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Personne :
Bernatchez, Louis

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Bernatchez

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Louis

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Université Laval. Département de biologie

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ncf10177475

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  • PublicationRestreint
    RAD sequencing reveals within-generation polygenic selection in response to anthropogenic organic and metal contamination in North Atlantic eels
    (John Wiley & Sons, Inc., 2015-12-12) Laporte, Martin; Pavey, Scott; Bernatchez, Louis; Rougeux, Clément; Pierron, Fabien; Lauzent, Mathilde; Budzinski, Hélène; Labadie, Pierre; Geneste, Emmanuel; Couture, Patrice; Baudrimont, Magalie
    Measuring the effects of selection on the genome imposed by human-altered environment is currently a major goal in ecological genomics. Given the polygenic basis of most phenotypic traits, quantitative genetic theory predicts that selection is expected to cause subtle allelic changes among covarying loci rather than pronounced changes at few loci of large effects. The goal of this study was to test for the occurrence of polygenic selection in both North Atlantic eels (European Eel, Anguilla anguilla and American Eel, A. rostrata), using a method that searches for covariation among loci that would discriminate eels from ‘control’ vs. ‘polluted’ environments and be associated with specific contaminants acting as putative selective agents. RAD-seq libraries resulted in 23 659 and 14 755 filtered loci for the European and American Eels, respectively. A total of 142 and 141 covarying markers discriminating European and American Eels from ‘control’ vs. ‘polluted’ sampling localities were obtained using the Random Forest algorithm. Distance-based redundancy analyses (db-RDAs) were used to assess the relationships between these covarying markers and concentration of 34 contaminants measured for each individual eel. PCB153, 4′4′DDE and selenium were associated with covarying markers for both species, thus pointing to these contaminants as major selective agents in contaminated sites. Gene enrichment analyses suggested that sterol regulation plays an important role in the differential survival of eels in ‘polluted’ environment. This study illustrates the power of combining methods for detecting signals of polygenic selection and for associating variation of markers with putative selective agents in studies aiming at documenting the dynamics of selection at the genomic level and particularly so in human-altered environments.
  • PublicationRestreint
    Growth, female size, and sex ratio variability in American Eel of different origins in both controlled conditions and the wild : implications for stocking programs.
    (Taylor & Francis, 2015-02-18) Pavey, Scott; Bernatchez, Louis; Stacey, Joshua A.; Audet, Céline; Pratt, T. C; Castonguay, Martin; Côté, Caroline
    Freshwater eels Anguilla spp. are declining worldwide, and a major challenge is understanding why these panmictic species show contrasting patterns of intraspecific phenotypic variation and recruitment. We present results on studies of the American Eel A. rostrata to understand and discriminate the effects of origin and plasticity on growth and sex determination. We considered two separate growth and one length-at-age data sets. The first growth data set originated from a 34-month rearing experiment starting from the glass eel life stage to test the effects of origin, salinity, and density on growth and sex determination. The second growth data set originated from a shorter rearing experiment of 18 months starting at the yellow eel stage (around 3 years old) and compared transplanted individuals in Lake Ontario (LO) with natural migrants to the LO area. The third data set compared transplanted individuals in LO sampled by electrofishing with naturally migrating individuals. Sex ratios were identical for all origins and treatments in the long-term growth experiment (34–35% females). While male size distribution had little variability, certain female groups had a large variation in growth and presented fast- and slow-growing clusters. On the other hand, both cases of natural migrants to the LO area were consistent with being only slow-growing females. We found that wild individuals rearing in the LO area were nearly exclusively transplanted individuals and that males, as well as fast-growing females, were present. Even though the entire species is panmictic, these results support a role for spatially varying selection in explaining the phenotypic variation observed among regions and among individuals of the same region, and such factors must be considered for any successful management strategies of American Eel.
  • PublicationRestreint
    How does salinity influence habitat selection and growth in juvenile American eels Anguilla rostrata?
    (Wiley, 2015-01-21) Pavey, Scott; Dionne, Mélanie; Bernatchez, Louis; Audet, Céline; Castonguay, Martin; Boivin, Brian
