Filogeografia e genética de populações de jacaré-paguá (Paleosuchus palpebrosus) ao longo do rio Madeira e bacia do rio Paraguai (Pantanal)

Abstract

Paleosuchus palpebrosus is a crocodilian of the subfamily Caimaninae that is distributed widely in the Neotropics. It has behavior associated with, and in the Amazon it is concentrated in headwaters of rivers, tributaries and flooded forests. In the Pantanal, its occurrence is restricted to the periphery, near mountains, not being found in the floodplain of the Paraguay River. Paleosuchus palpebrosus is usually associated with clean, cold running water. Scientific knowledge of Paleosuchus palpebrosus is deficient which adversely affects their conservation. Therefore, we used sequences of the mitochondrial cytochrome b gene to investigate, for the first time, the pattern of distribution of genetic variability, evaluating historical and/or physical barriers to gene flow between populations, as well as investigating historical demographic events. We sequenced the complete cytochrome b from 172 individuals of Paleosuchus palpebrosus sampled from localities along the Madeira and Mamore/Guaporé Rivers, in various localities in the Pantanal and one locality on the Solimões River, Cururu lake. We use different types of Bayesian inference to investigate the number of biological populations, the divergence time between populations, rates of gene flow and historical changes in effective size of each population. The population structure was obtained by AMOVA and demographic events were investigated via tests of Tajima's D and Fu's Fs. We also calculated indexes of genetic diversity of the species. Paleosuchus palpebrosus is composed of genetically highly structured populations as a result of no or low rate of gene flow between them. The population of P. palpebrosus Cururu lake is isolated from the Madeira River basin, and restricted to the paleovárzea region of the Solimões. Populations of the Madeira and Bolivia showed bidirectional gene flow, but asymmetrical. The mountains that divide the sub-basins of the Madeira and Bolivia and the rapids of the upper Rio Madeira are barriers that limit gene flow between populations. The complex of Parecis mountains divide the basins of the Amazon and Paraguay and are a likely vicariant barrier that isolated populations of Bolivia and the Pantanal. The population of Madeira suffered population expansion, probably after the last Ice Age, and genetic diversity in P. palpebrosus was high and comparable to other Caimaninae. Important implications arise from this work for the better understand the species. Populations of Cururu lake, Madeira/Bolivia and the Pantanal can be considered Evolutionary Significant Units and should be treated as completely independent populations. Individuals of P. palpebrosus can also disperse between water bodies via land, thus gene flow does not need to occur via the main river channel. In addition, our characterization provides the natural pattern of the distribution of genetic diversity which is important for future studies to assess more accurately human impacts on this species generated, for example, by hydroelectric dams and plants.