Especiação ecológica mediada pelos tipos de água em um peixe amazônico

Abstract

The Amazon harbors the largest river drainage in the world. Within its water bodies lies an immense diversity of habitats, with several forest streams (igarapés), large river channels, floating vegetation, flooded forest and water with very distinct physical and chemical properties. Such environments are home to the greatest diversity of freshwater fish on Earth. Several species can be readily recognized by morphological characteristics, however, other form cryptic species complex whose identification is very difficult. Such scenario suggests that several diversification mechanisms can have contributed to the formation of new species. However, few studies have directly investigated the processes that mediate the formation of new species as distinguished by the biological species concept. In fact, studies on the origin and maintenance of reproductive isolation in Amazonian fish are largely absent. The present thesis aimed

IX at investigating diversification process by analyzing ecological and evolutionary characteristics of the sailfin tetra Crenuchus spilurus (Characiformes: Crenuchidae), a species that occurs over a huge geographical range (over three million squared kilometers), encompassing rivers of the Amazon basin, Orinoco basin and coastal rivers of the Guianas. Using direct field observations, diet analysis and analysis of reproductive parameters, we raised which intrinsic and extrinsic characteristic of the species could contribute to the expansion of geographical range and which characteristics could point toward a morphological conservatism in the species. Based on sequencing of genetic markers, we found a clear distinction between two linages that occur at ecogeographical parapatric distribution. One of the lineages is restricted to the blackwaters of the Rio Negro, an environment that is acidic and nutrient poor; the second lineage occurs throughout the remainder of the distribution, mostly within drainages that flow to whitewater rivers. Although possessing little morphological distinction, such lineages are reproductively isolated, with acidic and nutrient poor waters penalizing the fitness of the lineage that does not occur in such environment. These results suggest that the two lineages developed adaptations to the local chemical conditions. The low fitness of individuals from whitewater drainages that were exposed to blackwater-like conditions result in reproductive isolation between the lineages, which strongly suggests that distinct water types hampers gene flow between the lineages, thus mediating the (ecological) speciation process. Our results are aligned with recent studies that suggest, for other species, that amazon water types represent an important component in the formation of new species in the Amazon