A magnet to draw a bright needle out from the haystack -- RADOrgMiner, an automated pipeline to genotype organellar reads from RADseq data

Abstract

Different versions of Restriction-site Associated DNA sequencing (RADseq) have become powerful and popular tools in molecular ecology. Although RADseq datasets are regarded as representative of the nuclear genome, reduced representation genomic libraries may also sample the organellar (mitochondrial and, in case of plants, plastid) DNA. Extraction of organellar loci from RADseq data can provide additional insights into the phylogenetics of the study group which comes at no additional sequencing effort. Cytoplasmic genetic variance can help better understand the evolutionary history by uncovering past hybridization and identifying the maternal (or, rarely, the paternal) lineage due to rapid lineage sorting. We developed a pipeline in bash that is based on existing bioinformatic tools to automatically mine and genotype organellar loci contained RADseq libraries. The utility of our pipeline is tested on eight, publicly available datasets spanning different phylogenetic levels (i.e. from family-level phylogenies to phylogeography) and RADseq methods (sdRAD, ddRAD, ezRAD, GBS) for genotyping both mitochondrial and plastid loci, which were subject to phylogenetic tree reconstruction. In all cases, organellar phylogenies adequately supplemented the original studies either by corroborating the large-scale picture based on RADseq or by bringing additional evidence on past or contemporary hybridization. RADseq methods designed to achieve a larger horizontal coverage (i.e. ddRAD, ezRAD) evidently yielded longer organellar alignments, but sdRAD and GBS still provided useful polymorphic loci found in the cytoplasmic DNA. Our newly developed pipeline for the above purpose can be run under a Unix-line operating system and is freely accessible at https://github.com/laczkol/RADOrgMiner