Adaptive significance of amylase polymorphism in Drosophila I. The geographical pattern of allozyme polymorphism at the amylase locus in Drosophila subobscura

Allelic variation at the Amy locus was studied in eight natural populations from the central and northern range of D. subobscura, and the geographical pattern of Amy polymorphism over the range of this species was described. Even though regional and local differences in gene frequencies were found, in general the same alleles occur at high, intermediate and low frequencies, in nearly all populations. There are no significant differences in allele frequencies, but there is significant difference in the degree of heterozygosity among groups of populations from the northern, central and southern range. An analysis of population subdivision indicates that heterogeneity within populations is higher than between populations. Genetic distance values indicate that there is a variable degree of geographical differentiation between local populations. Variability within and between continental and insular populations is also discussed.     

Adaptive significance of amylase polymorphism in Drosophila

Laboratory populations of D. busckii flies were kept for one generation on media containing different carbohydrate sources (maltose and rice, potato or maize starch). The flies maintained on standard potato medium served as a control. Progeny were analyzed for -amylase activity and Amy-electromorph frequencies.Spectrophotometrically assayed amylase activity was highest in the flies cultured on potato starch medium and lowest in specimens kept on maltose. Carbohydrate source in some substrates affected both frequencies of Amy-alleles and Amy-genotypes. Phenotypic differences at a biochemical level, i.e. in -amylase activity, might be connected to Amy-structural gene polymorphism in the examined Drosophila species.     

Adaptive significance of amylase polymorphism in Drosophila: XIV. Effect of substrates with different carbohydrate composition on some life-history traits of Drosophila subobscura

The Amy-locus polymorphism of Drosophila subobscura is used as a model-system for an experimental population genetic study of adaptive significance of alpha-amylase activity on substrates of different carbohydrate compositions. So far, fitness components have not commonly been included in ecological-genetic studies of alpha-amylase polymorphism in this species. In the present paper fitness components are analyzed in relation to different amylase activities in D. subobscura individuals homozygous for "slow" and "fast" Amy allele, associated with substrates of different carbohydrate compositions. The results indicate a significant effect of substrate carbohydrate composition on fitness components of the genotypes homozygous for S or F Amy allele in D. subobscura through their enzyme activity.     

Adaptive significance of amylase polymorphism in Drosophila . XII. density‐ and frequency‐dependent selection at the Amy locus in Drosophila subobscura reared on media with different carbohydrate composition

Egg‐to‐adult viability is studied in the progeny of the flies of different genotypes according to S and F alleles of Amy locus of Drsophila subobscura . This component of fitness is observed in the single and mixed cultures with various frequencies of three genotypes (S/S, F/F and S/F) under conditions of low (LD) and high densities (HD) on three types of media with different carbohydrate composition. In such multifactorial experimental conditions, density‐ and frequency‐dependent selection on certain Amy genotypes was observed. Genotype frequencies and carbohydrate composition have significant effect on the viability of Amy genotypes. The significant intergenotypic differences exist, mostly at HD conditions. The heterozygous genotype S/F has generally lower viability which decreases with its increased frequencies, on all media at LD or HD. The results suggest a high level of complexity and interaction between these two types of balanced selection.     

Patterns of puffing activity and chromosomal polymorphism in Drosophila subobscura

Summary The effect of inbreeding on the puffing patterns of polytene chromosomes of Drosophila subobscura was analysed. Puffing activity was studied in two strains of D. subobscura: one which had been subject to inbreeding for 288 generations, and in the hybrids from a cross between them. A strong overall decrease in puffing activity was found in the inbred line. In general, hybrids behaved in a similar way to the inbred line or showed activity intermediate between the two lines. The fertility and viability of the two homozygous lines and of the hybrids were also determined. These parameters of fitness are very low in the inbred line. Hybrids displayed intermediate behaviour.Publication No. 109, Departamento de Genética, Universidad de Valencia, Spain     

Patterns of puffing activity and chromosomal polymorphism in Drosophila subobscura

The puffing patterns in polytene E chromosomes of Drosophila subobscura were followed in third-instar larvae and throughout the prepupa period. Two gene arrangements, E_st and E_1·2+9–12 were studied. A majority of puffs exhibit a similar pattern, but the puffs 61AC and 67AB behave differently in the two chromosomal arrangements, both in homozygotes and in heterozygotes. These two puffs are located at the end of the E₁₂ inversion. This position effect is an interesting phenomenon that probably is not due to a heterochromatinization effect.     

The effect of lead on fitness components and developmental stability in Drosophila subobscura

We analyzed the developmental time, egg-to-adult viability, and developmental stability (fluctuating wing size asymmetry) in Drosophila subobscura, maintained for six generations on different concentrations of lead. Development time is significantly affected by generation and lead concentration, but interaction of these factors is not a significant source of variability for this fitness component. Generation and the interaction generation x concentration of lead significantly affect egg-to-adult viability. Levene's test of heterogeneity of variance showed that variability of FA is not significant in any of the samples. Within both lead concentrations females showed significantly higher FA indices for the wing width than males. Within sexes, a significantly higher FA was found only in females for wing width FA between the control and the lower concentration of lead. The results show that if strong relationship between FA and the studied fitness components exists, it results in a stronger selection of unstable genotypes under lead as a stress factor and, consequently, FA needs to be used with caution as a biomarker in natural populations under environmental stress.     

