Populasjonsstruktur hos fire vårgytende fiskearter i Lågendeltaet: effekt av vannføring og temperatur på initiering av gytevandring

Elvedeltaområder er svært dynamiske, og bruken av slike områder under gyteperioden varierer blant vårgytende fiskearter. Fotoperioden og vanntemperaturen er sentrale miljøfaktorer som forbereder fisk til gytingen, men hvordan virker disse og andre miljøfaktorer sammen for å forme gytingen, samt gytevandringene for fiskene? Dette er et viktig spørsmål som bør adresseres for å forstå og best mulig forvalte de belastede deltaøkosystemene i en verden i endring. Dette studiet undersøkte effekten av miljøfaktorer på initieringen av gytevandring hos fire vårgytende arter: abbor (Perca fluviatilis), brasme (Abramis brama), gjedde (Esox lucius) og mort (Rutilus rutilus) i det tempererte elvedeltaøkosystemet Lågendeltaet i Norge. Deltaområdet munner ut i Norges største innsjø Mjøsa, som er regulert. Det var forventet at rovfiskene gjedde og abbor, ankom tidligere enn karpefiskene for å øke sjansene sine for å oppnå en størrelsesmessig fordel før byttedyrene deres (karpefiskene) klekkes. Studien brukte daglige fangstdata samlet inn i mai-juni ved hjelp av ruser i seks potensielle gyteområder med differensierte temperaturregimer. Fangstdataene ble analysert i lys av antatte viktige miljøvariabler: vannføring i Gudbrandsdalslågen, vannstand i Mjøsa og vanntemperatur. Et ytterligere mål var å studere veksten hos gjedde, abbor og mort. Resultatene viste at gjedde og abbor ankom før karpefiskene som forventet, men stimer med abbor vandret inn overlappende med mort. Sannsynligheten for gjeddeinnvandring økte med økende vannstand i Mjøsa. For abbor, brasme og mort antydet resultatene at fallende vannstand i Mjøsa økte sannsynligheten for innvandring til gyteplassene. De høyeste fangstene av disse tre artene kom etter vårflommen med synkende vannstand, noe som indikerte at en flom var nødvendig for å initiere gytevandringen. For mort var også fallende vannføring i elven Gudbrandsdalslågen en initierende faktor. Temperatur initierte migrasjonen for gjedde, abbor og brasme i modellene. For gjedde antydet resultatene at laveste observerte temperatur økte sannsynligheten for innvandring, noe som betyr i biologiske termer at gjedda ankom så snart det var vann i området. For brasme økte en vanntemperatur på rundt 11 °C, etter flommen, sannsynligheten for innvandring. Abbor viste en optimal sannsynlighet for innvandring ved 10,3 °C. Vekstkurvene viste stabil vekst for gjedde og en høy asymptotisk lengde. 34 % av gjeddeindividene var eldre enn 10 år, noe som indikerer lav høsting i området.River delta areas are highly dynamic, and the use of such areas during the spawning period vary among spring-spawning fish species. Photoperiod and water temperature are key environmental drivers that prepare the fishes for the spawning, but how do these and other environmental factors act complementary in shaping the spawning, as well as the spawning migration for the fishes? This is a key question that needs to be addressed to understand and best manage the multi-stressed delta ecosystems in a changing world. This study looked at effects of environmental cues on initiating spawning migration in four spring-spawning species: the Eurasian perch (Perca fluviatilis), common bream (Abramis brama), the Nordic pike (Esox lucius) and roach (Rutilus rutilus) in the temperate river-delta ecosystem Lågendeltaet in Norway. The delta area empty into the regulated lake Mjøsa. It was anticipated that the predatory fishes pike and perch arrive earlier than the cyprinids, to enhance their chances of getting an advantage in size prior to the hatching of their prey (cyprinids). The study used daily catch data sampled during May- June using fyke nets in six potential spawning areas with differential temperature regimes. The catch data was analysed in the light of assumed key environmental variables: water discharge, water level in Mjøsa and water temperature. An additional objective was to study the growth for pike, perch and roach. The results showed that the pike and perch arrived prior to the cyprinid- species. The pike immigration probability increased by rising water levels in lake Mjøsa. For common bream, perch and roach, the results suggested that decreasing water-level in Mjøsa increased immigration probability to the spawning grounds. The highest catches of these three species were post-spring flood with decreasing water levels, indicating that a flood is required to initiate the spawning migration. For roach the decreasing water discharge in river Gudbrandsdalslågen was also an initiating predictor. Temperature initiated migration for pike, perch and common bream in the models. For pike, the results suggested that the lowest temperatures observed increased immigration probability, meaning in biological terms, that the pike arrived as soon as there was water in the area. For bream, a water temperature around 11 °C after flood, increased immigration probability. Perch showed an optimum immigration probability at 10.3 °C. The growth curves showed a stable growth for the pike and a high asymptotic length. 34 % of pike individuals was older than 10 years indicating a low harvest in the area

