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Allochronic Speciation in Field Crickets, and a New Species, Acheta veletis
Richard D. Alexander and Robert S. Bigelow
Vol. 14, No. 3 (Sep., 1960), pp. 334-346
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2405976
Page Count: 13
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Analysis of what has seemed to be a single species of field cricket, abundant and widely distributed in northeastern North America, shows that it is actually composed of two closely related species which are distinguished as follows: (1) they diapause only in the late nymphal instars and in the egg stage, respectively, (2) they are unable to produce viable eggs in controlled crossing experiments in the laboratory, and (3) most females from the same locality can be separated by ovipositor length. Breeding populations of these two species are seasonally isolated because of the difference in overwintering stage and the short adult life of four to eight weeks. Ecologically and geographically the two species have always been found together, with the exception that Acheta pennsylvanicus (Burmeister), the egg-over-winterer, occurs in Nova Scotia, while A. veletis, n. sp., the nymph-overwinterer, does not. All of the communicative sounds of the two species appear to be identical, indicating that there has been no interaction with respect to characters involved in sexual selection. It is suggested that these species have become isolated through a seasonal separation of breeding populations imposed by a duality in winter-hardiness originally due to the deposition of the eggs below the soil surface and the burrowing of late juveniles. This initial isolation is then believed to have been re-inforced by the appearance of genetically-based diapauses which not only increased winter-hardiness but also aided in synchronizing the appearance of the adults. The term "allochronic speciation" is applied because of the role of temporal isolation; it is suggested that various forms of cyclic isolation may have been important factors in initiating speciation among insects in temperate climates.
Evolution © 1960 Society for the Study of Evolution