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Disentangling the causes and consequences of ontogenetic niche shifts has been a pivotal challenge in ecology, aiming to enhance the understanding of biological processes that function at the individual, population, and community levels. Studies on ontogenetic dietary shifts have traditionally focused on short time scales, mostly including sampling covering just one or a few consecutive years, thus neglecting possible aspects of temporal variation and ecosystem stability that can only be revealed on long-term scales. We address ontogenetic dietary shifts of two fish predators in an intraguild system (Arctic charr and brown trout) using a long-term dataset spanning 20 consecutive years. Our study revealed distinct ontogenetic niche shifts of the two intraguild predators and demonstrated that these patterns were stable over time, suggesting large stability in prey acquisition and resource partitioning despite changes in their abundances and relative species composition. Some interannual variation was observed, but this was primarily due to sampling bias from low observation numbers for some ontogenetic stages, reflecting a common methodical challenge for ontogenetic niche shift studies. The persistent patterns in the trophic ontogeny of intraguild predators likely facilitate population and community stability by reducing inter- and/or intraspecific competition, thereby having important consequences for ecosystem functioning and resilience. Our study provides a strong rationale for performing ontogenetic niche shift studies over several consecutive years, enabling important insights into temporal variation, enhancement of observation numbers by merging data from multiple years, and the facilitation of a less intrusive sampling scheme for more vulnerable populations.

Cercarial activity and survival are crucial traits for the transmission of trematodes. Temperature is particularly important, as faster depletion of limited cercarial energy reserves occurs at high temperatures. Seasonal climate conditions in high latitude regions may be challenging to complete trematode life cycle during the 6-month ice-free period, but temperature effects on the activity and survival of freshwater cercariae have not been previously identified. After experimentally simulating natural subarctic conditions during warmer and colder months (13 and 6°C), a statistical approach identifying changes in the tendency of cercarial activity loss and mortality data was used to detect differences in three trematode genera, represented by four taxa (Diplostomum spp., Apatemon spp., small- and large-sized Plagiorchis spp.). A strong temperature-dependent response was identified in both activity loss and mortality in all taxa, with Diplostomum spp. cercariae showing the most gradual changes compared to other taxa. Furthermore, whilst activity loss and mortality dynamics could not be divided into ‘fish- vs invertebrate-infecting cercariae’ groups, the detected taxa-specific responses in relation to life-history traits indicate the swimming behaviour of cercariae and energy allocation among larvae individuals as the main drivers. Cercariae exploit the short transmission window that allows a stable continuance of trematodes’ life cycles in high-latitude freshwater ecosystems.

1. Competition for shared resources is commonly assumed to restrict population-level niche width of coexisting species. However, the identity and abundance of coexisting species, the prevailing environmental conditions, and the individual body size may shape the effects of interspecific interactions on species’ niche width. 2. Here we study the effects of interspecific and intraspecific interactions, lake area and altitude, and fish body size on the trophic niche width and resource use of a generalist predator, the littoral-dwelling large, sparsely rakered morph of European whitefish (Coregonus lavaretus; hereafter LSR whitefish). We use stable isotope, diet and survey fishing data from 14 subarctic lakes along an environmental gradient in northern Norway. 3. The isotopic niche width of LSR whitefish showed a humped-shaped relationship with increasing relative abundance of sympatric competitors, suggesting widest population niche at intermediate intensity of interspecific interactions. The isotopic niche width of LSR whitefish tended to decrease with increasing altitude, suggesting reduced niche in colder, less productive lakes. 4. LSR whitefish typically shifted to a higher trophic position and increased reliance on littoral food resources with increasing body size, although between-lake differences in ontogenetic niche shifts were evident. In most lakes, LSR whitefish relied less on littoral food resources than coexisting fishes and the niche overlap between sympatric competitors was most evident among relatively large individuals (>250 mm). Individual niche variation was highest among >200 mm long LSR whitefish, which likely have escaped the predation window of sympatric predators. 5. We demonstrate that intermediate intensity of interspecific interactions may broaden species’ niche width, whereas strong competition for limited resources and high predation risk may suppress niche width in less productive environments. Acknowledging potential humped-shaped relationships between population niche width and interspecific interactions can help us understand species’ responses to environmental disturbance (e.g. climate change and species invasions) as well as the driving forces of niche specialization.

This is the data, parametersand results for the publication “Mining various genomic resources to resolve old alpha-taxonomy questions: A test of the species hypothesis of the Proteocephalus longicollis species complex (Cestoda: Platyhelminthes) from salmonid fishes” in International Journal for Parasitology 2023.

Competition is assumed to shape niche widths, affecting species survival and coexistence. Expectedly, high interspecific competition will reduce population niche widths, whereas high intraspecific competition will do the opposite. Here we test in situ how intra- and interspecific competition affects trophic resource use and the individual and population niche widths of two lacustrine fish species, Arctic charr and brown trout, covering a 40 year study period with highly contrasting competitive impacts prior to and following a large-scale fish culling experiment. Initially, an overcrowded Arctic charr population dominated the study system, with brown trout being nearly absent. The culling experiment reduced the littoral Arctic charr density by 80%, whereupon brown trout gradually increased its density in the system. Thus, over the study period, the Arctic charr population went from high to low intraspecific competition, followed by increasing interspecific competition with brown trout. As hypothesized, the relaxed intraspecific competition following the experimental culling reduced individual diet specialization and compressed population niche width of Arctic charr. During the initial increase of the brown trout population, there was a large dietary overlap between the two species. Over the subsequent intensified interspecific competition from the population build-up of brown trout, their trophic niche overlap chiefly declined due to a dietary shift of Arctic charr towards enhanced zooplankton consumption. Contrary to theoretical expectations, the individual and population niche widths of Arctic charr increased with intensified interspecific competition. In contrast, the diet and niche width of brown trout remained stable over time, confirming its competitive superiority. The large-scale culling experiment and associated long-term research revealed pronounced temporal dynamics in trophic niche and resource use of the inferior competitor, substantiating that intra- and interspecific competition have large and contrasting impacts on individual and population niches.

