Contrasting phylogeographic patterns of mitochondrial and genome-wide variation in the groundwater amphipod (Crangonyx islandicus) that survived the Ice age in Iceland

In this zip "DataAvailability.zip" all the data and parameter files, as well as R scripts and bash codes used to perform the analyses of the mitochondrial and the RADseq data are provided. A ReadMe file is available at the root describing the content of the different folders and files. Below is the abstract of the associated manuscript: Analysis of phylogeographic patterns have often been based on mitochondrial DNA variation, but recent analyses dealing with nuclear DNA have in some instances revealed mito-nuclear discordances and complex evolutionary histories. These enigmatic scenarios which may involve stochastic lineage sorting, ancestral hybridization, past dispersal, and secondary contacts are increasingly scrutinized with a new generation of genomic tools such as RADseq, which pose also additional analytical challenges. Here, we revisited the previously inconclusive phylogeographic history, showing mito-nuclear discordance, of an endemic groundwater amphipod from Iceland, <em>Crangonyx islandicus,</em> which is the only metazoan known to have survived the Pleistocene beneath the glaciers. Previous studies based on three DNA markers documented a mitochondrial scenario with the main divergence occurring between populations in northern Iceland and an ITS scenario with the main divergence between the south and north. We used double digest restriction-site-associated DNA sequencing (ddRADseq) to clarify this mito-nuclear discordance by applying several statistical methods while estimating the sensitivity to different analytical approaches (data-type, differentiation indices and base call uncertainty). A majority of nuclear markers and methods support the ITS divergence. Nevertheless, a more complex scenario emerges, possibly involving introgression led by male-biased dispersal among northern locations or mitochondrial capture which may have been further strengthened by natural selection.