Informing the Exposure Landscape: The Fate of Microplastics in a Large Pelagic In-Lake Mesocosm Experiment.

Understanding microplastic exposure and effects is critical to understanding risk. Here, we used large, in-lake closed-bottom mesocosms to investigate exposure and effects on pelagic freshwater ecosystems. This article provides details about the experimental design and results on the transport of microplastics and exposure to pelagic organisms. Our experiment included three polymers of microplastics (PE, PS, and PET) ranging in density and size. Nominal concentrations ranged from 0 to 29,240 microplastics per liter on a log scale. Mesocosms enclosed natural microbial, phytoplankton, and zooplankton communities and yellow perch (Perca flavescens). We quantified and characterized microplastics in the water column and in components of the food web (biofilm on the walls, zooplankton, and fish). The microplastics in the water stratified vertically according to size and density. After 10 weeks, about 1% of the microplastics added were in the water column, 0.4% attached to biofilm on the walls, 0.01% within zooplankton, and 0.0001% in fish. Visual observations suggest the remaining >98% were in a surface slick and on the bottom. Our study suggests organisms that feed at the surface and in the benthos are likely most at risk, and demonstrates the value of measuring exposure and transport to inform experimental designs and achieve target concentrations in different matrices within toxicity tests.

Interindividual behavioural variation in response to elevated CO2 predicts mRNA transcript abundance of genes related to acid-base regulation in medaka (Oryzias latipes).

Rising carbon dioxide (CO2) in aquatic ecosystems due to climate change is a challenge for aquatic ectotherms. We examined whether interindividual variation in behavioural responses to CO2 could predict how a teleost fish would respond to elevated CO2 for multiple phenotypic and molecular traits. To this end, we first quantified behavioural responses of individuals exposed to acute elevated CO2, and used these to assign individuals as either high or low responders relative to the population mean. Subsequently, we exposed both high and low responders to elevated CO2 for 6 weeks and quantified the effect on body condition, behaviour, and mRNA transcript responses of gill and liver genes associated with relevant physiological processes. Generally, we found few relationships between the phenotypic groups and body condition and behaviour following the CO2 exposure period; however, stark differences between the phenotypic groups with respect to gene transcripts from each tissue related to various processes were found, mostly independent of CO2 exposure. The most pronounced changes were in the gill transcripts related to acid-base regulation, suggesting that the observed behavioural variation used to assign fish to phenotypic groups may have an underlying molecular origin. Should the link between behaviour and gene transcripts be shown to have a fitness advantage and be maintained across generations, interindividual variation in behavioural responses to acute CO2 exposure may be a viable and non-invasive tool to predict future population responses to elevated aquatic CO2.

Are the effects of catch-and-release angling evident in changes to mRNA abundances related to metabolism, acid-base regulation and stress in lake trout (Salvelinus namaycush) gills?

Catch-and-release (C&R) angling is a conservation-oriented practice intended to reduce the impact recreational angling has on fish populations. Even though most recreationally angled fish are released, little is known about how C&R angling impacts fish at the cellular or tissue level. As the first to explore the impacts of C&R angling on mRNA abundances, our study aimed to identify how the stress of angling influenced metabolism, acid-base regulation and cellular stress in the gills of lake trout (Salvelinus namaycush). Because gills are responsible for metabolic gas exchange, are crucial sites of acid-base homeostasis and respond to stressors quickly, we hypothesized that the relative mRNA abundance of genes related to these three physiological processes would be altered after angling. We took gill samples of live lake trout at 0, 2 or 48 h after fish were angled by rod and reel, and then used quantitative PCR (qPCR) to measure the relative abundance of nine candidate mRNA transcripts. Heat shock protein 70 (hsp70) mRNA levels significantly increased over 5-fold 2 h after angling, indicating a potential activation of a cytoprotective response. However, contrary to our hypothesis, we observed no change in the relative mRNA abundance of genes related to metabolism or acid-base regulation in response to C&R angling within a 48-h period. As C&R angling can negatively impact fish populations, further use of transcript-level studies will allow us to understand the impact C&R has on specific tissues and improve our knowledge of how C&R influences overall fish health.

Simulating the effects of long-distance dispersal and landscape heterogeneity on the eco-evolutionary outcomes of range expansion in an invasive riverine fish, Tench (Tinca tinca).

