Claudia Rohde

Transposable elements P and gypsy in natural populations of Drosophila willistoni

The presence and integrity of the P transposon and the gypsy retrotransposon in the genome of 18 samples of natural Drosophila willistoni populations collected from a large area of South America were Southern blot screened using Drosophila melanogaster probes. The aim of this screening was provide further knowledge-base on the geographical distribution of D. willistoni and to carry out an inter-population analysis of the P and gypsy elements present in the genomes of the populations analyzed. The fragment patterns obtained indicate that both the P and gypsy elements are ancient in the D. willistoni genome, but whereas the gypsy retroelement appears to be invariable and stable the P element varies between populations and appears to still have some capacity for mobilization.

Chromosomal evolution of sibling species of the Drosophila willistoni group. I. Chromosomal arm IIR (Muller's element B)

The phylogenetic relationships among nine entities of Drosophila belonging to the D. willistoni subgroup were investigated by establishing the homologous chromosomal segments of IIR chromosome, Muller’s element B (equivalent to chromosome 2L of D. melanogaster). The sibling species of the D. willistoni group investigated include D. willistoni, D. tropicalis tropicalis, D. tropicalis cubana, D. equinoxialis, D. insularis and four semispecies of the D. paulistorum complex. The phylogenetic relationships were based on the existence of segments in different triads of species, which could only be produced by overlapping inversions. Polytene banding similarity maps and break points of inversions between species are presented. The implications of the chromosomal data for the phylogeny of the species and comparisons with molecular data are discussed. The aim of this study is to produce phylogenetic trees depicting accurately the sequence of natural events that have occurred in the evolution of these sibling species.

Two decades of colonization of the urban environment of Porto Alegre, southern Brazil, by Drosophila paulistorum (Diptera, Drosophilidae)

Drosophila paulistorum Dobzhansky & Pavan, 1949 had initially been considered absent in anthropogenically disturbed environments, but in 1985 the detection of the species in Porto Alegre city, southern Brazil, suggested its potential to colonize new habitats and laid the foundations for ecologic studies on this species populations. This study followed the variations in D. paulistorum populations in this town almost 20 years after its first local record. Drosophilid specimens were collected in sites with different urbanization grades and the results point to the expressive decline in D. paulistorum populations in Porto Alegre. This decline may be linked to urban growth and to naturally driven population decline, as imputed to climatic changes like variations in maximum and minimum temperatures as a consequence of a global climate warming. Also, the recent introduction of exotic species Zaprionus indianus Gupta, 1970 seems to play a role in this scenario, changing the interactions between native species.

Temperature-dependent gonadal hybrid dysgenesis in Drosophila willistoni

Temperature-dependent gonadal dysgenesis was shown to occur in the progeny of both inter- and intrastrain crosses involving two populations of Drosophila willistoni, one of which was an old laboratory stock, and the other, freshly collected from a natural population. We propose that the phenomenon observed was caused by the mobilization of transposable elements, as occurs in several other Drosophila species.

Inversion polymorphism and a new polytene chromosome map of Zaprionus indianus Gupta (1970) (Diptera: drosophilidae)

Zaprionus indianus is a recent invader in Brazil and was probably introduced from the West Afrotropical zone. So far, studies regarding its chromosomal polymorphism were limited to India. We found that Brazilian populations were very different from Indian ones. Five new inversions have been discovered. In(II)A, already described in India, where it is quite common, has also been found in Brazil, where it is very rare. The X-chromosome has three inversions; In(X)Na, In(X)Ke and In(X)Eg, which are frequent in all Brazilian populations studied. In every case, we observed strong linkage disequilibrium among these gene arrangements. During the primary collection period (2001–2002), we noticed a significant positive correlation between the frequency of these inversions and latitude, but this was not confirmed in later investigations. Rearrangement In(IV)EF was also common in all populations, while inversion In(V)B was only found in southern populations. Our data suggest that the founders that recently invaded Brazil were polymorphic for the six inversions observed. The place of origin might be identified more precisely by investigating West African populations. In order to facilitate further investigations, we present an updated polytene chromosome photomap, locating the breakpoints of every inversion observed in Brazilian populations.

Chromosomal polymorphism in Drosophila willistoni populations from Uruguay

Chromosomal polymorphism in natural populations of Drosophila willistoni from Uruguay and southern Brazil was investigated in order to understand the genetic characteristics and evolutionary potential of these almost geographically marginal populations. The level of chromosomal polymorphism in samples from Uruguay was higher than in those from the southernmost Brazilian state of Rio Grande do Sul. The increase in the polymorphism of these populations, in which the species almost reaches its southern limit, contradicts the low level of paracentric inversion polymorphism expected under the central-marginal chromosomal polymorphism cline previously reported. The high frequency of some inversions and the presence of unique inversions in samples from Uruguay indicate the uniqueness of these populations.

Temperature, urbanization and body color polymorphism in South Brazilian populations of Drosophila kikkawai (Diptera, Drosophilidae)

Body color polymorphism of urban populations of cosmopolite fly Drosophila kikkawai Burla, 1954 was investigated in relation to its possible association with environmental temperature. Samples of D. kikkawai were collected in spring, summer, autumn and winter between 1987 to 1988, in zones with different levels of urbanization in the southern Brazilian city of Porto Alegre, Rio Grande do Sul. A clear association was observed between darker flies and both seasons with low temperatures and areas of low urbanization (where temperature is generally lower than in urbanized areas). Results of preliminary laboratory experiments involving six generations of flies grown in chambers at temperatures of 17o and 25oC confirmed this tendency to a relationship between body color and temperature, with allele frequency of the main gene involved in body pigmentation changing over time.

Three decades of studies on chromosomal polymorphism of Drosophila willistoni and description of fifty different rearrangements

Drosophila willistoni (Insecta, Diptera) is considered a paradigm for evolutionary studies. Their chromosomes are characterized by multiple paracentric inversions that make it hard to identify and describe chromosomal polymorphisms. In the present report we attempted to systematize the description of all the 50 inversions found in the last three decades, since we have been studying the chromosomes of several individuals of 30 different populations, including the one used in the genome sequencing project (Gd-H4-1). We present the photographic register of 11 arrangements in the left arm of the X chromosome (XL), eight in the right arm (XR), 10 in the left arm of chromosome II (IIL), eight in its right arm (IIR) and 13 in chromosome III. This information also includes their breakpoints on the reference photomap. A clear geographic difference was detected in XL and XR, with different fixed arrangements depending on the origin of the population studied. Through the comparison of all X arrangements it was possible to infer the putative ancestral arrangements, i.e., those related to all the remaining arrangements through the small number of inversions that occurred in the past, which we will call XL-A and XR-A. In the autosomes (IIL/IIR and III), fixed inversions were detected, but most are segregating in different frequencies along the geographical distribution of the D. willistoni populations.