@article{xie_buchwalter_2011, title={Cadmium exposure route affects antioxidant responses in the mayfly Centroptilum triangulifer}, volume={105}, ISSN={["1879-1514"]}, DOI={10.1016/j.aquatox.2011.06.009}, abstractNote={Aquatic organisms accumulate metals directly from water and from their diets. Exposure to metals is known to generate oxidative stress in living organisms and this stress may be ameliorated via activation of antioxidant enzymes and non-enzymatic antioxidants. To determine if antioxidant physiology is dependent on Cd exposure route in the mayfly Centroptilum triangulifer, we exposed larvae to environmentally relevant concentrations of Cd from isolated dissolved or dietary exposure routes to achieve comparable tissue concentrations. Dissolved Cd had no effect on the antioxidant enzymes examined. However, dietary Cd significantly suppressed catalase and superoxide dismutase activities, and decreased concentrations of the reduced (active) form of glutathione in C. triangulifer larvae. These findings suggest that dietary Cd is potentially more toxic than aqueously derived Cd in this mayfly. We further examined the effect of dietary Cd tissue loading rates on antioxidant enzyme suppression and found that absolute tissue load appeared more important than loading rate. These results may help explain why insects are routinely unresponsive to dissolved metal exposures in the laboratory, yet highly responsive to metal pollution in nature.}, number={3-4}, journal={AQUATIC TOXICOLOGY}, author={Xie, Lingtian and Buchwalter, David B.}, year={2011}, month={Oct}, pages={199–205} }
 @article{klerks_xie_levinton_2011, title={Quantitative genetics approaches to study evolutionary processes in ecotoxicology; a perspective from research on the evolution of resistance}, volume={20}, number={3}, journal={Ecotoxicology}, author={Klerks, P. L. and Xie, L. T. and Levinton, J. S.}, year={2011}, pages={513–523} }
 @article{xie_funk_buchwalter_2010, title={Trophic transfer of Cd from natural periphyton to the grazing mayfly Centroptilum triangulifer in a life cycle test}, volume={158}, ISSN={["1873-6424"]}, DOI={10.1016/j.envpol.2009.07.010}, abstractNote={In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 μg L−1 for 6–7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly – approximately 1315 (±442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 ± 1.55) than from periphyton grown in Jan 2009 (0.85 ± 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers.}, number={1}, journal={ENVIRONMENTAL POLLUTION}, author={Xie, Lingtian and Funk, David H. and Buchwalter, David B.}, year={2010}, month={Jan}, pages={272–277} }
 @article{xie_flippin_deighton_funk_dickey_buchwalter_2009, title={Mercury(II) Bioaccumulation and Antioxidant Physiology in Four Aquatic Insects}, volume={43}, ISSN={["1520-5851"]}, DOI={10.1021/es802323r}, abstractNote={We examined Hg(II) bioaccumulation and compartmentalization patterns in conjunction with antioxidant responses in four aquatic insect species: two caddisflies (Chimarra sp. and Hydropsyche betteni) and two mayflies (Maccaffertium modestum and Isonychia sp). Total antioxidant capabilities differed among unexposed larvae, with both caddisfly species exhibiting elevated antioxidant activities relative to the mayflies. We were able to account for these differences by examining the constitutive activities of catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), and superoxide dismutase (SOD), in the four species. We also examined levels of reduced and oxidized glutathione and cysteine in the insects. Glutathione peroxidase and SOD were the most responsive to Hg exposure, with GPx catalytic activity increasing between 50 and 310%. Superoxide dismutase activity decreased between 35 and 50%. This SOD suppression was shown to be dose-dependent in both caddisflies, butthe strength of this suppression did not appear to be related to rates of uptake. Surprisingly, little Hg (<10%) was found in the heat-stable cytosolic protein subcellular compartment in each of the four species, suggesting that Hg was not well detoxified. By combining bioaccumulation studies with other physiological measures, we can begin to better understand the consequences of trace metal pollutants in nature.}, number={3}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Xie, Lingtian and Flippin, Jennifer L. and Deighton, Nigel and Funk, David H. and Dickey, David A. and Buchwalter, David B.}, year={2009}, month={Feb}, pages={934–940} }
