Lake Whitefish Research Articles

Arsenic Bioconcentration in Freshwater Fish Species in a Pristine Lake in Yellowknife, NT

Yellowknife hosts one of the largest gold mining industries in Canada, including the renowned Giant Mine actively operating from 1948 to 2004, The mining operation in Giant Mine released enormous amounts of arsenic trioxide dust to the environment from the burning of arsenopyrite ores necessary to extract gold. Studies have revealed up to 100-fold increases in the concentration of arsenic in the surface water of lakes located within a 5-km radius of the mine. We summarized different factors from previous studies that contribute to the high arsenic levels found in lakes in Yellowknife: distance from the Giant Mine, prevailing wind direction to the Northwest, and the size of the lake. In this study, Small Lake was chosen as a pristine lake; a medium-sized lake located 27-km East of the mine and away from the city centre. Small Lake has the background concentration of arsenic of 1.4 µg/L in its surface water, unaffected by the historical activities from the Giant Mine. This background level of arsenic is expected from the slow natural weathering process of the bedrock geology. We collected two most common freshwater fish species in lakes in Yellowknife: adult Lake Whitefish (Coregonus clupeaformis) (n=8) and adult Northern Pike (Esox lucius) (n=8). Total arsenic concentration in the tissues was measured using ICP-MS method following FDA standard. Results show arsenic concentrations of 0.567 ± 0.216 mg/kg dry weight in the muscle tissue of Lake Whitefish and 0.458 ± 0.115 mg/kg dry weight in the muscle of Northern Pike. Although the Northern Pike species in this study is in a higher trophic position than the Lake Whitefish species, no significant difference in the arsenic concentration is observed in the muscle tissues (p > 0.05). The results of this study serve as reference data for fish arsenic monitoring programs and risk assessment projects in Yellowknife.

Daily, repeating fluctuations in embryonic incubation temperature alter metabolism and growth of Lake whitefish (Coregonus clupeaformis)

Lake whitefish (Coregonus clupeaformis) utilize overwintering embryonic development (up to 180 days), and such stenothermic, cold-water embryos may be particularly susceptible to thermal shifts. We incubated whitefish embryos in temperature treatments that were constant temperature (2.0 ± 0.1 °C, 5.0 ± 0.1 °C, and 8.0 ± 0.1 °C; mean ± SD) or variable temperature (VT, mean = 5.0 ± 0.3 °C). In the VT, a daily 2 °C temperature change followed a continuous pattern throughout development: 2-4-6-8-6-4-2 °C. Hatchling survival proportion from fertilization to hatch was significantly impacted by incubation temperature (P < 0.001): 2 °C (0.88 ± 0.01) and 5 °C (0.91 ± 0.01) showed higher survival than both the VT (0.83 ± 0.02) and 8 °C groups (0.15 ± 0.06), which were statistically distinct from each other. Time to hatch (dpf) was significantly different across all treatments (P < 0.001): 8 °C (68 ± 2 dpf), VT (111 ± 4 dpf), 5 °C (116 ± 4 dpf), 2 °C (170 ± 3 dpf). Likewise, hatchling yolk-free dry mass (mg) and total body length (mm) were significantly different across all treatments (P < 0.001): 8 °C (0.66 ± 0.08 mg; 11.1 ± 0.08 mm), VT (0.97 ± 0.06 mg; 11.7 ± 0.05 mm), 5 °C (1.07 ± 0.03 mg; 12.0 ± 0.02 mm), 2 °C (1.36 ± 0.04 mg; 12.8 ± 0.05 mm). Oxygen consumption rate (V̇o2) was significantly affected by the interaction between treatment and measurement temperature (P < 0.001). Hatchling VT whitefish showed mean V̇o2 that was higher compared to the 2 °C group measured at 2 °C, and lower compared to the 2 °C and 5 °C group measured at 8 °C. This study demonstrates that the VT incubation treatment produced fewer (increased mortality), smaller embryos that hatched earlier than 2 °C and 5 °C embryos. The plasticity of V̇o2 for this stenothermic-incubating fish species under variable incubation conditions reveals a metabolic cost to cycling thermal incubation conditions.

