Relationships between lake ecology and morphological characters in Icelandic Arctic charr,Salvelinus alpinus

The common occurrence of parallel phenotypic patterns suggests that a strong relationship exists between ecological dynamics and micro‐evolution. Comparative studies from a large number of populations under varying sets of ecological drivers could contribute to a better understanding of this relationship. We used data on morphology of arctic charr (Salvelinus alpinus) and ecological factors from 35 Icelandic lakes to test the hypothesis that morphological patterns among monomorphic charr populations from different lakes are related to interlake variation in ecological characteristics. There is extensive phenotypic diversity among populations of Icelandic charr, and populations are easily distinguished based on overall body morphology. The results obtained in the present study showed that the morphological diversity of charr was related to large‐scale diversity in lake ecology. Variation in charr morphology was related to water origin (e.g. spring fed versus run‐off), bedrock age, and fish community structure. The present study shows how various ecological factors can shape the biological diversity that we observe. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 761–771.     

SSU rRNA gene sequence reveals two genotypes of Spironucleus barkhanus (Diplomonadida) from farmed and wild Arctic charr Salvelinus alpinus

Spironucleus barkhanus isolated from the blood of Arctic charr Salvelinus alpinus from a marine fish farm were genetically compared with S. barkhanus isolated from the gall bladder of wild Arctic charr. The wild Arctic charr were caught in the lake used as the water source for the hatchery from which the farmed fish originated. Sequencing of the small subunit ribosomal RNA gene (SSU rDNA) from these 2 populations showed that the isolates obtained from farmed and wild Arctic charr were only 92.7 % similar. Based on the sequence differences between these isolates, it is concluded that the parasites isolated from the farmed fish have not been transmitted from wild Arctic charr in the hatchery's fresh water source. It is therefore most likely that the farmed fish were infected by S. barkhanus after they were transferred to seawater. S. barkhanus isolated from diseased farmed Arctic charr were 99.7% similar to the isolates obtained from diseased farmed Chinook (Canada) and Atlantic salmon (Norway). The high degree of sequence similarity between S. barkhanus from farmed Arctic charr, Chinook and Atlantic salmon indicates that systemic spironucleosis may be caused by specific strains/variants of this parasite. The genetic differences between the isolates of farmed and wild fish are of such magnitude that their conspecificity should be questioned.     

Diversification, Sympatric Speciation, and Trophic Polymorphism of Arctic Charr, Salvelinus Alpinus Complex, in Transbaikalia

In northern Transbaikalia, independently evolving landlocked populations of Arctic charr are found in mountain lakes. To assess the diversity of charr in this region, speciation modes involved in the evolution of charr forms, and the role of trophic polymorphism in their divergence, we studied the morphology and feeding of dwarf, small, and large forms of Arctic charr from a number of Transbaikalian lakes. Meristic data on charr from five lakes support the earlier conclusion that the three forms do not represent separate lineages but have independently diverged in sympatry in each of the lakes. In 10 lakes, the dwarf form showed varying degrees of differentiation from normal (small and large) charr in meristic characters (up to morphologically distinct and presumably reproductively isolated groupings), which is viewed as various levels of sympatric divergence. Indexes of gill raker length in fish from 20 lakes vary among populations of both dwarf and normal charr, with forms having short and long rakers being sympatric in some of these lakes. However, the index can be used only for comparing charr of different forms up to about 32cm fork length (FL) because it is strongly negatively correlated with size in larger fish. The study of charr diets in 21 lakes indicates that large charr are piscivorous whereas dwarf and small charr feed on a wide range of invertebrates, partitioning these resources in different ways. Planktivores, including very specialized ones, and non-planktivores (benthic feeders, insectivores) can be identified within the small and dwarf forms. The proportion of plankton in the diets of dwarf and small charr is positively correlated with the number and length of gill rakers while the proportion of benthos is negatively correlated. Allopatric planktivorous and non-planktivorous small charr differ in body proportions; parallel emergence of such morphotypes in different parts of the range is a characteristic feature of the Salvelinus alpinus complex.     