Implications of transient methane flux on associated biological communities in high-arctic seep habitats, Storbanken, Norwegian Barents sea

The continental margins of the Arctic Ocean basin contain methane seeps, where transient fluxes of seafloor methane are released due to the thermal dissociation of gas hydrates. An increase in shallow methane seeps identified over the past decade, potentially due to enhanced warming of the Arctic Ocean bottom water and associated destabilization of hydrate structure. Biological communities associated with methane release east of Svalbard in the Barents Sea (Storbanken Crater site, 76° 46.7′N, 35° 43.5′E, depths between 120 m–300 m depths) were investigated using towed camera imagery and ship-based platforms during a 2017 CAGE17-2 cruise on the RV Helmer Hanssen. We analyzed relationships among methane flux data, seafloor habitat characteristics, and biological community structure (i.e., presence and distribution of megafauna and expression of microbial mats) from a total of 14 surveys (6827 images and 40 multicore sediment cores) within the Storbanken Crater area and compared it to 2015 data. Unlike seep expressions at deeper sites (∼1200 m) in the Norwegian margin region, no seep-endemic, chemosynthetic-associated megafaunal species were observed at the shallow surveyed sites and all sites hosted similarly diverse communities of non-seep species, including commercially important fish and crustaceans. Methane concentrations did not markedly differ between the crater and non-crater sites. Rates of methane gas advection through sediments (in the form of flares) were relatively low and concentration of methane was even lower in porewater samples at the crater site. We present the first evidence of methane flare flux and intermittent microbial mat distribution with associated folliculinid ciliates, which suggests a long history of methane emissions and a transient seep environment in spatial and temporal flux. Together, this study presents a critical baseline on the temporal release of arctic methane and benthic biological communities to initiate temporal studies that identify future changes and predict the impact of climate chang

Demographic history has shaped the strongly differentiated corkwing wrasse populations in Northern Europe

Understanding the biological processes involved in genetic differentiation and divergence between populations within species is a pivotal aim in evolutionary biology. One particular phenomenon that requires clarification is the maintenance of genetic barriers despite the high potential for gene flow in the marine environment. Such patterns have been attributed to limited dispersal or local adaptation, and to a lesser extent to the demographic history of the species. The corkwing wrasse (Symphodus melops) is an example of a marine fish species where regions of particular strong divergence are observed. One such genetic break occurred at a surprisingly small spatial scale (FST ~0.1), over a short coastline (<60 km) in the North Sea‐Skagerrak transition area in southwestern Norway. Here, we investigate the observed divergence and purported reproductive isolation using genome resequencing. Our results suggest that historical events during the post‐glacial recolonization route can explain the present population structure of the corkwing wrasse in the northeast Atlantic. While the divergence across the break is strong, we detected ongoing gene flow between populations over the break suggesting recent contact or negative selection against hybrids. Moreover, we found few outlier loci and no clear genomic regions potentially being under selection. We concluded that neutral processes and random genetic drift e.g., due to founder events during colonization have shaped the population structure in this species in Northern Europe. Our findings underline the need to take into account the demographic process in studies of divergence processes

Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor

Widespread methane release from thawing Arctic gas hydrates is a major concern, yet the processes, sources, and fluxes involved remain unconstrained. We present geophysical data documenting a cluster of kilometer-wide craters and mounds from the Barents Sea floor associated with large-scale methane expulsion. Combined with ice sheet/gas hydrate modeling, our results indicate that during glaciation, natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates. Upon ice sheet retreat, methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters. We propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets.authorsversionPeer reviewe

Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation

Life on Earth has been characterized by recurring cycles of ecological stasis and disruption, relating biological eras to geological and climatic transitions through the history of our planet. Due to the increasing degree of ecological abruption caused by human influences many advocate that we now have entered the geological era of the Anthropocene, or “the age of man.” Considering the ongoing mass extinction and ecosystem reshuffling observed worldwide, a better understanding of the drivers of ecological stasis will be a requisite for identifying routes of intervention and mitigation. Ecosystem stability may rely on one or a few keystone species, and the loss of such species could potentially have detrimental effects. The Atlantic cod (Gadus morhua) has historically been highly abundant and is considered a keystone species in ecosystems of the northern Atlantic Ocean. Collapses of cod stocks have been observed on both sides of the Atlantic and reported to have detrimental effects that include vast ecosystem reshuffling. By whole-genome resequencing we demonstrate that stabilizing selection maintains three extensive “supergenes” in Atlantic cod, linking these genes to species persistence and ecological stasis. Genomic inference of historic effective population sizes shows continued declines for cod in the North Sea–Skagerrak–Kattegat system through the past millennia, consistent with an early onset of the marine Anthropocene through industrialization and commercialization of fisheries throughout the medieval period.publishedVersionPaid open acces

