Scriber, J. M., K. Keefover, and S. Nelson. 2002. Hot summer temperatures may stop genetic introgression of Papilio canadensis south of the hybrid zone in the North Amercian Great Lakes region. Ecography 25:184-192.

Citable PDF link: https://lter.kbs.msu.edu/pub/2581

The reasons that the northern tiger swallowtail butterfly Papilio canadensis does not move south of the Great Lakes hybrid zone, where it meets P. glaucus, may be largely due to natural temperature-induced stress on diapausing pupae, Temperatures of 36° C for only four days killed all P. canadensis (from northern Michigan) and most of the Papilio troilus, a species that lives south of the hybrid zone (sympatrically with P. glaucus). In contrast, interspecific hybrids (P. glaucus mother x P. canadensis father) had significant adult eclosion or pupal survival at both 30° and 36° C. All surviving hybrid pupae were only females (the heterogametic sex, which are known to express the prolonged diapause due to Haldane effects). The southern species, P. troilus, had almost all (81%) normal (non-deformed) adults eclose at 30° C, whereas only 20% of the A canadensis females and ca 30% or the A canadensis males eclosed to produce non-deformed adults. Unlike the case with P. troilus and P. canadensis, no hybrid females eclosed at 30° C (only males did). Unlike P. troilus and P. canadensis pupae, hybrid (female) pupae remain viable, some of which have already successfully emerged after the chamber experiments. A follow-up study using P. glaucus, P. canadensis (from Vermont), and their hybrids with more normal lower thermal regimes included (27°, 30°, 33°, and 36° C) again showed higher hybrid survival as uneclosed (living) pupae at 36° C. In addition, A glaucus and P. canadensis showed high mortality and wing deformity of eclosing adults at 36° C, suggesting that geographic source of the P. canadensis may reflect differential tolerances of the extreme 36° C temperature.

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