Ecological genetics of the Adh-1 locus of Drosophila buzzatii

The Adh-1 polymorphism of Drosophila buzzatii was studied in terms of the effects of the larval substrate (laboratory food and Opuntia stricta tissue inoculated with live yeast species) on larval survival, development time and subsequent adult size, using the three common Adh-1 genotypes. Studies with laboratory food yielded mixed results, but in general the Adh-1^b/Adh-1^b genotype was superior to Adh-1^c/Adh-1^c with the heterozygote intermediate. Studies with the natural substrate (Opuntia stricta tissue) using mono- and bicultures of four associated yeast species also showed that the Adh-1^b/Adh-1^b genotype develops faster and survives better than Adh-1^c/Adh-1^c. There were no genotype-by-yeast interactions which might explain the maintenance of the polymorphism. Drosophila buzzatii larvae develop faster and attain larger adult sizes when raised on bicultures of yeasts as compared with the corresponding monocultures.     

The evolutionary history of Drosophila buzzatii

Introgression of a chromosome segment from Drosophila serido into the genome of its sibling D. buzzatii brought about the release of mutator potential in the hybrids. Mutator activity was determined by examining the frequency of new chromosomal rearrangements, that appeared only in the progeny of hybrid individuals. Mutation frequency was 30 times greater in the progeny of hybrid males than in that of hybrid females. There was a remarkable influence of the D. buzzatii genetic background on the frequency of production of these new rearrangements. The appearance of a new rearrangement did not depend on the genotype of the larva that bore it, but only on that of its hybrid progenitor. Among the new rearrangements there were inversions, translocations, and duplications. The number of translocations was significantly lower than that of inversions or duplications; this last type was the most frequently recorded. The distribution of the aberrations among the four major autosomes seemed to be homogeneous, although the total number of breakpoints was significantly greater in chromosome 4 than in the others. No rearrangement was found on the X chromosome. Breakpoints within three of the four affected autosomes were not randomly distributed.     

The evolutionary history of Drosophila buzzatii XXVII

The correlation between body size and longevity was tested in an Argentinian natural population of Drosophila buzzatii. Mean thorax length of flies newly emerging from rotting cladodes of Opuntia vulgaris was significantly smaller than that of two samples of flies caught at baits. The present results which might be interpreted as directional selection for longevity favoring larger flies are in agreement with previous results achieved in a Spanish natural population of D. buzzatii. Flies emerging from different substrates showed significant differences in thorax length, suggesting that an important fraction of phenotypic variance can be attributed to environmental variability. However, laboratory and field work in different populations of D. buzzatii showed a significant genetic component for thorax length variation.     

Transposition of the bobbed locus in Drosophila melanogaster

Due to the complete absence of ribosomal DNA (genetic symbol bb-), the Xbb- chromosome of Drosophila is lethal both in homozygous conditions and in compound with the Xbb- chromosome. However, in the cross between the C(1)RM/Ybb- females and the Xbb-/BSYbb+ males, characterized by the development of lethal Xbb-/Ybb- zygotes, two fertile males were detected. These males possessed all the markers of the Xbb- chromosome but lacked the Y chromosome BS marker. Genetic analysis of their progeny showed that genes responsible for restoration of viability and fertility of these exceptional males were associated with the X chromosome. The crossover tests showed that in one case these genes were tightly linked to the w locus (the bbAM1 allele), and in the second case they were located 12.6 map units to the right of the Tu locus (the bbAM7 allele). It has also been shown that the bb locus was transposed to the X chromosome within the short arm of Y chromosome. Transposition of the BSYbb+ chromosome-specific rDNA sequences to the X chromosome was confirmed by means of Southern blotting. These data indicate that replacement of the bb locus is realized by transposition rather than recombination.     

Geographical distributions,relative abundance and coexistence of Drosophila aldrichi and Drosophila buzzatii in Australia

Abstract Climatic data and collection records for the cactophilic Drosophila aldrichi and Drosophila buzzatii for 97 localities were used to examine the effects of geographical location, season, host plant species and climatic factors on their range and relative abundance. Temporal variation in relative abundance was assessed from monthly collections over 4 years at one locality. Effects of weather variables over the 28 days before each collection were examined. A generalized linear model of the spatial data showed significant geographical variation in relative abundance, and significant climatic effects, with the proportion of D. aldrichi higher in the warm season, and increasing as temperature variation decreased and moisture indices increased. The temporal data gave generally concordant results, as D. aldrichi proportion was higher in summer and autumn, and increased as maximum and minimum temperatures increased, and as variation in maximum temperature decreased. In a laboratory competition experiment, D. aldrichi eliminated D. buzzatii at 31°C, but was itself eliminated at 18°C and 25°C. The range of D. buzzatii is constrained only by availability of its host plant, Opuntia species, although its relative abundance is reduced in the northern part of its distribution. The range of D. aldrichi, from central Queensland to northern NSW, Australia, is entirely within that of D. buzzatii, and its relative abundance decreases from north to south. Both climate and weather, particularly temperature variability, have direct effects on the relative abundances of the two species, and both likely act indirectly by influencing the outcome of interspecific competition.     

