GÉNÉTIQUE MOLÉCULAIRE ET OBSERVATIONS SUR LE TERRAIN AU SECOURS DE L'OURS DES PYRÉNÉES

摘要

En six années de travaux de recherche, le Laboratoire de Biologie des Populations d'altitude a mis au point des techniques de la biologie moléculaire qui ont permis de déve-lopper une biologie des populations basée sur la génétique moléculaire et cela pour une petite population en danger d'extinction, les Ours des Pyrénées. À partir de séquences d'ADN (zone de contrôle de l'ADN mitochondrial) extraites, en très faibles quantités, de poils ou de crottes recueillis sur le terrain, il a été possible (ⅰ) d'évaluer les degrés de parenté entre différentes populations européennes, (ⅱ) de connaître le sexe des individus, (ⅲ) d'élaborer une sorte de carte d'identité (à l'aide de six séquences microsatellites) pour chaque individu d'où une connaissance précise de l'effectif et cela sans avoir à capturer des ours (méthodes dites non-invasives). Les résultats obtenus ouvrent de nouvelles perspectives en biologie de la conservation.%The remnant Brown Bear (Ursus arctos) population in the Pyrenees mountains on the border between France and Spain is among the most threatened in Europe.To obtain critical information for the management of this Brown Bear population, the French Ministry of the Environment initiated a research programme in 1991 with three major goals : (ⅰ) identify the potential conservation units at the European level, (ⅱ) develop a method to determine the sex of free-ranging bears, (ⅲ) establish unique genetic identification of all remaining individuals using noninvasive sampling techniques. Previous studies have demonstrated the potential for hair or faeces collected in the field to provide a suitable source of DNA for genotyping and sexing free-ranging animals. Despite recent advances, noninvasive genetic sampling represents a difficult challenge as hair and faeces provide only picogram quantities of degraded template DNA. Under these limiting conditions, there are two major genotyping errors which may lead to inaccurate results : an allele of a heterozygous individual may not be detected, or PCR-generated alleles or false alleles may arise. To overcome these difficulties, a multiple-tubes approach has been recently developed. Using this method, the DNA extract is distributed among seven tubes and amplified separately to determine the genotype with a 99% accuracy. Before the beginning of this genetic study, field data based mainly on the recording of track sizes suggested the presence of only several animals. Five unique genotypes were identified from the six polymorphic microsatellite loci. The genotypic data for each sample were compared with the corresponding track size in order to obtain a minimum estimate of the population size. Because one genotype was found with two nonoverlapping track sizes, we were able to detect six individual bears. The genotype of one bear was not observed after 1993. The population is composed of one yearling, three adult males and one adult female. This work extends the application.of molecular methods in conservation biology by demonstrating that not only is population size accessible, but also sex ratios and individual home ranges can be established.