Breaking RAD: An evaluation of the utility of restriction site associated DNA sequencing for genome scans of adaptation

Abstract

Understanding how and why populations evolve is of fundamental importance to molecular ecology. RADseq (Restriction site-Associated DNA sequencing), a popular reduced representation method, has ushered in a new era of genome-scale research for assessing population structure, hybridization, demographic history, phylogeography, and migration. RADseq has also been widely used to conduct genome scans to detect loci involved in adaptive divergence among natural populations. Here, we examine the capacity of those RADseq-based genome scan studies to detect loci involved in local adaptation. To understand what proportion of the genome is missed by RADseq studies, we developed a simple model using different numbers of RAD-tags, genome sizes, and extents of linkage disequilibrium (length of haplotype blocks). We then surveyed recent studies that have used RADseq for genome scans and found that that the median density of RADseq markers across these studies was one marker per 3.96 megabases. Given that the length of linkage disequilibrium is often orders of magnitude less than a megabase, we conclude that genome scans based on RADseq data alone are unlikely to advance our understanding of molecular ecology or evolutionary genetics for most systems. This article is protected by copyright. All rights reserved.