THE INFLUENCES OF QUATERNARY PROCESSES ON NATIVE FRESHWATER DIVERSITY IN PATAGONIA: MOLECULAR INSIGHTS FROM THE GALAXIID FISHES

Abstract

Using GIS-based tools and a review of the relevant geological and climatic literature, I attempt to identify the key implications of Quaternary glacial cycles for drainage evolution in eastern Patagonia. In doing so, the stage is set for the proper integration of existing biogeographic and phylogeographic ideas to develop a suite of inferences aimed at elucidating how these processes influenced aquatic biodiversity of Patagonian Argentina. A primary finding of this research is that the southern mainland and/or Tierra del Fuego served as an important cryptic refuge for cold-adapted species, including aquatic taxa. At least one additional aquatic refuge is likely to have existed in either central or northern Patagonia. The low position of the Atlantic shoreline during glacial periods also revealed a much larger and inter-connected drainage network in southern Patagonia. During sea-levels stands below 100m, two new drainage coalescence points on the exposed continental shelf can be recognized among the Chico/Santa Cruz, Coyle and Gallegos river basins and between the Grande and Fuego rivers. Enhanced hydrological discharge during the deglaciation period of Late-Quaternary cycles is expected to have facilitated extensive inter-drainage connections within each of the northern and southern regions of eastern Patagonia via proglacial lake and/or stream coalescence. A large proglacial lake in the Nahuel Huapi Lake region is also recognized as the most likely temporary gateway for aquatic organisms to disperse between the Neuquen and Northern Patagonian Tablelands. I also recognize climate-induced drainage reversals as a bidirectional mechanism of trans-Andean dispersal and an important factor in determining the biogeography of widespread aquatic organisms in Patagonia.