Biology subjects

Enders, E. C.

Publications and source records attributed to Enders, E. C..

6 recordsLinked to original sources

bioRxiv2025

Cumulative effects of high temperature and low dissolved oxygen alter the acute thermal tolerance and cellular stress response in lake trout

Lake trout (Salvelinus namaycush) is an important food fish in Northern communities, inhabiting cool, well-oxygenated water. Yet, climate change is reducing available habitat with extended summer stratification of lakes creating an upper thermal barrier ([~]15 {degrees}C) and lower dissolved oxygen (DO) boundary (4-7 mg L-1). Together, these environmental factors can influence tolerance thresholds and climate change may lead to abiotic factors exceeding these physiological thresholds in lake trout habitats. Thresholds can shift with environmental acclimation in lake trout populations, but the functional basis of this shift has yet to be examined. The abundance of mRNA transcripts offers insight into underlying cellular responses to environmental stressors that can provide an early warning of fitness consequences. Here, we used a stress-response transcriptional profiling chip to investigate a suite of genes involved in thermal and general stress in lake trout acclimated to a range of temperatures (6-18 {degrees}C) and DO (normoxia: > 8.5 mg L-1 or hypoxia: 5.5-6.5 mg L-1), as well as following an acute thermal stress (i.e., CTmax). Transcriptional profiles were assessed in the gill, liver, and and epidermal mucus. Generally, fish acclimated to the greatest combined stressor (18 {degrees}C and hypoxia) had the largest transcriptional response, suggestive of a transition from a routine stress response to an extreme survival response. A noted temperature dependence occurred in liver tissue, which was not evident in gill or mucus tissues. Further, transcriptional responses in the gill and mucus were highly correlated (r = 0.74-0.87), highlighting the potential use of these tissues for non-lethal sampling methods to enhance management and conservation strategies for lake trout across their distribution.

physiology↗

bioRxiv2024

Behavioural responses to acute warming precede critical shifts in the cellular and physiological thermal stress responses in fish

From a conservation perspective, it is important to identify when sub-lethal temperatures begin to adversely impact an organism. However, it is unclear whether, during acute exposures, these cellular thresholds occur at similar temperatures to other physiological or behavioural changes. To test this, we estimated temperature preference (15.1 {+/-} 1.1 {degrees}C) using a shuttle box, thermal optima for aerobic scope (10-15 {degrees}C) using respirometry, agitation temperature (22.0 {+/-} 1.4 {degrees}C) as the point where a fish exhibits a behavioural avoidance response and the CTmax (28.2 {+/-} 0.4 {degrees}C) as the upper thermal limit for 1 yr old Brook Trout (Salvelinus fontinalis) acclimated to 10 {degrees}C. We then acutely exposed a different subset of fish to these temperatures and sampled tissues when they reached the target temperature or after 60 min of recovery at 10 {degrees}C. We used qPCR to estimate mRNA transcript levels of genes associated with heat shock proteins, oxidative stress, apoptosis, and inducible transcription factors. A major shift in the transcriptome response occurred near the agitation temperature, which may identify a link between the cellular stress response and the behavioural avoidance response.

physiology↗

bioRxiv2021

A chromosomal inversion may facilitate adaptation despite periodic gene flow in a freshwater fish

Differences in genomic architecture between populations, such as chromosomal inversions, may play an important role in facilitating adaptation despite opportunities for gene flow. One system where chromosomal inversions may be important for eco-evolutionary dynamics are in freshwater fishes, which often live in heterogenous environments characterized by varying levels of connectivity and varying opportunities for gene flow. In the present study, reduced representation sequencing was used to study possible adaptation in n = 345 walleye (Sander vitreus) from three North American waterbodies: Cedar Bluff Reservoir (Kansas, USA), Lake Manitoba (Manitoba, Canada), and Lake Winnipeg (Manitoba, Canada). Haplotype and outlier-based tests revealed a putative chromosomal inversion that contained three expressed genes and was nearly fixed for alternate genotypes in each Canadian lake. These patterns exist despite several opportunities for gene flow between these proximate Canadian lakes, suggesting that the inversion may be important for facilitating adaptive divergence between the two lakes despite gene flow. Our study illuminates the importance of genomic architecture for facilitating local adaptation in freshwater fishes. Furthermore, our results provide additional evidence that inversions may facilitate local adaptation in many organisms that inhabit connected but heterogenous environments.

evolutionary biology↗

bioRxiv2020

Molecular and physiological responses predict acclimation limits in juvenile brook trout ( Salvelinus fontinalis )

