Siken (Coregonus lavaretus L., 1758 ) : et artskompleks med en spennende evolusjonær historie og forvaltningmessige utfordringer

Siken varierer mye i utseende innen og mellom vann. Her oppsummerer jeg egen, og til dels annen, relevant litteratur, for å reflektere rundt hvordan sikens utseende kan være påvirket av slektskap og tilpasninger til ulike forhold i innsjøen, og hvilke forvaltningsmessige konsekvenser dette kan ha. Tre genetiske hovedlinjer (basert på mitokondrie-DNA (mtDNA)), som sannsynligvis overlevde i ulike refugier gjennom siste istid, har kolonisert nordlige deler av Europa. Også innen innsjøer kan ulikt utseendemessige sikbestander være delvis genetisk adskilt. Slike bestander har en form for ufullstendig adferdsbarriere mot å parre seg med hverandre. Basert bare på utseendemessig variasjon kan nesten hver sikbestand beskrives innen binær nomenklatur til å være ulike taxonomiske arter, men dette er ikke hensiktsmessig av ulike årsaker. En viktig grunn her er at bestander som ikke er nært beslektet kan ha utviklet utseendemessige karaktertrekk gjennom parallell evolusjon. Det betyr at de uavhengig har utviklet seg mot samme form fordi de har levd under samme forhold, der karaktertrekk er strukturert av naturlig seleksjon. Like eller ulike karaktertrekk hos sik innen og mellom innsjøer kan oppstå via fenotypisk plastisitet (der den samme genotypen gir ulikt fenotypisk uttrykk i ulike miljøer) og naturlig seleksjon der morfene som er mest tilpasset et gitt miljø, får flest avkom. Mekanismene bak oppsplitting i genetikk og utseende innen- og mellom vann kan være bestemt av ulike faktorer. Den evolusjonære historien om hvor forfedrene kom fra med sine gener, er grunnleggende. Naturlig seleksjon plukker ut hvilke genkombinasjoner og karaktertrekk som går videre i neste generasjon gitt tilpasningsdyktighet utfra eksisterende variasjon. For mange arter og populasjoner kan oppvekstforholdene påvirke utseende og livshistorien ved at de er fenotypisk plastiske. Genetisk struktur og assosierte karaktertrekk kan også bli påvirket av tilfeldig genetisk drift og genflyt mellom populasjoner. Mekanismen bak sympatrisk oppdeling i ulike former av sik innen ett og samme vann kan være økologisk nisje-deling, det vil si at de forekommende formene av siken er tilpasset til å utnytte de ulike delene av innsjøen forskjellig. Gitt tid og geografisk separasjon kan slike økologiske former være på vei til å bli gode biologiske arter via økologisk artsdannelse, noe våre data støtter. Det ser også ut til at flere innvandringer av ulikt utseende sik kan forekomme i samme vann via sekundær kontakt av allopatrisk utviklede (geografisk isolerte) mtDNA-linjer. Slike forhold gir forvaltningen utfordringer med identifisering av bestander, definering av enheter for bevaring, og høsting av denne evolusjonært interessante og gode matfisken. En kombinasjon av genetikk-, utseende- og livshistorieanalyser bør ligge til grunn for å foreslå og iverksette gode forvaltningsenheter. I Norge har vi en stor sik-diversitet som vi må forvalte på en fornuftig og effektiv måte, slik at vi kan både høste av den og forske på den i framtiden

Occurrence and habitat choice of waders in a high mountain sedimentation flat on Hardangervidda, South Norway

