design: We prepared double-digest RADseq libraries using a protocol adapted from Parchman et al. (2012) and Brelsford et al. (2016). We digested genomic DNA with restriction enzymes EcoRI and MseI (New England Biolabs) and ligated Illumina primer and adapter sequences to the cut sites with an individual 8-nucleotide barcode on the EcoRI side. We amplified the resulting library in four replicate PCR of 20 cycles. We then size-selected fragments of 300  400 bp on a 2.5% agarose gel. The final library was single-end sequenced (125 bp) on eight Illumina HiSeq 2500 lanes