Ontogenetic dietary shifts are common in fish and often impact trophically transmitted parasite communities. How parasite species composition and relative abundances change among size classes, and at what rate these changes occur, is rarely examined. Hosts with a broad trophic niche are potentially exposed to a large variety of parasite species. The degree of ontogenetic changes in parasite species composition versus changes in parasite abundance should suggestively differ between thropically generalist and specialist host species. In the present study, we explore ontogenetic dietary shifts and their impact on species composition and relative abundance of intestinal parasites in two sympatric salmonid fish species, Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) caught in the littoral habitat of a subarctic lake. Our results highlight a close interplay between ontogenetic dietary niche shifts and alterations in the acquisition of trophically transmitted parasites, leading to host-specific differences in the component community of parasites. Ontogenetic changes in the intestinal parasite community related to dietary niche shifts were distinct but less pronounced in Arctic charr than in brown trout due to a broader and more consistent dietary niche of the former and an ontogenetic shift toward piscivory in the latter. At the component community level, changes in parasite assemblages of both host species were driven by a faster increase in the heterogeneity of parasite relative abundance than in the compositional heterogeneity, a pattern that partly may be related to a rather species-poor parasite community of this subarctic study system. Separating compositional heterogeneity from heterogeneity in relative parasite abundance is important to understand how size-dependent variability shapes parasite communities of host populations., Graphical abstract Image 1, Highlights • Ontogenetic dietary niche shifts generated host-specific differences in the component community of parasites. • Ontogenetic changes in the intestinal parasite community were less pronounced in Arctic charr than in brown trout. • Heterogeneity of parasite relative abundance increased faster than the compositional heterogeneity.

Life history strategies and potential marine niche use of Arctic charr Salvelinus alpinus (n = 237, 84–652 mm, total body length, LT) were determined during the ice‐free season (2012) at three different watercourses in south‐western Greenland. All Arctic charr were collected from freshwater habitats. Based on stable isotopes of δ34S, the Arctic charr were categorized as either marine‐ or freshwater‐dependent feeders. The use of time‐integrated trophic tracers (stable isotopes of δ13C, δ15N, δ34S) suggested that several trophic groups of Arctic charr operate alongside within each fjord system. The groups suggested were one group that specialized in the marine habitat, in addition to two freshwater resident morphs (small‐sized resident and/or large‐growing cannibalistic individuals). Stomach contents consisted entirely of freshwater and terrestrial prey (i.e., insects), indicating that marine‐dependent feeders also fed in freshwater habitats after return from their marine migration. Growth and maturity patterns further supported variable life history strategies within each watercourse. The life history strategy patterns and marine trophic niche use were consistent across the watercourses along several hundred kilometres of coastline. This study represents the first ecological baseline for partially anadromous populations of Greenland Arctic charr. © 2020 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of The Fisheries Society of the British Isles. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

This is a pre-copyedited, author-produced version of an article accepted for publication in Zoological Journal of the Linnean Society following peer review. The version of record Danielle Božena de Carle, Łukasz Gajda, Aleksander Bielecki, Stanisław Cios, Joanna M Cichocka, Heidi E Golden, Andrew D Gryska, Sergey Sokolov, Marina Borisowna Shedko, Rune Knudsen, Serge Utevsky, Piotr Świątek, Michael Tessler, Recent evolution of ancient Arctic leech relatives: systematics of Acanthobdellida, Zoological Journal of the Linnean Society, Volume 196, Issue 1, September 2022, Pages 149–168 is available online at: https://doi.org/10.1093/zoolinnean/zlac006 Acanthobdellida gnaw into the sides of salmonid fishes in frigid Arctic lakes and rivers, latching on with fearsome facial hooks. Sister to leeches, they are an ancient lineage with two described species. Unfortunately, Acanthobdellida are rarely collected, leading to a paucity of literature despite their unique morphology. Populations range from Eurasia to Alaska (USA), but few specimens of Acanthobdella peledina are represented in molecular studies, and no molecular data exist for Paracanthobdella livanowi, making their taxonomic position difficult to assess. We use phylogenetics and morphology to determine whether allopatric populations of A. peledina are distinct species and assess the current classification scheme used for Acanthobdellida. We produce a new suborder, Acanthobdelliformes, to match the taxonomy within Hirudinea. Scanning electron micrographs indicate species-level differences in the anterior sucker and facial hooks; molecular phylogenetics mirrors this divergence between species. We assign both species to the family Acanthobdellidae and abandon the family Paracanthobdellidae. Alaskan and European A. peledina populations are morphologically similar, but appear phylogenetically divergent. Our data strongly suggest that members of the order Acanthobdellida diverged relatively recently in their ancient history, but based on genetic distance, this divergence appears to pre-date the most recent cycles of glaciation.