The effect of different concentrations of lead on inversion polymorphism in Drosophila subobscura

Drosophila subobscura is a wild Drosophila species that is spread over almost all of Europe. It possesses an uniquely rich inversion polymorphism on all five long chromosomes. This polymorphism is to a certain degree associated with the variation and dynamics of ecological factors in space and time. We analyzed the changes of inversion polymorphism components of Drosophila subobscura flies maintained on media with different concentrations of lead in laboratory conditions. The effects of lead on inversion polymorphism were observed by cytological analysis of gene arrangements on all of the five acrocentric chromosomes, as well as by cytological analysis of karyotypes on all of the four autosomes. The frequencies of particular gene arrangements on the four autosomes changed significantly in the samples maintained on medium not supplemented with lead. The frequencies of some gene arrangements on all of the five acrocentric chromosomes changed significantly in the flies maintained on media supplemented with lead. The length of exposure to different lead concentrations results in a significant change in the frequency of a few gene arrangements on two autosomes. However, the results show that different concentrations of lead, as well as the length of exposure, do not affect major parameters of inversion polymorphism. The results suggest that some gene arrangements could be linked with adaptive processes in evolving heavy metal resistance.     

Patterns of puffing activity and chromosomal polymorphism in Drosophila subobscura I. J. and U chromosomes

A study of the puffing patterns of the J_st, J₁, U_1–2, U_1–2–8 and U_st chromosomal arrangements of Drosophila subobscura, from different geographical origins, has been carried out. Twenty-eight puffs were observed, 10 on the J chromosome, and 18 on the U chromosome. No differences, whether qualitative or quantitative, have been found between the puffing pattern of the J chromosome, whether from the same of different geographical background. In the U chromosome, the U_1–2 and U₁₊₂₊₈ arrangements show the same puffing pattern, and neither quantitative nor qualitative differences were found. However, the puffing pattern of these chromosomes alters considerably in the U_st arrangement of the K228 laboratory strain.     

The functional significance of amylase polymorphism in Drosophila melanogaster VI. Duration of development and amylase activity in larvae when starch is a limiting factor

Two stocks homozygous for the amylase alleles Amy ¹ and Amy ^{4, 6} were compared for amylase activity during larval development and duration of larval development on a food medium on which addition of starch promotes survival. The two stocks have the same development time when reared under optimal food conditions. Then, the higher amylase activity which characterizes the Amy ^{4, 6} stock appears far into the third instar. On the food used in the present experiments in which starch is a limiting factor for survival, the activity difference appears already in the 2nd instar. Moreover, Amy ^{4, 6} has a duration of larval development which is almost one day shorter than the Amy ¹ stock. This would result in a large selective advantage for the Amy ^{4, 6} stock when brought in competition on this food with the Amy ¹ stock.These rrsults support the explanation given for the results of earlier competition experiments between the Amy ¹ and the Amy ^{4, 6} stock, that the relative fitness of the stock with the high amylase activity improves when starch is added to a food medium in which it is a limiting factor for survival because the Amy ^{4, 6} stock by virtue of its higher amalyse activity utilizes starch better than its competitor.     

Adaptive significance of amylase polymorphism in Drosophila XIII. Old World obscura species subgroup divergence according to biochemical properties of alpha-amylase

Biochemical properties of enzyme alpha-amylase were surveyed in Drosophila obscura Old world group of species (D. subobscura, D. ambigua, D. obscura and D. tristis) sampled in the same habitat, with the aim to reveal some ecological and evolutionary aspects of amylase polymorphism, which has been studied extensively in D. subobscura, but not compared with other species in the group. The data obtained show that D. subobscura is distinct from the other three species regarding all biochemical amylase properties. Such a divergence also correlates with the niche breadth and relative abundance of these species in the same habitat.     

Patterns of puffing activity and chromosomal polymorphism in Drosophila subobscura II. Puffing patterns at the prepupa stage

Puffing activity patterns of the five large polytene chromosomes of Drosophila subobscura were studied during the late third-larval instar and through the prepupal period. A total of 166 loci active in some of the eleven stages studied were described. The distribution of these active loci per chromosome is the following: 25 on chromosome A, 33 on chromosome J, 31 on chromosome U, 34 on chromosome E and 43 on chromosome O. Seven principal patterns of puffing activity were defined taking into account the different curves of the puffing histograms. Gene activities per chromosome as well as total were analysed. Three peaks of gene activity at the beginning, middle and ending of prepupation can be observed. U is the most active chromosome and A (the sex chromosome), and J the least active. Chromosomes E and O show a medium activity. A possible biological explanation for these results is discussed.Publication No. 107, Departamento de Genética, Universidad de Valencia (Spain).     

Inversion polymorphism in two Serbian natural populations of Drosophila subobscura: Analysis of long-term changes

To study whether inversions (or arrangements) by themselves or karyotypes are the main global warming adaptive target of natural selection, two Drosophila subobscura Serbian populations (Apatin and Petnica) were re-analyzed using different statistical approaches. Both populations were sampled in an approximately 15 years period: Apatin in 1994 and 2008 + 2009 and Petnica in 1995 and 2010. For all chromosomes, the four colleptions studied were in Hardy-Weinberg equilibrium. Thus, it seems that inversions (or arrangements) combined at random to constitute populations’ karyotypes. However, there were differences in karyotypic frequencies along the years, although they were significant only for Apatin population. It is possible to conclude that inversions (or arrangements) are likely the target of natural selection, because they presented long-term changes, but combine at random to generate the corresponding karyotypic combinations. As a consequence, the frequencies of karyotypes also change along time.     

The genetics of Drosophila subobscura populations. 3. Inversion polymorphism and climatic factors

Summary 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.