FILOGEOGRAFIA DE DUAS ESPÉCIES DE DROSOPHILA DOS GRUPOS GUARAMUNU E GUARANI

Abstract

Phylogeography is a research field that can evidence geographic and genetic patterns resulted from historic events that a species or population has suffered along its evolutionary history. The main goal of this work was to study the populational structure, evolutionary history and distribution of the Neotropical Drosophila species, Drosophila maculifrons (guaramunu group) and D. ornatifrons (guarani group), collected in the Atlantic Forest biome from southern Brazil. Sequences of the mitochondrial genes Cytochrome Oxidase I (COI) and II (COII), from three populations of D. maculifrons and nine populations of D. ornatifrons, were analyzed. The mean nucleotide diversity (?) found for D. maculifrons in the COI gene was 0.000476, and in COII was 0.000651. The AMOVA, Analysis of Molecular Variance, revealed considerable variation for COI (63.51%; ?ct = 0.63328 - p < 0.05) among G1 and G2 groups (categorized according to the Atlantic Forest phytophysiognomy were the population was located), and for COII among populations within the groups (101.12%; ?sc = -0.01481 - p < 0.05). The Mismatch Distribution (MD) graphics for both genes presented multimodal curves, which suggest the occurrence of demographic equilibrium or population subdivision. The pattern of haplotipic variation distribution for D. maculifrons can be also explained by balancing selection, with genetic diversity reduction and maintenance of ancestral polymorphism; the difference in the variation found among populations could be due to the distinct flora composition of the sampled Atlantic Forest areas, Semideciduous Seazonal Forest (FES) and Mixed Ombrophylous Forest (FOM), or as a consequence of the higher geographic proximity among the FOM populations than among the FES populations, resulting in restrict by distance gene flow. For D. ornatifrons, the COII neutrality tests, MD graphics and Bayesian analysis indicated that this species may have suffered a population expansion event. This event is possible to have initiated from coastal or near to the coast populations of the Rio Grande do Sul state, more humid ones, as indicated by the higher variation and the position of Ilha dos Marinheiros-RS population in the haplotype net. The BSP dating suggested that this expansion would have occurred between 20,000 and 25,000 years ago, period that the temperatures were five to six degrees lower than the current mean temperature. Therefore, the haplotype diversity distribution analysis of the COI and COII genes of D. maculifrons revealed a possible relation with the type of habitat (FES or FOM), however, a wider geographic sampling could contribute more precisely to elucidate this species evolutionary history. The phylogegraphic study of D. ornatifrons suggested that the coastal region of the Rio Grande do Sul state is possibly the ancestral area that originated the other populations analysed. The restriction of the diversity distribution observed in the coastal ancestral population analyzed, Ilha dos Marinheiros-RS, toward to the colonized areas could be due to the limited capacity of dispersion of these insects, associated with the difficulty of overcoming clinal barriers, specially humidity, which are considerably frequent in forest environments, such as the Atlantic Forest.