Hybridization as a Causal Mechanism of Mixed Color Broods and Unusual Color Morphs of Female Offspring in the Eastern Tiger Swallowtail Butterflies, Papilio glaucus

Abstract

The eastern tiger swallowtail butterfly, Papilio glaucus L., is comprised of three putative subspecies (P. g. canadensis R & J, P. g. glaucus L. and P. g. australis Maynard) which have a total range of approximately one billion hectares across the eastern half of the U. S. and nearly all of Canada (Fig. 1). Based upon multivariate discriminant analyses of adult mor-phometric traits, diapause differences, differential foodplant detoxication abilities of larvae, and reproductive incompatibilities of the hybrids and backcrosses (i.e., fecundity, fertility and viability) we believe that P. g. canadensis may warrant species status (Scriber et al., unpublished, and Fig. 2). The zone of potential hybrid interaction between P. g. canadensis and P. g. glaucus is felt to be restricted to the zone between latitudes of 40 and 45° north (Scriber 1982, 1983, and Fig. 1). However, the actual degree of reproductive isolation that exists between tiger swallowtails in nature is unknown. One factor which some researchers suggest should have an influence upon mating preferences of tiger swallowtails is female color (Brower 1957, Brower 1959a and 1959b, Burns 1966, Makielski 1972, Pliske 1972, Levin 1973).