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Many studies have investigated the loss of adaptive potential in endangered or exploited species experiencing recent population declines. Less research has studied adaptive genomic variation in small populations known to have persisted for long periods, despite the unique contribution that such populations provide for determining mechanisms underlying population persistence in evolutionary and conservation modeling. Small populations of Brook trout (Salvelinus fontinalis) have persisted in Cape Race, Newfoundland for >12 000 years. We used genotyping-by-sequencing data to investigate the demographic history and adaptive genomic variation of 26 populations with effective population sizes (Ne) ranging from 11 to 442, and to explore mechanisms underlying long-term persistence. We show that all populations experienced demographic declines following postglacial colonization but have remained in their current, small Ne state for thousands of years. We also reveal greater homozygosity in adaptive alleles within the smallest populations and found signatures of adaptive divergence in small populations relating to several abiotic and biotic factors. Our study illustrates how the demographic history of a species can influence the adaptive dynamics of small populations persisting over long time periods. [ABSTRACT FROM AUTHOR]

ABSTRACT Island ecosystems, particularly vulnerable to environmental challenges, host many endangered native species. Diadromous fish, in particular, are threatened throughout their marine and freshwater habitats. The conservation of these species requires an in‐depth understanding of their genetic diversity and structure, to better understand their adaptive potential. We investigated fine‐scale population diversity and structure in native brook charr (Salvelinus fontinalis) by genotyping 10 microsatellite loci in 244 individuals at three spatial scales in Saint‐Pierre and Miquelon, France. We found limited genetic variability across the archipelago, with particularly low genetic diversity in one island, Langlade. A significant difference in allelic richness was also detected among the three islands, indicating a difference in genetic composition across the archipelago, probably induced by historical stocking actions on both Saint‐Pierre and Miquelon. Finally, a strong genetic structure was detected across the archipelago among hydrosystems (overall FST = 0.19) and even within several of them. The presence of predominant interisland gene flow combined with complete genetic isolation from certain hydrosystems suggests that this contemporary genetic structure is the result of both natural demographic processes during the species postglacial colonization and recent restocking actions. The complex genetic structure of such isolated brook charr subpopulations highlights the importance of considering fine‐scale genetic structure in conservation management.

Brook trout (Salvelinus fontinalis) are a highly prized species found in lakes and streams throughout Ontario. A broadscale monitoring program (BsM) has been conducted in lakes throughout the province, in 5‐year cycles, which targets Salvelinus fontinalis populations. The objective of this study was to use the data gained from the BsM and establish a contemporary baseline on the variation of relative abundance and demographics of natural lake populations of S. fontinalis in Ontario. Additionally, given the variability in environmental conditions across the landscape, an objective was to assess the factors, abiotic and biotic, that influence relative abundance among waterbodies. Over the three BsM cycles (2008–2022), 273 S. fontinalis waterbodies were assessed, some multiple times, and 124 were unique populations. S. fontinalis were sampled in 112 of these unique lakes. In total, 7487 S. fontinalis were caught and 5372 were fully sampled (length, weight, and age assessed). The mean catch‐per‐unit‐effort (CPUE) in all waterbodies was 1.4 (0.12 standard error) S. fontinalis per net gang. There was not a significant trend in CPUE over the three BsM cycles nor did CPUE vary significantly among BsM cycles at the provincial scale, but CPUE varied significantly among fisheries management zones (FMZs). Multiple variables were examined to explain the variation in CPUE across the province; a negative association with species diversity was the only variable considered significant. Furthermore, S. fontinalis were more associated with the relative abundance of small cyprinids (i.e., chubs and shiners) and negatively associated with centrarchids, smelt, and other game species. Mean growth potential was greater for males than females but not significantly, whereas longevity favored females. Growth potential and parameters were similar between sexes within FMZs but varied among FMZs. Mean survival among these populations was 25.7%, ranging from 15.2% to 45.6%, with a mean instantaneous mortality of 1.41. This study provided a contemporary assessment of the current range and variability in relative abundance population dynamics of S. fontinalis in lakes within Ontario. This provides a benchmark to assess changes with the pending stressors of climate change and human expansion across the landscape. [ABSTRACT FROM AUTHOR]