Altitudinal patterns for longevity, fecundity and senescence in Drosophila buzzatii

We tested for variation in longevity, senescence rate and early fecundity of Drosophila buzzatii along an elevational transect in Argentina, using laboratory-reared flies in laboratory tests performed to avoid extrinsic mortality. At 25 °C, females from lowland populations lived longer and had a lower demographic rate of senescence than females from highland populations. Minimal instead of maximal temperature at the sites of origin of population best predicted this cline. A very different pattern was found at higher test temperature. At 29.5 °C, longevity of males increased with altitude of origin of population. No clinal trend was apparent for longevity of females at 29.5 °C. There was evidence for a trade-off between early fecundity and longevity at non-stressful temperature (25 °C) along the altitudinal gradient. This trait association is consistent with evolutionary theories of aging. Population-by-temperature and sex-by-temperature interactions indicate that senescence patterns are expressed in environment specific ways.     

Mutual regulation of magnified bobbed loci in Drosophila melanogaster

Summary rDNA magnification in D. melanogaster increases the redundancy of that locus to a value higher than the wild type. A magnified locus (bb ^m) can lose the express copies according to rDNA content of partner sexual chromosome. This paper is a study of behaviour of two bb ^m loci put together to show their interaction.     

Gene control of soluble protein levels during development of abnormal abdomen in Drosophila

The mutant genotype Abnormal abdomen (A^53g) of Drosophila melanogaster causes an increase in the amount of soluble protein per fly when compared to a wild-type strain (Ore-R). This increase is first detected at 50 hr after puparium formation and is preceded 2 hr earlier by an increase in total RNA. A direct correlation is found between the expressivity of the A^53g mutation in the adult fly and the total soluble protein per mg body weight of that fly. Quantitative analyses of supernatant protein from mutant and wild-type flies on polyacrylamide disk gel electrophoresis reveal that the increases observed in the mutant are due to increases in specific electrophoretic classes of proteins and not to a general stimulation of all proteins. Reciprocal crosses between mutant and wild-type flies indicate that the penetrance and expressivity of the A^53g phenotype is under maternal control and that an increased soluble protein content in F1 flies is found only when the mutant genotype is contributed to the F1 through the maternal gamete.     

The transmission of yeasts by Drosophila buzzatii during courtship and mating

The transmission of yeasts from generation to generation for Drosophila buzzatii was shown to occur vertically through the pupal stage and horizontally during mating. Males and females transmitted yeasts to the opposite sex most often during mating but also during courtship. Yeasts transferred from the male to the female were more often associated with the abdomens of the females, while yeasts transferred from the female to the male were associated with both the head and the abdomen of the male. Mate choice was affected by the previous yeast diet of both males and females. Yeast transmission during courtship and mating represents the potential for parental care because mate choice is affected by previous yeast diet, and progeny development is a function of the yeasts inoculated onto the larval substrate by the adults.     

Ribosomal DNA content and bobbed phenotype in Drosophila hydei.

The number of ribosomal RNA genes in different Drosophila hydei stocks has been determined by filter saturation hybridisation experiments. It has been shown that there is no marked correlation between the average rRNA gene number per cell in the whole animal and the bobbed phenotype when Y chromosomal nucleolar organisers are present.     

Comparative molecular population genetics of the Xdh locus in the cactophilic sibling species Drosophila buzzatii and D. koepferae

The Xdh (rosy) gene is one of the best studied in the Drosophila genus from an evolutionary viewpoint. Here we analyze nucleotide variation in a 1875-bp fragment of the second exon of Xdh in Argentinian populations of the cactophilic D. buzzatii and its sibling D. koepferae. The major electrophoretic alleles of D. buzzatii not only lack diagnostic amino acids in the region studied but also differ on average from each other by four to 13 amino acid changes. Our data also suggest that D. buzzatii populations belonging to different phytogeographic regions are not genetically differentiated, whereas D. koepferae exhibits a significant pattern of population structure. The Xdh region studied is twice as polymorphic in D. buzzatii as in D. koepferae. Differences in historical population size or in recombinational environment between species could account for the differences in the level of nucleotide variation. In both species, the Xdh region exhibits a great number of singletons, which significantly departs from the frequency spectrum expected under neutrality for nonsynonymous sites and also for synonymous sites in D. buzzatii. These excesses of singletons could be the signature of a recent population expansion in D. buzzatii, whereas they may be simply explained as the result of negative selection in D. koepferae.     