Effect of feeding strategy on digestive tract morphology and physiology of lake whitefish (Coregonus lavaretus)

The common whitefish (Coregonus lavaretus) plays an increasingly important role in European and North American aquaculture industry. At the same time a considerable decrease in whitefish abundance in natural waters is observed. Therefore, it is necessary to develop methods of whitefish rearing not only for commercial but also reintroduction purposes. Fish feeding with natural food (Artemia sp. nauplii) is much more expensive compared to the use of commercial feeds, and thus the attempts to develop optimal feeding strategies have been undertaken to obtain most satisfactory rearing effects at the lowest costs. The aim of the present study was to establish the best moment of commercial feed introduction (Otohime B1) and to evaluate the effects of various feeding strategies on morphological and physiological development of digestive tract in whitefish larvae. This was done using histological analysis of the digestive tract and measurements of digestive enzyme activity. The lowest mortality occurred in the group fed exclusively Artemia sp., while the highest was recorded in the group fed Otohime B1 diet exclusively. Histological analyses revealed no significant pathological alterations in the digestive tract, in all experimental groups. The analysis of digestive enzyme activity revealed the fastest development of gastric glands in fish fed only natural food, however, the intestinal epithelium developed at a similar rate in all groups. The results indicate that the initial feeding of larvae with natural food is not necessary in common whitefish pre-rearing when using the commercial feed Otohime B1, but the highest larval growth was observed in the group which was initially fed Artemia nauplii for one week before the transition to Otohime B1.

Potential for fisheries-induced evolution in the Laurentian Great Lakes

Abstract Fisheries are selective, capturing fish based on their body size, behaviour, life stage, or location. Over time, if harvest pressure is strong enough and variation in traits heritable, evolution can occur that affects key aspects of the ecology of fish stocks. Most compelling examples of rapid evolution in response to harvest have come from marine systems. Here, we review the state of knowledge on fisheries-induced evolution (FIE) in the Laurentian Great Lakes where subsistence, commercial, and recreational fisheries have operated for centuries. We conclude that stocks experienced harvest rates high enough and for long enough to undergo evolution. While historical fisheries exploited more juveniles, some contemporary Great Lakes fisheries target primarily adult size-classes thus reducing current selection for earlier maturation; however, other traits and behaviours could evolve (e.g., growth, timing of spawning, boldness). While commercial harvest previously dominated, recreational fishing is now expected to be a strong contributor to harvest selection in the Great Lakes. Environmental variation, density-dependence, invasive species, and the genetic legacy of population bottlenecks and stocking interact with, and make it more challenging to detect, FIE in the Great Lakes than in marine systems. Case studies are presented for Great Lakes stocks of yellow perch Perca flavescens and lake whitefish Coregonus clupeaformis for which FIE has been investigated. The evidence for FIE in the Great Lakes is currently sparse, potentially because of the low research focus on this topic or because of the interacting influence of environmental variation and anthropogenic stressors.

Mercury and omega-3 fatty acid profiles in freshwater fish of the Dehcho Region, Northwest Territories: Informing risk benefit assessments

Traditional foods have significant nutritional, sociocultural and economic value in subarctic First Nations communities of the Northwest Territories, and play a crucial role in promoting cultural continuity and sovereignty. Omega-3 polyunsaturated fatty acids (N-3 PUFAs), including eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), carry significant benefits for neurocognitive development and cardiovascular health. However, the health risks posed by methylmercury may serve to undermine the benefits of fish consumption in Northern Indigenous communities. The objective of this study was to characterize profiles for mercury (Hg) and fatty acids in fish species harvested across lakes of the Dehcho Region, in the Mackenzie Valley of the Northwest Territories, to better understand the risks and benefits associated with traditional foods. Hg levels increased with trophic position, with the highest levels found in Burbot, Lake Trout, Walleye, and Northern Pike. Lake Trout, along with planktivorous species including Lake Whitefish, Cisco, and Sucker, demonstrated higher N-3 PUFAs than other species. Negative associations were observed between Hg and N-3 PUFAs in Lake Trout, Northern Pike, Walleye and Burbot. Further stratifying these relationships revealed significant interactions by lake. Significant differences observed in fatty acid and Hg profiles across lakes underscore the importance of considering both species- and lake-specific findings. This growing dataset of freshwater fish of the Dehcho will inform future efforts to characterize human Hg exposure profiles using probabilistic dose reconstruction models.