    The influence of salinity on habitat selection and growth in juvenile American eels captured in four rivers across eastern Canada was assessed in controlled experiments in 2011 and 2012. Glass eels were first categorized according to their salinity preferences towards fresh (), salt () or brackish water () and the growth rate of each group of elvers was subsequently monitored in controlled and environments for 7 months. Most glass eels (78–89%) did not make a choice, . they remained in . Salinity preferences were not influenced by body condition, although a possible role of pigmentation could not be ruled out. Glass eels that did make a choice displayed a similar preference for (60–75%) regardless of their geographic origin but glass eels from the St Lawrence Estuary displayed a significantly higher locomotor activity than those from other regions. Neither the salinity preferences showed by glass eels in the first experiment nor the rearing salinities appeared to have much influence on growth during the experiments. Elvers from Nova Scotia, however, reached a significantly higher mass than those from the St Lawrence Estuary thus supporting the hypothesis of genetically (or epigenetically) based differences for growth between from different origins. These results provide important ecological knowledge for the sustained exploitation and conservation of this threatened species.
  • PublicationRestreint
    RAD Sequencing Highlights Polygenic Discrimination of Habitat Ecotypes in the Panmictic American Eel
    (Elsevier, 2015-06-15) Pavey, Scott; Dionne, Mélanie; Bernatchez, Louis; Audet, Céline; Gaudin, Jérémy; Castonguay, Martin; Normandeau, Éric
    The two primary ways that species respond to heterogeneous environments is through local adaptation and phenotypic plasticity. The American eel (Anguilla rostrata) presents a paradox; despite inhabiting drastically different environments [1], the species is panmictic [2, 3]. Spawning takes place only in the southern Sargasso Sea in the Atlantic Ocean [1]. Then, the planktonic larvae (leptocephali) disperse to rearing locations from Cuba to Greenland, and juveniles colonize either freshwater or brackish/saltwater habitats, where they spend 3-25 years before returning to the Sargasso Sea to spawn as a panmictic species. Depending on rearing habitat, individuals exhibit drastically different ecotypes [4-6]. In particular, individuals rearing in freshwater tend to grow slowly and mature older and are more likely to be female in comparison to individuals that rear in brackish/saltwater [4, 6]. The hypothesis that phenotypic plasticity alone can account for all of the differences was not supported by three independent controlled experiments [7-10]. Here, we present a genome-wide association study that demonstrates a polygenic basis that discriminates these habitat-specific ecotypes belonging to the same panmictic population. We found that 331 co-varying loci out of 42,424 initially considered were associated with the divergent ecotypes, allowing a reclassification of 89.6%. These 331 SNPs are associated with 101 genes that represent vascular and morphological development, calcium ion regulation, growth and transcription factors, and olfactory receptors. Our results are consistent with divergent natural selection of phenotypes and/or genotype-dependent habitat choice by individuals that results in these genetic differences between habitats, occurring every generation anew in this panmictic species.
  • PublicationRestreint
    Regional variation of gene regulation associated with storage lipid metabolism in American glass eels (Anguilla rostrata)
    (Elsevier Science, 2016-02-24) Pavey, Scott; Bernatchez, Louis; Audet, Céline; Tremblay, Réjean; Côté, Caroline; Lemire, Mélanie
    Variation in gene regulation may be involved in the differences observed for life history traits within species. American eel (Anguilla rostrata) is well known to harbor distinct ecotypes within a single panmictic population. We examined the expression of genes involved in the regulation of appetite as well as lipid and glycogen among glass eels migrating to different locations on the Canadian east coast and captured at two different periods of upstream migration. Gene expression levels of three reference and five candidate genes were analyzed by real-time PCR with Taqman probes in recently captured wild glass eels. All gene transcripts were detected in glass eels. Of the five candidate genes, bile salt activated and triacylglycerol lipases were respectively 7.65 and 3.25 times more expressed in glass eels from the St. Lawrence estuary than in those from Nova Scotia, and there was no effect related to the two-week difference in capture date. These two genes explained 82.41% of the dissimilarity between the two rivers. In contrast, glycogen phosphorylase, ghrelin, and leptin receptor genes showed no significant differences in gene transcription. These results confirmed at the molecular level an observation that was recently made at the phenotypic level that glass eels from the St. Lawrence estuary have a greater capacity to use lipid reserves to sustain their metabolic needs. These observations add to the body of evidence supporting the hypothesis that regional phenotypic variation observed in American eel is determined early in life and that part of this variation is likely under genetic control.