Rapid recovery of normal gill morphology and blood physiology in brown trout (Salmo trutta) after short-term exposure to toxic concentrations of aqueous aluminium under non-steady state chemical conditions

Freshwater acidification is characterised by elevated concentrations of aqueous aluminium. Global emissions of acidifying agents are reduced due to international agreements, and freshwater acidification has shifted from chronic to a more episodic character. The recovery of fish populations in acidified areas is likely to depend on the individual’s ability to recover from short-time aluminium exposures. We exposed brown trout (Salmo trutta) to an Al-rich medium, nominal concentration 600 µg L–1, for 0.5, 2, 6, 8 and 11 hours, before transfer to circumneutral Al-poor water for recovery. As controls, fish were either exposed for 11 hours to an acidified Al-poor medium or to untreated water. Some mortality during the first 24 hours of the recovery period occurred in fish exposed for 11, 8 and 6 hours to aluminium. No mortality during recovery was observed in the remaining groups. Aluminium exposure led to increased haematocrit and plasma lactate concentration, decreased plasma chloride concentration, deposition of aluminium on gill surfaces, and morphological alteration of the gill structures. The responses depended on exposure time. Aluminium deposited on the gill disappeared and plasma lactate levels were at control levels after 1 day in the recovery water, while haematocrit and plasma chloride levels were at control levels after 14 days of recovery. Gills in fish exposed to aluminium for 11 hours were almost fully recovered after 14 days. We conclude that the toxic response in brown trout exposed to an acutely toxic aluminium challenge is reversible. Moreover, the first 24 hours after aluminium exposures is the most critical period for the fish recovery. Further, it takes no more than 14 days for brown trout to fully recover from an acute toxic aluminium exposure, and only 1 day if the aluminium challenge is moderate.publishedVersio

Life history and demographic determinants of effective/census size ratios as exemplified by brown trout (Salmo trutta)

A number of demographic factors, many of which related to human-driven encroachments, are predicted to decrease the effective population size (Ne) relative to the census population size (N), but these have been little investigated. Yet, it is necessary to know which factors most strongly impact Ne, and how to mitigate these effects through sound management actions. In this study, we use parentage analysis of a stream-living brown trout (Salmo trutta) population to quantify the effect of between-individual variance in reproductive success on the effective number of breeders (Nb) relative to the census number of breeders (Ni). Comprehensive estimates of the Nb/N ratio were reduced to 0.16–0.28, almost entirely due to larger than binomial variance in family size. We used computer simulations, based on empirical estimates of age-specific survival and fecundity rates, to assess the effect of repeat spawning (iteroparity) on Ne and found that the variance in lifetime reproductive success was substantially higher for repeat spawners. Random family-specific survival, on the other hand, acts to buffer these effects. We discuss the implications of these findings for the management of small populations, where maintaining high and stable levels of Ne is crucial to extenuate inbreeding and protect genetic variability.publishedVersio

When phenology matters: age–size truncation alters population response to trophic mismatch

Climate-induced shifts in the timing of life-history events are a worldwide phenomenon, and these shifts can de-synchronize species interactions such as predator–prey relationships. In order to understand the ecological implications of altered seasonality, we need to consider how shifts in phenology interact with other agents of environmental change such as exploitation and disease spread, which commonly act to erode the demographic structure of wild populations. Using long-term observational data on the phenology and dynamics of a model predator–prey system (fish and zooplankton in Windermere, UK), we show that age–size truncation of the predator population alters the consequences of phenological mismatch for offspring survival and population abundance. Specifically, age–size truncation reduces intraspecific density regulation due to competition and cannibalism, and thereby amplifies the population sensitivity to climate-induced predator–prey asynchrony, which increases variability in predator abundance. High population variability poses major ecological and economic challenges as it can diminish sustainable harvest rates and increase the risk of population collapse. Our results stress the importance of maintaining within-population age–size diversity in order to buffer populations against phenological asynchrony, and highlight the need to consider interactive effects of environmental impacts if we are to understand and project complex ecological outcomes