Loss of genetic variation and effective population size of Kirikuchi charr: implications for the management of small, isolated salmonid populations

Small, isolated populations may face extinction due to a combination of inbreeding depression and other threats. Effective population size ( N _e) is one comprehensive measure that allows us to evaluate the genetic status of a population, and to make management decisions regarding genetic viability. We simulated loss of genetic variation and estimated N _e for two small, isolated populations of Kirikuchi charr Salvelinus leucomaenis japonicus , the endangered, southernmost local populations of the genus Salvelinus in the world, using VORTEX, an individual-based stochastic PVA model. Approximately half of the genetic variation was lost over 200 years regardless of census population size and demographic parameters, and N _e estimates were roughly 50 in each of the two populations, suggesting the possibility of inbreeding depression. The target population size of N _e>500, by securing long-term viability, is several times that of the present size of each of the populations studied, and no local habitats maintaining such a target number are considered to exist. The results strongly indicate a need for recovering natural connections and potential gene flow among local populations. However, the impending threat to these populations from non-native charr widely distributed throughout the drainage has prevented the recovery of the connections. Given the small N _e of the two populations, it would be necessary to retain gene flow artificially within or across local populations. This will be true of many other salmonid populations that have been isolated or fragmented recently.     

Effects of population,family, and diet on craniofacial morphology of Icelandic Arctic charr (Salvelinus alpinus)

We evaluated hypotheses of intralacustrine diversification and plastic responses to two diet environments in Icelandic Arctic charr (Salvelinus alpinus). Full‐sib families of progeny of wild polymorphic charr from two lakes where morphs vary in their degree of phenotypic and ecological divergence were split, with half of the offspring reared on a benthic and half on a limnetic type of diet to estimate family norms of reaction. We focused on variation in craniofacial traits because they are probably functionally related to diet and complement a previous study of body shape in these charr. A hierarchical analysis of phenotypic variation between lakes, pairs of morphs within each lake, and two families within each morph found that phenotypic variation partitioned between families relative to morphs was reduced in the more ecologically diversified population, which is consistent with adaptive diversification. The effect size of plastic responses between lake populations was similar, suggesting little difference in the degree of canalization in contrast to a previous analysis of body form plasticity. Thus, the role that plastic morphological responses play in the adaptive diversification of morphs and different lake populations of Arctic charr may depend on the trait. © 2013 The Linnean Society of London     

Salinity tolerance of freshwater acclimated, small-sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus , less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.     

Introgressive hybridization between Dolly Varden Salvelinus malma and white‐spotted charr Salvelinus leucomaenis on Hokkaido Island, Japan

Intra‐ and interspecific phylogenetic analysis of Dolly Varden Salvelinus malma and white‐spotted charr Salvelinus leucomaenis throughout Hokkaido Island was conducted using nucleotide sequences of the mitochondrial DNA control region and three nuclear DNA markers [ribosomal DNA (ITS‐1), microsatellite ( u ‐85), SINE ( Fok ‐223)]. A total of 19 mtDNA haplotypes from 271 individuals of Dolly Varden, nine haplotypes from 134 white‐spotted charr were defined, and identified two well‐supported monophyletic clades for each species. Two haplotypes of Dolly Varden, however, were clustered together in the white‐spotted charr clade. Those haplotypes were found only from several rivers in the Shiretoko Peninsula, and a neighbouring river of that region. Analyses of ribosomal DNA and Fok ‐223 loci revealed that both species are characterized by having completely species‐specific diagnostic sequence and fragment patterns. Dolly Varden of the Shiretoko populations are typically allopatric in distribution where white‐spotted charr do not currently occur. In addition, incongruence in genetic relationships between mtDNA and nuclear DNA markers give strong evidence of historical mtDNA introgression between Dolly Varden and white‐spotted charr. Some white‐spotted charr diagnostic alleles in a nuclear microsatellite locus ( u ‐85) were found in some Shiretoko Dolly Varden populations, suggesting that introgressive hybridization might have also occurred in relatively recent contact and potentially ongoing evolutionary event. The present study presents an example of historical hybridization and introgression at the southernmost distribution limits of Dolly Varden.     

Mitochondrial DNA variation of Salvelinus species found in Finland

Mitochondrial DNA (mtDNA) was purified from the Arctic charr, Salvelinus alpinus , the brook charr, Salvelinus fontinalis , and the lake charr, Salvelinus namaycush , and digested with restriction enzymes Ava II, Hinf I, Eco R V, Pst I and Xba I. Two Arctic charr samples were from natural populations and they represented two different morphotypes of Arctic charr. All other studied populations were hatchery maintained. Eight additional restriction enzymes and double digestions were employed to study morphotypes of Arctic charr. We distinguished two morphotypes with restriction enzyme Nci I. Sequence divergence among mtDNA types was 2.9–3.8% between S. alpinus and S. fontinalis , 3.4–4.6% between S. alpinus and S. namaycush , and 4.7–5.3% between S. fontinalis and S. namaycush . lntraspecific variation was lowest in Arctic charr, the average of nucleon diversity for three populations being 0.179, while for brook charr and for lake charr nucleon diversity was 0.334 and 0.550, respectively. According to the number of mtDNA types, it is obvious that introduction to Finland and hatchery propagation have not greatly affected the mtDNA variation of brook charr or lake charr.     

