Tectonics, Drainage Reorganization, and Riverine Biodiversity in the Northern Apennines (Italy)

Mountain building reorganizes drainage networks, affecting riverine biodiversity. Northern Italy offers a natural experiment in the impact of tectonic and geomorphic processes on genetic diversity within riverine fish species. The Northern Apennines are an active orogenic wedge formed by subduction and rollback of the Adriatic slab over the last 30 million years, with high rates of horizontal tectonic advection of topography from northeast to southwest. In contrast, the adjacent mountains of the Ligurian Alps are a remnant of the Alpine orogen with little modern deformation. In the Northern Apennines, horizontal shortening and topographic advection have been hypothesized as leading to river capture and drainage divide migration. In addition, slab rollback has produced a spatial transition from contraction to extension that is more pronounced from north to south, with normal faulting producing range-parallel drainage only in the southern regions. The orogen exhibits topographic asymmetry across the main drainage divide: the retrowedge on the Ligurian (generally southwestern) side is steeper than the prowedge on the Adriatic (generally northeastern) side. This thesis combines geomorphic analysis with environmental DNA collected from rivers in the Northern Apennines and Ligurian Alps to assess the influence of tectonically driven drainage reorganization on genetic diversity within the endemic riverine fish species Telestes muticellus (Risso, 1826). We find distinct zones of geomorphic characteristics from north to south, including the asymmetry of the main drainage divide between the Ligurian and the Adriatic and the frequency of drainages flowing parallel to the crest of the mountain range. Analysis of the assemblages of DNA sequences detected on either side of the main drainage divide shows patterns that correlate with the geomorphic zonation. In terms of directional measures of assemblage change, the Northern Apennines show higher values of overlap, gain, loss, turnover, and nestedness than those in the Ligurian Alps. Main drainage divide asymmetry correlates positively with genetic distance and gain, loss, and turnover of DNA sequences from Adriatic to Ligurian sites and negatively with overlap and nestedness. Since Telestes muticellus is confined to freshwater environments, tectonically driven drainage reorganization can explain its spatial genetic differentiation. In this thesis, we also present new catchment-averaged erosion rates and horizontal velocities from major drainage basins in the Northern Apennines derived from cosmogenic 10Be concentrations in order to quantify the erosional fluxes from the orogen and compare the pattern of modern erosion rates with the topographic asymmetry. Catchment-averaged erosion rates and horizontal velocities increase from west to east throughout the study area; rates on the steeper Ligurian side of the main drainage divide are lower than those on the gentler Adriatic side. We reconcile these data with a kinematic model of subduction and slab rollback, where the erosional flux is described as a vector with horizontal and vertical components. The model predicts that the topography and erosion rates can be sustained by horizontal motion on the Ligurian side, while both horizontal motion and vertical uplift are required on the Adriatic side. Finally, we use a numerical model of coupled landscape and biological evolution to explore differential uplift and horizontal tectonic advection in an asymmetric orogenic wedge, drainage reorganization, and ensuing dispersal and divergence for an aquatic clade (riverine fish) over geological time. Model input parameters are informed by, and model results are compared to, genetic and geomorphological data collected from the Northern Apennines and Ligurian Alps. Our results provide insights into tectonically driven drainage reorganization, where horizontal shortening and topographic advection lead to river capture and drainage divide migration opposite the direction of the horizontal tectonic advection of topography, which has key implications for the intraspecific genetic diversity of riverine fish.