Diversity of nosed charrs <Emphasis Type="Italic">Salvelinus malma</Emphasis> (Salmonidae) of Lake Kronotskoe (Kamchatka)

The littoral benthivorous charrs Salvelinus malma with subterminal mouth distributed in Lake Kronotskoe basin are separated into three distinct morphs. These morphs significantly differ in head proportions, jaws' length, skull structure, and degree of gill rakers' reduction. The morphs spawn in distant lake tributaries at the spawning grounds of various types. Joint spawning has never been observed for these morphs in any type of spawning grounds. The differences in the external morphology and growth rate of the morphs become evident during the riverine life stage. The adult charrs inhabit the same sites of the littoral zone. No reliable difference is found in the diet among morphs, since all nosed charrs dominantly feed on amphipods with the exception of a few individuals that fed on chironomid larvae.     

Heterochrony in skeletal development and body size in progeny of two morphs of Arctic charr from Thingvallavatn, Iceland

Planktivorus Arctic charr had larger eggs than small benthivorous charr and the progeny of the former were longer (total length) at days 125, 145 and 159 after fertilization. Size differences remained significant after the removal of egg size effect on embryo size. Size of hybrid progeny tended to be similar to their maternal pure progeny group, suggesting maternal effects not directly related to yolk volume. In general, fin ray number increased faster in small benthivorous charr progeny than in planktivorous charr progeny, hybrid progeny tending to have intermediate fin ray numbers. The results indicate that morph differences in embryonic growth and skeletal development have a genetic and maternal component. Results support the hypothesis that in the period from hatching until just after first external feeding small benthivorous charr allocate more energy towards bone development, e.g. formation of fin rays, while planktivorous charr allocate more energy to body growth. The different developmental trajectories may reflect adaptations to discrete differences in habitats between the morphs.     

Trophic specialization in Arctic charr Salvelinus alpinus (Pisces; Salmonidae): morphological divergence and ontogenetic niche shifts

Lake Thingvallavatn supports four trophic morphs of Arctic charr, Salvelinus alpinus (L.); two of the morphs are benthic (small and large benthivorous charr) one exploits pelagic waters (planktivorous charr) and the fourth is found in both habitats (piscivorous charr). The morphological variation among these morphs was analysed by use of principal component analysis and canonical discriminant analysis. The benihic morphs have a short lower jaw and long pectoral fins. The benthic fish also have fewer gillrakers than the other morphs. Small and large benthivorous charrs attain sexual maturity from 2 and 6 years of age, and at fork lengths from 7 and 22 cm, respectively. Small benthivorous charr retain their juvenile parr marks as adults, have beige ventral colours, and are frequently melanized under the lower jaw. Planktivorous and piscivorous charr attain sexual maturity from 4 and 6 years of age, from fork lengths of 15 and 23 cm, respectively. This phenotypic polymorphism is associated with habitat utilization and diet of the fish, and has probably arisen within the lake system through diversification and niche specialization. The pelagic morphs apparently stem from a single population, and are possibly diversified through conditional niche shifts which affect ontogeny. Juveniles reaching a body length of 23 cm may change from zooplankton to fish feeding. Asymptotic length increases thereby from 20.5 cm in planktivorous charr to 30.2 cm in piscivorous charr. The benthic morphs appear to represent separate populations, although both feed chiefly on the gastropod Lymnaea peregra. Their co-existence seems to be facilitated by size dependent constraints on habitat use. The small morph (asymptotic length 13.3 cm) exploit the interstitial crevices in the lava block substratum, whereas the large morph (asymptotic length 55.4 cm) live epibenthically.     

Juvenile divergence in adaptive traits among seven sympatric fish ecomorphs arises before moving to different lacustrine habitats