Critical thermal maximum (CTmax) is widely used to measure upper thermal tolerance in fish but is rarely examined in embryos. Upper thermal limits generally depend on an individual's thermal history, which molds plasticity. We examined how thermal acclimation affects thermal tolerance of brook trout (Salvelinus fontinalis) embryos using a novel method to assess CTmax in embryos incubated under three thermal regimes. Warm acclimation was associated with an increase in embryonic upper thermal tolerance. However, CTmax variability was markedly higher than is typical for juvenile or adult salmonids. [ABSTRACT FROM AUTHOR]

Individual- and population-level responses to thermal change will be pivotal for species' resilience and adaptive responses to climate change. Thermal tolerance of ectotherms has been extensively studied under laboratory conditions, but comparatively few studies have assessed intra- and interpopulation variation under natural conditions or in situ. We measured field critical thermal maximum (CTmax) of brook trout (Salvelinus fontinalis) populations at twenty sites across Ontario, Canada, to assess their thermal tolerance in situ and examine potential factors underlying intraspecific variation in thermal performance. We modelled CTmax as a function of acclimation using short-term stream temperature data to assess interpopulation variation, and used full-season stream temperatures to calculate thermal safety margins (TSM) for each population. CTmax ranged between 27.41 and 30.46°C and acclimation periods between 4 and 40 days were strong predictors of site CTmax, aligning closely with lab-based studies. Seasonal temperature profiles varied substantially among sites, with mean 30-day stream temperature accounting for 66% of the among-site variation in CTmax. TSMs ranged between 0.51 and 15.51°C and reflected differences among site thermal regimes. Streams in watersheds with more urban or agricultural development had the lowest TSMs in addition to those that were fed by lake surface water. This work emphasizes the importance of locally based conservation and management practices that act at or below the population level, as local factors beyond acclimation temperature were partly responsible for variation in thermal tolerance and thus dictate the resiliency of brook trout under climate change. [ABSTRACT FROM AUTHOR]

Many salmonid species are particularly susceptible to chronic and acute temperature changes caused by global warming. We aimed to study the differences in metabolic and transcriptomic responses of a chronic heat stress on a control and selected (absence of early sexual maturation and growth) line of brook charr Salvelinus fontinalis (Mitchill, 1814). We exposed individuals to different temperatures for 35 days (15, 17, and 19 °C). High temperature reduced the growth rate (in length) and the Fulton condition factor. Both maximal metabolic rate and the aerobic scope were higher in fish reared at 17 °C, while they decreased in fish maintained at 19 °C. The relative gene expression of cytochrome c oxidase was lower at 19 °C than at 15 °C. The relative gene expressions of both liver and gill hsp90 was higher at the highest temperature. The standard metabolic rate, while not affected by temperature, was higher for the control line over the selected line. Only in the control line, the relative expression of catalase and of receptor of insulin-like growth factor-1 increased at 19 °C. Our results showed that the selected line was able to cope more effectively with the oxidative stress caused by the rise in temperature. [ABSTRACT FROM AUTHOR]

In many freshwater ecosystems, carbon dioxide (CO2) is increasing. Unknown are the risks that high CO2 poses for freshwater organisms, especially fish. The objective of this study was to determine how CO2 may influence the growth rate, metabolic rate, feeding rate, and volitional behaviour of young-of-year Arctic charr (Salvelinus alpinus (Linnaeus, 1758)), brook charr (Salvelinus fontinalis (Mitchill, 1814)), and rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). For this study, fish stayed in control (1100 microatmospheres (µatm)) or elevated (5236 µatm) CO2 levels for 15 days. During this time, metabolic rate and behavioural tests were conducted on alternating days for each treatment. Weight and length of each fish were taken on days 0, 7, and 15. There was no evidence that elevated CO2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr differed based on CO2 exposure. Therefore, salmonids can withstand short periods of elevated CO2 under these conditions. By comparing closely related species, the implications of this work are more ecologically relevant and will also help industry quantify the effects of high CO2 on young salmonids. [ABSTRACT FROM AUTHOR]

