Sex-Linked Diapause, Color, and Allozyme Loci in Papilio glaucus: Linkage Analysis and Significance in a Hybrid Zone

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Abstract
Two subspecies of the tiger swallowtail butterfly, Papilio glaucus (Lepidoptera: Papili–onidae), hybridize along a narrow latitudinal band in eastern North America. Several traits that distinguish P. g. glaucus and P. g. canadensis are sex-linked, including control of pupal diapause; female color polymorphism; and two enzyme loci, lactate dehydrogenase (Ldh) and phosphogluconate dehydrogenase (Pgd). We tested progeny from known hybrid males backcrossed to melanic, nondiapausing P. g. glaucus females. Pgd is closely linked to another sex-linked enzyme locus, acid phosphatase {Acp), and loosely linked to Ldh. Melanic color in P. g. glaucus females is inherited maternally (Y–[W] linkage) but is suppressed by hybridization with P. g. canadensis. Suppression of melanism in glaucus x canadensis hybrids is due to an X– (Z) linked locus (s) that is closely linked to Pgd and to a locus (od) responsible for obligate diapause in P. g. canadensis. The most probable order is od–Pgd–s. Interactions among sex-linked loci may control the shape and dynamics of the hybrid zone.