Cytogenetic and molecular studies on neotropical small rodents from Brazil

Abstract

Neotropical region has the highest biodiversity of our planet and Brazil is one of the hotspots of the biodiversity in the world, particularly for mammals. However, little is known about this diversity and there is still a lack of basic information about these groups, such as the real number of species and genus, their distribution, reproductive patterns, phylogeny and evolutionary history. Our project intends to promote integration among cytogenetic, molecular systematic, classic systematic and biogeography approaches in order to study small rodents of Brazilian ecosystems and to understand their chromosomal and gene diversity as well as their phylogenetic relationships and evolutionary processes. Only in a multidisciplinary view will be possible to comprehend and consequently to increase knowledge about Brazilian biodiversity. Our first aim is to develop cytogenetic analysis using conventional staining, banding patterns and fluorescence 'in situ' hybridization (FISH) with specific probes o Brazilian rodents. In this group of vertebrates, several new species have been described based on chromosomal characterization, since the importance of cytogenetic data is not only restricted to identifying the diploid number, morphology, structure and organization of sequences on chromosomes. This information has been especially useful to identify cryptic species and has been applied to their cytotaxonomy. These data have also been extensively used to elucidate problems of chromosomal evolution. We will also develop molecular studies based on mitochondrial DNA sequences in order to reconstruct phylogenetic relationships and to conduct phylogeographical analysis. Mitochondrial genes sequences (especially citochrome b) will be used to reach this aim and, when necessary, sequences of the nuclear gene IRBP (interphotoreceptor retinoid binding protein) will be also included. In Brazil, there are several examples that illustrate the importance of cytogenetic and molecular data on the characterization of species among the rodents. Within Akondontini tribe, only by using karyotype it is possible to distinguish some species. In Akodon cursor, the frequencies of chromosome rearrangements along their geographical distribution in Atlantic Forest have provided information about their dispersal pattern and population differentiation. Oryzomyini represents another complex group of rodents in which the number of species is not known and the phylogenetic relationships are not well established. Several new species have been described based on karyotype and molecular data (mainly citochrome b). Some examples can be found within the Oryzomys from the groups nitidus, subflavus and capito; also in Oligoryzomys from the groups nigripes, fulvescens and microtis; and as well as within Nectomys squamipes, N. rattus and in Oecomys, etc. (AU)