Size-selective fishing and the potential for fisheries-induced evolution in lake whitefish.

The long‐term evolutionary effects of fishing on maturation schedules can depend on gear type, the shape of the gear type's size‐selectivity function, and the size and age structure of a population. Our goal was to better understand how environmentally induced differences in somatic growth influence the evolutionary effects of size‐selective fisheries, using lake whitefish (Coregonus clupeaformis) in Lake Huron as a case study. Using a state‐dependent optimization model of energy allocation parameterized for lake whitefish, we show that fishing with gill nets (bell‐shaped selectivity) and trap nets (sigmoid‐shaped selectivity) can be potent agents of selection on size thresholds for maturity. Compared to trap nets and large mesh (114 mm) gill nets, small mesh (89 mm) gill nets are better able to buffer populations from fishing‐induced evolution by safeguarding large, fecund fish, but only when overall fishing mortality is low and growth rates sufficiently fast such that fish can outgrow vulnerable size classes. Regardless of gear type, and all else being equal, high fishing mortality in combination with low growth rates is expected to intensify the long‐term evolutionary effects of fishing.

Holobionts and ecological speciation: the intestinal microbiota of lake whitefish species pairs

BackgroundIt is well established that symbionts have considerable impact on their host, yet the investigation of the possible role of the holobiont in the host’s speciation process is still in its infancy. In this study, we compared the intestinal microbiota among five sympatric pairs of dwarf (limnetic) and normal (benthic) lake whitefish Coregonus clupeaformis representing a continuum in the early stage of ecological speciation. We sequenced the 16s rRNA gene V3-V4 regions of the intestinal microbiota present in a total of 108 wild sympatric dwarf and normal whitefish as well as the water bacterial community from five lakes to (i) test for differences between the whitefish intestinal microbiota and the water bacterial community and (ii) test for parallelism in the intestinal microbiota of dwarf and normal whitefish.ResultsThe water bacterial community was distinct from the intestinal microbiota, indicating that intestinal microbiota did not reflect the environment, but rather the intrinsic properties of the host microbiota. Our results revealed a strong influence of the host (dwarf or normal) on the intestinal microbiota with pronounced conservation of the core intestinal microbiota (mean ~ 44% of shared genera). However, no clear evidence for parallelism was observed, whereby non-parallel differences between dwarf and normal whitefish were observed in three of the lakes while similar taxonomic composition was observed for the two other species pairs.ConclusionsThis absence of parallelism across dwarf vs. normal whitefish microbiota highlighted the complexity of the holobiont and suggests that the direction of selection could be different between the host and its microbiota.

Contemporary factors influencing genetic diversity in the Alaska humpback whitefish Coregonus clupeaformis complex.

Thirteen microsatellite loci were used to address three hypotheses regarding genetic diversity in the humpback whitefish Coregonus clupeaformis complex in Alaska. The test results provided further insight into the factors influencing C. clupeaformis complex population structure and level of genetic variation. First, the microsatellite data did not provide evidence of two spatially distinct Beringian and Eurasian refugial groups as revealed in previous phylogeographic analyses of mitochondrial DNA variation. Rather, the population structure inferred from the microsatellite variation appears to reveal the influence of factors on a more recent time scale, including gene flow among the refugial groups and isolation of some anadromous and freshwater resident populations. Second, anadromous C. clupeaformis complex collections exhibited higher intra-population genetic diversity than freshwater resident collections. This outcome is consistent with previous meta analyses suggesting that freshwater resident populations probably have smaller historical effective population sizes and less conspecific gene flow because the habitat tends to be smaller and supports fewer and smaller populations. Finally, the analysis of contemporary immigration rates was consistent with, but did not provide statistical support for, the hypothesis that gene flow among anadromous C. clupeaformis complex populations along coastal Alaska is influenced by the Alaska Coastal Current. Further studies are needed to evaluate gene flow among coastal Alaska C. clupeaformis complex populations.

