GENETIC-VARIATION IN CRICKET CALLING SONG ACROSS A HYBRID ZONE BETWEEN 2 SIBLING SPECIES

The sibling ground crickets Allonemobius fasciatus and A. socius meet along a mosaic hybrid zone at approximate to 40 degrees N latitude in eastern North America. In this paper we report the findings of a genet ic analysis of calling-song variation within and among six cricket pop ulations sampled along a transect through the hybrid zone in southern New Jersey. We compared aspects of the calling song of both wild-caugh t and laboratory-reared crickets to test the hypothesis that populatio n differences in song observed in the wild were genetically based. We found significant, species-level differences in all aspects of the cal ling song, and these differences persisted even after a generation of common-garden rearing in the laboratory, supporting the hypothesis tha t interspecific variation observed in the wild largely reflects geneti c differentiation between the two taxa. A discriminant function analys is indicated that individual crickets could be assigned to the proper taxon with less than 10% error, supporting the premise that calling so ng could be used by female crickets as a mechanism for species recogni tion. One population, collected from within the hybrid zone and contai ning significant numbers of hybrid individuals, was intermediate in it s calling song, presumably reflecting this population's mixed genetic makeup. In this hybrid zone population, song phenotype was highly corr elated to a hybrid index score generated using species-specific allele s at four diagnostic allozyme markers, suggesting a multigenic basis t o calling-song variation in these crickets as well as linkage disequil ibrium between markers and song. Based on an analysis of laboratory-re ared full-sib families, broad-sense heritabilities for calling-song ch aracteristics were generally significant in the two A. socius populati ons, whereas many components of song showed no significant family effe cts in the three A. fasciatus populations. The genotypically mixed, hy brid zone population showed very high heritabilities for most calling- song components, which likely reflect the influence of interspecific g ene flow on genetic variation for quantitative traits.