Project description:This study aimed to investigate the hepatic transcriptional response of brown trout to glyphosate, and its formulated product, Roundup. We exposed juvenile female brown trout to three concentrations of glyphosate (0.01, 0.5 and 10 mg/L) and Roundup (0.01, 0.5 and 10 mg/L glyphosate acid equivalent) for 14 days and sequenced the hepatic transcriptome of 6 individual females per treatment group in order to determine the global mechanisms of toxicity of this widely used herbicide. We assembled the brown trout transcriptome using an optimised de novo approach, and subsequent differential expression analysis identified a total of 1020 differentially-regulated transcripts across all treatments. Differentially-expressed transcripts included those encoding components of the antioxidant system, a number of stress-response proteins and pro-apoptotic signalling molecules. Functional analysis also revealed over-representation of pathways involved in regulation of cell-proliferation and turnover, and up-regulation of energy metabolism and other metabolic processes. Together, these transcriptional changes are consistent with generation of oxidative stress and the widespread induction of compensatory cellular stress response pathways. The mechanisms of toxicity identified were similar across both glyphosate and Roundup treatments, including for environmentally relevant concentrations. The significant alterations in transcript expression observed at the lowest concentrations tested raises concerns for the toxicity of this herbicide to fish populations inhabiting contaminated rivers. Fish were exposed to 3 concentrations of glyphosate (0.01, 0.1 and 10 mg/L), 3 concentrations of Roundup (0.01, 0.5 and 10 mg/L glyphosate acid equivalent) and water controls for 14 days. Liver mRNA from 6 replicate individuals per treatment was sequenced in an Illumina HiSeq 2500 platform. Two control groups (n=6 fish per group) were included. Using a de novo approach, we assembled the hepatic transcriptome for brown trout. Sequence reads were re-mapped to the assembled transcriptome using Bowtie2 and transcript expression profiling was conducted using EdgeR. ERCC spike controls were added to all individual samples, allowing for the assessment of the reproducibility and dynamic range for transcript expression quantification in our experiments. For the group exposed to 0.1 mg/L glyphosate, only 3 females were available to sequence and the variability between individuals was very high with 1 female identified as an outlier. For this reason, data from this treatment group was deemed unreliable and excluded from the analysis.

Project description:Local adaptation and its underlying molecular basis has long been a key focus in evolutionary biology. There has recently been increased interest in the evolutionary role of plasticity and the molecular mechanisms underlying local adaptation. Using transcriptome analysis, we assessed differences in gene expression profiles for three brown trout (Salmo trutta) populations, one resident and two anadromous, experiencing different temperature regimes in the wild. The study was based on an F2 generation raised in a common garden setting. A previous study of the F1 generation revealed different reaction norms and significantly higher QST than FST among populations for two early life-history traits. In the present study we investigated if similar reaction norm patterns were present at the transcriptome level. Eggs from the three populations were incubated at two temperatures (5 and 8 degrees C) representing conditions encountered in the local environments. Global gene expression for fry at the stage of first feeding was analysed using a 32k cDNA microarray. The results revealed differences in gene expression between populations and temperatures and population M-CM-^W temperature interactions, the latter indicating locally adapted reaction norms. Moreover, the reaction norms paralleled those observed previously at early life-history traits. We were able to identify 90 cDNA clones among the genes with an interaction effect that were differently expressed between the ecologically divergent populations. These included genes involved in immune- and stress response. We observed less plasticity in the resident as compared to the anadromous populations, possibly reflecting that the degree of environmental heterogeneity encountered by individuals throughout their life cycle will select for variable level of phenotypic plasticity at the transcriptome level. Our study demonstrates the usefulness of transcriptome approaches to identify genes with different temperature reaction norms. The responses observed suggest that populations may vary in their susceptibility to climate change. Brown trout populations from three rivers in Denmark were studied: the Karup (KAR), Norring Moellebaek (NOR) and Lilleaa Rivers (LIL). These rivers experience different temperature regimes during the period lasting from egg incubation until fry emergence. During the autumn of 2004 and the winter of 2004/2005, adults from the three populations were collected by electro fishing. The fish were stripped for milt and eggs to establish an F1 generation. In autumn/winter 2008/2009, mature F1s were used to establish F2 offspring for each of the three populations. For KAR and LIL, 20 full-sib families were established, whereas for NOR, 15 full-sib families were established. Eggs from each full sib family were divided into two pools that were incubated at 5 and 8M-BM-!C in separate hatching troughs. At the time of first feeding (ca. 750-780 day-degrees), 10 individuals from each family and temperature were collected and transferred to separate tubes containing RNAlater (QIAGEN, Hilden, Germany). A 32K cDNA microarray developed for salmonids by cGRASP was used for the analyses. Ten families were randomly selected from each population. From each family two individuals were analyzed for each temperature (5 and 8oC, respectively), amounting to a total of 120 individuals. Of the two individuals from each temperature treatment within a family, one was labeled with CY5 and the other with CY3. For each family there were two comparisons of individuals representing different temperatures, but with dyes swapped between comparisons.

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Brown trout metal tolerance

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