Concomitant predation, which occurs when parasites are consumed and digested along with their hosts, has previously been suggested as a profound factor determining food web structure. Few studies have adressed the impact of concomitant predation in research on behaviourally parasite-modified prey or in biological control studies. However, empirical evidence of concomitant predation effects on hosts infected with multiple parasite taxa is lacking. We investigated the importance of concomitant predation on digenean trematodes by examining the degree of snail (Radix balthica, first intermediate host) seasonal predation by Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) by contrasting infection rates of free-living snails obtained from a lake vs predated snails retrieved from fish stomachs and intestines. The fish consumed infected snails nearly at all seasons, demonstrating that concomitant predation in the model subarctic lake is common, likely indirectly affecting trematode transmission by reducing host and parasite populations. The overall trematode prevalence in both snail groups was season-independent, being however substantially higher in free-living compared to predated snails. The net effects of underlying mechanisms related to prey availability, fish feeding ecology, continuous presence of dominant trematodes and, most importantly, size of fish and snails drove the strength of predator-prey interactions and infection patterns in both snail groups. Larger fish preying upon larger snails, which simultaneously harboured more infections, may induce a substiantial negative effect of concomitant predation on snail and parasite population dynamics, with serious implications for food web structure and ecosystem functioning. This study contributes to a better understanding of the role of non-host predators in regulating trematode infection, community structure and transmisison patterns, biomass transfer and energy flow in food webs. Our findings also highlight the importance of studying the impact and extent of concomitant predation in terms of parasite seasonal dynamics and biological control of infectious diseases.

The use of translocations to establish new or ‘refuge’ populations for species with high conservation value is controversial but widely used in conservation management. One of the risks of this approach is that an establishing population does not adequately capture the genetic diversity of the donor gene pool. This effect, rarely examined, is tested here. In this study the genetic consequences of two conservation translocations after five generations (16 years) of the European whitefish, Coregonus lavaretus, were quantified. Both translocations were made using almost the same genetic groups and thus represent a partly replicated natural study. Analysis of 12 informative microsatellites showed that expected heterozygosity, the mean number of alleles per locus and allelic richness did not differ between donor and translocated populations. There was also no loss of heterozygosity in the translocated populations, nor deviations from Hardy–Weinberg equilibrium expectations, nor signs of linkage disequilibrium. All populations were genetically differentiated but pairwise FST values were low, indicating that the magnitude of divergence was small. There was no evidence of inbreeding but there were significant differences in private allelic richness between donor and translocated populations. Of 50 alleles found in the donor population, 16% of the rarer alleles were lost in one translocated population and 8% in the other. Allele loss without a reduction in heterozygosity strongly points to stochastic drift effects having occurred following translocation. The evidence indicates that alleles that were not detected in the donor population have arisen de novo in the translocated populations. It is concluded that conservation translocations comprising even a modest number of propagules can successfully capture a high proportion of genetic variation of the host population, and that reduced genetic variation in the translocated population may be mitigated by the emergence of new variation over short time periods.

This is the peer reviewed version of the following article: Henriksen, E.H., Frainer, A., Knudsen, R., Kristoffersen, R., Kuris, A.M., Lafferty, K.D. & Amundsen, P-A. (2019). Fish culling reduces tapeworm burden in Arctic charr by increasing parasite mortality rather than by reducing density-dependent transmission. Journal of Applied Ecology, 56(6), 1482-1491, which has been published in final form at https://doi.org/10.1111/1365-2664.13369. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Two common Dibothriocephalus (formerly Diphyllobothrium) tapeworm species were significantly reduced by experimental culling of their fish host Arctic charr (Salvelinus alpinus) in a subarctic lake. Between 1984 and 1991, funnel traps were used to cull ~35 metric tons of Arctic charr, reducing charr density by ~80%. As charr densities decreased, tapeworm prevalence and then intensity also declined over the following three decades, with D. dendriticus (formerly dendriticum) responding faster than D. ditremus (formerly ditremum). The two main hypotheses for how culling a host can decrease parasitism are reductions in parasite transmission due to reduced host density and reductions in parasite survival through increases in host mortality rates. We found little evidence that charr density was the main driver for reduced parasite transmission. Instead, decreased survivorship in charr, initially, through fishing‐induced changes in charr age structure, and later through increased predation rates by brown trout, led to increased parasite mortality. Although brown trout, which increased significantly after fish culling, are also hosts, they are often too big for the final host birds to eat, thus becoming parasite sinks. Synthesis and applications. Fish populations with heavy parasite burdens constitute a management problem. Our results show how fish culling can indirectly reduce transmitted parasites through increased parasite mortality. Managing overcrowded fish populations by culling can produce two desirable outcomes: an increase in fish growth rates and reduced parasite burdens.

Accepted manuscript version. Final version published in Hydrobiologica, 840(1), 261-270, is avaialble at https://doi.org/10.1007/s10750-018-3865-8. Trophically transmitted parasites are known to impair fish growth in experimental studies, but this is not well documented in natural populations. For Arctic charr [Salvelinus alpinus (L.)], individual growth is positively correlated with food consumption. However, increased food consumption will increase the exposure to trophically transmitted parasites. Using a correlative approach, we explore the association between parasite abundance and the individual growth of Arctic charr from five lakes within the same watercourse. The studied parasite species differ in their life cycles and cost to the host. We predicted a positive association between parasite abundance and fish growth for parasites of low pathogenicity reflecting high consumption rates, and a negative association at higher parasite abundances for more costly parasites. We found no direct negative associations between parasite abundance and fish growth. The relationship between parasite abundance and growth was linearly positive for the low costly Crepidostomum sp. and concave for the more costly Eubothrium salvelini. In natural fish populations, the negative effects of parasites on fish growth might be outweighed by the energy assimilated from feeding on the intermediate host. However, experimental studies with varying food consumption regimes are needed to determine the mechanisms underlying our observations.

