Paleoclimatic influences in the evolution of periodical cicadas (Insecta: Homoptera: Cicadidae: Magicicada spp.)

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Presents a paleoclimatic model of Magicicada evolution that predicts increased probabilities of survival for broods having longer cycle lengths and periodical emergences. This model assumes a hypothetical probability that summer maximum temperatures in deciduous forest refuges duing Pleistocene glacial stades failed to sustain threshold temperatures required for cicada flight and copulation. If hybridization of individuals of differing cycle lengths produced adverse effects on the timing accuracy of the cycle lengths of the offspring, then less frequently hybridizing prime-valued cycle lengths would have been characterized by more precise periodicity and higher population densities. if 13yr and 17yr life cycle forms are the only prime-valued forms in a sequence of life cycle lengths, the sequence will ultimately be reduced to only these life cycle lengths. Hybridization of 13yr and 17yr broods can produce new broods temporally removed from the parental brood by 4yr. Environmentally triggered 4yr accelerations and decelerations of sympatric, temporally offset broods may have developed due to the selective advantage of high population densities during emergences of conspecifics. -from Authors

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American Midland Naturalist

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