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73 results for “charr”

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Data from: Density-dependent diel activity in stream-dwelling Arctic charr Salvelinus alpinus

Intraspecific competition plays a significant role in shaping how animals use and share habitats in space and time. However, the way individuals may modify their diel activity in response to increased competition has received limited attention. We used juvenile (age 1+) Arctic charr Salvelinus alpinus to test the prediction that individuals at high population density are more active and distribute their foraging activity over a greater portion of the 24-h cycle than individuals at low population density. Individually tagged fish were stocked in seminatural stream enclosures at low (2 fish/m2) and high (6 fish/m2) density. During each of two 2-week experimental rounds, activity of all fish within each enclosure was recorded every 3 h over seven 24-h cycles. At high density, fish were more active and distributed their activity over a greater portion of the 24-h cycle, with increased activity particularly at crepuscular times. Fluctuations in ecological conditions (e.g., water temperature and light intensity) also affected activity. Fish at high density grew as fast as fish at low density. This study demonstrates that individuals exhibit a degree of behavioral flexibility in their response to changes in ecological conditions and suggests that intraspecific competition can cause animals to modify temporal aspects of their activity to gain access to resources and maintain growth.

opencc-zeroDec 2015View details →

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Data from: Genetic variability and structuring of Arctic charr (Salvelinus alpinus) populations in northern Fennoscandia

Variation in presumably neutral genetic markers can inform us about evolvability, historical effective population sizes and phylogeographic history of contemporary populations. We studied genetic variability in 15 microsatellite loci in six native landlocked Arctic charr (Salvelinus alpinus) populations in northern Fennoscandia, where this species is considered near threatened. We discovered that all populations were genetically highly (mean FST ≈ 0.26) differentiated and isolated from each other. Evidence was found for historical, but not for recent population size bottlenecks. Estimates of contemporary effective population size (Ne) ranged from seven to 228 and were significantly correlated with those of historical Ne but not with lake size. A census size (NC) was estimated to be approximately 300 individuals in a pond (0.14 ha), which exhibited the smallest Ne (i.e. Ne/NC = 0.02). Genetic variability in this pond and a connected lake is severely reduced, and both genetic and empirical estimates of migration rates indicate a lack of gene flow between them. Hence, albeit currently thriving, some northern Fennoscandian populations appear to be vulnerable to further loss of genetic variability and are likely to have limited capacity to adapt if selection pressures change.

opencc-zeroDec 2014View details →

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Data from: Does egg carotenoid improve larval quality in Arctic charr (Salvelinus alpinus)?

Females in mutually ornamented species are often less conspicuously ornamented than their male conspecifics. It has been hypothesized that offspring quality may decrease if females invest more resources into ornaments at the expense of resources in eggs. An experiment was carried out to test whether natural variation in carotenoid in the eggs from a wild population of Arctic charr (Salvelinus alpinus) was associated with survival and growth of their offspring until hatching. Wild Arctic charr were caught at a spawning ground during the spawning period. Eggs from two different females, one female with yellowish carotenoid-rich eggs and one with paler eggs, were fertilized by sperm from the same male. This was repeated until gametes were collected from 42 females and 21 males, giving a total of 21 groups. After fertilization, the zygotes from each of the two females were reared in four replicated groups. These 168 groups were reared separately until hatching when the surviving larvae were counted and their body length measured. For the two response variables survival and body length at hatching, no effect was demonstrated of any of the predictors (i) amount of carotenoid in the unfertilized eggs, (ii) the mothers' body condition or (iii) ornament intensity of their red carotenoid-based abdominal ornament. Thus, this study gives no support for the hypothesis that females investing less carotenoid into their eggs suffer from decreased offspring quality until hatching. This lack of association between female ornament intensity and their fitness is not as expected if female ornaments evolved due to direct sexual selection from males on the more ornamented females ("direct selection hypothesis").

opencc-zeroApr 2022View details →

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Intraspecific competition and temperature drive habitat-based resource polymorphism in brook charr