Polyandrous mating systems result in females mating with multiple males, generating opportunities for strong pre‐mating and post‐mating sexual selection. Polyandry also creates the potential for unintended matings and subsequent sperm competition with hybridizing species. Cryptic female choice allows females to bias paternity towards preferred males under sperm competition and may include conspecific sperm preference when under hybridization risk. The potential for hybridization becomes particularly important in context of invasive species that can novelly hybridize with natives, and by definition, have evolved allopatrically. We provide the first examination of conspecific sperm preference in a system of three species with the potential to hybridize: North American native Atlantic salmon (Salmo salar) and brook char (Salvelinus fontinalis), and invasive brown trout (Salmo trutta) from Europe. Using naturalized populations on the island of Newfoundland, we measured changes in sperm swimming performance, a known predictor of paternity, to determine the degree of modification in sperm swimming to female cues related to conspecific sperm preference. Compared to water alone, female ovarian fluid in general had a pronounced effect and changed sperm motility (by a mean of 53%) and swimming velocity (mean 30%), but not linearity (mean 6%). However, patterns in the degree of modification suggest there is no conspecific sperm preference in the North American populations. Furthermore, female cues from both native species tended to boost the sperm of invasive males more than their own. We conclude that cryptic female choice via ovarian fluid mediated sperm swimming modification is too weak in this system to prevent invasive hybridization and is likely insufficient to promote or maintain reproductive isolation between the native North American species. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are predominant pollutants in the aquatic environment that can cause a variety of potentially toxic effects, affecting the entire ecosystem. PAHs were evaluated following the application of different heat treatments to fish meat by liquid chromatography (HPLC). The following polycyclic aromatic hydrocarbons were determined: acenaphthene, anthracene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(gy)pyrylene, chrysene, dibenzo(a,h)anthracene, phenanthrene, fluorene, fluoranthene, indeno(1,2,3-cd)pyrene, naphthalene and pyrene. The samples analyzed were from raw trout (Salvelinus fontinalis); fried in sunflower oil; fried in olive oil; fried with rapeseed oil; baked in the oven and fried in lard. The brook trout (Salvelinus fontinalis) was harvested from the Mărișel area, Cluj county. The highest values for the hydrocarbons analyzed from raw fish were for naphthalene (5.51±0.21) and benzo(a)anthracene (2.47±0.06). The trout fried in sunflower oil showed the highest values for anthracene (10.34±0.09) and pyrene (10.24±0.30) and Indeno(1,2,3-cd)pyrene was <0.05. Trout fried with rapeseed oil showed the highest values for anthracene (10.34±0.09), followed by pyrene (10.24±0.30) and indeno(1,2,3-cd)pyrene was below <0.05. Trout fried in olive oil showed very high values for pyrene (51.37±0.63) and fluoranthene (20.36±0.89) and dibenzo(a,h)anthracene was <0.05. According to this study, fish meat has the highest percentage of PAHs following the frying process. These compounds play a very important role in the ecosystem, therefore the most affected is the consumer due to the carcinogenic effect they can cause on the body. [ABSTRACT FROM AUTHOR]

Microplastic (MP) pollution is a major environmental concern for mountain ecosystem and for high-mountain lakes in particular, which are recognized indicators of global change. In this study, the presence of MPs was assessed in abiotic (water and sediment) and biotic (zooplankton, tadpoles, fish) compartments of two high-mountain lakes (Upper Lake Balma and Lower Lake Balma) in the Cottian Alps (northwest Italy). No MPs were found in water and zooplankton samples, whereas the mean MPs in sediment samples was 1.33 ± 0.67 items/m3 and 1.75 ± 0.62 items/m3 in Lower and Upper Lake Balma, respectively. The mean MPs in tadpoles of Rana temporaria was 0.33 ± 0.58 items/individual and 0.66 ± 0.58 items/individual in Lower and Upper Lake Balma, respectively. The mean number of MPs items found in the gastrointestinal tract (GIT) of fish (Salvelinus fontinalis) was considerably higher in specimens from the Lower (0.45 items/g GIT) than in those from the Upper Lake (0.20 items/g GIT). There was a negative relationship between fish size (weight and age) and MPs abundance in the GIT of fish, indicating that young fish accumulated more MP items probably due to the high prey ingestion rate compared to adults. The same MPs color (blue, white, black), shape (fibers and fragments), and chemical type (polypropylene and polyethylene) were found in the compartments of both lakes. Our findings suggest the use of S. fontinalis as an indicator of MP pollution in high-mountain lakes. Further studies are needed to better understand the sources and the effects of MPs in these remote ecosystems.