Identifying the mechanisms initiating sympatric diversification in vertebrates has remained a conceptual challenge. Here, we analyse an assemblage of sympatric charr (Salvelinus malma) morphs from landlocked Lake Kronotskoe basin as a model to uncover the divergence pathways in freshwater fishes during the early life history stages. All morphs have distinct developmental biology, but a similar developmental rate retardation compared to the ancestor. Our study reveals that adult morphological differences, which acquire functionality at maturation, originate in the early juvenile stages due to heterochrony in skeletogenesis and allometric changes triggered by variation in metabolic activity. The craniofacial differences among the morphs result from asynchronous development of several skeletal modules. The accelerated ossification of teeth‐armed bones occurs in predatory feeding morphs, whereas cranial cover ossification is promoted in benthivorous morphs. These contrasting growth patterns have led to seven phenotypes that span a range far beyond the ancestral variability. The most distinct morphs are a riverine spawning, epilimnetic predator and a lacustrine spawning, profundal benthic feeder. Taken together, we argue that the adaptive morphological differentiation in these sympatric freshwater fishes is driven by diverging patterns in ossification rate and metabolic activity against a background of uneven somatic growth. This divergence is primarily associated with basic environmental differences on the nursery grounds that might be unrelated to resource use. This nonheritable phenotype divergence is then exposed to natural selection that could result in further adaptive genetic changes.     

The functional significance of inherited differences in feeding morphology in a sympatric polymorphic population of Arctic charr

Artificially fertilised eggs from wild-caught Arctic charr parents of two sympatric morphs (benthivorous and planktivorous) from Loch Rannoch, Scotland were reared in the laboratory under identical conditions. During the subsequent 2 years, aspects of their trophic anatomy and feeding behaviour were compared. As previously described for wild-caught fish, charr derived from the benthivorous morph had an increasingly wider mouth gape for a given body length than those derived from the planktivorous morph. The functional significance of these differences in gape was tested by comparing the maximum size of prey that could be handled by each of the two morphs. In both forms, a larger gape enabled larger food particles to be eaten, but the elevation of the regression of maximum prey size on gape was higher in the benthivorous form, indicating the existence of additional morphological and/or behavioural differences influencing the size of prey consumed. When offered a choice between a typical benthic prey item and a typical pelagic food item, charr of benthivorous origin were more likely to feed on the former, whereas those of planktivorous origin were more likely to feed on the latter. Thus inherited differences in gape place constraints on foraging ability and are associated with inherited differences in dietary preference. We conclude that the functional significance of the foraging specialisations indicate a strong selection pressure for the evolution of the divergence and propose that heterochronic growth is the mechanism resulting in the divergence of tropic anatomy.     

Parallel phenotypic evolution of skull-bone structures and head measurements of Arctic charr morphs in two subarctic lakes

Interspecific morph variations in trophic morphology related to skull-bones and head traits is associated to ecological segregation of Arctic charr morphs (genus Salvelinus) in two sub-arctic lakes (Fjellfrøsvatn and Skogsfjordvatn, Norway). The replicated morph pair, the profundal spawning benthivorous PB-morph and the littoral spawning omnivorous LO-morph of Arctic charr, diverge along the shallow-deep-water resource axis. In Skogsfjordvatn there is also a profundal spawning piscivorous PP-morph. The PB-morphs from both lakes have similar skull-bone traits and head morphology such as elongated jaw-bones, small opercular bones and relatively longer heads. The PP-morph also has an elongated head, relatively small opercular bones as well as larger jaw-bones. In contrast, the LO-morphs in both lakes have shorter jaw-bones, larger opercular bones in addition to relatively small heads. However, some small non-parallel differences exist among the morphs from the two lakes. Overall, all profundal morphs (PB and PP) have relatively similar skull-bone structures, suggesting adaptations to the deep-water environment but also to their separated dietary niches. There is strong evidence for parallel evolution with some local adaptations in skull-bones and head morphology of the PB-morph and the LO-morph from separate lakes.     

Genetic analysis of four sympatric morphs of Arctic charr,Salvelinus alpinus,from Thingvallavatn,Iceland

Synopsis The degree of genetic differentiation among four morphs of Arctic charr (small benthivorous, large benthivorous, piscivorous, and planktivorous) from Thingvallavatn, Iceland, was determined electrophoretically. Five of 36 enzyme loci were found to be polymorphic (Est2, Gpi3, Ldh4, Mdh4, 5 and Pgm2). However, only Est2 and Mdh4,5 showed enough variability to permit statistical analysis of divergence among morphs. All four morphs are very closely related; the values of Nei's (D) range from 0.00004 to 0.00126. These morphs are conspecific and do not represent different evolutionary lineages. There is significant genetic differentiation between the small benthivorous charr and the other three morphs. The relative relatedness of morphs based on gene frequency data is only partially concordant with that based on morphology and ecological specialization. The biological significance of this result is unclear because of the limited number of polymorphic loci upon which the genetic analysis is based and the high degree of relatedness among morphs.     

