Riverscape genetics: linking river environments with adaptive potential in Neotropical freshwater fish

In rivers, the combination of dendritic shape and asymmetric migration due to water flow promotes high levels of genetic differentiation among populations. But the mechanism of how strong genetic structure from river characteristics and habitat heterogeneity interact to enable adaptation to local river conditions is debatable. The proposed research will tackle this knowledge gap by applying an integrative framework that combines empirical genomic and morphological data with simulation-based modeling to identify the mechanisms of population divergence and local adaptation in parallel yet isolated tributaries that flow through an environmental gradient. Specifically, we will study a freshwater fish biodiversity hotspot ¿ the tributaries of the Meta River (Orinoco Basin) in Colombia, that flow from the humid Andean foothills to the seasonally wet-dry Llanos. This spatial scenario will allow us to discern the genomic regions under local adaptation from the demographic signal among populations at each tributary, and the natural replicable set up provided by multiple tributaries will also let us to test for parallel local adaptation. For this research, we will use an endemic tetra species (Gephyrocharax valencia) that is broadly distributed in tributaries of the Meta River. This species is particularly interesting because it has evolved morphological adaptions to hypoxia ¿ a condition commonly found in the Llanos during the dry season. Instead of typical correlative methods, this proposed research will use a spatial modeling approach that it is currently being developed (by AT) to generate clear expectations for quantifying the contribution of specific evolutionary processes to population divergence (i.e., demography vs. local adaptation). This project will also investigate patterns of species diversity and why they differ across the landscape, i.e., how adaptive processes may contribute to the rich diversity of Neotropical ichthyofauna. Beyond enhancing our knowledge about the freshwater fishes in this region, the approach proposed here has the potential to be broadly applied to other structured environments, aquatic or terrestrial. In general, the findings from this proposal will provide insights into the properties of rivers that make them critical to conservation efforts because of their impact on population persistence and movement patterns of organisms living in structured, heterogeneous environments.