Françoise Lemeunier

Historical biogeography of the Drosophila melanogaster species subgroup

Whereas there has been increasing interest in the eight members of the melanogaster species subgroup of Drosophila, no comprehensive survey exists of the biogeography and ecology of these species in the Afrotropical region.

Relationships within the melanogaster species subgroup of the genus Drosophila (Sophophora) - II. Phylogenetic relationships between six species based upon polytene chromosome banding sequences

The melanogaster species subgroup of Drosophila comprises six sibling species. The interrelationship between these species has been studied by analysis of the banding patterns of their polytene chromosomes. The species fall into two groups: (1) melanogaster, simulans and mauritiana and (2) erecta, teissieri and yakuba. The former group are chromosomally closely related, indeed simulans and mauritiana are homosequential. The latter group (all African endemic species) are less closely related although they all share eight autosomal inversions of the standard (i. e. melanogaster) sequence. From this shared sequence the chromosomes of the three African endemic species have diverged considerably by many paracentric inversions. Both D. teissieri and D. yakuba are polymorphic; we describe nine and four inversion sequences in them respectively. D. erecta is monomorphic although our sample size is very small (only two populations). We discuss both the origin of interspecific inversions, especially the problem of inversion breakpoint coincidence, and the light this study throws upon evolutionary relationships within this group of species.

THE REPRODUCTIVE RELATIONSHIPS OF DROSOPHILA SECHELLIA WITH D. MAURITIANA, D. SIMULANS, AND D. MELANOGASTER FROM THE AFROTROPICAL REGION

Hybridization tests among the four sibling species of the Drosophila melanogaster complex were made to determine the reproductive status of the recently discovered D. sechellia (which is endemic to a few islands and islets of the Seychelles archipelago) with regard to its three close relatives, D. mauritiana (endemic to Mauritius) and Afrotropical strains of the two cosmopolitan species D. melanogaster and D. simulans. Interstrain variation in the ability to hybridize with other species was also analyzed for D. melanogaster and D. simulans. D. mauritiana and D. simulans appear to be more weakly isolated from each other than either species is from D. sechellia. A striking unilateral mating success is observed in the cross of D. sechellia with D. simulans. The most extreme isolation is between D. melanogaster and its three siblings. Variation in the ability of strains to hybridize is observed in heterospecific crosses between D. simulans and either D. melanogaster or D. mauritiana.

Visualization of Polydnavirus Sequences in a Parasitoid Wasp Chromosome

ABSTRACT Polydnaviruses, obligatorily associated with endoparasitoid wasps, are unique in that their segmented genome is composed of multiple double-stranded DNA circles. We present here the first cytological evidence that virus segments are integrated in the wasp genome, obtained by using in situ hybridization of virus probes with viral sequences in the chromosomes of a wasp from the braconid family of hymenopterans.

Relationships within the melanogaster Species Subgroup of the Genus Drosophila (Sophophora). I. Inversion Polymorphisms in Drosophila melanogaster and Drosophila simulans

Drosophila melanogaster from 67 collections have been analysed for their polymorphic inversions. Of the 53 inversions now known in this species 7 are widespread and 43 are endemic. The remaining 3 inversions may be widespread, but if so they are usually very rare. No X or fourth chromosome inversions were found. All the third chromosome inversions were paracentric, while six of the second chromosome inversions were pericentric. No inversions were found in D. simulans, of which 27 collections, from Africa, Europe, Australia and S. America, were studied.

Evolution of the chromosomal location of rDNA genes in two Drosophila species subgroups: ananassae and melanogaster.

The evolution of the chromosomal location of ribosomal RNA gene clusters and the organization of heterochromatin in the Drosophila melanogaster group were investigated using fluorescence in situ hybridization and DAPI staining to mitotic chromosomes. The investigation of 18 species (11 of which were being examined for the first time) belonging to the melanogaster and ananassae subgroups suggests that the ancestral configuration consists of one nucleolus organizer (NOR) on each sex chromosome. This pattern, which is conserved throughout the melanogaster subgroup, except in D. simulans and D. sechellia, was observed only in the ercepeae complex within the ananassae subgroup. Both sex-linked NORs must have been lost in the lineage leading to D. varians and in the ananassae and bipectinata complexes, whereas new sites, characterized by intra-species variation in hybridization signal size, appeared on the fourth chromosome related to heterochromatic rearrangements. Nucleolar material is thought to be required for sex chromosome pairing and disjunction in a variety of organisms including Drosophila. Thus, either remnant sequences, possibly intergenic spacer repeats, are still present in the sex chromosomes which have lost their NORs (as observed in D. simulans and D. sechellia), or an alternative mechanism has evolved.Heredity advance online publication, 23 February 2005; doi:10.1038/sj.hdy.6800612

The evolutionary genetics of thehobo transposable element in theDrosophila melanogaster complex

Hobo elements are a family of transposable elements found inDrosophila melanogaster and its three sibling species:D. simulans, D. mauritiana andD. sechellia. Studies inD. melanogaster have shown thathobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level somehobo-hybridizing sequences have also been found in the other members of themelanogaster subgroup and in many members of the relatedmontium subgroup. Surveys of older collected strains ofD. melanogaster suggest that completehobo elements were absent prior to 50 years ago and that they have recently been introduced into this species by horizontal transfer. In this paper we review our findings and those of others, in order to precisely describe the geographical distribution and the evolutionary history ofhobo in theD. melanogaster complex. Studies of the DNA sequences reveal a different level of divergence between the groupD. melanogaster, D. simulans andD. mauritiana and the fourth speciesD. sechellia. The hypothesis of multiple transfers in the recent past into theD. melanogaster complex from a common outside source is discussed.

Active mariner transposable elements are widespread in natural populations of Drosophila simulans

The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peach mutant Drosophila simulans females with wild-type males from various geographic origins. From a total of 194 experimental crosses only 17 failed to produce progeny with eye mosaicism (MOS, i. e. pigmented spots in otherwise white-peach eyes). Therefore, active mariner elements inducing somatic excision of the copy inserted at the white locus are abundant in all populations sampled. In the experimental crosses the frequency of mosaic offspring ranged from 0 to 100%, showing that the phenotypic expression is highly variable. The MOS phenotype, measured by the number of spots on the eyes, is quite variable within the progeny of single crosses. Although a difference was observed in the average MOS score (percentage of mosaic flies) between northern and southern populations of France, there was no indication of long range variation between geographic populations. Neither was there a systematic difference between recently collected populations and samples kept several years as isofemale lines.

Multiple amylase genes in Drosophila ananassae and related species

The number and organization of amylase genes in Drosophila ananassae were investigated through classical genetic methods and in situ and filter hybridizations. At least four genes may be active in D. ananassae, organized as two independent pairs of closely linked copies on the 2L and 3L chromosomal arms. Several other species of the D. ananassae subgroup were studied and show the same chromosomal locations, suggesting an ancient duplication event. However, the number of Amy copies seems to be higher in the D. ananassae multigene family, and there is a striking intraspecific molecular differentiation.

The Historical Discovery of the Nine Species in the Drosophila melanogaster Species Subgroup

DROSOPHILA melanogaster has played a central role in genetics research since the Morgan lab in the early years of the previous century. Yet, it has played a lesser role in the study of speciation. This is due to the fact that, until recently, there was only one closely related species, D. simulans, and the hybrids between the two species were sterile. Other groups, such as pseudoobscura, provided better opportunities. This changed recently with the discovery in Africa of several closely related species, making a total of nine. This article describes the discovery of these species and some of their salient features not likely to be known to geneticists.