Ecological parasitology of polymorphic Arctic charr, Salvelinus alpinus (L.), in Thingvallavatn, Iceland

The helminth endoparasite fauna in four Arctic charr morphs, Salvelinus alpinus (L.), small benthivorous (SB), large benthivorous (LB), planktivorous (PL) and piscivorous (PI) charr, from Thingvallavatn, Iceland consisted of: Crepidostomum farionis (Trematoda: Allocreadiidae); Diplosttomum sp. (Trematoda: Diplostomatidae); Eubothrium salvelini; Diphyllobothrium dendriticum; D. ditremum (Cestoda: Pseudophyllidae); Proteocephalus longicollis (Cestoda: Proteocepha-lidae): and Philonema oncorhynchi (Nematoda: Filariidae). The morphs exhibited distinctive patterns in prevalences and parasite burdens (mean intensity and mean relative density of parasites). SB charr had high prevalence and parasite burden of the eye fluke Diplostomum sp. and none to very light infections of the other parasite species. LB charr had relatively high prevalence and parasite burden of the intestinal fluke C. farionis , whereas infections of the remaining parasite species were light to moderate. PL and PI charr had high prevalences and worm burdens of Diphyllobothrium spp. and P. longicollis . PL charr differed from PI charr in higher worm burden off P. longicollis and lighter burden of £. salvelini . Prevalences of P. oncorhynchi were high in PL and PI charr. Association of parasite intensities and age and length offish were investigated. The different infection patterns among the morphs agree well with their partitioning in food and habitat utilization, and confirm that there is a high degree of ecological segregation between the morphs. The results demonstrate the importance of ecological factors influencing transmission efficiency of parasites to the fish host.     

Stable isotope analysis reveals ecological segregation in a bimodal size polymorphism in Arctic charr from Loch Tay, Scotland

The serendipitous discovery of a body-size dimorphism amongst the sexually mature Arctic charr Salvelinus alpinus of Loch Tay is described. Sexually mature Arctic charr, collected by gill netting on spawning areas, showed a clear and distinct bimodal size distribution with no overlap in fork length distributions. The upper (19–29 cm L _F) and lower modes (8–16 cm) were not solely the result of sex or age differences. Analysis of stable isotope ratios of C and N in muscle showed highly significant differences in mean δ¹³C and δ¹⁵N between populations, demonstrating a difference in trophic ecology between the two body-size morphs. Overlap in the range of δ¹³C and δ¹⁵N values for the two morphs, however, suggested that they occasionally shared a common diet. Data from other studies strongly indicated that the proximate and ultimate mechanisms that control body-size dimorphisms in Arctic charr differed between sites. Clear differences in trophic ecology in the Loch Tay Arctic charr suggested that the available feeding opportunity may differ for the two morphs. The most likely proximate mechanism resulting in this dimorphism is growth rate differences resulting from differences in food availability for the two subgroups occupying alternative foraging niches in Loch Tay.     

Habitat use of arctic charrSalvelinus alpinus in Thingvallavatn,Iceland

Synopsis Habitat use by four morphs of arctic charr,Salvelinus alpinus, was investigated in Thingvallavatn, Iceland, by sampling with pelagic and benthic gill nets. Sampling was done in May/June and August/September. Greatest abundance of fish was recorded in the littoral and epipelagic zone in early autumn. Catches were low in early summer. The four morphs are partly segregated in habitat. Small (SB-) and large benthivorous (LB-) charr have a more restricted spatial distribution than piscivorous (PI-), and especially planktivorous (PL-) charr. Both benthivorous morphs are mainly found in the littoral zone, and occur in largest numbers in stony shallows at depths between 0 and 10 m. PL-charr usually dominates in numbers in all habitats. PI-charr is most abundant in epibenthic habitats, although numbers are always low. All morphs are caught in higher numbers at night than during the day, but the diurnal activity difference is highest among SB-charr. The habitat use by different morphs is as may be expected from their morphology and diets. Within the population of PL-charr, young and small fish are more abundant on the bottom than in the pelagic zone, and there is a surplus of females in the pelagic zone. Along the benthic profile, young, small and immature PL-charr are more abundant in deep than in shallow waters. The results are discussed in relation to food supply, competition and predation. Possible reasons for the occurrence of four arctic charr morphs are also discussed.Contribution from the Thingvallavatn project.     