Are Keratoacanthomas Variants of Squamous Cell Carcinomas? A Comparison of Chromosomal Aberrations by Comparative Genomic Hybridization

Keratoacanthoma (KA) is a benign keratinocytic neoplasm that usually presents as a solitary nodule on sun-exposed areas, develops within 6–8 weeks and spontaneously regresses after 3–6 months. KAs share features such as infiltration and cytological atypia with squamous cell carcinomas (SCCs). Furthermore, there are reports of KAs that have metastasized, invoking the question of whether or not KA is a variant of SCC. To date no reported criteria are sensitive enough to discriminate reliably between KA and SCC, and consequently there is a clinical need for discriminating markers. We screened fresh frozen material from 132 KAs and 37 SCCs for gross chromosomal aberrations by using comparative genomic hybridization (CGH). Forty-nine KAs (37.1%) and 31 SCCs (83.7%) showed genomic aberrations, indicating a higher degree of chromosomal instability in SCCs. Gains of chromosomal material from 1p, 14q, 16q, 20q, and losses from 4p were seen significantly more frequently in SCCs compared with KAs (P-values 0.0033, 0.0198, 0.0301, 0.0017, and 0.0070), whereas loss from 9p was seen significantly more frequently in KAs (P-value 0.0434). The patterns of recurrent aberrations were also different in the two types of neoplasms, pointing to different genetic mechanisms involved in their developments

Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation

Life on Earth has been characterized by recurring cycles of ecological stasis and disruption, relating biological eras to geological and climatic transitions through the history of our planet. Due to the increasing degree of ecological abruption caused by human influences many advocate that we now have entered the geological era of the Anthropocene, or “the age of man.” Considering the ongoing mass extinction and ecosystem reshuffling observed worldwide, a better understanding of the drivers of ecological stasis will be a requisite for identifying routes of intervention and mitigation. Ecosystem stability may rely on one or a few keystone species, and the loss of such species could potentially have detrimental effects. The Atlantic cod (Gadus morhua) has historically been highly abundant and is considered a keystone species in ecosystems of the northern Atlantic Ocean. Collapses of cod stocks have been observed on both sides of the Atlantic and reported to have detrimental effects that include vast ecosystem reshuffling. By whole-genome resequencing we demonstrate that stabilizing selection maintains three extensive “supergenes” in Atlantic cod, linking these genes to species persistence and ecological stasis. Genomic inference of historic effective population sizes shows continued declines for cod in the North Sea–Skagerrak–Kattegat system through the past millennia, consistent with an early onset of the marine Anthropocene through industrialization and commercialization of fisheries throughout the medieval period.publishedVersio

Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation

Life on Earth has been characterized by recurring cycles of ecological stasis and disruption, relating biological eras to geological and climatic transitions through the history of our planet. Due to the increasing degree of ecological abruption caused by human influences many advocate that we now have entered the geological era of the Anthropocene, or “the age of man.” Considering the ongoing mass extinction and ecosystem reshuffling observed worldwide, a better understanding of the drivers of ecological stasis will be a requisite for identifying routes of intervention and mitigation. Ecosystem stability may rely on one or a few keystone species, and the loss of such species could potentially have detrimental effects. The Atlantic cod (Gadus morhua) has historically been highly abundant and is considered a keystone species in ecosystems of the northern Atlantic Ocean. Collapses of cod stocks have been observed on both sides of the Atlantic and reported to have detrimental effects that include vast ecosystem reshuffling. By whole-genome resequencing we demonstrate that stabilizing selection maintains three extensive “supergenes” in Atlantic cod, linking these genes to species persistence and ecological stasis. Genomic inference of historic effective population sizes shows continued declines for cod in the North Sea–Skagerrak–Kattegat system through the past millennia, consistent with an early onset of the marine Anthropocene through industrialization and commercialization of fisheries throughout the medieval period.publishedVersio

Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species

Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with nonmigratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (double-digest restriction associated DNA) sequencing data to analyse spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long-term (~30-year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation-by-distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.publishedVersio