Brook trout are a species of conservation concern in Southwestern Ontario, Canada, and effective monitoring of their populations is crucial for making informed management decisions. Electrofishing is a traditional, yet invasive, method that allows for fish abundance estimation. Environmental DNA (eDNA) is an emerging molecular tool that presents a non-invasive alternative to electrofishing. This study was a collaborative effort between researchers in academia, industry, and an NGO, with the following objectives: 1) compare eDNA detections with electrofishing when monitoring brook trout populations in a site of known occupancy, 2) compare existing eDNA collection methods, and 3) extend eDNA surveys to regions of unknown occupancy that could be of conservation concern (Hanlon Creek and Twelve Mile Creek, Ontario). First, eDNA sampling methods were validated with standard electrofishing. Water samples were filtered in tandem at each site using two commercially available eDNA samplers. The results suggest a significant difference in total eDNA capture and incidence of PCR inhibitors between the two autosamplers. Brook trout eDNA was detected at all locations in Hanlon Creek in September and November, as well as 5/6 sampling locations in Twelve Mile Creek. Brook trout signal in Hanlon Creek was stronger in November compared to September 2019, suggesting possible spawning activity. Brook trout eDNA was also detected in Twelve Mile Creek where brook trout were previously unreported. This study provides a technical validation for the use of eDNA in brook trout monitoring and illustrates the opportunity to use eDNA surveys in regulated settings to complement and improve conventional biomonitoring methods for the management of elusive species. [ABSTRACT FROM AUTHOR]

Brook trout (Salvelinus fontinalis) are an iconic freshwater salmonid native to northeastern North America. They prefer cold, clean rivers and lakes, and have been culturally, socially and economically valued for decades. Overharvest and deforestation associated with European settlement in southern Ontario, Canada led to notable declines in brook trout abundance in rivers and streams by the late 1800s. Today, they are threatened by further habitat degradation, non‐native species, and climate change. In this study, we document brook trout occupancy in rivers and streams of the Mixedwood Plains Ecozone in southern Ontario, between 1970–1980 and 2000–2010. We used generalised linear models to determine occupancy variation between the two time periods at five spatial scales spanning multiple watershed levels. We detected a decline in occupancy between time periods for the tertiary (from 23% to 17%) and quaternary (from 35% to 22%) watershed scales. In the Credit River‐Sixteen Mile Creek watershed, mean occupancy decreased to a third of past estimate (from 31% to 10%). For a subset of 86 sites with overlapping sampling in both periods no temporal trend was detected, but a post‐hoc analysis indicated low statistical power (0.07), which suggested that more intensive sampling would be needed to better quantify brook trout occupancy changes at this scale. The occupancies quantified for the past period in our study may serve as benchmarks for brook trout restoration efforts. [ABSTRACT FROM AUTHOR]

Throughout their range, Brook Trout (Salvelinus fontinalis) occupy thousands of disjunct drainages with varying levels of disturbance, which presents substantial challenges for conservation. Within the southern Appalachian Mountains, fragmentation and genetic drift have been identified as key threats to the genetic diversity of the Brook Trout populations. In addition, extensive historic stocking of domestic lineages of Brook Trout to augment fisheries may have eroded endemic diversity and impacted locally adapted populations. We used 12 microsatellite loci to describe patterns of genetic diversity within 108 populations of wild Brook Trout from Tennessee and used linear models to explore the impacts of land use, drainage area, and hatchery stockings on metrics of genetic diversity, effective population size, and hatchery introgression. We found levels of within-population diversity varied widely, although many populations showed very limited diversity. The extent of hatchery introgression also varied across the landscape, with some populations showing high affinity to hatchery lineages and others appearing to retain their endemic character. However, we found relatively weak relationships between genetic metrics and landscape characteristics, suggesting that contemporary landscape variables are not strongly related to observed patterns of genetic diversity. We consider this result to reflect both the complex history of these populations and the challenges associated with accurately defining drainages for each population. Our study highlights the importance of genetic data to guide management decisions, as complex processes interact to shape the genetic structure of populations and make it difficult to infer the status of unsampled populations. [ABSTRACT FROM AUTHOR]