Amphipods are often key species in aquatic food webs due to their functional roles in the ecosystem and as intermediate hosts for trophically transmitted parasites. Amphipods can also host many parasite species, yet few studies address the entire parasite community of a gammarid population, precluding a more dynamic understanding of the food web. We set out to identify and quantify the parasite community of Gammarus lacustris to understand the contributions of the amphipod and its parasites to the Takvatn food web. We identified seven parasite taxa: a direct life cycle gregarine, Rotundula sp., and larval stages of two digenean trematode genera, two cestodes, one nematode, and one acanthocephalan. The larval parasites use either birds or fishes as final hosts. Bird parasites predominated, with trematode Plagiorchis sp. having the highest prevalence (69%) and mean abundance (2.7). Fish parasites were also common, including trematodes Crepidostomum spp., nematode Cystidicola farionis, and cestode Cyathocephalus truncatus (prevalences 13, 6, and 3%, respectively). Five parasites depend entirely on G. lacustris to complete their life cycle. At least 11.4% of the overall parasite diversity in the lake was dependent on G. lacustris, and 16% of the helminth diversity required or used the amphipod in their life cycles. These dependencies reveal that in addition to being a key prey item in subarctic lakes, G. lacustris is also an important host for maintaining parasite diversity in such ecosystems.

The European whitefish Coregonus lavaretus complex represents one of the most diverse radiations within salmonids, with extreme morphological and genetic differentiation across its range. Such variation has led to the assignment of many populations to separate species. In Great Britain, the seven native populations of C. lavaretus (two in Scotland, four in England, one in Wales) were previously classified into three species, and recent taxonomic revision resurrected the previous nomenclature. Here we used a dataset of 15 microsatellites to: (1) investigate the genetic diversity of British populations, (2) assess the level of population structure and the relationships between British populations. Genetic diversity was highest in Welsh (HO = 0.50, AR = 5.29), intermediate in English (HO = 0.41–0.50, AR = 2.83–3.88), and lowest in Scottish populations (HO = 0.28–0.35, AR = 2.56–3.04). Population structure analyses indicated high genetic differentiation (global FST = 0.388) between all populations but for the two Scottish populations (FST = 0.063) and two English populations (FST = 0.038). Principal component analysis and molecular ANOVA revealed separation between Scottish, English, and Welsh populations, with the Scottish populations being the most diverged. We argue that the data presented here are not sufficient to support a separation of the British European whitefish populations into three separate species, but support the delineation of different ESUs for these populations.

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.

The nosed charr Salvelinus schmidti that inhabits the littoral zone of Lake Kronotskoe is divided into two groups according to food preferences and parasite fauna. Fish of the first group (G) predominantly feed on gammarids and are characterized by a high infestation with Cystidicola farionis, Cyathocephalus truncatus, and Crepidostomum spр. Fish of the second group (A) do not consume gammarids but feed mostly on chironomid larvae and pupae and on mollusks; the predominant parasites are Phyllodistomum umblae and Proteocephalus longicollis. The significant difference in the abundance of C. farionis, which remains in fish at least for 2 years, is indicative of a long-term and persistent trophic diversification between the charr groups. Moreover, significantly higher growth rates, a larger body size, and a longer lifespan are observed for fish of group G. The feeding strategy of the nosed charr is maintained throughout the life and does not depend on the sex of fish and their distribution within the littoral zone of the lake.

This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at https://doi.org/10.1007/s10750-019-3953-4. Niche diversification of polymorphic Arctic charr can be altered by multiple anthropogenic stressors. The opossum-shrimp (Mysis relicta) was introduced to compensate for reduced food resources for fish following hydropower operations in Lake Limingen, central Norway. Based on habitat use, stomach contents, stable isotopes (δ13C, δ15N) and trophically transmitted parasites, the zooplanktivorous upper water-column dwelling ‘normal’ morph was clearly trophically separated from two sympatric deep-water morphs (the ‘dwarf’ and the ‘grey’) that became more abundant with depth (> 30 m). Mysis dominated (50–60%) charr diets in deeper waters (> 30 m), irrespective of morph. Mysis and/or zooplankton prey groups caused high dietary overlap (> 54%) between the ‘dwarf’ morph and the two other ‘normal’ and ‘grey’ morphs. After excluding Mysis, the dietary overlap dropped to 34% between the two profundal morphs, as the ‘dwarf’ fed largely on deep-water zoobenthos (39%), while the ‘grey’ morph fed on fish (59%). The time-integrated trophic niche tracers (trophically transmitted parasites and stable isotopes) demonstrated only partial dietary segregation between the two deep-water morphs. The high importance of Mysis in Arctic charr diets may have reduced the ancestral niche segregation between the deep-water morphs and thereby increased their resource competition and potential risk of hybridization.

Catchment-scale variation between lake habitats has the potential to simultaneously influence the trophic niche and parasite community of fish hosts. In this study, we investigated the trophic niche and parasite community of sympatric Arctic charr and brown trout populations from two inter-connected southern Norwegian lakes at different altitudes. Arctic charr and brown trout occupied profundal and littoral habitats in each lake, respectively, whereas brown trout replaced Arctic charr in pelagic habitats of the lower altitude lake. Distinct between-lake differences in diet and parasite community composition were noted for brown trout; however, both fish species showed highly overlapping trophically transmitted parasite communities regardless of the habitats each species used. Our results suggest that environmental differences over relatively limited geographical distances have the potential to influence fish habitat use and parasite community structure.