Lake Sturgeon, Lake Whitefish, and Walleye Egg Deposition Patterns with Response to Fish Spawning Substrate Restoration in the St. Clair–Detroit River System

AbstractEgg deposition and use of restored spawning substrates by lithophilic fishes (e.g., Lake SturgeonAcipenser fulvescens, Lake WhitefishCoregonus clupeaformis, and WalleyeSander vitreus) were assessed throughout the St. Clair–Detroit River system from 2005 to 2016. Bayesian models were used to quantify egg abundance and presence/absence relative to site‐specific variables (e.g., depth, velocity, and artificial spawning reef presence) and temperature to evaluate fish use of restored artificial spawning reefs and assess patterns in egg deposition. Lake Whitefish and Walleye egg abundance, probability of detection, and probability of occupancy were assessed with detection‐adjusted methods; Lake Sturgeon egg abundance and probability of occurrence were assessed using delta‐lognormal methods. The models indicated that the probability of Walleye eggs occupying a site increased with water velocity and that the rate of increase decreased with depth, whereas Lake Whitefish egg occupancy was not correlated with any of the attributes considered. Egg deposition by Lake Whitefish and Walleyes was greater at sites with high water velocities and was lower over artificial spawning reefs. Lake Sturgeon eggs were collected least frequently but were more likely to be collected over artificial spawning reefs and in greater abundances than elsewhere. Detection‐adjusted egg abundances were not greater over artificial spawning reefs, indicating that these projects may not directly benefit spawning Walleyes and Lake Whitefish. However, 98% of the Lake Sturgeon eggs observed were collected over artificial spawning reefs, supporting the hypothesis that the reefs provided spawning sites for Lake Sturgeon and could mitigate historic losses of Lake Sturgeon spawning habitat.

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Estimating the Size Selectivity of Trap Nets using a Gill‐Net Selectivity Experiment: Method Development and Application to Lake Whitefish in Lake Huron

AbstractFisheries management requires information about the size selectivity of the fishing gears, but often the experimental data to estimate size selectivity are absent. We developed a two‐stage method to use data from an experimental survey for one type of gear (gill nets) to estimate the size selectivity of another type of gear (trap nets) based on the commercial catch data from both gear types, and we applied this method to Lake Whitefish Coregonus clupeaformis in Lake Huron. In stage I, an information‐theoretic approach (Akaike's information criterion) was used to select among five candidate models for the size selectivity of experimental gill nets. A double logistic function (a dome‐shaped curve skewed to the right) was chosen as the best model to describe the size selectivity of gill nets targeting Lake Whitefish. In stage II, we estimated the size selectivity of trap nets by applying the model of size selectivity from experimental gill nets to commercial catch data from trap‐net and gill‐net fisheries operating in a similar region and temporal period. Trap‐net selectivity was fitted by using a symmetric logistic equation. This two‐stage method predicted that 513‐mm FL Lake Whitefish are fully selected by gill nets with a mesh size of 114 mm, whereas ≥615‐mm FL fish are fully selected by commercial trap nets.Received April 12, 2017; accepted September 8, 2017 Published online November 9, 2017

Intensity and duration of effects of impoundment on mercury levels in fishes of hydroelectric reservoirs in northern Québec (Canada)

