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

Homologous genes for alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) are expressed in qualitatively different patterns during the development of two closely related species of Hawaiian Drosophila. In interspecific hybrids, each parental structural allele is expressed according to the developmental program characteristic of the species from which it is derived. This provides strong evidence for a cis-acting control element.The genome of higher eukaryotes appears to contain substantial amounts of programmatic information concerned with regulating the time, place, and quantity of production of various gene products. Although relatively little is known about the organization and function of such regulatory information, there is a significant body of evidence that suggests the existence of a class of regulatory elements with the following set of properties. (i) Allelic variants at these loci alter the developmental programs of specific proteins without apparently altering the structure. (ii) The regulatory site is in close proximity to the structural gene it affects. (iii) In heterozygotes, variants are expressed additively and, where tested, each allele acts only on the structural gene in the cis position (i.e., the structural gene on a given DNA strand is expressed according to the developmental program specified by the regulatory allele on the same strand regardless of the regulatory allele present on the homolog).Evidence for such regulatory sites has been obtained in studies of strain-specific quantitative differences in the spatiotemporal pattern of expression of enzymes and other proteins in maize, mice, and Drosophila. Examples include genes controlling: an esterase (1) and alcohol dehydrogenase (2) in maize; 3-glucuronidase (3, 4), 3-galactosidase (5), aryl-sulfatase (6), and H2 antigen (7) in mice; and aldehyde oxidase in Drosophila (8, 9). Somewhat similar results have been obtained with variants that alter the overall level of activity of xanthine dehydrogenase (10,11) and alcohol dehydrogenase (12) in Drosophila. These variants map close to their respective structural genes, alter number rather than structure of enzyme molecules, and act only on the cis structural gene. Paigen (13) has used the term "temporal gene" (t gene) for such regulatory elements.He has recently summarized work on several of the systems that illustrate this characteristic set of properties (14,15 members of the grimshawi subgroup of Hawaiian picturewinged Drosophila. The former is found on all major islands except Hawaii. Stocks derived from individual females collected at Apee (S30G10) and Hanalilolilo (U81Y1), Molokai, and at Auwahi, Maui (Gl), were used in the present study. D. orthofascia is found on Lanai, Maui, and Hawaii. Three stocks from Auwahi, Maui (U58G1, U58G6, and U58B3), and one from Volcano, Hawaii (U55G11), were used. The polytene chromosome sequences of the two species are known in detail and are exceedingly similar (17,18). Genomic comparisons show that they differ by only a single fixed i...

A revolution is brewing in contemporary systematics, especially at or near the level of species differences (1). Data on genetic variability within and between closely related populations can be used to establish highly sensitive indices of genetic similarity (2). A review of the biochemical variation within and between the members of the Drosophila willistoni group of species has recently appeared. A direct relationship between indices of genetic similarity and certain systematic designations was proposed (3). If identity is taken as 1.0, local geographic populations of a species were shown to have mean genetic similarities of 0.97, subspecies and semispecies about 0.8, sibling species 0.52, and nonsibling species 0.35. The present paper reports genetic similarities within and between a pair of partially sympatric, very closely related species endemic to the Island of Hawaii. We introduce the use of indices based on chromosomal variability and compare them with indices based on allozymes. Biochemical similarity both within and between the species is high, although they are strongly differentiated morphologically and chromosomally. These species evidently are very new in the historical biological sense. We propose that their biochemical similarities are directly correlated with this circumstance.

Genetic studies of two closely related endemic Hawaiian species show that in one area of sympatry about 2 percent of the naturally occurring individuals are hybrids. More than 20 times this many would be expected if the population consisted of a single panmictic unit. Despite hybridization, natural selection appears to maintain the essential integrity of each separate gene pool.

No abstract