GENETICS OF MIMICRY IN THE TIGER SWALLOWTAIL BUTTERFLIES, PAPILIO-GLAUCUS AND PAPILIO-CANADENSIS (LEPIDOPTERA, PAPILIONIDAE)

The tiger swallowtail butterfly, Papilio glaucus, exhibits a female-li mited polymorphism for Batesian mimicry; the Canadian tiger swallowtai l, Papilio canadensis, lacks the mimetic (dark) form entirely. The spe cies hybridize to a limited extent where their ranges overlap. Field c ollections and censuses indicate that mimetic females occur throughout the range of P. glaucus but at lowest frequencies in populations at t he latitudinal edges of its geographic range such as the southernmost part of Florida and along the entire northern edge of its distribution from Massachusetts to Minnesota. Frequencies of mimetic females have remained relatively stable over time. Inheritance of the mimetic form is controlled primarily by two interacting sex-linked loci. The typica l matrilineal pattern of inheritance in P. glaucus can be explained by polymorphism at a Y-linked locus, b. Analysis of P. glaucus X P. cana densis crosses has also revealed an X-linked locus, s, which controls the expression of the mimetic phenotype. The P. canadensis allele, s(c an), suppresses the mimetic phenotype in hybrid and backcross females. Results from more than 12 yr of rearing tiger swallowtails, including interspecies hybrids, indicate that the absence of mimetic P. canaden sis females is due to both a high frequency of the ''suppressing'' all ele s(can) and low frequency of the black-pigment-determining b+ allel e. The frequency of s(can) (or other suppressing alleles of s) in P. g laucus populations outside the hybrid zone is low. Some males heterozy gous at the s locus and some suppressed mimetic females occur within t he hybrid zone. A simple genetic model predicts the frequency of daugh ters that differ in phenotype from their mothers.