Studies of the occurrence and nesting habitat choice of waders were conducted at Finsefetene (1200 m a.s.l.), a high mountain sedimentation flat on the Hardangervidda plateau, South Norway during 1967-1984. Eight species occurred in the study area during the period, either regularly such as Calidris temminckii, Actitis hypoleucos, Charadrius hiaticula, Calidris alpina, or occasionally, such as Tringa totanus, Calidris maritima, Pluvialis apricaria and Phalaropus lobatus. The densities of the whole wader community on the sedimentation flat were related to the proportion of snow-free areas at Finse around 10 July, and on the date when Finsefetene becomes totally snow-free (DFSF). Of the eight species, only C. temminckii and P. lobatus were found to be positively correlated with the extent of snow-free area, while C. alpina and C. lobatus were positively correlated with DFSF. In low density years the nests were usually placed in the same locations, these obviously being optimal sites. The majority of C. temminckii nests were located in the two intermediate fen vegetation associations, and according to its availability the Caricion canescentis-nigrae was clearly selected for. Two other preferred plant associations on drier ground, Lactucion alpinae and Arctostaphyleto-Cetrarion nivalis, were also selected for. Nest location preferences for vegetation associations are also indicated for the other wader species, but the data on these are limited. Changes in river flow causing varying water levels in the surroundings are a pronounced ecological trait on Finsefetene. In years with a heavy spring flood many nests would be submerged. The location of the nests in relation to a so-called «Zero point», varied from 34 cm below to 210 cm above. In high density years the nests of the most common species, C. temminckii, were spread over most of the flat. In years with a late spring flood, after the nesting had started, some low situated nests were flooded. To visualize the wader community pattern, the distribution of the variable number and scattered nest locations were plotted on maps. Details in nest locations of C. temminckii are given for each year; for the other recorded species the map covers all years. The Finsefetene sedimentation flat proved to be a valuable high mountain habitat for wader populations on Hardangervidda

The role of predation risk in structuring life-history traits of crucian carp (Carassius carassius) in a series of small boreal lakes

Predation is a major evolutionary force determining life-history traits in prey by directand indirect mechanisms. This study focuses on life-history trait variation in cruciancarp (Carassius carassius), a species well known for developing a deep body as aninducible morphological defence against predation risk. Here, the authors tested vari-ation in growth and reproductive traits in 15 crucian carp populations in lakes along apredation risk gradient represented by increasingly efficient predator communities.Lakes were located in south-eastern Norway and were sampled in summer 2018 and2019. The authors expected crucian carp to attain higher growth rate, larger size, andlater age at maturity with increasing predation risk. In the absence of predators, theyexpected high adult mortality, early maturity and increased reproductive effortcaused by strong intraspecific competition. They found that the life-history traits ofcrucian carp were clearly related to the presence of piscivores: with increasing preda-tion risk, fish grew in body length and depth and attained larger asymptotic lengthand size at maturity. This growth was evident at young age, especially in productivelakes with pike, and it suggests that fish quickly outgrew the predation window byreaching a size refuge. Contrary to the authors’predictions, populations had similarage at maturity. High-predation lakes also presented low density of crucian carp. Thissuggests that fish from predator lakes may experience high levels of resource avail-ability due to reduced intraspecific competition. Predation regulated life-history traitsin crucian carp populations, where larger size, higher longevity and size at maturitywere observed in lakes with large gaped predators.publishedVersio

Predicting Habitat Properties Using Remote Sensing Data: Soil pH and Moisture, and Ground Vegetation Cover

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Remote sensing data comprise a valuable information source for many ecological landscape studies that may be under-utilized because of an overwhelming amount of processing methods and derived variables. These complexities, combined with a scarcity of quality control studies, make the selection of appropriate remote sensed variables challenging. Quality control studies are necessary to evaluate the predictive power of remote sensing data and to develop parsimonious models underpinned by functional variables, i.e., cause rather than solely correlation. Cause-based models yield superior model transferability across different landscapes and ecological settings. We propose two basic guidelines for conducting such quality control studies that increase transferability and predictive power. The first is to favour predictors that are causally related to the response. The second is to include additional variables controlling variation in the property of interest and testing for optimum processing method and/or scale. Here, we evaluated these principles in predicting ground vegetation cover, soil moisture and pH under challenging conditions with forest canopies hindering direct remote sensing of the ground. Our model using lidar data combined with natural resource maps explained most of the observed variation in soil pH and moisture, and somewhat less variation of ground vegetation cover. Soil pH was best predicted by topographic position, sediment type and site index (R 2 = 0.90). Soil moisture was best predicted by topographic position, radiation load, sediment type and site index (R 2 = 0.83). The best model for predicting ground vegetation cover was a combination of lidar-based estimates for light availability below canopy and forest type, including an interaction between these two variables (R 2 = 0.65).publishedVersio

