Geographic Patterns of Genetic Variation and Conservation Consequences in Three South American Rodents
Gustavo B. Miranda1, Jaqueline Andrades-Miranda1, Luiz F. B. Oliveira2, Alfredo Langguth3, Margarete S. Mattevi1,4,5
1Departamento de Genética, PPG Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; e-mail: [email protected].
2Museu Nacional do Rio de Janeiro, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
3Departamento de Sistemática e Ecologia, Universidade Federal da Paraíba, João Pessoa, Brazil.
4PPG Genética e Toxicologia Aplicada, Universidade Luterana do Brasil, Canoas, Brazil.
5To whom correspondence should be addressed; e-mail: [email protected].
Short Title: Genetic variation in Oryzomyini rodents
In this study the geographic patterns of genetic variation of three rodent species belonging to the tribe Oryzomyini were investigated using the mitochondrial cytochrome b and nuclear IRBP genes in biomes that are undergoing degradation process to a greater or lesser degree. The samples are from 25 collecting localities distributed throughout the Amazon, Cerrado, Atlantic Forest and Pampa biomes. The results show that the three species have a population and geographic structure, besides being in demographic equilibrium. The phylogenetic analyses performed on Euryoryzomys russatus and Hylaeamys megacephalus showed their specimens grouped in three distinct clades forming geographic gradients (North-South direction in H.
megacephalus). Intraspecific genetic divergence was higher in H. megacephalus (4.53%), followed by E. russatus (1.79%) and lower in Sooretamys angouya (0.88%).
The results obtained indicate that, necessarily, the management strategies to preserve genetic diversity should be different for each species, since each of them presented specific population parameters.
KEY WORDS: Euryoryzomys russatus; Hylaeamys megacephalus; Sooretamys angouya; cytochrome b; IRBP.
INTRODUCTION
Many threatened species are found in naturally small or remnant populations and often are product of altered or fragmented landscapes. Estimating the geographic patterns and the levels of genetic variation of the species in these fragile habitats is essential to manage and preserve this biodiversity, and molecular techniques have proved to be a powerful tool to reveal the population structure of endangered species (Smith and Hellmann, 2002).
The different Brazilian biomes have been markedly affected by anthropogenic interventions caused mainly by European settlement in the XVI, XVII, and XVIII centuries which have been severe in the past, and will continue in present-days carried out by the Brazilian society. Few studies attempted to investigate the effects of this environmental damage on genetic variation, evolutionary relations and priorities for taxa management and conservation, as well as the places where they occur (Rodrigues, 2001; Solé-Cava, 2001; Umetsu and Pardini, 2007).
The three species studied belong to three recently proposed genera (Weksler et al., 2006) of rodents of the tribe Oryzomyini, subfamily Sigmodontinae, which is one of the most abundant taxon of Neotropical mammals and were chosen for genetic characterization because occur on different biomes of Brazil. These species are endemic in four biomes, two of they only occurring in Brazil (Cerrado and Atlantic Forest) and the other two (Amazon and Pampa) distributed through Brazil and also by other South American countries.
Sooretamys angouya and Euryoryzomys russatus are partially sympatric in the Atlantic Forest and the Pampa. The Atlantic Forest, constituted by dense and mixed Tropical Humid Forest, occupies mainly the coastal region (about 13% of the Brazilian territory). Today only 5 to 7% of the original cover of this forest is left. It is considered the fifth richest area of endemic species (about 40% of the vertebrate species are endemic), and, at the same time, the fifth most threatened area of the world (Por et al., 2005). The Pampa cover the southern fields of Brazil (about 2% of the territory), besides Uruguay and Argentina. Poaceae, Asteraceae and leguminous plants prevail.
Field and forest formations of temperate climates, different from other formations in Brazil, are part of the biome. The regional vocation is to produce beef for slaughter and
rice, maize, wheat and soy crops. The inadequate use of this biome is taking to the disappearance of natural pastures and forest formations (Porto, 2002).
Hylaeamys megacephalus occupies two other biomes: Amazon and Cerrado.
The Amazon has the largest biological diversity in the world, and is the largest Brazilian biome in surface, occupying almost half the Brazilian territory (49.29%). This biome holds the largest hydrographic network of the planet, which runs off about 1/5 of the fresh water volume in the world. Illegal logging, mining, prospecting, agriculture and livestock are the activities which change and degrade the natural ecosystems of the Amazon. It is estimated that 15% of the Amazon has already been deforested (Por et al., 2005). The core area of the Cerrado is distributed mainly through the Brazilian Planalto Central, covering about one fourth of the total surface of Brazil. This biome is recognized as the richest savannah of the world with several ecosystems, but the growing agricultural expansion (sugar cane, soy, and others), together with livestock, has already led to the destruction of 80% of it (Por et al., 2005).
This paper studied the geographic patterns of genetic variation, using the mitochondrial cytochrome b (cyt-b) and nuclear interphotoreceptor retinoid binding protein (IRBP) genes of three rodent taxa, Sooretamys angouya which is partially sympatric with Hylaeamys megacephalus and Euryoryzomys russatus (which, by it turns, is parapatric with H. megacephalus) in biomes that are undergoing a degradation process to a greater or lesser extent (Fig. 1).
MATERIALS AND METHODS