At the La Grande Hydroelectric Complex (Québec, Canada), total mercury (THg) levels in fish were monitored from 1978 to 2012 in more than 37 000 fish comprising 5 species: lake whitefish (Coregonus clupeaformis), longnose sucker (Catostomus catostomus), northern pike (Esox lucius), walleye (Sander vitreus), and lake trout (Salvelinus namaycush). In reservoirs, concentrations of all species increased rapidly after impoundment, peaking after 4–11 yr in nonpiscivorous species and after 9–14 yr in piscivorous species, at levels 2–8 times higher than those measured in surrounding natural lakes. In fish of standardized length, maximum levels reached 0.33–0.72 μg g−1 in nonpiscivorous species and 1.65–4.66 μg g−1 in piscivorous species. Depending on the reservoir, the return to levels equivalent (p < 0.05) to those found in fish in surrounding natural lakes was completed after 10–20 yr for all nonpiscivorous species and after 20– 31 yr in most piscivorous species, if no additional flooding occurred. These results tend to confirm the findings of other authors suggesting that the following reservoir characteristics play a major role in determining the intensity and duration of after-impoundment THg increases in fish: flooded area, annual volume of water flowing through the reservoir, filling period, water temperature, and percentage of flooded area located in the drawdown zone.

Lung alveoli array-on-chip with a bioartificial membrane

Spatially separated fish populations may display synchrony in annual recruitment if the factors that drive recruitment success, particularly abiotic factors such as temperature, are synchronised across broad spatial scales. We examined inter-annual variation in recruitment among lake whitefish (Coregonus clupeaformis) populations in lakes Huron, Michigan and Superior using fishery-dependent and -independent data from 1971 to 2014. Relative year-class strength (RYCS) was calculated from catch-curve residuals for each year class across multiple sampling years. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. This suggests that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. While our method primarily evaluated year-to-year recruitment variation, it is plausible that recruitment of lake whitefish varies at coarser temporal scales (e.g. decadal). Nonetheless, our findings differ from research on some other Coregonus species and suggest that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors.

Estimation of omega-3 fatty acid (EPA + DHA) intake from Lake Ontario fish based on provincial consumption advisories

Abstract Elevated contaminant levels in the North American Great Lakes have resulted in restrictive fish consumption advisories. Avoiding the risks associated with fish consumption may also decrease the intake of omega-3 fatty acids, eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids; compounds that have been associated with human health benefits. We evaluated whether eating Lake Ontario fish, following the consumption advisories, would result in a sufficient intake of EPA + DHA. Fatty acids and contaminants known to be elevated in fish muscle tissue were analyzed for 282 Lake Ontario fish, representing 21 species. Salmonids had the highest EPA + DHA content among the analyzed species, but the calculated EPA + DHA intake for humans following the consumption advisory was not the highest due to the stringent advisory reflecting elevated contaminant levels, specifically polychlorinated biphenyls. The intake of EPA + DHA from lean fish (with correspondingly lower EPA + DHA contents) could reach values comparable to fatty fish because of the less stringent advisories. In general, the intake of EPA + DHA was more influenced by the consumption advisory than the EPA + DHA content. We suggest that final advisories should be formulated such that they promote maximizing EPA + DHA intake. We found that people, who generally do not consume large amounts of fish from Lake Ontario, may benefit from choosing salmonids, such as lake whitefish, which maximizes the EPA + DHA intake per meal. People who frequently consume Lake Ontario fish may benefit more from choosing panfish like black crappie or yellow perch.

Is There a Trade-Off between Radiation-Stimulated Growth and Metabolic Efficiency?

Beneficial protective effects may result from an adaptive respose to low dose radiation exposure. However, such benefits must be accompanied by some form of cost because the responsible biological mechanisms are not normally maintained in an upregulated state. It has been suggested that stimulation of adaptive response mechanisms could be metabolically costly, or that the adaptive response could come at a sacrifice to other physiological processes. We exposed developing lake whitefish embryos to a fractionated regime of gamma radiation (662 keV; 0.3 Gy min-1) to determine whether radiation-stimulated growth was accompanied by a trade-off in metabolic efficiency. Developing embryos were exposed at the eyed stage to different radiation doses delivered in four fractions, ranging from 15 mGy to 8 Gy per fraction, with a 14 day separation between dose fractions. Dry weight and standard length measurements were taken 2-5 weeks after delivery of the final radiation exposure and yolk conversion efficiency was estimated by comparing the unpreserved dry weight of the yolk to the unpreserved yolk-free dry weight of the embryos and normalizing for size-related differences in somatic maintenance. Our results show that the irradiated embryos were 8-10% heavier than the controls but yolk conversion efficiency was slightly improved. This finding demonstrates that stimulated growth in developing lake whitefish embryos is not "paid for" by a trade-off in the efficiency of yolk conversion.