Genetics of wing size asymmetry in Drosophila buzzatii

Contemporary approaches that use fluctuating asymmetry (FA) as a possible target for natural and sexual selection are based on the premise that FA is a quantifiable expression of developmental instability (DI) that is inherited. Previous work with Drosophila buzzatii found that male mating success was correlated positively to body size (wing length) and negatively to FA, but these relationships seem to be environmentally induced. Heritability of FA was low and not significantly different from zero, but statistical power was also estimated to be very low and, hence, no conclusive evidence could be obtained. A large half‐sib mating design is used here to examine the relationships of different aspects of development for wing size. Consistently with previous findings, I found high heritabilities for wing length (WL) and wing width (WW), and positive correlations between both traits. Heritabilities of FA (FA_WL, FA_WW) were low (0.037) but significantly different from zero, and the genetic correlation between FA_WL and FA_WW was estimated as ?1 because the absolute value for the genetic covariance was similar in magnitude or even larger than the estimated genetic variances of both traits. This suggests that these two traits should be considered to be the same character. The between‐trait phenotypic correlation in FA, which reduces to the repeatability in this situation, was positive and statistically significant thus rendering an estimate of heritability for DI in D. buzzatii of . Nevertheless, the fact that left/right wing sizes were found to be determined by the same set of genes is difficult to reconcile with the presence of special genetic mechanisms that stabilize left/right development in this species. A qualitatively different pattern for asymmetry was observed when the nonlinear composite character wing area (WA ≈ WL × WW) was used, and . Although the results could be made compatible with the existence of a diallelic locus with antagonistic pleiotropic effects on FA_WL and FA_WW that combine multiplicatively to produce overdominance for FA_WA, the available evidence is extremely weak at best. Finally, a test to the null hypothesis of a nongenetic basis of FA, particularly relevant to those situations when directional asymmetry may be heritable, is suggested.     

Partial reversion at the bobbed locus of Drosophila melanogaster

In Drosophila melanogaster the tandemly arranged repetitive sequences coding for 18S and 28S rRNA are heterogenous at the level of the spacers between units and insertions that interrupt many 28S rRNA genes. This heterogeneity contrasts with the homogeneity of the regions transcribed into 18S and 28S rRNA. Homogenization and evolution of repetitive genes are usually explained by conversion, amplification events or unequal crossovers. In this paper we studied the change in rDNA patterns associated with partial reversion of bobbed mutations. In most cases, no increase in rDNA gene number, but a new repartition of gene types were found.     

Partial reversion at the bobbed locus of Drosophila melanogaster

In Drosophila melanogaster the tandemly arranged repetitive sequences coding for 18S and 28S rRNA are heterogenous at the level of the spacers between units and insertions that interrupt many 28S rRNA genes. This heterogeneity contrasts with the homogeneity of the regions transcribed into 18S and 28S rRNA. Homogenization and evolution of repetitive genes are usually explained by conversion, amplification events or unequal crossovers. In this paper we studied the change in rDNA patterns associated with partial reversion of bobbed mutations. In most cases, no increase in rDNA gene number, but a new repartition of gene types were found.     

Multiple paternity and sperm competition in the sibling species Drosophila buzzatii and Drosophila koepferae

Sperm competition (SC) is a major component of sexual selection that enhances intra‐ and intersexual conflicts and may trigger rapid adaptive evolution of sexual characters. The actual role of SC on rapid evolution, however, is poorly understood. Besides, the relative contribution of distinctive features of the mating system to among species variation in the strength of SC remains unclear. Here, we assessed the strength of SC and mating system factors that may account for it in the closely related species Drosophila buzzatii and Drosophila koepferae. Our analyses reveal higher incidence of multiple paternity and SC risk in D. buzzatii wild‐inseminated females. The estimated number of fathers per brood was 3.57 in D. buzzatii and 1.95 in D. koepferae. In turn, the expected proportion of females inseminated by more than one male was 0.89 in D. buzzatii and 0.58 in D. koepferae. Laboratory experiments show that this pattern may be accounted for by the faster rate of stored sperm usage observed in D. koepferae and by the greater female remating rate exhibited by D. buzzatii. We also found that the male reproductive cost of SC is also higher in D. buzzatii. After a female mated with a second male, first‐mating male fertility was reduced by 71.4% in D. buzzatii and only 33.3% in D. koepferae. Therefore, we may conclude that postmating sexual selection via SC is a stronger evolutionary force in D. buzzatii than in its sibling.