Incidence of a skeletal deformity (truncated upper jaw) in an isolated population of white-spotted charr Salvelinus leucomaenis

Although dorsal and caudal fin deformities (curvature), abnormal body color patterns, and fluctuating asymmetry of meristic characters have been previously reported for white-spotted charr (Salvelinus leucomaenis), the incidence of skeletally deformed individuals in the wild are extremely rare. Here, we report on skeletally deformed individuals of white-spotted charr with extremely truncated upper jaw, in a headwater reach of the Yoneshiro River, northern Honshu, Japan. In this study, we examined the genetic diversity of deformed and non-deformed populations of white-spotted charr using polymorphic microsatellite DNA markers. We also compared individual growth histories of deformed individuals with normal individuals using a back-calculation of fish lengths at previous ages from otolith annuli. We collected 41 and 100 individuals from the below- and above-waterfall sites, respectively. Of these, two individuals from the above-waterfall site were skeletally deformed, whereas the other individuals had a normal morphology. Microsatellite DNA genetic diversities of the above-waterfall population were notably lower than those of the just below-waterfall population. Individuals of the above-waterfall population had significantly higher internal relatedness and lower standardized heterozygosity values compared with those of the below-waterfall population, indicating higher inbreeding situation of the above-waterfall individuals compared with individuals in the below-waterfall site. Back-calculation of individual growth using otoliths revealed that deformed individuals grew significantly slower than sympatric normal individuals. Although incidence of deformed individuals in the wild might be related with accumulated inbreeding as suggested for other fishes, mechanisms for their long-term persistence in the wild remain unclear.     

Ongoing localized extinctions of stream-dwelling white-spotted charr populations in small dammed-off habitats of Hokkaido Island,Japan

Habitat fragmentation caused by damming can greatly reduce the population viability of aquatic organisms, with smaller fragmented populations at higher risk of extinction due to increased demographic, genetic, and environmental stochasticity. However, empirical evidence demonstrating that smaller natural populations are more vulnerable to extinction is limited. We studied the vulnerability to extinction of white-spotted charr (Salvelinus leucomaenis) populations in 30 dammed-off streams in Oshima Peninsula, southwestern Hokkaido Island, Japan, by comparing the incidence of charr populations in streams between 1999 and 2014. Using electrofishing and environmental DNA surveys, we identified three localized extinctions, with the probability of extinction increasing with decreasing watershed area (our surrogate for habitat size). We also found a new population in one dammed-off stream in which white-spotted charr were previously unknown, after installation of a fish ladder, indicating the capacity of white-spotted charr to recolonize reconnected habitat in a short period. Our results suggest that localized extinction of white-spotted charr in small dammed-off streams is ongoing, but that appropriate fish migration corridors can reduce localized extinction risk and increase the probability of species persistence.

     

Genetic divergence of sympatric charrs of the genus Salvelinus from Nachikinskoe Lake (Kamchatka)

We studied genetic differentiation of two charr species, Dolly Varden Salvelinus malma malma Walbaum and resident lacustrine charr Salvelinus sp., which sympatrically inhabit Nachikinskoe Lake (the Bol'shaya River basin) in southwestern Kamchatka Peninsula. Using restriction analysis (RFLP), three mitochondrial DNA fragments (ND1/ND2, ND5/ND6, and Cytb/D loop) amplified in polymerase chain reaction (PCR) were compared. The divergence of the mtDNA sequences between Salvelinus sp. and S. malma malma was 2.8%; Salvelinus sp. and S. taranetzi, 0.36%; Salvelinus sp. and S. krogiusae, 0.21%; Salvelinus sp. and S. alpinus, 3.0%. These results point to reproductive isolation of charrs in Nachikinskoe Lake and support the earlier suggestion on a close relationship between Salvelinus sp., S. taranetzi, and S. krogiusae.     

