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- Population genetic structure and colonization sequence of Drosophila subobscura in the Canaries and Madeira Atlantic islands as inferred by autosomal, sex-linked and mtDNA traitsPublication . Pinto, F. M.; Brehm, A.; Hernández, M.; Larruga, J. M.; González, A. M.; Cabrera, V. M.The genetic structure In Atlantic Islands and continental populations of Drosophila subobscura has been studied using autosomal and sex-linked allozymes and ml tochondrial DNA (mtDNA) haplotypes. From the data it Is deduced that whereas the Canary Islands have long been isolated, the neighboring island of Madeira has been subjected to continuous migration from the mainland. In addition, sex-linked allo zymes and mtDNA data show a large divergence between the geologically younger western Islands of the Canarian Archipelago and the older central ones, finding strong founder effects In the former. Divergence rates of sex-linked and mltochon drlal genes relative to autosomlc loci several times higher than expected under neutrality have been explained by differential migration between sexes. The Ca narian Archipelago colonization fits in well with a stepping-stone model of a direc tional east-west migration that parallels the geological origin of these Islands.
- Distribution of the retrotransposable element 412 in Drosophila speciesPublication . Cizeron, G.; Lemeunier, F.; Loevenbruck, C.; Brehm, A.; Biemont, C.Copy numbers of sequences homologous to the Drosophila melanogaster retrotransposable element 412, their dis tribution between the chromosome arms and the chromocenter, and whether they contain full-size copies were analyzed for 55 species of the Drosophila genus. Element 412 insertion sites were detected on the chromosome arms of D. melanogaster, Drosophila simulans, and a few species of the obscura group, but the chromocenter was labeled in almost all species. The presence of element 412 sequences in the majority of species shows that this element has a long evolutionary history in Drosophilidae, although it may have recently invaded the chromosomes in some species, such as D. simulans. Differences in copy number between species may be due to population size or specific endogenous or environmental factors and may follow the worldwide invasion of the species. Putative full-length copies were detected in the chromocenters of some species with no copies on the chromosome arms, suggesting that the chromocenter may be a shelter for such copies and not only for deleted ones.
- Evolution of the obscura group Drosophila species.: III. phylogenetic relationships in the subobscura cluster based on homologies of chromosome APublication . Brehm, A.; Krimbas, C. B.The Drosophila subobscura cluster comprises D. subobscura, D. madeirensis and D. guanche, species closely related to some interspecific crosses are possible. This paper clarifies definitively the homologies of the segments of the sex chromosome A (= X) among these species and thus permits a phylogenetic seriation of them. This seriation is identical to the one suggested by the study of chromosome O and concordant with similar data for the remaining three rod autosomes (J, U and E), which, however, do not provide qualitative evidence on this subject.
- Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene regionPublication . Khadem, M.; Rozas, J.; Segarra, C.; Brehm, A.; Aguade, M.been analysed by fine restriction mapping in a sample of 47 lines from a population from Madeira. Five restriction-site (out of 37 sites scored) and 3 length polymor phisms have been detected, resulting in 14 different haplotypes. This population shows less variation than both continental and Canary Island populations. The population from Madeira shows some differentiation from mainland populations, which does not favor the idea of extensive migration between the continent and Madeira. Chromosomal and restriction-map variation of the rp49 region in D. subobscuru populations, together with data on sequence comparison of this nuclear region in D. guanche and D. mudeirensis clearly indicate that the Canary Islands underwent at least two colonization events from the nearby continent. Although the data for Madeira are compatible with a single colonization event by a continental sample polymorphic for gene arrangements 0, and 0, + 4, an alternative scenario with at least two colonization events seems more likely.
- The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of the chromosomal regions. IV. Element CPublication . Brehm, António; Krimbas, Costas B.Homologies of the sections of the polytene chromosomes of element C, among several species of the obscura group of the genus Drosophila, were established according to the similarity of their banding patterns. The information gathered was used to construct an unrooted phylogenetic tree based on qualitative criteria. This tree is compared to three other similar trees derived from independent information provided by the study of chromosomal elements B, D and E. The general congruence of the patterns of these trees proves the well-foundedness of this approach. A single exception to this congruence is discussed. Finally a consensus tree, encapsulating information from all chromosomal elements, is presented and its topology is compared to those derived from electrophoretic data.