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Paleoclimatic Influences in the Evolution of Periodical Cicadas (Insecta: Homoptera: Cicadidae: Magicicada spp.)
Randel Tom Cox and C. E. Carlton
The American Midland Naturalist
Vol. 120, No. 1 (Jul., 1988), pp. 183-193
Published by: The University of Notre Dame
Stable URL: http://www.jstor.org/stable/2425898
Page Count: 11
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We present 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 during 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 13-yr and 17-yr 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 13-yr and 17-yr broods can produce new broods temporally removed from the parental brood by 4 years. Environmentally triggered 4-yr accelerations and decelerations of sympatric, temporally offset broods may have developed due to the selective advantage of high population densities during emergences of conspecifics. This paleoclimatic model predicts the climatically zoned distribution of the two life cycle forms of Magicicada.
The American Midland Naturalist © 1988 The University of Notre Dame