Geology topics

Creagh W Breuner

Publications and source records attributed to Creagh W Breuner.

5 recordsLinked to original sources

USGS2022

Testing whether adrenal steroids mediate phenotypic and physiologic effects of elevated salinity on larval tiger salamanders

Salinity (sodium chloride, NaCl) from anthropogenic sources is a persistent contaminant that negatively affects freshwater taxa. Amphibians can be susceptible to salinity, but some species are innately or adaptively tolerant. Physiological mechanisms mediating tolerance to salinity are still unclear, but changes in osmoregulatory hormones such as corticosterone (CORT) and aldosterone (ALDO) are prime candidates. We exposed larval barred tiger salamanders ( Ambystoma mavortium ) to environmentally relevant NaCl treatments (<32–4000 mg·L −1 ) for 24 days to test effects on growth, survival, and waterborne CORT responses. Of those sampled, we also quantified waterborne ALDO from a subset. Using a glucocorticoid antagonist (RU486), we also experimentally suppressed CORT signaling of some larvae to determine if CORT mediates effects of salinity. There were no strong differences in survival among salinity treatments, but salinity reduced dry mass, snout–vent length, and body condition while increasing water content of larvae. High survival and sublethal effects demonstrated that salamanders were physiologically challenged but could tolerate the experimental concentrations. CORT signaling did not attenuate sublethal effects of salinity. Baseline and stress-induced (after an acute stressor, shaking) CORT were not influenced by salinity. ALDO was correlated with baseline CORT, suggesting it could be difficult to decouple the roles of CORT and ALDO. Future studies comparing ALDO and CORT responses of adaptively tolerant and previously unexposed populations could be beneficial to understand the roles of these hormones in tolerance to salinity. Nevertheless, our study enhances our understanding of the roles of corticosteroid hormones in mediating effects of a prominent anthropogenic stressor.

Integrative Zoology↗

USGS2022

Effects of salinity and a glucocorticoid antagonist, RU486, on waterborne aldosterone and corticosterone of northern leopard frog larvae

Increased salinity is an emerging contaminant of concern for aquatic taxa. For amphibians exposed to salinity, there is scarce information about the physiological effects and changes in osmoregulatory hormones such as corticosterone (CORT) and aldosterone (ALDO). Recent studies have quantified effects of salinity on CORT physiology of amphibians based on waterborne hormone collection methods, but much less is known about ALDO in iono- and osmoregulation of amphibians. We re-assayed waterborne hormone samples from a previous study to investigate effects of salinity (sodium chloride, NaCl) and a glucocorticoid receptor antagonist (RU486) on ALDO of northern leopard frog ( Rana pipiens) larvae. We also investigated relationships between ALDO and CORT. Waterborne ALDO marginally decreased with increasing salinity and was, unexpectedly, positively correlated with baseline and stress-induced waterborne CORT. Importantly, ALDO increased when larvae were exposed to RU486, suggesting that RU486 may also suppress mineralocorticoid receptors or that negative feedback of ALDO is mediated through glucocorticoid receptors. Alternatively, CORT increases with RU486 treatment and might be a substrate for ALDO synthesis, which could account for increases in ALDO with RU486 treatment and the correlation between CORT and ALDO. ALDO was negatively correlated with percent water, such that larvae secreting more ALDO retained less water. Although sample sizes were limited and further validation and studies are warranted, our findings expand our understanding of adrenal steroid responses to salinization in amphibians and proposes new hypotheses regarding the co-regulation of ALDO and CORT.

General and Comparative Endocrinology↗

USGS2021

Evaluating corticosterone as a biomarker for amphibians exposed to increased salinity and ambient corticosterone

