Geogenomics and biogeodynamics in the Northern Apennines and Ligurian Alps (Italy) 

Complex interactions between tectonics and surface processes influence the evolution of aquatic species across orogens. These processes are likely to be important in tectonically active areas where faulting and uplift lead to drainage reorganization. The Northern Apennines are an active orogenic wedge, where horizontal shortening and topographic advection lead to river capture and drainage divide migration, which can separate or connect ecological domains and thus isolate or mix aquatic populations. In contrast, the adjacent Ligurian Alps are a remnant of the Alpine orogen with little modern deformation. In this study, we combine geomorphic analysis with environmental DNA (eDNA) collected from rivers in the Northern Apennines and Ligurian Alps to assess the influence of tectonic advection and subsequent drainage reorganization on the genetic diversity of native freshwater fish. Geomorphic metrics are asymmetric across the main drainage divide (MDD) in both orogens, and divide asymmetry indices based on these metrics suggest an MDD migration direction from Ligurian (coast) to Adriatic (Po Plain), accompanied by river captures. In the Northern Apennines, this suggested drainage divide migration direction is towards the NE, opposite that of the tectonic advection of topography. Geomorphic metrics show greater contrast across the MDD in the Northern Apennines than in the Ligurian Alps. Five native freshwater fish species show statistically significant correlations between genetic distance and divide asymmetry indices across the MDD. Genetic distance is greater across the MDD in the Northern Apennines than in the Ligurian Alps. Endemic species such as Telestes muticellus exhibit greater amplicon sequence variant (ASV) richness on the Ligurian than the Adriatic side of the MDD in both orogens; greater ASV richness in the Northern Apennines than in the Ligurian Alps; and greater ASV richness on the retrowedge of the Northern Apennines than on the prowedge.  Tectonically driven drainage reorganization may promote greater genetic diversity in coastal basins, although we can not rule out anthropogenic population transfer in some cases.