Regressive evolution of the pelvic complex in stickleback fishes: a study of convergent evolution

Background: Regressive evolution of the pelvic complex has been observed in populations of three of five stickleback genera, Gasterosteus, Pungitius, and Culaea, from young freshwater habitats (<18,000 years old). It has been hypothesized to be selected for by ion limitation, lack of predation by fishes, and increased predation by large aquatic insects. Stickleback pelvic reduction is often caused by deletion mutations of the Pitx1 gene, which prevent its expression during pelvic development. Lack of Pitx1 expression may be partly compensated for by Pitx2, which is preferentially expressed on the left side of the body, causing the left pelvic vestige to be larger than the right. Thus, left-biased directional asymmetry of pelvic vestiges implicates null Pitx1 alleles. Aim: Review the geographical patterns of pelvic variation in the three stickleback genera and consider their implications for hypotheses regarding the genetics and evolution of pelvic reduction in the Gasterosteidae. Data: We review published data on pelvic reduction and add previously unpublished information from populations in Scotland and Norway. Methods: We assign individual stickleback to one of three pelvic phenotypes – normal, vestigial, and lost pelvis – and explore the distribution of these three broad classes among populations. We study bilateral symmetry of the pelvis by scoring pelvic phenotypes on the left and right sides. Results: Pelvic reduction is rare in sticklebacks and occurs only in fresh water. Sticklebacks with pelvic reduction tend to occur in the western and northern parts of their ranges in Eurasia and North America, but this pattern is less evident for the ninespine stickleback. Pelvic phenotype frequency distributions within populations differ among stickleback genera. The vestigial pelvic phenotype dominates in many populations of Gasterosteus aculeatus, rarely in Pungitius, and never in Culaea inconstans. In Culaea, the lost and normal pelvic phenotypes are often dimorphic, but a vestigial pelvis is rare. This dimorphism does not occur in the other two genera. Monomorphism of the lost pelvic phenotype does not occur in Gasterosteus, and is rare in the other two genera. Asymmetry of pelvic vestiges is common in all three genera, but left-larger directional asymmetry predominates only in Gasterosteus. This bias could be due to the suggested regulatory mutation in the Pitx1 gene and/or mutations in downstream targets of Pitx1, and suggests involvement of other genes for pelvic reduction in the other genera.2014-08-3

Structure and dynamics of a high mountain wetland bird community in southern Norway: An 18-year study of waders and gulls