Extant and extinct forms of arctic charr Salvelinus alpinus (L.) complex from the Leprindo lake system (Transbaikalia): Differentiation in life history, morphology, and genetics

Interconnected lakes Bol’shoe Leprindo and Maloe Leprindo in Transbaikalia hosted large (extinct) and dwarf charr forms. Rarely “small” individuals intermediate in size between these forms are caught. In order to assess morphological, ecological, and genetic differentiation of sympatric charr forms and parapatric charr populations we studied their meristic and morphometric characters, feeding, breeding, and growth; we also investigated variation at 8 microsatellite loci using DNA isolated both from contemporary and historic samples. Profound differences were found between large and dwarf charr in growth rate, feeding (piscivores and highly specialized zooplanktivores, respectively), spawning time, and morphology. Dwarf charr from the two lakes demonstrate minor differences in morphology and growth rate. “Small” individuals are morphologically similar with dwarf charr and spawn together with them, they are recruited from dwarf form in late ontogeny as the result of transition to piscivorous feeding and growth acceleration. Microsatellite analysis showed that: (1) large and dwarf charr forms display high degree of genetic differentiation and reproductive isolation; (2) dwarf charr from interconnected lakes belong to different isolted populations; (3) “small charr” are genetically identical with dwarfs. The degree of ecomorphological and genetic differentiation between large and dwarf forms places charr from Leprindo Lakes among the most strongly differentiated Arctic charr forms’ flocks known at the vast range of S. alpinus complex.     

New endemic deepwater charr morphs of the genus <Emphasis Type="Italic">Salvelinus</Emphasis> (Salmoniformes: Salmonidae) from Lake Kronotskoe,Kamchatka

Two previously unknown profundal dwelling charr morphs of the genus Salvelinus from Lake Kronotskoe are described in this article. According to their lifestyle peculiarities, these morphs were named the “bigmouth charr” and “smallmouth charr.” The former group is near-bottom benthivorous, while the latter one inhabits the water column and occupies the omnivorous niche. Bigmouth and smallmouth charrs are distinguished from the rest of the sympatric charr morphs by their smaller size, shorter snout, larger eyes, as well as by several craniological traits and lower parasite abundance. Spawning of both morphs takes place directly in the profundal zone and lasts from late October to February. Additional studies are required to determine the systematic status of the new morphs.     

Polymorphism and speciation in Arctic charr

The Arctic charr Salvelinus alpinus exhibits 1–4 sympatric morphs in postglacial lakes, of which one or two are epibenthic zoobenthos feeders, one is a limnetic planktivore and one is a piscivorous form. In addition, northern rivers support partly migratory populations with anadromous and freshwater resident fish. The morphs vary in their coloration, morphology, life history, behaviour and genetic characteristics. The morphs usually differentiate according to their ontogenetic stage at maturity, which parallels paedomorphism in amphibians. The young usually start as epibenthic zoobenthivores, but may become pelagic at a certain size according to the predation risk experienced at that time. From a length of > 20–25 cm, charr start to become piscivorous. The proportion of piscivorous fish increases with increasing body size. In partly anadromous populations, fish that mature before smolting become freshwater resident, the others anadromous. In some rivers, the morphs occupy separate niches (epibenthic and limnetic), from emergence onwards. The morphs exhibit different degrees of reproductive isolation that vary from a high degree of interbreeding to complete isolation. Usually, they spawn within morph (assortative mating), but alternative male mating behaviour (sneaking, fighting) may occur in stream‐spawning populations and at great depths in lakes. Morphologically specialized morphs appear to feed more effectively than intermediate forms, and selection according to feeding mode, site fidelity and associated assortative mating are prerequisites for the evolution of the different morphs. Charr morphs develop into stable feeding niches under conditions of intense intraspecific competition when there is little competition with other species. Sympatric morphs exhibit different degrees of speciation, but similar morphs in different systems are not individual species because of (1) their polyphyletic origin, (2) the supporting systems are often young, transient environments making the future situation for the populations uncertain, and (3) the genetic differentiation among morphs is low. Sympatric morphs may interbreed and produce fertile hybrids. Nevertheless, sympatric charr morphs should be managed as separate species. Changes in the natural conditions or human impacts to which the morphs are adapted will have a strong influence on the persistence and survival of each different morph.     