The present state of an Arctic charr (Salvelinus alpinus L.) population in Lake Imandra subjected to over-fishing

The influence of fishery on the state of Arctic charr (Salvelinus alpinus L.) population in Lake Imandra. The largest freshwater water body of the Kola Peninsula, is considered. Retrospective analysis of the catches during the period 1930–2010 revealed that the consequences of uncontrolled fishing are comparable with those of technogenic pollution. As a result of intensive and long-term antropogenic influence on the lake the number of age-groups decreased; the weight and length indices changed; the structure of fish population was simplified. Even after improving of environmental conditions, the numbers of fish continued to decrease due to uncontrolled angling and poaching which led to almost complete extinction of charr in the lake.     

PCB impairs smoltification and seawater performance in anadromous Arctic charr (Salvelinus alpinus)

The impacts of polychlorinated biphenyl (PCB) exposure on smoltification and subsequent seawater performance were investigated in hatchery-reared, anadromous Arctic charr (Salvelinus alpinus). The fish were subjected to a 2-month summer seawater residence, after which they were orally dosed with 0 (Control, C), 1 (Low Dose, LD) or 100 mg Aroclor 1254 kg(-1) body mass (High Dose, HD) in November. They were then held in fresh water, without being fed (to mimic their natural overwintering in freshwater), until they had smolted in June the next year. The smolts were then transferred to seawater and fed to mimic their summer feeding residence in seawater, followed by a period without food in freshwater from August until maturation in October. Compared with C and LD charr, the HD charr had either a transient or a permanent reduction in plasma growth hormone, insulin-like growth factor-1, and thyroxin and triiodothyronine titers during the period of smoltification. These hormonal alterations in the HD charr corresponded with impaired hyposmoregulatory ability in May and June, as well as reduced growth rate and survival after transference to seawater. Consequently, fewer fish in the HD group matured in October compared to the other two treatments. The HD fish had a liver PCB concentration ranging between 14 and 42 mg kg(-1) wet mass, whereas there were similar, and very low, liver PCB concentrations in LD and C fish throughout the smolting period. Our findings suggest that PCB might compromise mechanisms important for fitness in a fish species living in an extreme environment.     

Experimental evidence of cannibalism and prey specialization in Arctic charr,Salvelinus alpinus

Synopsis Use of a radiographic technique enabled the study of prey selection and individual specialization in Arctic charr, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions. Both naive and experienced fish (mean weight 475 g, mean length 34.9 cm), selected the smallest individuals when offered juvenile charr (6–16 cm) as prey. The selected prey were, on average, 22% of the predator length. Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised: cannibals, pellet eaters and non-feeding fish.     

Abundance, Annual Survival, and Recruitment of Unexploited and Exploited Lake Charr, Salvelinus Namaycush, Populations at the Experimental Lakes Area, Northwestern Ontario

We studied abundance, annual survival, and recruitment of nine lake charr, Salvelinus namaycush, populations at the Experimental Lakes Area, Ontario, for periods of 9–24 years. We used the Jolly–Seber mark-recapture method to evaluate abundance and annual survival in all populations, and total catches of individual year classes to evaluate recruitment. Seven populations were unexploited and unaffected by whole-lake experiments. One population was exploited prior to mark-recapture study and another was affected by experimental acidification. Abundance ranged from 8 to 24 fish ha^–1 in the unaffected populations. Annual survival ranged from 78% to 93%yr^–1 in all populations except the exploited population. This population may have been additionally affected by northern pike, Esox lucius, predation. Yearly recruitment was relatively constant in all populations and related to lake charr abundance. Lake charr abundance did not recover in populations affected by exploitation or acidification. Unexploited lake charr populations were characterized by relatively constant abundance, high annual survival, and relatively constant annual recruitment.     

Contrasting life history strategies of sympatric Arctic charr morphs, Salvelinus alpinus

In polymorphic populations morphs usually diverge in morphology, ecology and life history, which is most likely driven by adaptations to different environments or resources. Sympatric morphs may develop differences in several life history traits to be able to maximize fitness in alternative niches and habitats. Here, the contrasting life history traits of three sympatric Arctic charr (Salvelinus alpinus (L.)) morphs in a deep and oligotrophic lake in sub-arctic Norway are addressed. The charr morphs differ in spawning habitat and trophic niche. One is a littoral spawning morph that feeds on benthic invertebrates and zooplankton in the littoral and pelagic zones (referred to as the LO-morph), and two other are profundal spawning morphs that either utilize profundal soft bottom benthos as food resource (the PB-morph) or are piscivorous (the PP-morph). The LO-morph typically had intermediate life-history traits relative to the two profundal morphs that had highly contrasting life history traits, especially in growth and age and size of maturity. The PB-morph matured at a young age (～3 years) and at a small body size (～8.5 cm), thereby increasing their fitness by investing in reproduction early in life, which results in a short generation time and decreased probability of being predated before first reproduction. The PP-morph on the other hand, matured at an old age (～9.2 years) and a large body size (～26 cm), thereby increasing their fitness by investing in somatic growth to enhance initial fecundity, and also to reach a large body size profitable for piscivory. The different trade-off regime between the PP- and PB-morphs seems to be caused by adaptation to alternative trophic niches, and appears to be an important factor for the co-occurrence of the two sister-morphs in the profundal zone.     

