Estimation of genome size
The genome size of B. l. tsinlingensis was estimated using the K-mer method with all filtered Illumina genome reads. The K-mer number was set to 17; the genome size was estimated using the total number of 17-mers divided by the peak 17-mer frequency. Thus, the genome size was estimated using the formula: Genome size = total 17-mer number / peak frequency (Liu et al. 2013).