Myxozoa are endoparasites cnidarians, characterized by transmission via multicellular spores. So far 2,400 species have been described, parasitizing most commonly fish and aquatic invertebrates. This group have been attracted extensive attention due to the pathogenic potential of some species, by the complexity of its life cycle, morphological simplification and its enigmatic evolution. The species of the Plagioscion genus are native to the Amazonas and Paraná rivers basins and play a relevant economic role. Those fish are also a biogeographic indicator of key events relating to the marine incursions into the Amazon, which may have favored ecological species shifts from saltwater to freshwater and the diversification of the species. In this context, the main aim of this study is to describe the new myxozoan species found parasitizing all Plagioscion species described from the Amazon and Paraná rivers basin. Besides that, carry out studies on the host-parasite interaction and genetic diversity at the population level. Finally, we also aim to explore the phylogenetic relationships of the new species found parasiting Plagioscion spp. The specimens will be collected from different rivers in the Amazon basin (Solimões river [Manacapuru, AM] and Amazon river [Santarém, PA and Macapá, AP]) and Paraná basin [Porto Rico, PR]. The species will be described based on morphological and sequences of the nuclear genes 18S and 28S rDNA, and of the mitochondrial gene cytochrome c oxidase. The study of host-parasite interaction will be done by histopathological analyzes. Sequences of the nuclear gene ITS-1 and of cytochrome b will be used to estimate populational parameters. The sequences will be compared in order to determine the phylogenetic relationship among the species, besides proposing hypotheses about the role of marine insurgencies into the Amazon in the Myxozoa radiation.
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