This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at https://doi.org/10.1007/s10750-019-3969-9. Parallelism in trophic niches of polymorphic populations of Arctic charr was investigated in two similar subarctic lakes, Tårnvatn and Skøvatn, in northern Norway. Analysis of eleven microsatellite loci confirmed, respectively, the existence of three and two genetically differentiated morphs. Three methods were used to describe their trophic niches: habitat choice and stomach contents for the recent feeding behaviour, and trophically transmitted parasites and stable isotopes (δ13C and δ15N) as proxies for the longer term trophic niche differences. The results showed a distinct segregation in trophic resource utilization of the different morphs. Tårnvatn has three morphs: a littoral omnivorous (LO), a small-sized profundal benthivorous (PB), and a large-sized profundal piscivorous (PP). In contrast, a novel Arctic charr morph was discovered in Skøvatn: a small-sized profundal zooplanktivorous-morph (PZ), which when compared to the sympatric LO-morph, had distinct stable isotope values and a contrasting parasite community. A parallelism in habitat choice and external morphology was found among the small-sized, deep-water morphs and between the upper-water, omnivorous LO-morphs in both lakes. There was a no parallel pattern in diet choice between the PB- and the PZ-morphs. These findings show how evolution can produce diverse outcomes, even among systems with apparently similar environmental and ecological conditions.

A major goal of evolutionary science is to understand how biological diversity is generated and altered. Despite considerable advances, we still have limited insight into how phenotypic variation arises and is sorted by natural selection. Here we argue that an integrated view, which merges ecology, evolution and developmental biology (eco evo devo) on an equal footing, is needed to understand the multifaceted role of the environment in simultaneously determining the development of the phenotype and the nature of the selective environment, and how organisms in turn affect the environment through eco evo and eco devo feedbacks. To illustrate the usefulness of an integrated eco evo devo perspective, we connect it with the theory of resource polymorphism (i.e. the phenotypic and genetic diversification that occurs in response to variation in available resources). In so doing, we highlight fishes from recently glaciated freshwater systems as exceptionally well‐suited model systems for testing predictions of an eco evo devo framework in studies of diversification. Studies on these fishes show that intraspecific diversity can evolve rapidly, and that this process is jointly facilitated by (i) the availability of diverse environments promoting divergent natural selection; (ii) dynamic developmental processes sensitive to environmental and genetic signals; and (iii) eco evo and eco devo feedbacks influencing the selective and developmental environments of the phenotype. We highlight empirical examples and present a conceptual model for the generation of resource polymorphism – emphasizing eco evo devo, and identify current gaps in knowledge., Biological Reviews, 94 (5), ISSN:1469-185X, ISSN:1464-7931, ISSN:0006-3231

The use of translocations to establish new or ‘refuge’ populations for species with high conservation value is a controversial, but widely used, technique in conservation management. Two of the risks of this approach are that a new population will fail to establish, or that, if it does establish, it will fail to adequately capture the genetic diversity of the donor gene pool. This latter effect has however, been rarely tested. In this study we quantify the genetic consequences of two conservation translocations after five generations (16 years) of the European whitefish, Coregonus lavaretus, which is rare in the UK. Both translocations were made using almost the same genetic groups and thus represent a partly replicated natural study. Analysis of 12 informative microsatellites showed that expected heterozygosity, the mean number of alleles per locus and allelic richness did not differ between donor and translocated populations and there also was also no loss of heterozygosity in the translocated populations, nor deviations from expectation under the Hardy-Weinberg equilibrium, nor signs of linkage disequilibrium. There was clear and statistically robust evidence that all populations were genetically differentiated but the FST values were low, indicating that the magnitude of divergence was small. There was no evidence of inbreeding but there were significant differences in private allelic richness between donor and translocated populations. Of the 50 alleles found in the donor population 16% of the rarer alleles were lost in one translocated population and 8% in the other. The loss of alleles without a reduction in heterozygosity strongly points to stochastic drift effects having occurred following the translocation. However, surprisingly, both translocation populations showed evidence of having accumulated new, but different, alleles. Several strands of evidence suggest this this is not because these alleles were not detected in the donor population but because they have arisen de novo in the translocated populations.

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 (Fjellfrosvatn 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.

The first international symposium on Arctic charr (Salvelinus alpinus) was held in May, 1981, in Winnipeg, Manitoba, Canada, following shortly after the release of the seminal publication Charrs: Salmonid Fishes of the Genus Salvelinus (Balon, 1980), and sought to bring together scientists from nations in the circumpolar region containing Arctic charr or its close relatives in the S. alpinus complex. Since then, symposia have been held in Japan (1988), Norway (1994), Canada (2000), Iceland (2006), Scotland (2009) and Russia (2012). On the 14th June 2015, reflecting a buoyant research interest in Salvelinus, 112 participants from 13 countries gathered for the 8th International Charr Symposium in Tromso, Norway. Hosted by the UiT, The Arctic University of Norway, delegates included: 9 from Russia, 13 from USA, 15 from Canada, 9 from Japan, 8 from Iceland, 6 from Sweden, 3 from Scotland, 2 from Finland, 1 each from France, The Netherlands, Switzerland and Spain and 43 from Norway. In total, there were 79 oral presentations and 28 posters presented over the 4 days of meetings. Topical themes covered by the presentations and posters included anadromy, aquaculture, climate change, ecology, evolution, genetics, fisheries management, life history, parasitology and pollution impacts. Although the majority (two-thirds) of studies presented at the symposium focused on Arctic charr, there were many devoted to Dolly Varden charr (Salvelinus malma), Lake charr (Salvelinus namaycush), Brook charr (Salvelinus fontinalis) and Whitespotted charr (Salvelinus leucomaenis). The contributions covered two major geographic areas: northern Europe, and the Pacific basin drainages of the Asian and North American coasts. The vast area comprising the range of Salvelinus between these two more highly investigated regions was represented by only a few presentations from the Kola Peninsula, Siberia and Greenland, with the geographic spread of studies Guest editors: M. Power, R. Knudsen, C. E. Adams, M. J. Hansen, J. B. Dempson, M. Jobling & M. Ferguson / Advances in Charr Ecology and Evolution

