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| Papilio solstitius DeRoller, Wang, Dupuis & Schmidt, 2025 |
Abstract
In the eastern Great Lakes region of North America, two tiger swallowtail species have previously been recognized, Papilio glaucus Linnaeus, 1758 and Papilio canadensis Rothschild & Jordan, 1906. A third entity, the Midsummer Tiger Swallowtail, has been treated as a P. glaucus × canadensis hybrid, and exhibits a mosaic of both intermediate and unique morphological and biological traits. Here we demonstrate that rather than being a localized, historically recent hybrid phenomenon, the Midsummer Tiger Swallowtail maintains its morphological and physiological distinctness over a large geographic region in the absence of one or both putative parental species, and was first documented in the literature nearly 150 years ago. Papilio solstitius sp. nov. is physiologically unique in delaying post-diapause development, which results in allochronic isolation between the spring flights of P. glaucus and P. canadensis, and the late summer flight of P. glaucus. Similarly, the geographic range of Papilio solstitius spans the region between the northern terminus of P. glaucus and southern limits of P. canadensis, remaining distinct in areas of sympatry. Defining the taxonomic identity of this unique evolutionary lineage provides an important baseline for further inquiry into what has served as an exemplary species group in evolutionary study.
Key words: cryptic species, hybrid, Papilio glaucus, Papilionidae, Pterourus, speciation
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| Papilio solstitius a dorsum of male, holotype, ventrum on right. Long Swamp, Old Almonte Rd., Ottawa, Ontario, CAN. CNC voucher # CNCLEP00342771 b dorsum of female allotype, ventrum on right. Vanalstine Lake, Frontenac Co., Ontario, CAN; ovipositing on Prunus serotina. Scale bar:10 mm. |
Papilio solstitius sp. nov.
Etymology: The epithet solstitius is derived from solstitium, the Latin term for solstice. The species’ unique midsummer flight period commences near the summer solstice.
Differential diagnosis. Papilio solstitius is closely related to P. glaucus, P. canadensis and P. appalachiensis, but differs from all in a suite of characters (Table 1). The most significant differences are apparent in developmental biology and phenology. Papilio solstitius is unique in its long post-diapause emergence delay, with adult eclosion beginning in late June to early July, compared to May for all other species (Fig. 2). Unlike the facultatively multivoltine P. glaucus, P. solstitius is obligately univoltine (like P. canadensis and P. appalachiensis). In the northern part of its range, P. solstitius overlaps with P. canadensis, and in the south with P. glaucus; it is not known to overlap with P. appalachiensis (Fig. 1). Identification difficulties are therefore largely limited to confusion with either P. canadensis or P. glaucus. In combination with location and date, the comparative morphological characters summarized in Table 1 and discussed in the “Comparative Morphology” section below will serve to identify most specimens.
Charles J. DeRoller, Xi Wang, Julian R. Dupuis, B. Christian Schmidt. 2025. A cryptic New Species of Tiger Swallowtail (Lepidoptera, Papilionidae) from eastern North America. ZooKeys. 1228: 69-97. DOI: doi.org/10.3897/zookeys.1228.142202