Predicting how quickly populations expand their range and whether they will retain genetic diversity when they are introduced to new regions or track environmental conditions suited to their survival is an important applied and theoretical challenge. The literature suggests that long-distance dispersal, landscape heterogeneity and the evolution of dispersal influence populations' expansion rates and genetic diversity. We used individual-based spatially explicit simulations to examine these relationships for Tench (Tinca tinca), an invasive fish expanding its geographical range in eastern North America since the 1990s. Simulated populations varied greatly in expansion rates (1.1-28.6 patches year-1 ) and genetic diversity metrics, including changes in observed heterozygosity (-19 to +0.8%) and effective number of alleles (-0.32 to -0.01). Populations with greater dispersal distances expanded faster than those with smaller dispersal distances but exhibited considerable variation in expansion rate among local populations, implying less predictable expansions. However, they tended to retain genetic diversity as they expanded, suggesting more predictable evolutionary trajectories. In contrast, populations with smaller dispersal distances spread predictably more slowly but exhibited more variability among local populations in genetic diversity losses. Consistent with empirical data, populations spreading in a longer, narrower dispersal corridor lost more neutral genetic variation to the stochastic fixation of alleles. Given the unprecedented pace of anthropogenic environmental change and the increasing need to manage range-expanding populations, our results have conservation ramifications as they imply that the evolutionary trajectories of populations characterised by shorter dispersal distances spreading in narrower landscapes are more variable and, therefore, less predictable.

Genetic diversity and structure of a recent fish invasion: Tench (Tinca tinca) in eastern North America.

Introduced and geographically expanding populations experience similar eco-evolutionary challenges, including founder events, genetic bottlenecks, and novel environments. Theory predicts that reduced genetic diversity resulting from such phenomena limits the success of introduced populations. Using 1900 SNPs obtained from restriction-site-associated DNA sequencing, we evaluated hypotheses related to the invasion history and connectivity of an invasive population of Tench (Tinca tinca), a Eurasian freshwater fish that has been expanding geographically in eastern North America for three decades. Consistent with the reported history of a single introduction event, our findings suggest that multiple introductions from distinct genetic sources are unlikely as Tench had a small effective population size (~114 [95% CI = 106-123] individuals), no strong population subdivision across time and space, and evidence of a recent genetic bottleneck. The large genetic neighbourhood size (220 km) and weak within-population genetic substructure suggested high connectivity across the invaded range, despite the relatively large area occupied. There was some evidence for a small decay in genetic diversity as the species expanded northward, but not southward, into new habitats. As eradicating the species within a ~112 km radius would be necessary to prevent recolonization, eradicating Tench is likely not feasible at watershed-and possibly local-scales. Management should instead focus on reducing abundance in priority conservation areas to mitigate adverse impacts. Our study indicates that introduced populations can thrive and exhibit relatively high levels of genetic diversity despite severe bottlenecks (<1.5% of the ancestral effective population size) and suggests that landscape heterogeneity and population demographics can generate variability in spatial patterns of genetic diversity within a single range expansion.

Developing specific molecular biomarkers for thermal stress in salmonids.

BACKGROUND: Pacific salmon (Oncorhynchus spp.) serve as good biological indicators of the breadth of climate warming effects on fish because their anadromous life cycle exposes them to environmental challenges in both marine and freshwater environments. Our study sought to mine the extensive functional genomic studies in fishes to identify robust thermally-responsive biomarkers that could monitor molecular physiological signatures of chronic thermal stress in fish using non-lethal sampling of gill tissue. RESULTS: Candidate thermal stress biomarkers for gill tissue were identified using comparisons among microarray datasets produced in the Molecular Genetics Laboratory, Pacific Biological Station, Nanaimo, BC, six external, published microarray studies on chronic and acute temperature stress in salmon, and a comparison of significant genes across published studies in multiple fishes using deep literature mining. Eighty-two microarray features related to 39 unique gene IDs were selected as candidate chronic thermal stress biomarkers. Most of these genes were identified both in the meta-analysis of salmon microarray data and in the literature mining for thermal stress markers in salmonids and other fishes. Quantitative reverse transcription PCR (qRT-PCR) assays for 32 unique genes with good efficiencies across salmon species were developed, and their activity in response to thermally challenged sockeye salmon (O. nerka) and Chinook salmon (O. tshawytscha) (cool, 13-14 °C and warm temperatures 18-19 °C) over 5-7 days was assessed. Eight genes, including two transcripts of each SERPINH1 and HSP90AA1, FKBP10, MAP3K14, SFRS2, and EEF2 showed strong and robust chronic temperature stress response consistently in the discovery analysis and both sockeye and Chinook salmon validation studies. CONCLUSIONS: The results of both discovery analysis and gene expression showed that a panel of genes involved in chaperoning and protein rescue, oxidative stress, and protein biosynthesis were differentially activated in gill tissue of Pacific salmon in response to elevated temperatures. While individually, some of these biomarkers may also respond to other stressors or biological processes, when expressed in concert, we argue that a biomarker panel comprised of some or all of these genes could provide a reliable means to specifically detect thermal stress in field-caught salmon.

