La perchaude (Perca flavescens) constitue une ressource socioéconomique de grande importance dans le Lac Saint-Pierre (Québec, Canada). Bien que ce lac fluvial soit désigné réserve de la biosphère par l’UNESCO, le statut de la perchaude est préoccupant. Afin de permettre à l’espèce de persister en fonction des diverses pressions anthropiques, il est important de comprendre sa dynamique populationnelle et les mécanismes qui en sont responsables. La perchaude est connue pour sa philopatrie ; le fait de toujours se reproduire à son site de naissance peut entraîner la subdivision d’une espèce en de multiples populations, où chacune pourra être pourvue d’adaptations locales distinctes. Il est possible d’étudier ces processus à l’aide des signaux génétiques associés à la reproduction des individus. Toutefois, une faible différentiation génétique entre les populations du Lac Saint-Pierre est envisagée en raison de la colonisation récente du système (moins de 8000 ans). L’objectif de cette étude est de déterminer s’il existe plusieurs populations de perchaude dans le Lac Saint-Pierre. Les simulations réalisées ont révélé que l’utilisation de marqueurs AFLP (amplified fragment length polymorphism), permettant une analyse globale du génome, affiche une meilleure détection de la différentiation des populations que celle des marqueurs microsatellites. Afin d’associer les individus à leur site de naissance, la méthode d’AFLP et des microsatellites ont été utilisées sur des larves capturées suite à l’éclosion des oeufs. Trois analyses distinctes d’AFLP ont indiqué une corrélation entre la composition génétique des individus et des sites géographiques, confirmant ainsi la présence de plusieurs populations sympatriques dans le Lac Saint-Pierre, découlant vraisemblablement de la philopatrie de l’espèce. L’absence de différentiation génétique relatée par les marqueurs microsatellites vient confirmer l’importance du choix des marqueurs génétiques. Bien que la différentiation génétique observée soit relativement faible, la gestion de la perchaude devrait tenir compte de la dynamique des populations distinctes dans ce système. / Yellow perch (Perca flavescens) is a commercially-exploited freshwater fish species in Lake Saint-Pierre (Quebec, Canada). Even if this fluvial lake is designated as a biosphere reserve by UNESCO, the yellow perch status is of concern. To ensure the persistence of species facing to anthropogenic pressures, understanding dynamics and mechanism that structure populations are of major importance. Because the habitat characteristics are spatially structured and this species is known to display natal site fidelity, a subdivision of the species in multiple populations and local adaptations may occur. It is possible to detect these processes according to genetic signal associated with individuals’ reproduction. However, low genetic differentiation is hypothesised due to the recent colonization of the system (< 8 K years). This study aims at determining if there are multiple populations of yellow perch in Lake Saint-Pierre. Simulations was first performed to confirm that population differentiation is better depicted by amplified fragment length polymorphism (AFLP) than microsatellite markers. In order to associate individuals to their site of birth, larvae captured after hatching were used. A survey of the variation throughout the entire genome was then performed by using the AFLP approach and variations at microsatellite loci were used to further investigate the organization of these populations. Three distinct AFLP analyses indicated a correlation between genetic composition of individuals and spawning sites, and thus confirmed the presence of multiple sympatric populations in Lake Saint-Pierre, resulting likely from natal site fidelity. At the opposite, the lack of genetic differentiation reported by microsatellites markers confirms the importance of the choice of genetic markers. While the genetic differentiation is very low, the management of this species should take into account the existence of distinct population structures in this system.

