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Viability selection on overwintering eggs in a field cricket mosaic hybrid zone


  • Charles L. Ross,

  • Richard G. Harrison

C. L. Ross and R. G. Harrison, Dept of Ecology and Evolutionary Biology, Cornell Univ., Ithaca, NY 14853, USA. Present address for CLR: Dept of Biology, MSC-3AF, PO Box 30001, New Mexico State Univ., Las Cruces, NM 88003, USA (


Habitat segregation allows recently diverged taxa to minimize competition and maximize fitness. Consequently, the overall distribution of a species in part will be determined by interactions with their close relatives. Two recently diverged but hybridizing field crickets, Gryllus firmus and G. pennsylvanicus, form a mosaic hybrid zone in Connecticut in which each species is associated with a specific soil type: G. firmus is found on sand soils and G. pennsylvanicus is found on loam soils. Both species produce diapausing eggs, which spend the winter in the ground. We investigate how viability selection on overwintering eggs in different soils influences the distributions of the two species, habitat partitioning between them, and the structure of the mosaic hybrid zone. Our results suggest that selection on eggs by soil types is not important in determining the success of crickets on different soils. However, winter climate has a strong effect on egg viability, and variation in egg survivorship over different winter climate regimes likely plays an important role in determining the distribution of these cricket species and the position of the hybrid zone.

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