The trade‐off between fecundity and egg size in a polymorphic population of Arctic charr (Salvelinus alpinus (L.)) in Skogsfjordvatn,subarctic Norway

Reproductive traits differ between intralacustrine Arctic charr morphs. Here, we examine three sympatric lacustrine Arctic charr morphs with respect to fecundity, egg size and spawning time/site to assess reproductive investments and trade‐offs, and possible fitness consequences. The littoral omnivore morph (LO‐morph) utilizes the upper water for feeding and reproduction and spawn early in October. The large profundal piscivore morph (PP‐morph) and the small profundal benthivore morph (PB‐morph) utilize the profundal habitat for feeding and reproduction and spawn in December and November, respectively. Females from all morphs were sampled for fecundity and egg‐size analysis. There were large differences between the morphs. The PB‐morph had the lowest fecundity (mean = 45, SD = 13) and smallest egg size (mean = 3.2 mm, SD = 0.32 mm). In contrast, the PP‐morph had the highest fecundity (mean = 859.5, SD = 462) and the largest egg size (mean = 4.5 mm, SD = 0.46 mm), whereas the LO‐morph had intermediate fecundity (mean = 580, SD = 225) and egg size (mean = 4.3, SD = 0.24 mm). Fecundity increased with increasing body size within each morph. This was not the case for egg size, which was independent of body sizes within morph. Different adaptations to feeding and habitat utilization have apparently led to a difference in the trade‐off between fecundity and egg size among the three different morphs.     

Assessment of the Feasibility of Preventing Reproduction of Lake Charr, Salvelinus Namaycush, in Shallow Areas of Reservoirs Affected by Drawdowns

Lake charr, Salvelinus namaycush, spawn almost exclusively in lakes, in the fall. Spawning sites in inland lakes are generally located close to the shore in areas with coarse-textured substrate, and in depths of less than 2m. Because of the type of water management system applied in reservoirs where water levels are lowered during the winter, eggs deposited during the fall around the shallow shoreline of reservoirs can be exposed. The depth of spawning sites relative to drawdowns may be a limiting factor for lake charr survival in reservoirs. In 1995 and 1996, we evaluated the ability to induce lake charr reproduction in deeper water, below the range of fluctuating water levels by the sequential construction of artificial reefs and limiting access to natural spawning habitat. The creation of artificial deeper water spawning areas, adjacent to natural sites, produced a partial transfer of reproduction. However when natural spawning sites were covered with tarpaulins almost all the eggs were laid in the artificial deeper water spawning areas. Complete or partial transfer of reproduction activities to sites below the depth not affected by water level fluctuations is therefore a potential way of alleviating the effects of hydroelectric reservoir management.     

Arctic charr in sympatry with burbot: ecological and evolutionary consequences

The trophic niche and parasite infection of Arctic charr (Salvelinus alpinus) were explored in two lakes with sympatric burbot (Lota lota) and two lakes without burbot in subarctic Norway. The CPUE of burbot and charr were similar in one lake, but burbot had a low population density in the other. Burbot were benthivorous in both lakes. Other co-occurring species like brown trout (Salmo trutta), Atlantic salmon parr (Salmo salar), grayling (Thymallus thymallus) and minnow (Phoxinus phoxinus) were also benthivores. At high densities, benthivorous burbot forced the whole Arctic charr population to utilise mainly the limnetic trophic niche. In contrast, at low burbot density or without burbot present, Arctic charr were primarily benthivorous in the littoral zone. Thus, a clear interactive segregation in diet was observed between Arctic charr and burbot at high burbot densities. There was also a high predation pressure from burbot on young Arctic charr along the benthic zones. The extensive use of zooplankton as prey caused a high parasite infection pressure of copepod transmitted Diphyllobothrium spp. larvae, with the potential for high negative impact on the Arctic charr population. As the benthivore trophic niche was occupied by burbot, the ecological opportunities for polymorphism with benthivorous ecotypes or morphs of Arctic charr were probably prevented. Therefore, the sympatry with burbot seems to have large ecological and evolutionary consequences for this Arctic charr population compared with neighbouring lakes where burbot is absent.     

