Alexis Champigneulle

Life history shapes gene expression in salmonids

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Population transcriptomics of life-history variation in the genus Salmo

In this study, we demonstrate the power of applying complementary DNA (cDNA) microarray technology to identifying candidate loci that exhibit subtle differences in expression levels associated with a complex trait in natural populations of a nonmodel organism. Using a highly replicated experimental design involving 180 cDNA microarray experiments, we measured gene‐expression levels from 1098 transcript probes in 90 individuals originating from six brown trout (Salmo trutta) and one Atlantic salmon (Salmo salar) population, which follow either a migratory or a sedentary life history. We identified several candidate genes associated with preparatory adaptations to different life histories in salmonids, including genes encoding for transaldolase 1, constitutive heat‐shock protein HSC70‐1 and endozepine. Some of these genes clustered into functional groups, providing insight into the physiological pathways potentially involved in the expression of life‐history related phenotypic differences. Such differences included the down‐regulation of genes involved in the respiratory system of future migratory individuals. In addition, we used linear discriminant analysis to identify a set of 12 genes that correctly classified immature individuals as migratory or sedentary with high accuracy. Using the expression levels of these 12 genes, 17 out of 18 individuals used for cross‐validation were correctly assigned to their respective life‐history phenotype. Finally, we found various candidate genes associated with physiological changes that are likely to be involved in preadaptations to seawater in anadromous populations of the genus Salmo, one of which was identified to encode for nucleophosmin 1. Our findings thus provide new molecular insights into salmonid life‐history variation, opening new perspectives in the study of this complex trait.

Mass-marking of bone tissue of Coregonus lavaretus L. and its potential application to monitoring the spatio-temporal distribution of larvae, fry and juveniles of lacustrine fishes

Mass labelling techniques have great potential for the study of larval fish dynamics in closed habitats (lakes, ponds and flooded quarries). Different methods of mass labelling of bone tissue were tested: bathing in tetracycline solutions with or without osmotic shock, and modification of otolith microstria by temperature, photoperiod or feeding manipulations using different batches of eggs, eleuteroembryos, larvae and prefed fry of Coregonus lavaretus L. from Lake Leman. A short period of immersion with osmotic shock produced better results than longer bathing (6 to 18 h) in low concentration (400 mg 1-1) tetracycline solutions. At the ‘eyed’ stage of eggs when otoliths appear, it is possible to use the immersion technique in a hyperosmotic solution (5 to 12% sodium chloride) with 1% tetracycline (as the Hydrochloride or Oxytetracycline). Optimal immersion times (maximal labelling with minimal mortality) were determined as follows: 10 to 15 minutes for ‘eyed’ eggs, 3.5 min. for eggs just before hatching and eleuteroembryos, 1.5 min. for prefed larvae and less than 1 min. for fry of more than 20 mm total length. Microscopic examination of otoliths and caudal vertebrae from coregonid larvae and juveniles reared for two years has allowed us to determine the effectiveness and persistence of fluorescent tetracycline makers.

Evidence of two contrasting brown trout Salmo trutta populations spatially separated in the River Borne (France) and shift in management towards conservation of the native lineage.

A multidisciplinary study was made of brown trout Salmo trutta in the Borne River, a typical fast-flowing mountain stream in the Northern French Alps, in the geographical range of the Mediterranean lineages (ML). Information on (1) the proportion of stocked fluoro-marked fish in the angling harvest, (2) the introgression of introduced DNA microsatellite alleles into the native gene pool and (3) the demography of the population in situ in autumn revealed two contrasting populations separated by a physical barrier to upstream migration. A native S. trutta population (c. 10 000 adults) lives downstream of the barrier and is characterized by a large frequency of ML alleles (82-97%) and high densities (43-55 fish 100 m(-2)). This population is maintained predominantly by natural recruitment of juveniles (51-82%). In contrast, the upstream population is characterized by a large frequency of Atlantic lineage (AL) alleles (78-100%) and low densities (1-2 fish 100 m(-2)) and appears to be maintained by restocking (90-100%). The origins of these sharply contrasting populations appear to reflect isolation by an impassable barrier, catastrophic flooding, a downstream gradient in water quality, stocking and fishing pressure. The native downstream population has been resilient to large sudden floods and to intensive stockings of domesticated AL fish. The results of this study justify a shift in management towards conservation and rehabilitation of the native population.

Studies on the improvement of the first feeding on a dry diet for Coregonus lavaretus L. larvae

Abstract Larvae of Coregonus lavaretus were fed for 36 days on a commercial dry diet under laboratory conditions (small tanks of 6.51 stocked at an initial density of 100 larvae/1). Two feeding durations (24 h or 9 h/day) and temperature patterns (10.5 °C constant; first 16 days at 16 °C and last 20 days at 10.5 °C) were tested. For each temperature condition, continuous feeding supported a significant increase in growth (74–91% average wet weight gain) at 36 days, without changing the survival rates (>79%) for all groups. For a given feeding duration, the initial growth was significantly better at 16 °C than at 10 °C. No growth advantage was obtained by 16 days of initial daily feeding at 16 °C when compared to continuous feeding at 10 °C. However, continuous feeding allowed the best utilization of warmer water as large (50 mg) larvae were obtained in only 16 days at 16 °C and these prefed larvae adapted well to a change to colder (10 °C) water.