@article{cochran_funk_buchwalter_2023, title={Physiological and life history responses in a mayfly (Callibaetis floridanus) inhabiting ponds with saltwater intrusion}, volume={11}, ISSN={["2296-701X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85153383683&partnerID=MN8TOARS}, DOI={10.3389/fevo.2023.1135924}, abstractNote={Freshwater salinity varies in natural systems and plays a role in species distribution. Anthropogenic alterations to freshwater salinity regimes include sea level rise and subsequent intrusion of saline waters to inland habitats. While mayflies are generalized to be sensitive to increasing salinity, we still know remarkably little about the physiological processes (and their plasticity) that determine the performance of species in a changing world. Here, we explored life-history outcomes and physiological plasticity in a population of Callibaetis floridanus (Ephemeroptera: Baetidae) from a coastal pond that routinely experiences saltwater intrusion. We reared naiads from egg hatch to adulthood across a gradient of increasing salinities (113, 5,020, 9,921 μS/cm). Radiotracer flux studies (22Na, 35SO4, and 45Ca) were conducted in naiads reared at each salinity, revealing a positive association between ionic concentration and uptake rates. However, the influence of rearing history on ionic influx rates was apparent when naiads were transferred from their respective rearing water to the other experimental conditions. For example, we observed that naiads reared in the low salinity treatment (113 μS/cm) had 10.8-fold higher Na uptake rates than naiads reared at 9,921 μS/cm and transferred to 113 μS/cm. Additionally, naiads acclimated to the higher salinity water exhibited reduced uptake in ion-rich water relative to those reared in more dilute conditions (e.g., in 9,921 μS/cm water, 113 and 5,020 μS/cm acclimated naiads had 1.5- and 1.1-fold higher Na uptake rates than 9,921 μS/cm acclimated naiads, respectively). We found no significant changes in survival (80 ± 4.4%, mean ± s.e.m.) or naiad development time (24 ± 0.3 days, mean ± s.e.m.) across these treatments but did observe a 27% decrease in subimago female body weight in the most dilute condition. This reduction in female weight was associated with higher oxygen consumption rates in naiads relative to the other rearing conditions. Collectively, these data suggests that saline adapted C. floridanus may be more energetically challenged in dilute conditions, which differs from previous observations in other mayfly species.}, journal={FRONTIERS IN ECOLOGY AND EVOLUTION}, author={Cochran, Jamie K. and Funk, David H. and Buchwalter, David B.}, year={2023}, month={Mar} }
 @article{cochran_banks_buchwalter_2023, title={Respirometry reveals major lineage-based differences in the energetics of osmoregulation in aquatic invertebrates}, volume={226}, ISSN={["1477-9145"]}, url={https://doi.org/10.1242/jeb.246376}, DOI={10.1242/jeb.246376}, abstractNote={ABSTRACT
               All freshwater organisms are challenged to control their internal balance of water and ions in strongly hypotonic environments. We compared the influence of external salinity on the oxygen consumption rates (ṀO2) of three species of freshwater insects, one snail and two crustaceans. Consistent with available literature, we found a clear decrease in ṀO2 with increasing salinity in the snail Elimia sp. and crustaceans Hyalella azteca and Gammarus pulex (r5=−0.90, P=0.03). However, we show here for the first time that metabolic rate was unchanged by salinity in the aquatic insects, whereas ion transport rates were positively correlated with higher salinities. In contrast, when we examined the ionic influx rates in the freshwater snail and crustaceans, we found that Ca uptake rates were highest under the most dilute conditions, while Na uptake rates increased with salinity. In G. pulex exposed to a serially diluted ion matrix, Ca uptake rates were positively associated with ṀO2 (r5=−0.93, P=0.02). This positive association between Ca uptake rate and ṀO2 was also observed when conductivity was held constant but Ca concentration was manipulated (1.7–17.3 mg Ca l−1) (r5=0.94, P=0.05). This finding potentially implicates the cost of calcium uptake as a driver of increased metabolic rate under dilute conditions in organisms with calcified exoskeletons and suggests major phyletic differences in osmoregulatory physiology. Freshwater insects may be energetically challenged by higher salinities, while lower salinities may be more challenging for other freshwater taxa.}, number={20}, journal={JOURNAL OF EXPERIMENTAL BIOLOGY}, author={Cochran, Jamie K. and Banks, Catelyn and Buchwalter, David B.}, year={2023}, month={Oct} }
 @article{cochran_buchwalter_2022, title={The acclimatory response of the mayfly Neocloeon triangulifer to dilute conditions is linked to the plasticity of sodium transport}, volume={289}, ISSN={["1471-2954"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85135123029&partnerID=MN8TOARS}, DOI={10.1098/rspb.2022.0529}, abstractNote={
            Relative to a growing body of knowledge about the negative consequences of freshwater salinization, little is known about how aquatic insects respond to progressively ion-poor conditions. Here, we examined life-history and physiological acclimation in
            Neocloeon triangulifer
            by rearing nymphs from 1-day post-egg hatch to adulthood across a gradient of decreasing Na concentrations (15, 8, 4, 2 and 1 mg l
            −1
            Na). We found no significant changes in survival, growth, development time and whole-body Na content across these treatments. Radiotracer data revealed that nymphs acclimated to their dilute exposures by increasing their rates of Na uptake and were able to maintain a relatively narrow range of uptake rates (±s.e.m.) of 38.5 ± 4.2 µg Na g
            −1
            h
            −1
            across all treatments. By contrast, the Na uptake rates observed in naive nymphs were much more concentration dependent. This acclimatory response is partially explained by differences in ionocyte counts on the gills of nymphs reared under different salinities. Acclimated nymphs were surprisingly less retentive of their sodium composition when subjected to deionized water challenge. By contrasting our findings with a previous
            N. triangulifer
            salinity acclimation study, we show a physiological affinity for dilute conditions in this emerging mayfly model.