Accepted manuscript version. Published version available in Effects of fish species composition on Diphyllobothrium spp. infections in subarctic brown trout - is three-spined stickleback a key species? (2016) 39(11), s.1313-1323. . Subarctic populations of brown trout (Salmo trutta) are often heavily infected with cestodes of the genus Diphyllobothrium, assumedly because of their piscivorous behavior. This study explores possible associations between availability of fish prey and Diphyllobothrium spp. infections in lacustrine trout populations. Trout in i) allopatry (group T); ii) sympatry with Arctic charr (Salvelinus alpinus) (group TC); and iii) sympatry with charr and three-spined stickleback (Gasterosteus aculeatus) (group TCS) were contrasted. Mean abundance and intensity of Diphyllobothrium spp. were higher in group TCS compared to group TC and group T. Prevalence however was similarly higher in group TCS and group TC compared to group T. Zero-altered negative binomial modelling identified lowest probability of infection in group T and similar probabilities of infection in group TC and group TCS, whereas the highest intensity was predicted in group TCS. Evidently, the most infected trout were from the group co-occurring with stickleback (TCS), assumedly due to a high availability of suitable prey fishes. In conclusion, our study demonstrates elevated Diphyllobothrium spp. infections in lacustrine trout populations where fish prey are available, and suggests that highly available and easily caught stickleback prey may play a key role in the transmission of Diphyllobothrium spp. parasite larvae.

Seasonal dietary shifts by Arctic charr (Salvelinus alpinus (L.)) are common in subarctic lakes, but less is known about how the shift to pelagic zooplankton feeding during the growing season affects stable isotope ratios and mercury concentrations. We sampled Arctic charr, zooplankton and benthic macroinvertebrates from oligotrophic Lake Galggojavri, northern Norway, in June, August and September. Stomach content, age, total length, weight, condition and sex were recorded for all individuals, and liver and muscle tissues were sampled for stable isotope (δ13C, δ15N) and total mercury analyses. We predicted that a dietary shift to zooplankton would lead to depleted 13C and increased mercury levels in charr. Arctic charr consumed benthic prey in June, but shifted to zooplankton feeding in August–September. Stable isotope mixing models revealed increased pelagic reliance towards September. Mercury content in liver increased from June to September, whereas muscle showed opposite trend. In stepwise multiple regression analyses, mercury content in muscle was explained by fish length, month and δ13C (R 2 = 0.46), whereas in liver month, δ13C and δ15N were the main explaining factors (R 2 = 0.69). Seasonal dietary shifts appeared to have an effect on total mercury content in charr, and thus sampling month should be considered when designing future monitoring programmes.

Parasite communities can show large differences in species composition between sympatric host species. Here, we assessed how divergent resource use of polymorphic populations of Arctic charr from two environmentally similar sub-arctic lakes was related to parasite community composition. Large similarities in parasite infections were found for both the reproductively isolated littoral-spawning omnivore LO-morph and the profundal-spawning benthivore PB-morph, reflecting cross-lake similarities in resource use. Furthermore, whereas the PB-morph had the lowest richness and abundance of parasite species in both lakes, a third morph, the profundal-spawning piscivorous PP-morph (one lake only), had the highest parasite richness and accumulated parasites by preying upon fish. These results highlight that host ecology and abiotic factors are important for structuring parasite communities. The dissimilarities in the local parasite species pool between the lakes suggest that stochastic events as well as transmission abilities are involved in structuring the parasite communities. The parallel divergent parasite infections between morphs may form an arena for parasite-mediated selection promoting the incipient speciation process in concert with other factors. The deep-water PB-morphs may avoid parasites by specialising in parasite-poor but low-productive habitats, while the piscivorous PP-morph aggregates infections of detrimental parasites through specialising on energetically rich but generally more heavily parasitised prey.

Arctic charr (Salvelinus alpinus) is generally considered an inferior piscivore compared to brown trout (Salmo trutta). However, we demonstrate that a recently described profundal spawning piscivore PP-morph of Arctic charr in a subarctic lake has evolved typical piscivore traits (i.e. large jaws, robust skulls), similar to the co-occurring brown trout but different from the sympatric littoral spawning omnivore LO-morph of Arctic charr. A few large-sized LO-morph, most large-sized PP-morph and trout constitute the piscivore guild, but they differed in prey fish selection. Of the fish-eating deep-water PP-morph, 52% had consumed charr, with a peak during the polar night period (68–80% in November–January). In contrast, the LO-morph and trout were mainly (~90%) inter-specific piscivores eating stickleback. Consequently, the PP-morph was the main charr predator and started to feed on fish at a smaller size and took larger prey relative to their body length than the trout. Stable isotope (δ13C, δ15N) ratios reflect the dietary specialisations in the upper-water (LO-morph, trout) and the deep-water (PP-morph) environments, besides the piscivorous behaviour of the PP-morph and trout. The existence of a shallow-water piscivore (trout) may explain the origin of this PP-morph, taking benefit of underutilised resources of small-sized Arctic charr in the deep-water habitat.