Intra- and interspecific competition, two density-dependent processes, are the two main driving forces suggested to promote habitat-based resource polymorphism, but very few studies have provided empirical support for this hypothesis. Furthermore, external drivers like temperature, an important environmental constraint in ectotherms, are often omitted when studying density-dependent habitat selection. Specifically, ambient temperature may have important effects on habitat-based resource polymorphism in ectotherms. Using mixed-effects modelling and isodar analyses, we quantified the effects of water temperature as well as intra- and interspecific competition on abundance and density-dependent habitat selection of brook charr (Salvelinus fontinalis) between littoral and pelagic habitats in 27 Canadian Shield lakes. We found that interspecific competition with white sucker (Catostomus commersonii) reduced brook charr abundances in both habitats but did not affect their density-dependent habitat selection. In contrast, the isodar analysis showed density-dependent habitat selection, confirming that intraspecific competition is a driver of brook charr habitat use in this system. Furthermore, brook charr preferred the littoral habitat at water temperatures below 20.8°C, but preferred the pelagic habitat above this threshold and no longer used the littoral habitat when its temperature was above ~22.2°C. By incorporating an external driver in the density-dependent habitat selection model, we show how the littoral temperature can shape brook charr distribution patterns between the littoral and pelagic habitats by acting as a thermal barrier and thus limiting the willingness of fish to use resources in the littoral habitat. This result suggests that global warming could constrain the diversifying effect of intraspecific competition and prevent resource polymorphism, a phenomenon that promotes adaptive radiation and speciation.

opencc-zeroOct 2022View details →

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EcoEvo Icelandic Arctic charr population divergence

Conceptual models of adaptive divergence and ecological speciation in sympatry predict differential resource use, phenotype-environment correlations, and reduced gene flow among diverging phenotypes. While these predictions have been assessed in past studies connections among them have rarely been assessed collectively. We examined relationships among phenotypic, ecological, and genetic variation in Arctic charr (Salvelinus alpinus) from six Icelandic localities that have undergone varying degrees of divergence into sympatric benthic and pelagic morphs. We characterized morphological variation with geometric morphometrics, tested for differential resource use between morphs using stable isotopes, and inferred the amount of gene flow from single nucleotide polymorphisms. Analysis of stable isotopic signatures indicated that sympatric morphs showed similar difference in resource use across populations, likely arising from the common utilization of niche space within each population. Carbon isotopic signature was also a significant predictor of individual variation in body shape and size, suggesting that variation in benthic and pelagic resource use is associated with phenotypic variation. The estimated percentage of hybrids between sympatric morphs varied across populations (from 0 to 15.6%) but, the majority of fish had genotypes (ancestry coefficients) characteristic of pure morphs. Despite evidence of reduced gene flow between sympatric morphs, we did not detect the expected negative relationship between divergence in resource use and gene flow. Three lakes showed the expected pattern, but morphs in the fourth showed no detectable hybridization and had relatively low differences in resource use between them. This coupled with the finding that resource use and genetic differentiation had differential effects on body shape variation across populations, suggests that reproductive isolation maintains phenotypic divergence between benthic and pelagic morphs when the effects of resource use are relatively low. Our ability to assess relationships between phenotype, ecology, and genetics deepens our understanding of the processes underlying adaptive divergence in sympatry.

opencc-zeroOct 2022View details →

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Data from: Size‐dependent stress response in juvenile Arctic charr (Salvelinus alpinus) under prolonged predator conditioning

Predator conditioning can be used to improve post-release antipredator recognition of hatchery-reared salmonids. However, possible negative stress-related effects of prolonged predator conditioning on juvenile fish physiology are poorly understood. We studied the effects of prolonged (91 days) predator odour exposure on whole-body cortisol level and spleen size in six full-sib families of juvenile hatchery-bred Arctic charr (Salvelinus alpinus). Chemical cues from water containing charr-fed pikeperch (Sander lucioperca) were used as the predator exposure stimuli, and lakewater was used as a chemical control. Our study revealed that juvenile body cortisol levels post-predator conditioning were affected by treatment, fish size and their interaction. Importantly, among the smaller (i.e. slowest growing) charr, the predator-exposed fish had higher cortisol levels than control fish, while the opposite pattern was true for the larger fish. These results suggest that chemical cues from charr-fed predators induce a prolonged stress response in juvenile charr. As prolonged predation exposure seems to elevate stress levels in a size-dependent manner, the larger, faster growing fish could possibly have intrinsically lower stress responses to predation threats than smaller, slower growing fish. Possible coupling between stress sensitivity and growth requires further attention due to the likely implications for the management of unintended domestication among captive-reared salmonids.

opencc-zeroDec 2018View details →

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