Intraspecific karyotypic differentiation in the Australian phasmatid Didymuria violescens (Leach). I. The chromosome races and their structural and evolutionary relationships.

The phasmatid species Didymuria violescens comprises ten distinct chromosome races parapatrically distributed such that adjacent races meet in narrow zones of overlap. The interracial karyotypic variation is remarkable and involves both diploid number differences (in the range 26-40) and differences in the sex-chromosome mechanism. Karyotypic comparisons and analyses of the meiotic pairing relationships in interracial hybirds have shown that the differences derive in large part from a series of centric fusion events and X-autosome fusions, which together contribute to the reduction in chromosome number within the species. The origin and development of the current racial pattern can best be interpreted in terms of the stasipatric hypothesis of White.