Species formation is usually accompanied by chromosomal reorganization. Thus, even very closely related species frequently differ in chromosome number (polyploidy, aneuploidy, centric increase or decrease) or in gene sequence (inversions, centric shifts, translocations). The question arises whether such karyotypic changes are incidental or whether there is some causal relationship with the speciation process.In most organisms, chromosomal detail is not favorable enough to determine whether homologous chromosomes in two species differ by inverted segments. The giant polytene chromosomes of the Drosophila salivary glands, however, permit such comparisons. With a few exceptions,1 karyotypic reorganization has occurred. This is true even for morphologically cryptic (sibling) species of Drosophila from continental faunas.2 The present paper is a preliminary report of the results of interspecific comparisons of the chromosomes of 22 members of a highly isolated endemic drosophilid fauna existing on the oceanic islands of the Hawaiian archipelago. The fauna consists of over 400 species despite the smallness of the land area.3 Morphological divergence within the small group reported here is pronounced; nevertheless, extraordinary karyotypic stability prevails.Materials and Methods.-Drosophila specimens were collected on the six major Hawaiian islands from 1963-1966.4 On return to the laboratory each female was placed individually in a separate culture5 tube and challenged to produce F1 larvae. Using standard acetoorecein methods, salivary gland and metaphase chromosome preparations were made from these larvae;6 emerging F1 adults were used to verify the species.7 Table 1 presents the source of the material on which this report is based. Polytene examination was made of 200 strains (column 4); at least one but usually seven F1 larvae were examined from each isolated wild female (isofemale strain). Material for which polytene information is lacking is placed within parentheses in column 3. Smears of larval neuroblasts or adult testis smears (the latter are marked "ci " in Table 1) have been used for determination of metaphase chromosome configuration. The basic polytene chromosome sequences of Drosophila grimshawi were chosen as an arbitrary standard. Photomaps of the banding sequences of this species, as well as of D. adiastola and D. punalua were prepared by the method of Stalker.8 Band sequence comparisons were facilitated by the use of a drawing tube (Wild Heerbrugg Instruments, Inc.) wherein the image of a chromosome of unknown sequence is projected on a black table surface. A cut-out photograph of the homologous chromosomal standard is matched to this image at table level after being adjusted by zoom lens to the same magnification. Positions of chromosome inversions were recorded on photographic prints of standard photomaps which were cut at the observed break points with scissors. The segments were then inverted and refitted to prepare mockups in exact banding detail of the 1280
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