We studied the breeding bird density of wader and gull species for 18 years (1967-1984) at a study plot at Finse (1200 m a.s.l.) in the northwestern part of the 10 000 km2 high mountain plateau Hardangervidda, South Norway (60&deg;36&rsquo;N, 7&deg;30&rsquo;E). The study plot was a 1 km2 large sedimentation flat in the bottom of the Finse Valley. Eight species of waders were recorded as territorial, and their combined densities varied from 2 to 19 (mean 10) territories/km2. Four species, the Temminck&rsquo;s Stint, Calidris temminckii, the Common Sandpiper, Actitis hypoleucos, the Ringed Plover, Charadrius hiaticula and the Dunlin, Calidris alpina, occurred regularly (&gt;half of the study period) and constituted about 87% of the annual community densities in the study plot. One species, C. temminckii, was the dominant species, and held on average 60% of the territories. Four species, the Redshank, Tringa totanus, the Purple Sandpiper, Calidris maritima, the Golden Plover, Pluvialis apricaria, and the Red-necked Phalarope, Phalaropus lobatus, occurred only irregularly, with a low number of territories, and did not breed every year. Only one gull species was recorded as territorial, the Common Gull, Larus canus, and the density varied from 1 to 5 (mean 2.4) territories/km2. The variations in density of the wader community was correlated positively with the mean temperature in June, and negatively with the NAO index for June, the date of snow-melt and the percentage of snow cover in the area, showing that an early snow-melt was important for the establishing of territories. Both the wader community, the combined wader and gull community, each of the species C. temminckii, C. alpina and P. lobatus fluctuated in synchrony with the populations in the passerine community of the area. The wader community, the combined wader and gull community and the species C. temminckii and L. canus also varied with the fluctuations of the small rodent populations in the area. The densities of territories of the different wader species are compared with literature data from other parts of their distributional area

Genetic population structure of the monogenean parasite Gyrodactylus thymalli and its host European grayling (Thymallus thymallus) in a large Norwegian lake

Understanding how populations are structured in space and time is a central question in evolutionary biology. Parasites and their hosts are assumed to evolve together, however, detailed understanding of mechanisms leading to genetic structuring of parasites and their hosts are lacking. As a parasite depends on its host, studying the genetic structure of both parasite and host can reveal important insights into these mechanisms. Here, genetic structure of the monogenean parasite Gyrodactylus thymalli and its host the European grayling (Thymallus thymallus) was investigated in 10 tributaries draining into the large Lake Mjøsa in Norway. The population genetic structure of spawning grayling was studied using microsatellite genotyping, while G. thymalli was studied by sequencing a mitochondrial DNA gene (dehydrogenase subunit 5). Two main genetic clusters were revealed in grayling, one cluster comprising grayling from the largest spawning population, while the remaining tributaries formed the second cluster. For both taxa, some genetic differentiation was observed among tributaries, but there was no clear isolation-by-distance signature. The structuring was stronger for the host than for the parasite. These results imply that moderate to high levels of gene flow occur among the sub-populations of both taxa. The high parasite exchange among tributaries could result from a lack of strong homing behavior in grayling as well as interactions among individual fish outside of the spawning season, leading to frequent mixing of both host and parasite.publishedVersio

Spatio-temporal patterns in pelvic reduction in threespine stickleback (Gasterosteus aculeatus L.) in Lake Storvatnet

Questions: The pelvic girdle with associated spines is an integrated anti-predator defence apparatus, and is assumed to protect against piscivores in the threespine stickleback. On the other hand, it might be costly to produce the pelvic apparatus in ion-poor and mineralchallenging freshwater. Hypothesis: Stickleback with a reduced pelvic apparatus should use more shelter and be more nocturnal, avoiding predation risk. In contrast, stickleback with a well-developed pelvic apparatus should have reduced mortality during ontogeny in encounters with piscivores and thus have a longer expected lifespan. Given these two life-history strategies, we expect assortative mating as a result of divergent selection. Organism: Marine and freshwater threespine stickleback (Gasterosteus aculeatus L.). Places and times: Two representative ancestral marine populations and 36 freshwater populations in northwestern Norway (Lake Storvatnet, the main focus of the study, and three lakes downstream of it). Material was collected from 2006 to 2009. Analytical methods: We categorized nominal pelvic apparatus development (CPS morphs) in all fish, and measured metrics associated with these categories in a subsample. We also studied temporal, spatial, and habitat variation in the distribution of pelvic morphs in Lake Storvatnet. In this population, and downstream populations, we contrasted the detailed pelvic morphology with the measured genetic diversity (microsatellites), also estimating gene flow. In Lake Storvatnet, we tested for genetic divergence and signs of potential build-up of reproductive isolation via assortative mating among the observed nominal categories of pelvic reduction (CPS). Results: Pelvic reduction was seen only in Lake Storvatnet, where more than 50% of fish had a reduced pelvis. The distribution of pelvic morphs was stable over time and did not differ between habitats. The proportion of fish with pelvic reduction decreased with age. Freshwater stickleback tended to have a smaller pelvis than marine fish. The Lake Storvatnet stickleback were genetically differentiated from the downstream Lake Gjerhaugsvatn population, and both of these were different from the marine populations, with little gene flow among populations. No apparent genetic structure was found between CPS morphs within Lake Storvatnet. However, genetic factorial correspondence axes were significantly correlated with pelvic principal component axes in Lake Storvatnet, suggesting some phenotype × genetic association. Conclusion: The weak association between phenotypes and genetic structure observed in this study may reflect the build-up of early steps of reproductive isolation. Given time, such mechanisms may lead to the evolution of assortative mating, which may drive adaptive pelvic morphs (niche peaks), further resulting in genetically divergent populations and pelvic morphs