 @article{buchwalter_cain_martin_xie_luoma_garland_2008, title={Aquatic insect ecophysiological traits reveal phylogenetically based differences in dissolved cadmium susceptibility}, volume={105}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.0801686105}, abstractNote={We used a phylogenetically based comparative approach to evaluate the potential for physiological studies to reveal patterns of diversity in traits related to susceptibility to an environmental stressor, the trace metal cadmium (Cd). Physiological traits related to Cd bioaccumulation, compartmentalization, and ultimately susceptibility were measured in 21 aquatic insect species representing the orders Ephemeroptera, Plecoptera, and Trichoptera. We mapped these experimentally derived physiological traits onto a phylogeny and quantified the tendency for related species to be similar (phylogenetic signal). All traits related to Cd bioaccumulation and susceptibility exhibited statistically significant phylogenetic signal, although the signal strength varied among traits. Conventional and phylogenetically based regression models were compared, revealing great variability within orders but consistent, strong differences among insect families. Uptake and elimination rate constants were positively correlated among species, but only when effects of body size and phylogeny were incorporated in the analysis. Together, uptake and elimination rates predicted dramatic Cd bioaccumulation differences among species that agreed with field-based measurements. We discovered a potential tradeoff between the ability to eliminate Cd and the ability to detoxify it across species, particularly mayflies. The best-fit regression models were driven by phylogenetic parameters (especially differences among families) rather than functional traits, suggesting that it may eventually be possible to predict a taxon's physiological performance based on its phylogenetic position, provided adequate physiological information is available for close relatives. There appears to be great potential for evolutionary physiological approaches to augment our understanding of insect responses to environmental stressors in nature.}, number={24}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Buchwalter, David B. and Cain, Daniel J. and Martin, Caitrin A. and Xie, Lingtian and Luoma, Samuel N. and Garland, Theodore, Jr.}, year={2008}, month={Jun}, pages={8321–8326} }
 @article{xie_lambert_martin_cain_luoma_buchwalter_2008, title={Cadmium biodynamics in the oligochaete Lumbriculus variegatus and its implications for trophic transfer}, volume={86}, ISSN={["0166-445X"]}, DOI={10.1016/j.aquatox.2007.11.008}, abstractNote={It has become increasingly apparent that diet can be a major source of trace metal bioaccumulation in aquatic organisms. In this study, we examined cadmium uptake, efflux, and subcellular compartmentalization dynamics in the freshwater oligochaete Lumbriculus variegatus. L. variegatus is an important component of freshwater food webs in Europe and North America and is potentially useful as a standard food source for laboratory-based trophic transfer studies. Cadmium accumulation and depuration were each followed for 10 days. Rate constants of uptake (ku) and efflux (ke) were estimated and subcellular Cd compartmentalization was followed over the course of uptake and efflux. The partitioning of Cd into operationally-defined subcellular compartments was relatively consistent throughout the 20-day experiment, with the majority of Cd accumulating in the cytosol. No major changes in Cd compartmentalization were observed over uptake or depuration, but there appeared to be some exchange between heat-stable and heat-labile cytosolic protein fractions. Cadmium accumulation from solution was strongly affected by ambient calcium concentrations, suggesting competition between Cd and Ca for uptake sites. Finally, we demonstrate the ability to manipulate the whole body calcium content of L. variegatus as a potential tool for examining calcium influences on dietary Cd dynamics. The potential for this species to be an important conduit of Cd to higher trophic levels is discussed, along with its potential as a standardized food source in metal trophic transfer studies.}, number={2}, journal={AQUATIC TOXICOLOGY}, author={Xie, Lingtian and Lambert, Daniel and Martin, Caitrin and Cain, Daniel J. and Luoma, Samuel N. and Buchwalter, David}, year={2008}, month={Jan}, pages={265–271} }