine was a poor agonist. Indeed, nornicotine induced a ganglionic depolarization which was blocked by the nicotinic antagonist mecamylamine. In addition, we found that pretreatment of the sixth abdominal ganglion with 1 and 10 muM nornicotine and cotinine had no significant effect on acetylcholine and nicotine-induced depolarization. But pretreatment with 1 and 10 muM acetamiprid and imidacloprid had a strong effect. 1 and 10 muM acetamiprid completely blocked acetylcholine-induced depolarization, whereas imidacloprid had a partial effect. The present work therefore suggests, in agreement with previous studies, that nornicotine and cotinine bind to distinct cockroach postsynaptic nAChRs, whereas acetamiprid and imidacloprid have competitive effects with acetylcholine and nicotine on ganglionic depolarization

Imidacloprid and thiacloprid neonicotinoids bind more favourably to cockroach than to honeybee alpha6 nicotinic acetylcholine receptor: insights from computational studies

The binding interactions of two neonicotinoids, imidacloprid (IMI) and thiacloprid (THI) with the extracellular domains of cockroach and honeybee alpha6 nicotinic acetylcholine receptor (nAChR) subunits in an homomeric receptor have been studied through docking and molecular dynamics (MD) simulations. The binding mode predicted for the two neonicotinoids is validated through the good agreement observed between the theoretical results with the crystal structures of the corresponding complexes with Ac-AChBP, the recognized structural surrogate for insects nAChR extracellular ligand binding domain. The binding site of the two insect alpha6 receptors differs by only one residue of loop D, a serine residue (Ser83) in cockroach being replaced by a lysine residue (Lys108) in honeybee. The docking results show very close interactions for the two neonicotinoids with both alpha6 nAChR models, in correspondence to the trends observed in the experimental neonicotinoid-Ac-AChBP complexes. However, the docking parameters (scores and energies) are not significantly different between the two insect alpha6 nAChRs to draw clear conclusions. The MD results bring distinct trends. The analysis of the average interaction energies in the two insects alpha6 nAChRs shows indeed better affinity of neonicotinoids bound to alpha6 cockroach compared to honeybee nAChR. This preference is explained by tighter contacts with aromatic residues (Trp and Tyr) of the binding pocket. Interestingly, the non-conserved residue Lys108 of loop D of alpha6 honeybee nAChR interacts through van der Waals contacts with neonicotinoids, which appear more favourable than the direct or water mediated hydrogen-bond interaction between the OH group of Ser83 of alpha6 cockroach nAChR and the electronegative terminal group of the two neonicotinoids (nitro in IMI and cyano in THI). Finally, in both insects nAChRs, THI is consistently found to bind more favourably than IMI

Alchemy Series

As medieval alchemists did not distinguish between psyche and matter, so too the artist, the images, and the materials of art are partners in the process of revealing. The artist shares her process of working with the archetypal images presented here

Eliciting a predatory response in the eastern corn snake (Pantherophis guttatus) using live and inanimate sensory stimuli: implications for managing invasive populations

North America's Eastern corn snake (Pantherophis guttatus) has been introduced to several islands throughout the Caribbean and Australasia where it poses a significant threat to native wildlife. Invasive snake control programs often involve trapping with live bait, a practice that, as well as being costly and labour intensive, raises welfare and ethical concerns. This study assessed corn snake response to live and inanimate sensory stimuli in an attempt to inform possible future trapping of the species and the development of alternative trap lures. We exposed nine individuals to sensory cues in the form of odour, visual, vibration and combined stimuli and measured the response (rate of tongue-flick [RTF]). RTF was significantly higher in odour and combined cues treatments, and there was no significant difference in RTF between live and inanimate cues during odour treatments. Our findings suggest chemical cues are of primary importance in initiating predation and that an inanimate odour stimulus, absent of simultaneous visual and vibratory cues, is a potential low-cost alternative trap lure for the control of invasive corn snake populations