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A highly inbred, long-term selected for low fitness strain LA of Drosophila melanogaster possesses a significant mutational load and unusually high rates of spontaneous mutability as revealed by CyL/Pm method. Our results indicate that during cross of CyL/Pm to LA strains, destabilization of copia-like and mobile elements and induction of H-E hybrid dysgenesis take place. The role of these processes in causing considerable genetic variability of LA strain is discussed.

A set of Drosophila melanogaster strains of common origin, but with different fitness characteristics, established either spontaneously or after selection for the specific fitness parameters, appear to induce non-P-element-mediated gonadal atrophy in appropriate crosses to tester strains containing or lacking hobo elements (H and E strains). Using the gonadal dystrophy (GD) sterility assay, as well as genomic Southern blot hybridization and in situ hybridization on polytene chromosomes, it was found that all these strains possess hobo elements whose dysgenic activity, composition, copy number and cytogenetic locations appeared to be variable. In general, low fitness strains have moderate hobo-activity and hobo-repression potentials, while high fitness strains show no hobo-activity but also quite high hobo-repression potentials. Although distinct differences in the composition, copy number and location of the hobo elements in the genome were observed between these 2 groups of strains, these variations did not show any profound correlation with either hobo-related dysgenic potential or the fitness of the strains. Drosophila melanogaster / selection / fitness / transposable element / hobo Résumé-Des souches étroitement apparentées de Drosophila melanogaster avec des aptitudes reproductives modifiées manifestent aussi des changements dans les propriétés de leurs éléments hobo. Différentes lignées de Drosophila melanogaster, issues d'une population naturelle russe, ont été sélectionnées sur des caractéristiques de fitness. Ces lignées, comme les lignées témoins, présentent des activités dysgéniques variables non reliées à l'élément transposable P. Nous montrons que la stérilité GD (gonadal dystrophy) qu'elles induisent est due à l'élément hobo et, de plus, que ces lignées ont des potentiels * Correspondence and reprints