We contrast the genetic consequences of allopatric and sympatric divergence from the littoral spawning Arctic charr morph from Lake Fjellfrosvatn. The littoral spawning Arctic charr has sympatrically diverged into a natural profundal adapted morph and via a recent (1930) translocation of about 40 adult Arctic charr established a new allopatric population in a nearby lake (Takvatn). The sympatric morph-pair in Fjellfrosvatn was more genetically differentiated (F ST = 0.121), the derived profundal morph had higher genetic variation (H e = 0.740 ± 0.220; N PAR = 4.87), and had a higher proportion of linkage disequilibrium among loci, than the Takvatn charr derived in allopatry (F ST = 0.066; H e = 0.584 ± 0.193; N PAR = 0.29). The genetic differentiation in allopatry supports a scenario of rapid population expansion, despite genetic founder effects, whereas the genetic differentiation found in the sympatric morph-pair suggests that this divergence is older and supports a scenario of divergence under ongoing gene flow. We suggest that the differences between the two types of divergence may originate from temporal effects and differences in life histories between the two derived populations along with specific factors related to the initial stages of the divergence.

A population of small-sized Arctic charr living their entire life cycle in deep water was recently found in Lake Skogsfjordvatn, Northern Norway. Their phenotype and life history closely resembles the profundal charr morph in another subarctic Norwegian lake, Fjellfrosvatn. Fjellfrosvatn has one littoral omnivorous and one small profundal benthivorous (PB) charr morph coexisting with brown trout, whereas Skogsfjordvatn has migratory salmon, trout, charr and eel populations in addition to threespined sticklebacks, resident trout and three resident charr morphs of which one is a large piscivorous profundal morph. We predicted that the small profundal charr morph in Skogsfjordvatn would have a similar trophic niche to the PB-morph in Fjellfrosvatn and tested this by using stomach content and stable isotope (δ13C and δ15N) analyses. Profundal benthic invertebrates, mainly chironomid larvae, Pisidium sp. mussels and small crustaceans, dominated the diets, and the δ13C and δ15N values indicated almost identical long-term trophic niches of the PB-morphs in both lakes. The prediction was therefore supported. This seems to indicate that the small profundal Arctic charr morphs in these lakes have evolved in parallel, in nearly identical and stable habitat and dietary niches in spite of likely different ecological interactions within the contrasting fish communities.

This study revealed between-lake genetic structuring between Coregonus lavaretus collected from the only two native populations of this species in Scotland, U.K. (Lochs Eck and Lomond) evidenced by the existence of private alleles (12 in Lomond and four in Eck) and significant genetic differentiation (FST = 0·056) across 10 microsatellite markers. Juvenile C. lavaretus originating from eggs collected from the two lakes and reared in a common-garden experiment showed clear phenotypic differences in trophic morphology (i.e. head and body shape) between these populations indicating that these characteristics were, at least partly, inherited. Microsatellite analysis of adults collected from different geographic regions within Loch Lomond revealed detectable and statistically significant but relatively weak genetic structuring (FST = 0·001–0·024) and evidence of private alleles related to the basin structure of the lake. Within-lake genetic divergence patterns suggest three possibilities for this observed pattern: (1) differential selection pressures causing divergence into separate gene pools, (2) a collapse of two formerly divergent gene pools and (3) a stable state maintained by balancing selection forces resulting from spatial variation in selection and lake heterogeneity. Small estimates of effective population sizes for the populations in both lakes suggest that the capacity of both populations to adapt to future environmental change may be limited.

Most ecosystems are exposed to multiple stressors acting in concert and their combined effects on parasite prevalence in freshwater, marine and terrestrial habitats are largely unknown. We investigated the relationships between farming intensity, water abstraction intensity and parasite prevalence in the mud snail Potamopyrgus antipodarum from 20 stream sites within the Manuherikia River catchment (New Zealand) by using generalized linear models and an information-theoretic model-selection approach. Three trematode taxa that use water birds as definitive hosts were found in the snail host. The average prevalence of all parasites infecting Potamopyrgus in the catchment was 5%. Microphallus sp. “lively”, the most common parasite, was most prevalent at high farming intensity and low water abstraction, besides showing an antagonistic interaction between the two agricultural stressors. These findings highlight the importance of considering multiple stressors and their potential interactions when studying host–parasite systems. Because snails often play key roles in aquatic communities, providing an important link between primary producers and higher trophic levels, and are a common intermediate host to a high diversity of trematode parasites, this host–parasite model system may represent a promising bioassessment tool for detecting anthropogenic disturbances in freshwater systems.

Source at https://doi.org/10.1002/lno.10951. We review three long‐term research programs performed over the last four decades on the ecology and management of oligotrophic lake systems with different fish communities at 69° N in Norway. Through whole‐lake perturbation experiments, intensive culling of stunted fish removed 35 tons (1984–1991) of Arctic charr Salvelinus alpinus in Takvatn (15 km2) and 153 tons (1981–1983, 2002–2004) of European whitefish Coregonus lavaretus in Stuorajavri (25 km2). In Takvatn, the overcrowded charr population decreased to 20% of the initial abundance, whereas brown trout Salmo trutta abundance increased. Somatic growth improved strongly in both species. In charr, ontogenetic habitat shifts broke down, the diet changed to more benthos, and plankton‐borne parasites decreased. High abundance of juvenile, littoral charr provided new prey for trout, creating an alternative, predator‐regulated stable state. Similar density reductions, positive effects on growth and reduced parasite loads occurred in whitefish in Stuorajavri. Despite the heavy culling, however, a new stable state did not occur and the fish community returned to the pre‐culling situation. In the Pasvik watercourse, vendace Coregonus albula invaded around 1990 after an upstream introduction. The population of this non‐native, highly specialized planktivore increased rapidly, resulting in steep density declines in zooplankton and the native planktivorous whitefish morph, and large changes in energy flow and structure and dynamics of the lacustrine food web. These programs show that long‐term research is essential for understanding the ecology of manmade disturbances and providing a scientific basis for management efforts.

