ABSTRACT
Andean orogeny and Quaternary glacial cycles have played a major role in shaping the Patagonian freshwater fauna. However, few studies have compared the phylogeographic patterns across the Andes in this region using freshwater taxa. Here we used mitochondrial DNA sequence data to study the population structure of two Patagonian freshwater crabs of the genus Aegla and time their divergence. We reanalyzed previously published A. alacalufi cytochrome c oxidase subunit I (COI) and subunit II (COII) as well as 16S data from Chile (12 localities; 88 individuals) and newly collected A. neuqensis COI sequences from Argentina (7 localities; 28 individuals). Our phylogenetic and population genetic analyses showed that glaciated continental and nonglaciated insular A. alacalufi samples have been separated during the Last Glacial Maximum (LGM), with the insular samples showing deeper genetic and time divergence, and the continental ones showing sudden population expansion. The same analyses indicated isolation and dispersion of A. neuquensis populations along the Negro River Basin into the Chico-Chubut River Basin, with the Negro samples showing deeper genetic and time divergence and the Chico-Chubut samples showing demographic expansion. Evolution of A. alacalufi (21-104 ky) was greatly influenced by Late Pleistocene glaciations, while A. neuquensis differentiation (21-164 ky), although facilitated by the LGM, was mainly driven by drainage divides established long before the LGM. Similar phylogeographic patterns have been described in freshwater fishes on each side of the Patagonian Andes.