Abstract Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole‐genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule pressure should result in greater neutral genetic variation, while environmental differences should elicit selective pressures on introduced populations, leading to adaptive differentiation. We investigated neutral and adaptive variation among nine introduced brook trout (Salvelinus fontinalis) populations using whole‐genome pooled sequencing. The populations inhabit isolated alpine lakes in western Canada and descend from a common source, with an average of ~19 (range of 7–41) generations since introduction. We found some evidence of bottlenecks without recovery, no strong evidence of purifying selection, and little support that varying propagule pressure or differences in local environments shaped observed neutral genetic variation differences. Putative adaptive loci analysis revealed nonconvergent patterns of adaptive differentiation among lakes with minimal putatively adaptive loci (0.001%–0.15%) that did not correspond with tested environmental variables. Our results suggest that (i) introduction success is not always strongly influenced by genetic load; (ii) observed differentiation among introduced populations can be idiosyncratic, population‐specific, or stochastic; and (iii) conservatively, in some introduced species, colonization barriers may be overcome by support through one aspect of propagule pressure or benign environmental conditions.

Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole‐genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule pressure should result in greater neutral genetic variation, while environmental differences should elicit selective pressures on introduced populations, leading to adaptive differentiation. We investigated neutral and adaptive variation among nine introduced brook trout (Salvelinus fontinalis) populations using whole‐genome pooled sequencing. The populations inhabit isolated alpine lakes in western Canada and descend from a common source, with an average of ~19 (range of 7–41) generations since introduction. We found some evidence of bottlenecks without recovery, no strong evidence of purifying selection, and little support that varying propagule pressure or differences in local environments shaped observed neutral genetic variation differences. Putative adaptive loci analysis revealed nonconvergent patterns of adaptive differentiation among lakes with minimal putatively adaptive loci (0.001%–0.15%) that did not correspond with tested environmental variables. Our results suggest that (i) introduction success is not always strongly influenced by genetic load; (ii) observed differentiation among introduced populations can be idiosyncratic, population‐specific, or stochastic; and (iii) conservatively, in some introduced species, colonization barriers may be overcome by support through one aspect of propagule pressure or benign environmental conditions. [ABSTRACT FROM AUTHOR]

• Upland streams of New England frequently experience low pH, high inorganic Al conditions. • Acid-Al conditions are related to season, site buffer conditions and elevation. • Fish diversity and abundance is reduced at sites with high acid-Al. • Salmonid gill Al accumulation is significantly increased at sites with high acid-Al. • Elevated acid-Al impairs osmoregulatory proteins of Atlantic salmon. In spite of overall improvements in air and water quality, biological stress from low pH and high concentrations of inorganic aluminum continue to impact fish and fish habitat in northeastern North America, with independent and interactive effects on individuals, populations and communities. Integrative indicators can therefore be useful in monitoring both impact and recovery across multiple scales. Using coupled water chemistry (pH, conductivity, and base cation and inorganic aluminum concentration), geographic (site elevation and watershed area) and biological (fish diversity, fish abundance, gill aluminum concentration and gill physiology) data, we developed an integrated indicator of acid-aluminum stress across the White and Green mountains in central New England, USA. As has been established in a number of previous studies, preliminary analysis clearly indicated that across all sites, inorganic aluminum concentration was consistently greatest during the spring season. Structural Equation modeling (SEM) revealed that toxic conditions (concurrent low pH and high concentrations of inorganic aluminum) were well summarized with an integrated toxicity score, related to both base cation concentrations and elevation, with sites at higher elevations more likely to experience toxic conditions as well as low base cation concentrations. Fish diversity and abundance generally trended negatively with toxicity score, with fewer cyprinids and sculpins at high toxicity score sites. In spite of considerable variation among individuals, gill aluminum was positively related to toxicity score for both Atlantic salmon and brook trout. Observed elevated gill aluminum levels associated with reduced gill metabolic activity in Atlantic salmon smolts from impacted systems likely result in impaired osmoregulatory function and seawater tolerance. Overall, our results suggest that the integrated toxicity score metric is associated with a syndrome of acute physiological stress, reduced abundance, and low species diversity for sensitive stream fishes in New England, and can likely serve as a reliable indicator of continued impairment or recovery of acid-aluminum vulnerable systems in this ecoregion. [ABSTRACT FROM AUTHOR]