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

Contemporary ocean warming and freshwater conditions contribute to delay the completion of maturation in Atlantic salmon

The completion of maturation in Atlantic salmon (Salmo salar) depends on environmental conditions that affect both feeding opportunities and growth, which would provide sufficient lipid stores for reproduction. However, if the level of energy reserves of a given fish is below a certain genetic threshold at a critical decision time further gonadal development is arrested and fully maturation postponed. This individual development pattern suggests that the proportion of fish maturing at a given sea age could vary from year to year according to the feeding opportunities in the oceanic migratory habitat, and the growth rate during freshwater residence that might be associated with growth at sea. In this study we show that sea age at maturity of adults caught in multiple Norwegian rivers has increased with increasing sea surface temperature (SST) experienced by the fish in autumn months during their first year at sea. Furthermore, freshwater conditions measured by river discharge during summer months one year ahead of seaward migration is positively related with increasing sea age at maturity. This result is discussed within the broad changes occurring in the North-east Atlantic pelagic food web mostly related with the current ocean warming, and river conditions influencing growth rates

Within-species variation in the gut microbiome of medaka (Oryzias latipes) is driven by the interaction of light intensity and genetic background

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Size- and stage-dependence in cause-specific mortality of migratory brown trout

Evidence‐based management of natural populations under strong human influence frequently requires not only estimates of survival but also knowledge about how much mortality is due to anthropogenic vs. natural causes. This is the case particularly when individuals vary in their vulnerability to different causes of mortality due to traits, life history stages, or locations. Here, we estimated harvest and background (other cause) mortality of landlocked migratory salmonids over half a century. In doing so, we quantified among‐individual variation in vulnerability to cause‐specific mortality resulting from differences in body size and spawning location relative to a hydropower dam. We constructed a multistate mark–recapture model to estimate harvest and background mortality hazard rates as functions of a discrete state (spawning location) and an individual time‐varying covariate (body size). We further accounted for among‐year variation in mortality and migratory behaviour and fit the model to a unique 50‐year time series of mark–recapture–recovery data on brown trout (Salmo trutta ) in Norway. Harvest mortality was highest for intermediate‐sized trout, and outweighed background mortality for most of the observed size range. Background mortality decreased with body size for trout spawning above the dam and increased for those spawning below. All vital rates varied substantially over time, but a trend was evident only in estimates of fishers' reporting rate, which decreased from over 50% to less than 10% throughout the study period. We highlight the importance of body size for cause‐specific mortality and demonstrate how this can be estimated using a novel hazard rate parameterization for mark–recapture models. Our approach allows estimating effects of individual traits and environment on cause‐specific mortality without confounding, and provides an intuitive way to estimate temporal patterns within and correlation among different mortality sources

Habitat use and growth of yellow-stage European eel in coastal and freshwater ecosystems in Norway

Many anguillid eel species display facultative catadromy. Some eel spend their entire life cycle in marine coastal areas, but the geographical extent of this, especially at the extremes of their distributional ranges, is unknown.We analysed otolith Sr:Ca and Ba:Ca from yellow-stage European eel (Anguilla anguilla) sampled along the coast of Norway and in several freshwater lakes (58◦N–63◦N), to infer their initial settlement and later life movement patterns with regards to habitat salinity. Most eel (80%) sampled in marine habitats (n = 371) had settled and remained in marine water, but 20% had moved between marine and freshwater habitats and were hence classified as inter-habitat shifters. Among freshwater sampled eel (n = 99), 80% had settled and remained in fresh water, but 20% were classified as inter-habitat shifters. The average growth rates for marine water residents, inter-habitat shifters, and freshwater residents were 35, 27, and 17 mm·year–1, respectively. Northern European otolith microchemistry, anguillids, Anguilla anguilla, salinity, age, growth ratepublishedVersio