The growth of charr, Salvelinus willughbii Günther, in Windermere

The growth of charr ( Salvelinus willughbii Günther ) caught in Windermere from 1941–1952 has been studied. Scales were used for determination of age and back-calculation of length for age. Autumn and spring spawners, males and females, and charr of normal and dwarf growth were treated separately. In fish of normal growth, the spring spawners were significantly smaller than the autumn spawners at ages 1 and 2 years, and significantly larger from age 4 years onwards. There was little difference in growth between males and females within the two spawning populations. Charr of lengths of less than 200 mm at age 4 years were considered to be dwarfs. Mean lengths at capture of male charr were: autumn spawners normal growth 272 mm, dwarf 218 mm; spring spawners normal growth 327 mm, dwarf 194 mm. The oldest recorded age was 8 years.     

Migration, growth and survival of wild and hatchery-reared anadromous Arctic charr (Salvelinus alpinus) in Finnmark, Northern Norway

Two groups of anadromous Arctic charr ( Salvelinus alpinus ) (size 200–350 mm) reared in heated water (6–12° C) under simulated natural photoperiod were individually tagged and released in spring 1988. The fish were released at two sites, in the estuary of the River Halselva and in the fjord, 2 km from the river mouth. Growth, timing of migration and survival of these hatchery-reared fish was compared to that of wild anadromous charr of the same size over a 4-year period. The hatchery-reared charr had poorer growth than the wild fish during their first year in sea water. They also resided longer in the sea and had a slightly lower survival than wild fish. During the second year, hatchery-reared charr displayed good growth, and after the third sea-season the fish were ready for slaughter at a size of approximately 800g. The results suggest that the successful development of Arctic charr ranching will be dependent upon production and release strategies that lead to improved migratory and feeding behaviour of the fish during their first season at sea.     

The ecological interaction between arctic charr, Salvelinus alpinus (L.), and the plerocercoid stage of Diphyllobothrium ditremum

Six hundred and two arctic charr, Salvelinus alpinus , from a small lake (30 ha) were examined for infection with plerocercoids of Diphyllobothrium ditremum the only species of this genus present; 466 (77.4%) harboured the parasite in an overdispersed infection. The prevalence of infection increased with age and reached 100% at 7+ years for males and 8+ years for females. The rate of infection appeared to be related to the feeding biology of the charr which did not change within the age span studied. The rate of increase in density of infection (plerocercoids per fish) decreased with age as did the degree of overdispersion. It is concluded that the infection probably induces mortality in the fish population, and that such mortality is dependent on parasite density.     

Early developmental plasticity and integrative responses in arctic charr (Salvelinus alpinus): effects of water velocity on body size and shape

Environmental conditions such as temperature and water velocity may induce changes among alternative developmental pathways, i.e. phenotypic responses, in vertebrates. However, the extent to which the environment induces developmental plasticity and integrated developmental responses during early ontogeny of fishes remains poorly documented. We analyzed the responses of newly hatched Arctic charr (Salvelinus alpinus) to four experimental water velocities during 100 days of development. To our knowledge, this work is the first to analyze developmental plasticity responses of body morphology to an experimental gradient of water velocities during early ontogeny of fish. Arctic charr body size and shape responses show first, that morphometric traits display significant differences between low and high water velocities, thus revealing directional changes in body traits. Secondly, trait variation allows the recognition of critical ontogenetic periods that are most responsive to environmental constraints (40-70 and 80-90 days) and exhibit different levels of developmental plasticity. This is supported by the observation of asynchronous timing of variation peaks among treatments. Third, morphological interaction of traits is developmentally plastic and time-dependent. We suggest that developmental responses of traits plasticity and interaction at critical ontogenetic periods are congruent with specific environmental conditions to maintain the functional integrity of the organism.