Structure genetique de populations montrealaises de salamandres cendrees (Plethodon cinereus) et de salamandres a points bleus (Ambystoma laterale)

The human population has experienced an unprecedented growth in recent centuries. Along with this demographic boom, there is a increasing proportion of the population now living in cities. Urban areas are thus expanding at the expense of natural areas in and around cities. Although urbanization represents a serious threat to biodiversity, very few studies in conservation biology have been carried out in urban areas. My thesis focuses on the genetic structure of populations of two species of salamanders in a highly urbanized landscape: the city of Montreal. The first part of my work concentrates on the red-backed salamander (Plethodon cinereus). A comparative analysis of six microsatellite loci was performed for isolated populations from the Mont-Royal, a highly fragmented habitat, and populations from the Mont-Megantic, a continuous habitat. The results indicate that gene flow is reduced among the Mont-Royal populations, which are subject to the erosion of genetic diversity through genetic drift. The analysis of ten red-backed salamander populations located on Montreal and on two nearby islands revealed a high degree of genetic differentiation among populations from Montreal and from neighboring islands. Although no clear genetic structure was detected within Montreal, genetic differentiation was observed at a small spatial scale for three populations located on the Mount Royal, near downtown. We believe that these populations had very low effective population size for a long time, allowing for fast genetic drift and subsequent population differentiation. The second part of my dissertation is about the blue-spotted salamander ( Ambystoma laterale). This species is part of the Ambystoma complex, which also includes the Jefferson salamander ( Ambystoma jeffersonianum) and unisexual salamanders of different levels of ploidy. In a first step, a molecular method based on the analysis of mitochondrial DNA was developed to distinguish the two bisexual species from unisexuals. The analysis of six microsatellite loci from five populations, including one from Montreal and others from preserved area was subsequently realized. Results revealed that genomotype frequencies vary greatly among populations. One of the populations analyzed appears to be composed only of LJ unisexual salamanders, which raises some questions about the mode of reproduction used in this population. Finally, the population located in an urban environment presents a low genetic diversity, and some hypotheses are proposed to explain this situation.;Key words: Ambystoma complex, conservation, gene flow, genetic diversity, habitat fragmentation, microsatellites, molecular identification, population genetics, unisexual salamanders, urbanization...