Low satellite DNA variability in natural populations of Drosophila antonietae involved in different evolutionary events.

Drosophila antonietae is a cactophilic species that is found in the mesophilic forest of the Paraná-Paraguay river basin and in the dunes of the South Atlantic coast of Brazil. Although the genetic structure of the Paraná-Paraguay river basin populations has already been established, the relationship between these populations and those on the Atlantic coast is controversial. In this study, we compared 33 repetitive units of pBuM-2 satellite DNA isolated from individuals from 8 populations of D. antonietae in these geographic regions, including some populations found within a contact zone with the closely related D. serido. The pBuM-2 sequences showed low interpopulational variability. This result was interpreted as a consequence of both gene flow among the populations and unequal crossing over promoting homogenization of the tandem arrays. The results presented here, together with those of previous studies, highlight the use of pBuM-2 for solving taxonomic conflicts within the D. buzzatii species cluster.

Curvature measurement as a tool for the analysis of morphometric variation using Drosophila wings as a model

This article describes the use of geometric measurements of continuous, discrete parameters to studymorphometric variation in the wing cells of two sibling species, Drosophila mercatorum and Drosophilaparanaensis. To validate the results, the same wing samples were also analyzed using truss networks andpartial warps, in addition to a comparison with the ellipse method. The use of discriminative measurementsin conjunction with a Bayesian-based classification method yielded a relatively high number of correctclassifications for new individuals. These results compared favorably with those obtained using trussnetworks, partial warps and the ellipse method. These findings indicate that continuous curvature and arclength measurements may be useful parameters for the morphometric analysis of insect wings and possiblyother biological structures and shapes.

Conservation of pBuM-2 satellite DNA sequences among geographically isolated Drosophila gouveai populations from Brazil.

In this study, we have compared 34 repetition units of pBuM-2 satellite DNA of individuals from six isolated populations of Drosophila gouveai, a cactophilic member of Drosophila buzzatii cluster (repleta group). In contrast to the results of previous morphological and molecular data, which suggest differentiation among the D. gouveai populations, the sequences and the cluster analysis of pBuM-2 monomers showed that this repetitive element is highly conserved among the six D. gouveai populations (97.8% similarity), indicating a slow rate of evolution of pBuM-2 sequences at the population level. Probably, some homogenization mechanisms of tandem sequences, such as unequal crossing or gene conversion, have maintained the sequence similarity of pBuM-2 among D. gouveai populations. Alternatively, such a result may be associated with a functional role of pBuM-2 sequences, although it is not understood at present.

Cactophilic Drosophila in South America: a model for evolutionary studies.

The Drosophila buzzatii cluster is composed of seven cactophilic species and their known geographical distribution encompasses the open vegetation diagonal, which includes the morphoclimatic Domains of the Caatinga, Chaco and Cerrado, which are situated between the Amazon and the Atlantic forests. Besides these areas, these cactophilic species are also found in a narrow strip along the Atlantic coast from northeastern Brazil to the southern tip of the country. The hypothesis of vicariant events, defining the core areas of each species, is proposed to explain the historical diversification for the cluster. The intraspecific analysis for the cluster shows a population structure with gene flow restricted by distance, range expansion with secondary contact resulting in introgression and simpatry, especially in the limits of the species distribution, polytypic populations and assortative mating in inter population experiments. There is a variation related to these events that depends on the species and geographic origin of the population analyzed. These events are, hypothetically, described as the results of expansion and retraction of the population ranges, as a consequence of their association with cacti, which theoretically follow the expansion and retraction of dry areas during the paleoclimatic oscillations in South America, as that promoted by the glacial cycles of the Quaternary. The Drosophila buzzatii cluster is divided into two groups. The first one is composed of D. buzzatii, a species that has a broad geographic distribution and no significant differentiation between its populations. The second is the Drosophila serido sibling set, which encompasses the others species and is characterized by a significant potential for differentiation.

Chromosomal phylogeny of the Drosophila fasciola species subgroup revisited (Diptera, Drosophilidae)

The analysis of polytene chromosomes in 26 strains of seven species in the Drosophila fasciola subgroup, from several locations in Brazil, in addition to strains of two species belonging to the Drosophila mulleri subgroup (D. aldrichi and D. mulleri), enabled us to determine that the 3c inversion found in the latter species differ in one of its break points from that present in the species of the fasciola subgroup. Therefore, a change in the mulleri complex denomination from inversion 3c to inversion 3u is proposed. Accordingly, the fasciola subgroup is no longer a lesser phylogenetic part within the mulleri subgroup. Rather, it is directly related to the likely ancestor of the repleta group, called Primitive I. This information removes the main obstacle to considering the Drosophila fasciola subgroup as an ancestral group within the Drosophila repleta species group, according to the hypothesis of Throckmorton. Our data also support the conclusion that D. onca and D. carolinae are closely related species based on one new inversion in chromosome 4 (4f²), in both species. D. fascioloides and D. ellisoni also form a pair of sister species based on the presence of fusions of chromosomes 2-4 and 3-5. D. rosinae is related only to the likely ancestor of the fasciola subgroup, where the 3c inversion was fixed.