The coevolution of life and landscape in the Atacama Desert

The evolution of landscapes has often been inferred from the phylogenetic records of species that inhabit them, but it is rare to have a sufficiently detailed record of landscape evolution to be able to test the validity of links between bio- and geochronometers. Here we derive the history of fluvial incision of the Tiliviche River in the Central Depression of the northern Atacama Desert, Chile, using cosmogenic nuclide exposure dating of fluvial terraces and nearby paleochannels. We compare this to the timing of speciation from molecular clock dating of Ephemeroptera (Mayflies), collected from both the Tiliviche and proximal Camerones Rivers. Both these drainages source their discharge in the Western Cordillera of the Andes Mountains and drain westwards to the Pacific Ocean. Where they pass through the low relief Central Depression between the Andes and Coastal Cordillera they have formed steeply incised canyons. Our exposure dating shows that notable incision of the Tiliviche River into the Central Depression began around 2 Myr ago. The timing of the divergence of Ephemeroptera species from the Tiliviche and Camerones Rivers is coeval with the onset of Tiliviche incision at 2 Myr. Furthermore, this history of river incision and speciation is consistent with the timing of abandonment of smaller streams that used to flow across the pampa between the Tiliviche and Camerones rivers (Binnie et al., 2020).  Our results imply that the downcutting of the Tiliviche as a deep canyon and the contemporaneous drying out of smaller drainages between Tiliviche and Camerones were sufficient to isolate the Ephemeroptera clades.  This provides a positive test of a coupled bio- geochronometer approach for unravelling relationships between life and landscape. Whether the controls of river incision and consequently speciation are predominantly climatic, tectonic, or autogenous in nature is still to be resolved. Binnie S. A, Reicherter K. R., Victor P., González G., Binnie A., Niemann K., Stuart F.M., Lenting C., Heinze S., Freeman S.P.H.T. and Dunai T. J. (2020)The origins and implications of paleochannels in hyperarid, tectonically active regions: The northern Atacama Desert, Chile. Global and Planetary Change, Volume 185. https://doi.org/10.1016/j.gloplacha.2019.103083