Brook trout (Salvelinus fontinalis) populations are at risk of exposure to high water temperatures in the species native range in eastern North America. We quantified the physiological and molecular responses of juvenile brook trout to six acclimation temperatures that span the thermal distribution of the species (5, 10, 15, 20, 23, and 25{degrees}C). Using quantitative PCR (qPCR), we measured the mRNA transcript abundance of temperature-induced cellular stress genes to identify a potential sub-lethal temperature threshold for brook trout between 20-23{degrees}C. Brook trout exhibited an upregulation of stress-related genes (heat shock protein 90-beta; heat shock cognate 71 kDa protein; glutathione peroxidase 1) and a downregulation of transcription factors and osmoregulation-related genes (Na+/K+/2Cl- co-transporter-1-a; nuclear protein 1) at temperatures [≥]20{degrees}C. We also used respirometry to assess the effects of the acclimation temperatures on oxygen consumption. Standard metabolic rate results indicated that energy expenditure was higher at temperatures [≥]20{degrees}C. We then examined the effects of acclimation temperature on metabolic rate and blood plasma parameters in fish exposed to an acute exhaustive exercise and air exposure stress. Fish acclimated to temperatures [≥]20{degrees}C exhibited elevated levels of plasma cortisol, muscle lactate, and plasma glucose after exposure to the acute stressors. After 24 h of recovery, fish showed longer metabolic recovery times at 15 and 20{degrees}C and cortisol levels remaining elevated at temperatures [≥]20{degrees}C. Our findings suggest that brook trout may have a limited ability to acclimate to temperatures >20{degrees}C and increases in temperatures beyond 20{degrees}C may impact brook trout populations.

physiology↗

bioRxiv2020

Applying a gene-suite approach to examine the physiological status of wild-caught walleye (Sander vitreus)

Molecular techniques have been increasingly used in a conservation physiology framework to provide valuable information regarding the mechanisms underlying responses of wild organisms to environmental and anthropogenic stressors. In the present study, we developed a reference gill transcriptome for walleye (Sander vitreus) allowing us to pair a gene-suite approach with multivariate statistics to examine the physiological status of wild-caught walleye. For molecular analyses of wild fish, the gill is a useful target for conservation studies, not only because of its importance as an indicator of the physiological status of fish but also because it can be biopsied non-lethally. Walleye were non-lethally sampled following short- ([~]1.5 month) and long-term ([~]3.5 month) holding in the Delta Marsh, that is located south of Lake Manitoba in Manitoba, Canada. Large-bodied walleye are held in the Delta Marsh from late April to early August by exclusion screens used to protect the marsh from invasive common carp (Cyprinus carpio), exposing fish to potentially stressful water quality conditions. Principal components analysis (PCA) revealed patterns of transcript abundance consistent with exposure of fish to increasingly high temperature and low oxygen conditions with longer holding in the marsh. For example, longer-term holding in the marsh was associated with increases in the mRNA levels of heat shock proteins and a shift in the mRNA abundance of aerobic to anaerobic metabolic genes. Overall, the results of the present study suggest that walleye held in the Delta Marsh may be exhibiting sub-lethal responses to high temperature and low oxygen conditions and provides valuable information for managers invested in mediating these impacts to a local species of conservation concern. More broadly, we highlight the usefulness of pairing transcriptomic techniques with multivariate statistics to address potential confounding factors that can affect measured physiological responses of wild-caught fish. Lay summaryNon-lethal molecular techniques were used to assess the physiological status of wild-caught walleye confined in the Delta Marsh, Manitoba, Canada, because of common carp exclusion screens. Walleye sampled during the warmest months of the year exhibited responses to elevated temperature and low oxygen conditions, suggesting sub-lethal effects of local conditions.

physiology↗

bioRxiv2020

Genomic signals found using RNA sequencing support conservation of walleye (Sander vitreus) in a large freshwater ecosystem.

RNA sequencing is an effective approach for studying an aquatic species with little prior molecular information available, yielding both physiological and genomic data, but its genetic applications are not well-characterized. We investigate this possible role for RNA sequencing for population genomics in Lake Winnipeg, Manitoba, Canada, walleye (Sander vitreus). Lake Winnipeg walleye represent the largest component of the second-largest freshwater fishery in Canada. In the present study, large female walleye were sampled via nonlethal gill biopsy over two years at three spawning sites representing a latitudinal gradient in the lake. Genetic variation from sequenced messenger RNA was analyzed for neutral and adaptive markers to investigate population structure and possible adaptive variation. We find low population divergence (FST = 0.0095), possible northward gene flow, and outlier loci that vary latitudinally in transcripts associated with cell membrane proteins and cytoskeletal function. These results indicate that Lake Winnipeg walleye may be effectively managed as a single demographically connected metapopulation with contributing subpopulations, and suggest genomic differences possibly underlying observed phenotypic differences. Because RNA sequencing data can yield physiological in addition to genetic information discussed here, we argue that it is useful for addressing diverse molecular questions in the conservation of freshwater species.

genomics↗