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The phylogenetic relationships among nine species of Drosophila belonging to the obscura group were investigated by establishing (according to their banding similarities) the homologous chromosome segments of element E (equivalent to chromosome O of D. subobscura). The phylogenetic relationships were based on the existence of segments in different triads of species, which could only be produced by overlapping inversions. This permitted the ordering of the species belonging to each triad. Drosophila obscura, D. ambigua and D. tristis were found to be very closely related and thus forming a cluster in which D. ambigua occupies an intermediate position between the other two species. Drosophila obscura seems to be the species more directly linked to three other separate lineages, that of D. subsilvestris, the two African species (D. microlabis and D. kitumensis), and the subobscura cluster. The species from this last cluster may be ordered as follows: D. subobscura-D. madeirensis-D. guanche. It is not clear which species of this triad is the direct link to D. obscura. These results completely agree with those produced in an independent study, where element B was considered for the same nine species. Furthermore, the present study clarifies some ambiguities concerning the phylogenetic relationships which remained obscure due to the conservative nature of chromosome B.

The prevalence of Haldane's rule and the large effect of the X chromosome are examined by analysing the genetics of seven abnormal characters in interspecies hybrids between D. subobscura and D. madeirensis. In two cases Haldane's rule is not obeyed (viability and abnormality of the head). In all characters except the abnormal abdominal tergites, an important effect of the X chromosome is observed. There is an asymmetry in the importance of the effect of the X chromosome. The X of D. madeirensis origin induces abnormality mostly in a mixed background. The Y chromosome plays an important role in determining male sterility.

Homologies of the sections of the polytene chromosomes of element C, among several species of the obscura group of the genus Drosophila, were established according to the similarity of their banding patterns. The information gathered was used to construct an unrooted phylogenetic tree based on qualitative criteria. This tree is compared to three other similar trees derived from independent information provided by the study of chromosomal elements B, D and E. The general congruence of the patterns of these trees proves the well-foundedness of this approach. A single exception to this congruence is discussed. Finally a consensus tree, encapsulating information from all chromosomal elements, is presented and its topology is compared to those derived from electrophoretic data.

The phylogenetic relationships among nine species belonging to the obscura group of the genus Drosophila were deduced, based on similarities of the banding pattern of their polytene chromosomal element D. These similarities were inferred by the comparison of chromosomal photomaps. The phylogenetic reconstruction was the most parsimonious based on seriation by overlapping inversions and on the principle of conservation/disassociation of nearby located segments. The gene sequences of element D for all species studied were relatively easy to recognize in terms of the map of D. obscura, already found to occupy a relative central position in this group. Thus, three clusters of closely related species could be identified: obscura (D. obscura, D. ambigua, and D. tristis), African (D. kitumensis and D. microlabis), and subobscura (D. subobscura, D. madeirensis and D. guanche), with D. subsilvestris standing apart. The results are in agreement with those from the previously studied elements B and E, but element D was found to be much more conclusive concerning the links among the different clusters. Thus, it is inferred that D. guanche occupies an intermediate position between the other two species of its own cluster and all the others. The gene arrangement of D. obscura, directly related to those of the other species, has been identified. In the phylogenetic tree proposed, both the African cluster and D. subsilvestris derive from a hypothetical gene arrangement, intermediate in the pathway between the subobscura and obscura clusters.Key words: Drosophila obscura group, phylogeny, chromosomal inversions, element D, chromosomal gene arrangements.

Submitted by António Freitas (amsf@uma.pt) on 2020-12-30T13:25:54Z No. of bitstreams: 1 Evolution of the obscura group Drosophila species III. Phylogenetic relationships in the subobscura cluster based on homologies of chromosome ABrehm.pdf: 2785289 bytes, checksum: e23f67c8604baf118ad10a0a9dd0c329 (MD5) Made available in DSpace on 2020-12-30T13:25:54Z (GMT). No. of bitstreams: 1 Evolution of the obscura group Drosophila species III. Phylogenetic relationships in the subobscura cluster based on homologies of chromosome ABrehm.pdf: 2785289 bytes, checksum: e23f67c8604baf118ad10a0a9dd0c329 (MD5) Previous issue date: 1990 info:eu-repo/semantics/publishedVersion

The genetics of hybrid male sterility between Drosophila subobscura and D. madeirensis were studied with the help of 20 markers in backcross males. A major effect resides in the sex chromosomes: backcross males with the X and Y of different origin (mad X-sub Y or sub X-mad Y) have very small and empty testes. In compatible combinations testes are of normal size but males may be sterile or fertile depending on the genetic constitution of their autosomes. Six autosomal factors affecting hybrid male fertility could be postulated. This estimation is based on the assumption of the absence of interaction between viability and fertility. The presence and the mode of such interaction may modify the number of sterility factors.