Fishing for Effective Conservation: Context and Biotic Variation are Keys to Understanding the Survival of Pacific Salmon after Catch-and-Release.

Acute stressors are commonly experienced by wild animals but their effects on fitness rarely are studied in the natural environment. Billions of fish are captured and released annually around the globe across all fishing sectors (e.g., recreational, commercial, subsistence). Whatever the motivation, release often occurs under the assumption of post-release survival. Yet, capture by fisheries (hereafter "fisheries-capture") is likely the most severe acute stressor experienced in the animal's lifetime, which makes the problem of physiological recovery and survival of relevance to biology and conservation. Indeed, fisheries managers require accurate estimates of mortality to better account for total mortality from fishing, while fishers desire guidance on strategies for reducing mortality and maintaining the welfare of released fish, to maximize current and future opportunities for fishing. In partnership with stakeholders, our team has extensively studied the effects of catch-and-release on Pacific salmon in both marine and freshwater environments, using biotelemetry and physiological assessments in a combined laboratory-based and field-based approach. The emergent theme is that post-release rates of mortality are consistently context-specific and can be affected by a suite of interacting biotic and abiotic factors. The fishing gear used, location of a fishery, water temperature, and handling techniques employed by fishers each can dramatically affect survival of the salmon they release. Variation among individuals, co-migrating populations, and between sexes all seem to play a role in the response of fish to capture and in their subsequent survival, potentially driven by pre-capture pathogen-load, maturation states, and inter-individual variation in responsiveness to stress. Although some of these findings are fascinating from a biological perspective, they all create unresolved challenges for managers. We summarize our findings by highlighting the patterns that have emerged most consistently, and point to areas of uncertainty that require further research.

Exceptional aerobic scope and cardiovascular performance of pink salmon (Oncorhynchus gorbuscha) may underlie resilience in a warming climate.

Little is known of the physiological mechanisms underlying the effects of climate change on animals, yet it is clear that some species appear more resilient than others. As pink salmon (Oncorhynchus gorbuscha) in British Columbia, Canada, have flourished in the current era of climate warming in contrast to other Pacific salmonids in the same watershed, this study investigated whether the continuing success of pink salmon may be linked with exceptional cardiorespiratory adaptations and thermal tolerance of adult fish during their spawning migration. Sex-specific differences existed in minimum and maximum oxygen consumption rates (M(O2,min) and M(O2,max), respectively) across the temperature range of 8 to 28°C, reflected in a higher aerobic scope (M(O2,max)-M(O2,min)) for males. Nevertheless, the aerobic scope of both sexes was optimal at 21°C (T(opt)) and was elevated across the entire temperature range in comparison with other Pacific salmonids. As T(opt) for aerobic scope of this pink salmon population is higher than in other Pacific salmonids, and historic river temperature data reveal that this population rarely encounters temperatures exceeding T(opt), these findings offer a physiological explanation for the continuing success of this species throughout the current climate-warming period. Despite this, declining cardiac output was evident above 17°C, and maximum attainable swimming speed was impaired above ∼23°C, suggesting negative implications under prolonged thermal exposure. While forecasted summer river temperatures over the next century are likely to negatively impact all Pacific salmonids, we suggest that the cardiorespiratory capacity of pink salmon may confer a selective advantage over other species.