Physiological biomarkers are commonly used to assess the health of taxa exposed to natural and anthropogenic stressors. Glucocorticoid (GC) hormones are often used as indicators of physiological stress in wildlife because they affect growth, reproduction and survival. Increased salinity from human activities negatively influences amphibians and their corticosterone (CORT; the main amphibian GC) physiology; therefore, CORT could be a useful biomarker. We evaluated whether waterborne CORT could serve as a biomarker of salt stress for three free-living amphibian species that vary in their sensitivity to salinity: boreal chorus frogs ( Pseudacris maculata ), northern leopard frogs ( Rana pipiens ) and barred tiger salamanders ( Ambystoma mavortium ). Across a gradient of contamination from energy-related saline wastewaters, we tested the effects of salinity on baseline and stress-induced waterborne CORT of larvae. Stress-induced, but not baseline, CORT of leopard frogs increased with increasing salinity. Salinity was not associated with baseline or stress-induced CORT of chorus frogs or tiger salamanders. Associations between CORT and salinity were also not related to species-specific sensitivities to salinity. However, we detected background environmental CORT (ambient CORT) in all wetlands and spatial variation was high within and among wetlands. Higher ambient CORT was associated with lower waterborne CORT of larvae in wetlands. Therefore, ambient CORT likely confounded associations between waterborne CORT and salinity in our analysis and possibly influenced physiology of larvae. We hypothesize that larvae may passively take up CORT from their environment and downregulate endogenous CORT. Although effects of some hormones (e.g. oestrogen) and endocrine disruptors on aquatic organisms are well described, studies investigating the occurrence and effects of ambient CORT are limited. We provide suggestions to improve collection methods, reduce variability and avoid confounding effects of ambient CORT. By making changes to methodology, waterborne CORT could still be a promising, non-invasive conservation tool to evaluate effects of salinity on amphibians.

Montana, North Dakota↗

USGS2021

Low occurrence of ranavirus in the Prairie Pothole Region of Montana and North Dakota (USA) contrasts with prior surveys

Ranaviruses are emerging pathogens that have caused mortality events in amphibians worldwide. Despite the negative effects of ranaviruses on amphibian populations, monitoring efforts are still lacking in many areas, including in the Prairie Pothole Region (PPR) of North America. Some PPR wetlands in Montana and North Dakota (USA) have been contaminated by energy-related saline wastewaters, and increased salinity has been linked to greater severity of ranavirus infections. In 2017, we tested tissues from larvae collected at 7 wetlands that ranged in salinity from 26 to 4103 mg Cl l -1 . In 2019, we used environmental DNA (eDNA) to test for ranaviruses in 30 wetlands that ranged in salinity from 26 to 11754 mg Cl l -1 . A previous study (2013-2014) found that ranavirus-infected amphibians were common across North Dakota, including in some wetlands near our study area. Overall, only 1 larva tested positive for ranavirus infection, and we did not detect ranavirus in any eDNA samples. There are several potential reasons why we found so little evidence of ranaviruses, including low larval sample sizes, mismatch between sampling and disease occurrence, larger pore size of our eDNA filters, temporal variation in outbreaks, low host abundance, or low occurrence or prevalence of ranaviruses in the wetlands we sampled. We suggest future monitoring efforts be conducted to better understand the occurrence and prevalence of ranaviruses within the PPR.

Montana, North Dakota↗

USGS2020

Relative toxicity and sublethal effects of NaCl and energy-related saline wastewaters on prairie amphibians

Increasing salinity in freshwater environments is a growing problem due both to the negative influences of salts on ecosystems and their accumulation and persistence in environments. Two major sources of increased salinity from sodium chloride salts (NaCl) are saline wastewaters co-produced during energy production (herein, wastewaters) and road salts. Effects of road salts have received more attention, but legacy contamination from wastewaters is widespread in some regions and spills still occur. Amphibians are sensitive to contaminants, including NaCl, because of their porous skin and osmoregulatory adaptations to freshwater. However, similarities and differences between effects of wastewaters and road salts have not been investigated. Therefore, we investigated the relative influence of wastewaters and NaCl at equivalent concentrations of chloride on three larval amphibian species that occur in areas with increased salinity. We determined acute toxicity and growth effects on Boreal Chorus Frogs ( Pseudacris maculata ), Northern Leopard Frogs ( Rana pipiens ), and Barred Tiger Salamanders ( Ambystoma mavortium ). We posited that wastewaters would have additive effects on amphibians compared to NaCl because wastewaters often have additional toxic heavy metals and other contaminants. For NaCl, toxicity was higher for frogs than the salamander. Toxicity of wastewaters was also similar between chorus and leopard frogs. Only chorus frog survival was lower when exposed to wastewater compared to NaCl. Mass and length of leopard and chorus frog larvae decreased with increasing salinity after only 96 hours of exposure but did not for tiger salamanders. Size of leopard frogs was lower when exposed to NaCl compared to wastewater. However, growth effects were similar between wastewater and NaCl for chorus frogs. Taken together, our results suggest that previous studies on effects of road salt could inform future studies and management of wastewater-contaminated ecosystems, and vice versa. Nevertheless, effects of road salts and wastewaters may be context-, species-, and trait-specific and require further investigations. The negative influence of salts on imperiled amphibians underscores the need to restore landscapes with increased salinity and reduce future salinization of freshwater ecosystems.

Aquatic Toxicology↗