Submitted by António Freitas (amsf@uma.pt) on 2021-10-11T10:46:08Z No. of bitstreams: 1 Studies of the species barrier between Drosophila madeirensis and Drosphila subobscura. II. Genetic analysis of dvelopmental incompatibilities in hybrids.pdf: 515438 bytes, checksum: dc193a77f40b77aada0fa50ac66f390c (MD5) Made available in DSpace on 2021-10-11T10:46:08Z (GMT). No. of bitstreams: 1 Studies of the species barrier between Drosophila madeirensis and Drosphila subobscura. II. Genetic analysis of dvelopmental incompatibilities in hybrids.pdf: 515438 bytes, checksum: dc193a77f40b77aada0fa50ac66f390c (MD5) Previous issue date: 2008 info:eu-repo/semantics/publishedVersion

New African species in the Drosophila obscura species group: genetic variation, differentiation and evolution

Evolution of the obscura group drosophila species. II. Phylogeny of ten species based on electrophoretic data

An estimate is presented of the effective size of a natural, Greek population of Drosophila subobscura, based on data on lethal allelism. It is compared with further estimates for the same population obtained from newly-reported data by the “temporal” and the “ecological” methods. The lethal allelism and ecological estimates both suggest that the population is extremely large and effectively infinite. The conclusions from the temporal method conform to this, with the exception of data from two loci: Est-5 and Aph. Directional selection at these loci is therefore suggested. Each method is described and explained, and their validity discussed. The results are compared with the few previous estimates of effective population size.

The genetic polymorphism of a population of Pinus halepensis was studied using 12 electrophoretically detectable enzyme systems encoded by 7 monomorphic and 10 polymorphic loci. An estimation of population parameters revealed a relatively high average heterozygosity (H = 0.179). The total variation present in the population was partitioned into a high amount of genetic variation within groups, with only 1.3-4.4% of the total variation resulting from genic differences among groups.

Using a genetically-marked, translocation stock that balances second and third chromosomes simultaneously, 95 "genome" lethals were recovered in 119 tests of material from Bogota, Colombia (80% lethals). Eighty six of 89 tested resulted from lethals which could be located as follows: 18 were on the second alone, 31 on the third alone, and 37 were on both the second and the third. The remaining three genome lethals were caused by combinations of second and third chromosomes with individual deleterious effects too small to qualify as either lethal or semilethal. Of the lethals that were located on definite chromosomes, 55 were on the second and 68 were on the third; this does not differ significantly from a 1: I distribution. Consequently, the frequencies of lethal second and third chromosomes in the Colombia population appear to be similar at about 55 % each

Chromosomal inversion polymorphism is observed in natural populations of many species of Drosophila. Attempts have been made to correlate the amount of this polymorphism with the ecological characteristics of the populations in which it occurs. Dobzhansky and collaborators (da Cunha and Dobzhansky, 1954; da Cunha, Burla, and Dobzhansky, 1950) were able to find a good correspondence in D. willistoni between the mean number of inversion heterozygotes per individual and an index expressing the environmental diversification. Larvae of D. willistoni occur in several species of tropical fruits. At the margins of the geographical distribution of this species there is less polymorphism than at the center. The same pattern was found by Carson (1955, 1958) in D. robusta. The amount of polymorphism was in this case measured by an "index of free recombination" (IFR) (the mean percentage of euchromatin non-heterozygous for inversions). Here too the polymorphism was less at the margins (higher IFR) than at the center. Carson believes that the amount of recombination is an essential population variable, marginal populations being selected for structural (not necessarily genetic) homozygosity; this he has termed "homoselection," in contrast to the "heteroselection," which prevails at the center of the geographic distribution. In this paper we will deal with D. subobscura Coll., a Palaeartic species of the obscura group of the subgenus Sophophora. This species has a wide range, extending from northern Europe (Scotland, Sweden) to Portugal, Spain, Sicily, and Greece, and even to the Middle East (Lebanon and Israel). About 41 inversions were found distributed in the five acrocentric chromosomes of this species. Nearly every population examined showed polymorphism for these inversions. At first no relations between this inversion polymorphism and ecological characteristics of the species seemed to be present (StummZollinger, 1952; Kunze-Miihl and Sperlich, 1958; Goldschmidt, 1956). Later attempts were made to correlate the IFR of natural populations with their place within the distribution range of the species. Israeli populations showed a higher IFR than the European ones, and it was believed that this is related to the marginal place of Israel in the range of the species (StummZollinger and Goldschmidt, 1959). Knight (1961) showed, moreover, that inversion polymorphism is less in Scottish populations and this fitted well with the idea that marginal populations are less polymorphic. The pattern of inversion polymorphism of this species remains poorly understood. The study of Greek populations was undertaken in 1960 (Krimbas, 1963, 1964), in the belief that Greece was a submarginal place in the distribution range of this species. The data showed, however, that as far as polymorphism is concerned, Greece should be considered central rather than marginal territory. At the same time Burla (pers. comm.) obtained samples of populations from North Africa and Iran, extending the known range of the species. This fitted extremely well with the study of the southern Greek populations. Meanwhile, it was realized that the estimation of polymorphism by IFR is not very helpful in finding a pattern. It appeared clearly that clines of inversion types tend to go from north to south in every one of the five chromosomes.

