Hibridização e unidades evolutivas em peixes-bois (Trichechus sp.)

Abstract

There are two manatee species found in the America: Trichechus inunguis (Amazonian manatee) native to the basin of the Amazon River and inhabiting only freshwater regions, and, the Trichechus manatus (West Indian manatee) with a larger distribution, from Florida (USA) to Alagoas (Brazil), being found in coastal regions and in some rivers and lagoons close to the sea. Hybrids between these two species have been identified, in their sympatric region, through mitochondrial DNA (mtDNA) and microsatellites data. Although there is some disagreement, the West Indian manatee is divided in two subspecies: T. manatus latirostris (Florida manatee) and T. manatus manatus (Antilles manatee) with the first restricted to the Florida region and the other inhabiting the rest of the area. In light of these facts, the general aim of this thesis is to help the genetic understanding of the interspecific and intraspecific relationships of the American manatees (T. inunguis and T. manatus). This work is organized in three parts (chapters). The first part focused on the consensus between traditional taxonomic division and the evolutive units, which used the Generalised Mixed Yule method (GMYC) to define the mitochondrial lineage which supplied important data to the policy plan, management and conservation. This resulted in three evolutive lineages, corresponding to the already identified clusters, therefore, questioning the isolation of the Florida manatee and suggesting a taxonomic revision of the Brazilian manatee. The second part of this work regards the genomic composition of the manatees from the French Guiana which are outside theAmazon River basin, and which highlights the ecological importance of this region. In the last part of this work, we sequenced six nuclear fragments (2.768 bp) and region control of mtDNA (410 bp) to implement statistical phylogenetic analysis on them. The samples for this analysis were obtained from T. inunguis (n = 44), T. manatus from Brazil (n = 43), Florida (n = 23) and Puerto Rico (n=5) and also manatees from the hybrid zone (n=15). The results indicated the separation of the Brazilian manatee population (0.26 MYA) and no distinction between the populations of Florida and Puerto Rico. It also identified that the hybrid zone has its own population, with a bidirectional migration estimated between the marine and the fluvial populations and reconstructing the hybrid zone, indicating a major and ancient contribution of T. inunguis lineage (γ = 0,583) and a lesser of the all analyzed T. manatus lineage together (γ = 0,296). Finally, our results reinforce the importance of the Brazilian population due to their exclusive characteristics and the peculiar dynamics of the hybrid zone, that probably was formed as a “drain” for all its neighboring populations, forming an unique and well adapted admixture to the estuarine environment, between the Amazon Basin and the Orinoco River,directly influenced by the Amazon plume.