Development of the embryonic heat shock response and the impact of repeated thermal stress in early stage lake whitefish (Coregonus clupeaformis) embryos

Lake whitefish (Coregonus clupeaformis) embryos were exposed to thermal stress (TS) at different developmental stages to determine when the heat shock response (HSR) can be initiated and if it is altered by exposure to repeated TS. First, embryos were subject to one of three different TS temperatures (6, 9, or 12°C above control) at 4 points in development (21, 38, 60 and 70 days post-fertilisation (dpf)) for 2h followed by a 2h recovery to understand the ontogeny of the HSR. A second experiment explored the effects of repeated TS on the HSR in embryos from 15 to 75 dpf. Embryos were subjected to one of two TS regimes; +6°C TS for 1h every 6 days or +9°C TS for 1h every 6 days. Following a 2h recovery, a subset of embryos was sampled. Our results show that embryos could initiate a HSR via upregulation of heat shock protein 70 (hsp70) mRNA at all developmental ages studied, but that this response varied with age and was only observed with a TS of +9 or +12°C. In comparison, when embryos received multiple TS treatments, hsp70 was not induced in response to the 1h TS and 2h recovery, and a downregulation was observed at 39 dpf. Downregulation of hsp47 and hsp90α mRNA was also observed in early age embryos. Collectively, these data suggest that embryos are capable of initiating a HSR at early age and throughout embryogenesis, but that repeated TS can alter the HSR, and may result in either reduced responsiveness or a downregulation of inducible hsps. Our findings warrant further investigation into both the short- and long-term effects of repeated TS on lake whitefish development.

The effects of fluctuating temperature regimes on the embryonic development of lake whitefish (Coregonus clupeaformis)

Fluctuating incubation temperatures may have significant effects on fish embryogenesis; yet most laboratory-based studies use constant temperatures. For species that experience large, natural seasonal temperature changes during embryogenesis, such as lake whitefish (Coregonus clupeaformis), seasonal temperature regimes are likely optimal for development. Anthropogenic activities can increase average and/or variability of natural incubation temperatures over large (e.g. through climate change) or smaller (e.g. thermal effluent discharge) geographic scales. To investigate this, we incubated lake whitefish embryos under constant (2, 5, or 8°C) and fluctuating temperature regimes. Fluctuating temperature regimes had a base temperature of 2°C with: 1) seasonal temperature changes that modeled natural declines/inclines; 2) tri-weekly +3°C, 1h temperature spikes; or 3) both seasonal temperature changes and temperature spikes. We compared mortality to hatch, morphometrics, and heart rate at three developmental stages. Mortality rate was similar for embryos incubated at constant 2°C, constant 5°C, or with seasonal temperatures, but was significantly greater at constant 8°C. Embryos incubated constantly at >2°C had reduced body growth and yolk consumption compared to embryos incubated with seasonal temperature changes. When measured at the common base temperature of 2°C, embryos incubated at constant 2°C had lower heart rates than embryos incubated with both seasonal temperature changes and temperature spikes. Our study suggests that incubating lake whitefish embryos with constant temperatures may significantly alter development, growth, and heart rate compared to incubating with seasonal temperature changes, emphasizing the need to include seasonal temperature changes in laboratory-based studies.

Do differences in the activities of carbohydrate metabolism enzymes between Lake Whitefish ecotypes match predictions from transcriptomic studies?

