An Investigation into the Effects of Coldshock on the Eastern Tiger Swallowtail Butterfly Pterourus (Papilio) glaucus (C. Linnaeus 1758) (Lepidoptera: Papilionidae)
AbstractThis paper examines and documents the dramatic effects achieved through coldshock experiments performed on the North American Swallowtail butterfly Pterourus (Papilio) glaucus. For this study, duplicate consecutive experiments were conducted on two different lineages of P. glaucus, the first from extreme southern Illinois, U.S.A., and the second from northern Illinois, U.S.A. Both lineages were initiated from wild-collected normal looking dark morph female individuals that had mated prior to capture. The southern lineage was bred for five generations and yielded over 500 individuals. The northern lineage was bred for three generations and yielded more than 1500 individuals. This paper summarizes and compares the results from both experiments and details the technique used, the various types of aberrations identified, and offers some hypotheses as to the underlying causes of several of the resulting aberrant wing patterns. In the first series of experiments, it was demonstrated that the coldshock technique caused a wing-wide incremental reversion of the female dark morph into females resembling the ancestral yellow morph through a virtually uninterrupted cline of dusted looking intermediate morphs over the course of five generations. The second series of experiments resulted in coldshock-induced aberrations in the dark morph females encompassing a completely different range of variation than previously encountered in the first experiment, including a wider variation in the extent and positioning of the affected pigment colors, more pronounced zonal pigment aberrations, a long series of specimens in which wing-wide insufficient scale quantities resulted in semi-transparent wings, and specimens in which a disproportionate lightening of the ventral surface occurred, creating several distinctive reproducible patterns. Most of these aberrations did not occur in the first experiment. In addition to these severe aberrations produced in the females, several minor pattern aberrations were identified in both males and females that are presumed to be either caused by or enhanced by the coldshock. This is the first paper detailing coldshock in P. glaucus that discusses the results of multiple generations of inbred coldshocked individuals, and the first account of the heritability of coldshock-initiated aberrant patterns in a succeeding generation of inbred non-coldshocked P. glaucus individuals. Also discussed is the importance of the stripe and border pattern elements, their relative stability and resistance to alteration by coldshock, and the role they play in the formation of various coldshock aberrations. The coldshock-induced effects of Pattern Drift, Pattern Breakdown, Color Reversion, and Color Replacement are introduced and discussed as they relate to P. glaucus. Finally, a discussion and limited degree of speculative analysis is offered for each of the identified wing color and pattern aberrations.
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