          }, number={1979}, journal={PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES}, author={Cochran, Jamie K. K. and Buchwalter, David B. B.}, year={2022}, month={Jul} }
 @article{orr_cochran_wallace_gray_overmyer_buchwalter_2022, title={Weak differences in sensitivity to major ions by different larval stages of the mayfly Neocloeon triangulifer}, volume={41}, ISSN={["2161-9565"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85125037439&partnerID=MN8TOARS}, DOI={10.1086/719359}, abstractNote={Freshwater salinization is a global ecological concern because of the alarming biodiversity declines associated with increases in major ion concentrations. Loss of mayfly diversity appears to be a common ecological response to anthropogenic salinization worldwide. Remarkably few regulatory standards exist to protect aquatic life from major ions, and antiquated approaches for setting such standards rely on traditional laboratory toxicity tests, which do not address sensitivities of mayflies at different larval stages. The lab-reared mayfly Neocloeon triangulifer (McDunnough, 1931) has emerged as one of the very few useful aquatic insect models for studying the effects of environmental stressors, including salinity, in the laboratory. Here, we asked if different larval life stages are differentially sensitivity to ion concentrations by conducting traditional 96-h toxicity tests with NaCl, CaCl2, and Ca/MgSO4. We used a general linear model to determine if survivorship differed among larval stages as well as ion type and concentration. We also calculated median lethal concentrations (LC50) for each larval stage. Larval sensitivity to NaCl decreased slightly with age (2–6, 9–13, and 17–21 d, with LC50 values of 401, 441, and 570 mg/L, respectively, when expressed as Na concentrations). Similarly, larval sensitivity to Ca/MgSO4 differed slightly among age groups (LC50 = 748, 1503, and 1439 mg/L, respectively, when expressed as SO4 concentrations). Reliable confidence intervals on LC50 values for CaCl2 could not be calculated because of high survivorship. However, our general linear model revealed that age played a moderate role in survival (p = 0.0065) across all salts of interest. To assess the potential changes in ion flux between larval stages, we used radiotracers (22Na, 35SO4, or 45Ca) in 18- and 25-d-old larvae and found no strong differences in ion uptake rates. We also qualitatively examined morphological differences between larval life stages, including the appearance of gills and number of ionocytes. Our results indicate that younger N. triangulifer larvae may be more sensitive to major ions than mature larvae. These results should be considered when experimentally using larger, late-stage N. triangulifer larvae to study the physiological effects and acute toxicity of salinity.}, number={2}, journal={FRESHWATER SCIENCE}, author={Orr, Sarah E. and Cochran, Jamie K. and Wallace, Ian G. and Gray, Rachel W. and Overmyer, Gretta E. and Buchwalter, David B.}, year={2022}, month={Jun} }
 @article{cochran_orr_buchwalter_2022, title={Assessing the P-crit in relation to temperature and the expression of hypoxia associated genes in the mayfly, Neocloeon triangulifer}, volume={808}, ISSN={["1879-1026"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85120657476&partnerID=MN8TOARS}, DOI={10.1016/j.scitotenv.2021.151743}, abstractNote={Hypoxia is a growing concern in aquatic ecosystems. Historically, scientists have used the P crit  (the dissolved oxygen level below which an animal can no longer oxyregulate) to infer hypoxia tolerance across species. Here, we tested the hypothesis that the P crit  is positively correlated with temperature in the mayfly, Neocloeon triangulifer. Cross-temperature comparisons showed a modest (r = 0.47), but significant (p < 0.0001) association between temperature and P crit  despite relatively large interindividual variability (Coefficient of Variance (CV) = 39.9% at 18 °C). We used the expression of hypoxia-responsive genes EGL-9 (an oxygen sensing gene and modulator of HIF-1a activity) and LDH (a hypoxia indicator) to test whether oxygen partial pressure near the P crit  stimulates expression of hypoxia-responsive genes. Neither gene was upregulated at oxygen levels above the estimated P crit , however, at or below the P crit  estimates, expression of both genes was stimulated (~20- and ~3-fold change for EGL-9 and LDH, respectively). Finally, we evaluated the influence of hypoxic exposure time and pretreatment conditions on the mRNA expression levels of hypoxia-responsive genes. When larvae were exposed to a gradual reduction of DO, hypoxic gene expression was more robust than during instantaneous exposure to hypoxia. Our data provide modest support for traditional interpretation of the P crit  as a physiologically meaningful shift from aerobic to anaerobic metabolism in N. triangulifer. However, we also discuss limitations of the P crit  as a proxy measure of hypoxia tolerance at the species level.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Cochran, Jamie K. and Orr, Sarah E. and Buchwalter, David B.}, year={2022}, month={Feb} }