The inversion polymorphism in a population ofDrosophila subobscura from Holland is examined. The high frequency of the “Standard” gene arrangement in all five chromosomes, the high IFR value, and the low mean number of inversions show a low polymorphism expected in submarginal northern populations within the area of the geographic distribution of the species. The study of this population further confirms the existence of North-South clines for inversion types in every chromosome of this species.

The natural population of Drosophila subobscura of Mt. Parnes has been followed for two successive years and the frequency of the gene arrangements determined. Some changes occured in the first year but do not explain the existence of the geographical clines for these frequencies. Within the second year no changes were observed. For chromosomes J and U there is evidence for a greater fitness of the heterozygotes. Experiments on temperature effect on viability of adult male flies, on their temporal sterility, on the viability of flies during all their biological cycle and experiments on the effect of dryness on the viability of adult male flies did not show an important change of gene arrangement frequencies in the resistant individuals. Nor did diapausing females have very different gene arrangements, except for chromosome O. Cage experiments with temperature as a selective agent did not elucidate the action of this factor. It is concluded that temperature or dryness do not affect very much the polymorphic system, nor explain the existence of these clines. This polymorphic system is much more stable in D. subobscura than in D. pseudoobscura, its nearctic relative. It is also richer. It is concluded that it is historically older and helps the populations to cope with many environmental changes.

The mutational component of a genetic load consists of genetic variants and a balanced component. The genetic variants reduce the fitness of their homozygous, or of both homozygous and heterozygous carriers, in most environments. The balanced component of the load consists of heterotic genes and gene complexes, which yield highly fit heterozygotes but relatively less well adapted homozygotes. Balanced loads are maintained primarily by natural selection. The role of the genetic load was studied in populations of Drosophila pseudoobscura. Data are tabulated and discussed. (C.H.)

Two polymorphic genes controlling the synthesis of the main adult esterases in the olive fruit fly Dacus oleae (Gmel.) have been described. Gene A is responsible for the synthesis of an acetylcholinesterase and gene B for the synthesis of a pseudocholinesterase or lipase. Both genes are autosomal and unlinked (Zouros, Tsakas and Krimbas, 1968). Three faintly stained monomorphic esterase bands in adults are revealed by starch gel electrophoresis (Tsakas and Krimbas, unpublished). Genes A and B have the highest degree of polymorphism described to date. In a sample of five hundred individuals taken in 1966 from the natural population of Haghioi Apostoli, Attica, 14 active and one silent isoalleles have been found in gene A and 11 active plus one silent isoalleles in gene B. The frequencies of these isoalleles have been estimated (Zouros and Krimbas, 1969). Laboratory experiments revealed the selective action of an organophosphate ester, dimethoate, on these genetic polymorphisms. Organophosphate esters are insecticidal because they inhibit insect cholinesterases. Dimethoate kills preferentially flies homozygous or heterozygous for the silent isoallele of gene A, i.e., insects which have less acetylcholinesterase than those individuals endowed with two active gene copies. Thus, dimethoate selects for the quantity, not the quality, of active gene A isozymes. No selection has been observed on gene B polymorphism. Flies surviving dimethoate action are fertile (Tsakas and Krimbas, 1970).

Results are reviewed from previous studies on genetic loads in Drosophila. A series of studies was made on Drosophila pseudoobscura to determine whether individuals carrying different combinations of chromosomes are phenotypically uniform or heterogeneous, and if heterogeneous, whether or not the heterogeneity is correlated with the effects of the component chromosomes in homozygotes. The magnitude of the genetic loads carried in the second and third chromosomes of Drosophila pseudoobscura were estimated for samples from populations living near Austin, Tex., and Mather, Calif. The effects of the chromosomes on the viability of the homozygotes were found to differ in cultures raised at 25 and at l5 deg C. Data are tabulated. A negative correlation between viability and variability was observed for both homozygotes and heterozygotes. (C.H.)