Predator community and resource use jointly modulate the inducible defense response in body height of crucian carp

Phenotypic plasticity can be expressed as changes in body shape in response to environmental variability. Crucian carp (Carassius carassius), a widespread cyprinid, displays remarkable plasticity in body morphology and increases body depth when exposed to cues from predators, suggesting the triggering of an antipredator defense mechanism. However, these morphological changes could also be related to resource use and foraging behavior, as an indirect effect of predator presence. In order to de-termine whether phenotypic plasticity in crucian carp is driven by a direct or indirect response to predation threat, we compared twelve fish communities inhabiting small lakes in southeast Norway grouped by four categories of predation regimes: no predator fish, or brown trout (Salmo trutta), perch (Perca fluviatilis), or pike (Esox lucius) as main piscivores. We predicted the body shape of crucian carp to be associated with the species composition of predator communities and that the presence of efficient piscivores would result in a deeper body shape. We use stable isotope analyses to test whether this variation in body shape was related to a shift in individual resource use- that is, littoral rather than pelagic resource use would favor the development of a specific body shape- or other environmental characteristics. The results showed that increasingly efficient predator communities induced progressively deeper body shape, larger body size, and lower population densities. Predator maximum gape size and individual trophic position were the best variables explaining crucian carp variation in body depth among predation categories, while littoral resource use did not have a clear effect. The gradient in predation pressure also corresponded to a shift in lake productivity. These results indicate that crucian carp have a fine-tuned morpho-logical defense mechanism against predation risk, triggered by the combined effect of predator presence and resource availabilitypublishedVersio

Resource use of crucian carp along a lake productivity gradient is related to body size, predation risk, and resource competition

Generalist fish species can feed on a wide resource spectrum and across trophic levels depending on resource availability and trophic interactions. Crucian carp (Carassius carassius) represents a good candidate species to investigate variation in the trophic ecology of generalist fish as it can be found in highly variable fish communities and its resource use is well documented. In this study, we explored the trophic ecology of crucian carp at the individual and population levels using stable isotope and gut content analysis. We tested if trophic resource use varied according to lake productivity, predation risk, intra- and interspecific competition, or individual fish size. We found that crucian carp resource preference was highly variable among and within lakes. In predator-free lakes, small crucian carp occurred in high densities, showed increased interindividual specialisation, and relied mainly on pelagic zooplankton. In presence of predators, large crucian carp occurred in low densities and included greater proportions of benthic macroinvertebrates in their diet. This shift in resource use was further favoured in productive, shallow lakes where littoral prey was probably abundant. Resource partitioning was an important factor determining crucian carp niche use, as fish had higher trophic position in absence of other cyprinids. Crucian carp showed highly dynamic resource use and food preferences in response to variable environmental conditions. Overlooking complex diet preferences of generalist fish may lead to an oversimplification of freshwater community dynamics.publishedVersio