Transcriptomic studies are facilitating the search for the molecular bases of adaptation in natural populations, but the impact of these differences in mRNA content on animal physiology are often unknown. One way to determine if molecular changes have the potential to influence animal physiology and performance is to test for correlated changes at higher levels of biological organization, including enzyme activity. Here, we measure the activities of carbohydrate metabolism enzymes to test if previously documented genetic and transcriptomic variation between 'dwarf' and 'normal' Lake Whitefish ecotypes are associated with corresponding changes in enzyme activity (measured as maximal rate, Vmax) in liver and skeletal muscle. We use laboratory-reared fish from the same populations as prior transcriptomic studies and find that white muscle mRNA content is a good predictor of glycolytic and glycogen metabolism enzyme activity, and dwarf whitefish have evolved higher activities than normal whitefish. However, the differences in hepatic mRNA content found between ecotypes in prior studies are not associated with comparable changes in enzyme activity. For example, dwarf whitefish have lower enzyme activities, but higher transcript abundances for two glycolytic enzymes compared to normal whitefish. Overall, we find that transcriptomic studies successfully highlight evolutionary variation in enzyme activities, but not always in the direction predicted, indicating that a variety of tissue-specific regulatory mechanisms contributed to the evolution of energy metabolism in Lake Whitefish.

Polychlorinated Biphenyls and Polychlorinated Dioxins–Furans in Lake Trout and Whitefish Composite Samples from Commercial Fisheries in Lakes Erie, Huron, and Superior

Polychlorinated biphenyls (PCBs; sum of 36 congeners) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs; sum of 17 2,3,7,8-substituted congeners) were measured in 93 composite samples prepared from individual lake trout (Salvelinus namaycush) and whitefish (Coregonus clupeaformis) samples collected from Lake Erie, Lake Huron, and Lake Superior. All samples had detectable concentrations of PCBs and PCDD/Fs; maximum PCB concentrations in both trout (750 ng g-1 whole weight [ww]) and whitefish (210 ng g-1 ww) were found in composites from fish collected from Lake Huron. The maximum toxic equivalent concentration was found in a lake trout composite sample from Lake Huron (53 pg g-1 ww). PCB and PCDD/F congener profiles were comparable to patterns observed in fishes collected from other regions of Canada, although concentrations were above those found in other regions. A positive correlation was found between PCB concentrations determined using the historical Aroclor equivalency method and those determined using the sum of the congeners measured (r2 = 0.871; Spearman correlation r = 0.917) or using the six indicator PCB congeners (28, 52, 101, 138, 153, and 180; r2 = 0.850; Spearman correlation r = 0.935). PCBs were the dominant contributor to the overall toxic equivalent concentrations in the fish composite samples tested. These findings provide insight into PCB and PCDD/F concentrations in two commercially important fish species over a discrete time period.

Modeling the Multiple Facets of Speciation-with-Gene-Flow toward Inferring the Divergence History of Lake Whitefish Species Pairs (Coregonus clupeaformis).

Parallel divergence across replicated species pairs occurring in similar environmental contrasts may arise through distinct evolutionary scenarios. Deciphering whether such parallelism actually reflects repeated parallel divergence driven by divergent selection or a single divergence event with subsequent gene flow needs to be ascertained. Reconstructing historical gene flow is therefore of fundamental interest to understand how demography and selection jointly shaped genomic divergence during speciation. Here, we use an extended modeling framework to explore the multiple facets of speciation-with-gene-flow with demo-genetic divergence models that capture both temporal and genomic variation in effective population size and migration rate. We investigate the divergence history of replicate sympatric species pairs of Lake Whitefish (normal benthic and dwarf limnetic) characterized by variable degrees of ecological divergence and reproductive isolation. Genome-wide SNPs were used to document the extent of genetic differentiation in each species pair, and 26 divergence models were fitted and compared with the unfolded joint allele frequency spectrum of each pair. We found evidence that a recent (circa 3,000–4,000 generations) asymmetrical secondary contact between expanding postglacial populations has accompanied Whitefish diversification. Our results suggest that heterogeneous genomic differentiation has emerged through the combined effects of linked selection generating variable rates of lineage sorting across the genome during geographical isolation, and heterogeneous introgression eroding divergence at different rates across the genome upon secondary contact. This study thus provides a new retrospective insight into the historical demographic and selective processes that shaped a continuum of divergence associated with ecological speciation.