HYBRIDIZATION STUDIES ON BLATTELLA-GERMANICA AND B-ASAHINAI (DICTYOPTERA, BLATTELLIDAE) - SPECIES DIVERGENCE AND A POSSIBLE INFLUENCE OF A MAJOR CHROMOSOME MUTATION

An earlier study. indicated that.Blattella asahinai is separated from its close relative B. germanica by a nonreciprocal translocation that apparently involved the transfer of the nucleolus organizing region fr om the X chromosome of B. germanica or a B. germanica like ancestor to chromosome 12 in B. asahinai. Continued study on divergence of the tw o species included genetic analyses of fecundity, egg case hatch, nymp hal hatch, sex ratios, and segregation of X chromosomes and the segmen t carrying the B. asahinai nucleolar organizing region in interspecifi c and backcross matings. Overall, a complex of maternally related disa dvantages was associated with B. asahinai. The effects of cytoplasmic factors could not generally be distinguished from possible effects of X chromosome - cytoplasmic interactions. In two crossing systems, the data fit a hypothesis of lethal effects from the presence of an X chro mosome in alien cytoplasm. Cytologic differences occurred frequently i n backcrosses, especially with F1 hybrid females, but were limited to chromosomes and chromosome segments affected by the translocation. The possible relationship of the chromosome mutation to traits affecting reproduction and its role in species divergence are discussed.