In the Amazon region, formations of coastal vegetation on sandy soils {restinga) cover an area of approximately 1000 km2. In contrast to the restinga vegetation of southern and southeastern Brazil, restinga vegetation in the north of the country is not well known. This study presents a description of the woody vegetation of restinga dunes and the relationship between floristics, vegetation structure and topography near Vila Bonifácio, Ajuruteua península, Pará. A key to the woody species of the Vila Bonifácio restinga is presented as well as a short summary of the characters important for the identification of each species. The study site features a complex of dune ridges within an area of marshes, surrounded by mangroves. Vegetation structure was investigated along 4 transects of 10 m width and lengths of 100-170 m, each crossing obliquely the same dune ridge. Begin and end of ali transects were localized within the marsh-dune ecotone on either side of the transect. Elevation and influence of tidal inundation were documented along topographic profiles across each transect. Within transects, basal diameter, height as well as length of prostrate stem portions of ali trees and shrubs with a basal stem diameter >2.5 cm were recorded. If possible, fertile shoots of each occurring species were collected and deposited in local and regional herbaria. 15 woody plant species were identified within the sampling area, 3 additional species were found outside the transects. The species with the highest importance value was Pouteria ramiflora (Sapotaceae); other important constituents of the dune vegetation were members of Myrtaceae {Myrcia cuprea. Eugenia flavescens) and Arecaceae (Aslrocaryum sp.). Most plants were small trees or shrubs, with the notable exception of Humiria balsamifera (Humiriaceae) and P. ramiflora, reaching stem diameters of about 30 cm and heights >10 m in some parts of the area. The total basal area of ali transects accounted to 9.9 nr-ha'1, the overall tree density was 2.293,48 individuals-ha'1. Large stem diameters of P. ramiflora were only encountered at low elevation; similarly, height of P. ramiflora, Protium heptaphyllum and Ouratea ssp. was reduced at higher elevations. No convincing relationship between density and elevation was detected. The species inventory of Vila Bonifácio overlaps with that of the small number of other well-known restingas along the coast of Pará but future, more detailed surveys are necessary to arrive at a conclusive characterisation of the restinga flora of this state. / Na região amazônica, as formações de vegetação costeira de solos arenosos {restinga) cobrem uma área de aproximadamente 1000 km2. Ao contrário da vegetação de restingas do sul e sudeste do Brasil, na região norte esta vegetação ainda não é bem conhecida. Este estudo apresenta a descrição da vegetação arbustivo-arbórea de dunas e a relação entre composição florística, estrutural e topográfica próximo à Vila Bonifácio, península de Ajuruteua, Pará. Uma chave de identificação das espécies arbustivo-arbóreas ocorrentes na área também foi elaborada, bem como uma suscinta descrição das características vegetativas importantes para a identificação de cada espécie. A área de estudo apresenta um complexo de dunas com vegetação de campos, rodeadas por manguezais. A estrutura da vegetação foi analisada ao longo de quatro trasecções de 10 m de largura e comprimentos que variaram de 100-170 m, cada uma atravessando obliquamente o cordão de dunas. O início e o fim de todos os transectos estavam localizados dentro do ecótono campo-dunas. A elevação e a influência da inundação pela maré foram verificadas ao longo de perfis topográficos que atravessaram cada transecto. Dentro das transecções foram medidos o diâmetro à altura do solo (DAS), altura e comprimento (dos troncos sinuosos) de todos os indivíduos arbustivo-arbóreos com DAS >2,5 cm. Ramos férteis de cada espécie ocorrente foram coletados e depositados no herbário do campus de Bragança. Foram identificadas 15 espécies arbustivo-arbóreas no levantamento florístico, 3 espécies adicionais foram encontradas fora dos transectos e incluídas na chave taxonômica. A espécie com maior valor de impotância foi Pouteria ramiflora (Sapotaceae); outras famílias importantes da vegetação de dunas foram Myrtaceae {Myrcia cuprea. Eugenia f/avescens) e Arecaceae (Asírocaryum sp.). A maioria dos indivíduos foi de árvores pequenas ou arbustos, exceto, Humiria halsamifera (Humiriaceae) e P. ramiflora, que alcançaram diâmetros de cerca de 30 cm e alturas >10 m em alguns pontos da área. A área basal total de todas as transecções foi 9,9 nr-ha'1, a densidade total foi 2.293,48 ind-ha'1. Os maiores diâmetros de P. ramiflora foram encontrados somente em baixas elevações; a altura de P. ramiflora, Protium heptaphyllum e Ouratea sp. foram reduzidas em elevações mais baixas. Não houve uma relação significativa entre densidade e elevação. A análise do inventário das espécies arbustivo-arbóreas da restinga da Vila Bonifácio coincide com o pequeno número de espécies já bem conhecidas das restingas da costa do Pará mas, estudos futuros são necessários para se chegar a uma caracterização conclusiva da vegetação arbustivo- aebórea da restinga deste estado.

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