Parasite distribution patterns in lotic catchments are driven by the combined influences of unidirectional water flow and the mobility of the most mobile host. However, the importance of such drivers in catchments dominated by lentic habitats are poorly understood. We examined parasite populations of Arctic charr Salvelinus alpinus from a series of linear-connected lakes in northern Norway to assess the generality of lotic-derived catchment-scale parasite assemblage patterns. Our results demonstrated that the abundance of most parasite taxa increased from the upper to lower catchment. Allogenic taxa (piscivorous birds as final host) were present throughout the entire catchment, whereas their autogenic counterparts (charr as final hosts) demonstrated restricted distributions, thus supporting the theory that the mobility of the most mobile host determines taxa-specific parasite distribution patterns. Overall, catchment-wide parasite abundance and distribution patterns in this lentic-dominated system were in accordance with those reported for lotic systems. Additionally, our study highlighted that upper catchment regions may be inadequate reservoirs to facilitate recolonization of parasite communities in the event of downstream environmental perturbations.

Source at https://doi.org/10.1016/j.ijppaw.2018.01.007. Accepted manuscript version, licensed CC BY-NC-ND 4.0. The eye represents an immune privileged organ where parasites can escape host reactions. This study provides the first systematic evidence of the pathology associated with Diplostomum sp. infection in the eye retina of fish (i.e. Arctic charr). Histological sections showed that the trematodes caused mechanical disengagement between the retinal pigmentary epithelium and the neurosensory retina, with damaged cones and rods in the outer segment and epithelium reduced to a single layer of pigmentary cells. The metacercariae were “floating” in possibly fluid-filled vesicles together with several round cells, mostly located in the anterio-dorsal and anterio-ventral areas of the eye near the iris. The round cells may indicate internal retinal damage repair mechanisms, without connections to the general immune system. Metacercariae intestines contained pigmented cellular debris indicating that they feed on retinal epithelium. These retinal lesions may have similar vision effects as focal retinal detachment in vertebrates. Diplostomum metacercaria alters fish visual acuity but may in a lesser degree lead to a severe or total visual impairment because of repairing mechanisms. The pathology in the retina seems thereby to be dependent on fish size, age and dose.

Foraging trait specialization is important for polymorphic Arctic charr and whitefish, but visual capabilities of different morphs are unexplored. Photoreceptor complements and absorbance spectra of rod visual pigments were studied by microspectrophotometry in two sympatric Arctic charr morphs and three sympatric whitefish morphs from two subarctic lakes. Four spectral classes of photoreceptor cells, rods and three types of cones, were found in all morphs of both species. Arctic charr rods had a pure A1 pigment (rhodopsin) with wavelength of maximum absorbance λ max ≈ 511–512 nm and no significant differences either between littoral and profundal morphs or sampling times (January/August). Rods of littoral and pelagic whitefish had practically pure A2 pigment (porphyropsin), whereas profundal whitefish had chromophore mixtures with A2:A1 ≈ 0.8:0.2 in June, A1 decreasing to a smaller fraction in September. λ max values of littoral and pelagic whitefish rods were similar and did not change significantly with season (539.3 ± 0.3 nm/539.3 ± 1.1 nm and 538.4 ± 0.4/539.8 ± 0.3 nm in June/September) but differed from profundal whitefish (λ max = 531.5 ± 0.8/536.7 ± 1.0 nm). Differences between Arctic charr and whitefish morphs suggest importance of local light environment determining visual pigment composition.

Seasonal growth patterns have been investigated in juveniles of two reproductively isolated Arctic charr [Salvelinus alpinus (L.)] morphs, which coexist in distinct ecological niches (upper-water and deep-water environments) in a subarctic lake. Offspring (F1-generation) of each of the littoral spawning charr (LO) and the profundal spawning charr (PB) were reared individually over a period of 12 months under simulated natural photoperiod (at 69°N) and two different temperature regimes to mimic the profundal zone conditions with constantly low temperature (~4 °C) and the littoral zone conditions with seasonally cycling temperatures. All charr increased in weight during the experimental period. The LO-morph performed generally best at naturally fluctuating temperature, whereas the PB-morph grew best at a constantly low temperature (4 °C). The LO-morph showed a typical seasonal growth pattern found earlier for anadromous Arctic charr, with elevated specific growth rates (SGR) during June–October and profoundly reduced or negative SGR-values during November–February suggesting that the fish ceased feeding during this period. In contrast, the PB-morph maintained a steady growth rate, regardless of temperature regime, and showed less signs of reduced appetite during the polar night period and exhibited significantly higher SGR-values during late autumn and early winter compared to the LO-morph. This study suggests different heritable adaptations in somatic growth trajectories where the deep-water PB-morph do not show a down-regulation of appetite and voluntary fasting during winter conditions with typically low light intensity and low temperatures, and up-regulation of appetite with hyperphagia during summer, as characteristically found for the upper-water LO-morph and anadromous Arctic charr.