Map of sampling sites, population structure, and genetic diversity (observed heterozygosity). Larval sea lamprey were collected from Lake Michigan, Lake Champlain, and the Connecticut River, where the numbers reflect the number of muscle and liver samples of larval sea lamprey that were sequenced and used in this study (a). Larval sea lamprey collected from the three locations cluster clearly into three distinct groups (b). Mean observed heterozygosity across the genome is indicated by dashed lines and observed heterozygosity of chromosomes is indicated by points. Genetic diversity is the highest in Connecticut River, followed by Lake Michigan and Lake Champlain (c). Sea lamprey have 99 chromosomes, among which the first 90 are assembled. The map in (a) is modified with permission from Yin et al.