Life-history styles and somatic allocation in iteroporous arctic charr and semelparous pink salmon

Synopsis RNA/DNA ratios were used to estimate recent somatic allocation of spawning arctic charr,Salvelinus alpinus, and pink salmon,Oncorhynchus gorbuscha. Smaller arctic charr morphs had lower ratios than larger morphs. Larger male pink salmon had lower ratios than smaller males. Thus recent somatic allocation (anabolic metabolic activity and growth) is coupled with cumulative lifetime growth in iteroparous arctic charr, but is uncoupled in semelparous pink salmon. These data suggest that somatic investment in these species is being differentially effected by the energetic costs of reproduction.     

Inherited differences in head allometry in polymorphic Arctic charr from Loch Rannoch, Scotland

Planktivorous and benthivorous morphs of wild Arctic charr Salelinus alpinus from Loch Rannoch, Perthshire, Scotland, reared in the laboratory from artificially fertilized eggs under identical conditions, were morphologically distinct (based on a series of head measurements) from an early age. For some morphometric characters, these differences became more marked with increasing body size, reflecting differences in the allometric growth patterns of the two forms. These data show that the observed phenotypic differences between these two trophic variants were, to some extent at least, inherited. Thus it is concluded that the mechanisms regulating expression of phenotype in the sympatric morphs of Loch Rannoch are significantly different from the environmentally determined body size polymorphisms reported from Norway but are closer to the more completely divergent forms from Thingvalavatn, Iceland.     

Seasonal and ontogenetic variations in resource use by two sympatric Arctic charr morphs

The study compares the resource utilization of two sympatric Arctic charr morphs over an annual period in a subarctic lake. The two morphs are reproductively isolated in time and place of spawning, and are referred to as the littoral and profundal morphs (L-morph and P-morph) according to their spawning habitats. Fish were sampled monthly (ice-free season) or bimonthly (winter) using gillnets in the main lake habitats. The spatial range of the P-morph was restricted to the profundal zone throughout the whole annual period. The L-morph in contrast utilized all main habitats, exhibiting distinct seasonal and ontogenetic variations in habitat distribution. In the spring, the whole L-morph population was located along the bottom profile of the lake, in profundal and littoral habitats. During summer and autumn, habitat segregation occurred between different life-stages, juveniles mainly utilizing the profundal, pre-adults the pelagic and adult fishes the littoral zone. During winter the whole population was assembled in the littoral habitat. The L-morph also had large seasonal and ontogenetic variations in their feeding ecology, with littoral zoobenthos, zooplankton and surface insects being important prey. The P-morph had a narrower diet niche mainly consisting of chironomid larvae and other profundal zoobenthos. Hence, the two Arctic charr morphs exhibited a consistent resource differentiation during all annual seasons and throughout their life cycles, except for a dietary overlap between P-morph and juvenile L-morph charr in the profundal during summer. The findings are discussed in relation to resource polymorphism and incipient speciation.     

Basic description and some notes on the evolution of seven sympatric morphs of Dolly Varden Salvelinus malma from the Lake Kronotskoe Basin

The study examines the basic morphological and ecological features of Dolly Varden from Lake Kronotskoe (Russia, Kamchatka). Seven valid morphs different in head proportions, feeding, timing, and place of spawning have been determined in this ecosystem. The basic morphometric characteristics clearly separate Lake Kronotskoe morphs from each other, as well as from its potential ancestor (Dolly Varden). According to CVA analysis, the most notable morphological characteristics determining the mouth position are the length of a lower jaw and rostrum. Furthermore, five of seven morphs inhabit different depth zones of the lake and feed on different food resources. Our data suggest that reproductive isolation may be maintained by temporal/spatial isolation for two morphs with lacustrine spawning, and by spatial isolation only for the rest of the morphs with riverine spawning. The sympatric diversity of the Lake Kronotskoe charrs is exceptionally wide, and there are no other examples for seven sympatric morphs of genus Salvelinus to coexist within a single ecosystem. This study puts forward a three‐step hypothetical model of charr divergence in Lake Kronotskoe as a potential ground for future studies.