Sampling of secondary contacts in the ring species Ensatina eschscholtzii. The distribution of Ensatina in California is colored according to the assignment of individuals collected throughout its entire range and genotyped for 22 to 27 allozyme loci (see  for details). The seven main colors (inset) correspond to the distinct color patterns, taxonomically recognized as subspecies. Different shades of those main colors refer to the genetically distinct units identified within each subspecies (outset), and were drawn considering the geographic coordinates of sampling. Localities with genetically admixed individuals or sympatry of pure forms are represented by overlapping ranges of the pure parental populations. Black dots mark the 20 parental populations, black lines mark the 13 pairwise comparisons considered in this study, and white circles mark the localities used to estimate degrees of genetic admixture at each contact zone.