Frequency-dependent competitive abilities and differential resource use in competition between Drosophila hydei and D. melanogaster

Several experiments, each involving competition between Drosophila melanogaster and D. hydei in population cages, were set up and allowed to run for up to 50 weeks. The population sizes of both species, and hence the species frequencies, were monitored once a fortnight, i.e. approximately once per generation. Coexistence of the two species was observed in cages containing resource bottles with 5 g of food medium; cages whose resource bottles contained only 1.5 g resulted in competitive exclusion of D. hydei. Competitive abilities were frequency-dependent in the former case but not in the latter. Tests of larval depth distributions revealed that D. hydei larvae feed at a deeper level in the food medium than larvae of D. melanogaster. The explanation of the contrasting results of competition when bottles contained 5 g and 1.5 g of resources lies in the production of frequency-dependent competitive abilities by larval resource partitioning in the bottles with 5 g, and the preclusion of such partitioning in the 1.5 g bottles because of the very limited depth of food medium then available. The relevance of these results to a model of competition is discussed, and the potential generality of differential resource use as a stabilizing mechanism in both interspecific and intergenotypic competition is noted.     

The endogenous Drosophila melanogaster retrovirus gypsy can propagate in Drosophila hydei cells

The endogenous Drosophila melanogaster retrovirus gypsy (mdg4) forms virus-like particles (VLPs) which are found as extracellular particles in the medium used to culture D. melanogaster cells. The D. hydei somatic cell line DH14, which does not harbour gypsy sequences, was exposed to D. melanogaster VLPs. Subsequent PCR and Southern analysis revealed that gypsy elements had penetrated into the D. hydei cells, suggesting interspecific transmission of the retrovirus. A D. hydei cell line containing gypsy sequences was established and grown in a mixed culture together with the G418-resistant D. hydei cell line DH33, and gypsy was shown to be transmitted from cell to cell. The proportion of cells carrying gypsy increased with time. The rate of gypsy invasion of the lines DH14 and DH33 was 10(-3) and 10(-2) per cell per generation, respectively. The results demonstrate the possibility of interspecific horizontal transfer of gypsy in the form of its VLPs.     

The Evolution of Duplicate Glyceraldehyde-3-Phosphate Dehydrogenase Genes in Drosophila

In Drosophila melanogaster there are two genes which encode the enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Gapdh-43E and Gapdh-13F. We have shown that Gapdh-43E codes for the GAPDH subunit with an apparently larger molecular weight while Gapdh-13F encodes the GAPDH subunit having an apparently smaller molecular weight. Immunoblots of sodium dodecyl sulfate gels were used to survey species from throughout the genus and results indicated that two classes of GAPDH subunits are present only in Drosophila species of the melanogaster and takahashi subgroups of the melanogaster group. Only the smaller subunit is found in species of the obscura group while all other species have only a large subunit. Drosophila hydei was analyzed at the DNA level as a representative species of the subgenus Drosophila. The genome of this species has a single Gapdh gene which is localized at a cytogenetic position likely to be homologous to Gapdh-43 E of D. melanogaster. Comparison of its sequence with the sequence of the D. melanogaster Gapdh genes indicates that the two genes of D. melanogaster are more similar to one another than either is to the gene from D. hydei. The Gapdh gene from D. hydei contains an intron following codon 29. Neither Gapdh gene of D. melanogaster has an intron within the coding region. Southern blots of genomic DNA were used to determine which species have duplicate Gapdh genomic sequences. Gene amplification was used to determine which species have a Gapdh gene that is interrupted by an intron. Species of the subgenus Drosophila have a single Gapdh gene with an intron. Species of the willistoni and saltans groups have a single Gapdh gene that does not contain an intron.(ABSTRACT TRUNCATED AT 250 WORDS)     

Indiscriminate females and choosy males: within- and between-species variation in Drosophila

Abstract The classic view of choosy, passive females and indiscriminate, competitive males gained theoretical foundations with parental investment theory. When females invest more in offspring than males, parental investment theory says that selection operates so that females discriminate among males for mates (i.e., females are choosy and passive) and males are indiscriminate (i.e., males are profligate and competitive). Here we report tests of predictions using Drosophila pseudoobscura and D. melanogaster , with typical asymmetry in gamete sizes (females > males), and in D. hydei with far less asymmetry in gamete size. Experimental observations revealed that the labels "choosy, passive females" and "profligate, indiscriminate males" did not capture the variation within and between species in premating behavior. In each of the species some females were as active in approaching males (or more so) than males in approaching females, and some males were as discriminating (or more so) than females. In pairs focal males and females responded differently to opposite-sex than to same-sex conspecifics. Drosophila hydei were less sex-role stereotyped than the other two species consistent with parental investment theory. However, D. pseudoobscura females approached males more often than did D. melanogaster females, and male D. hydei approached females as often as males of the other two species, both results inconsistent with parental investment theory. Male D. pseudoobscura and D. hydei were more likely to approach males in same-sex pairs than male D. melanogaster , inconsistent with parental investment theory.     

Characterization of cloned ribosomal DNA from Drosophila hydei.

The structure of ribosomal genes from the fly Drosophila hydei has been analyzed. EcoRI fragments, cloned in a plasmid vector, were mapped by restriction enzyme analysis. The lengths of the regions coding for 18S and 28S rRNA were defined by R-loop formation. From these data a physical map of the rRNA genes was constructed. There are two major types of rDNA units in D. hydei, one having a size of 11 kb and the other a size of 17 kb. The 17 kb unit results from an intervening sequence (ivs) of 6.0 kb, interrupting the beta-28S rRNA coding region. Some homology between th D. hydei ivs and D. melanogaster type 1 ivs has been described previously (1). However, the restriction sites within these ivs show considerable divergence. Whereas D. hydei rDNA D. melanogaster rDNA, the nontranscribed spacer has little, if any, sequence homology. Despite difference in sequence, D. hydei and D. melanogaster spacers show structural similarities in that both contain repeated sequence elements of similar size and location.     

Regulative interactions between cells of wing discs from different dipteran species

The mechanism by which patterns are produced appears to be repeated in each segment of an animal, and it has been proposed that it may even have been conserved in evolution so that different species would have the same system of positional information. This idea has been tested by mixing cells of a defined fragment of the wing disc of Drosophila melanogaster with wing disc fragments of five other dipteran species to assay the ability of these disc fragments to stimulate intercalary regeneration of the D. melanogaster cells. The genetically marked (y; mwh) D. melanogaster fragment was mechanically mixed with wing discs or wing disc fragments of four drosophilids (D. melanogaster as a control, D. virilis, D. hydei, Zaprionus vittiger), of Musca domestica, and of Piophila casei. The mixed aggregates were cultured in vivo for 7 days, then metamorphosed in D. melanogaster larval hosts. The D. melanogaster fragments were only stimulated to regenerate when combined with complementary fragments from D. melanogaster or D. virilis wing discs. In the combination between D. melanogaster and D. hydei, the tissue formed integrated mosaic patterns, but no regeneration ensued. The one positive result (D. melanogaster mixed with D. virilis) shows that positional cues can be exchanged and correctly interpreted between cells of different species. The negative results do not prove that the mechanism for establishing patterns is different in the tested species, but may be due to incompatibilities that are not related to pattern formation.     

The wild side of life: Drosophila reproduction in nature

Drosophila species vary in the rates at which females remate and the number of sperm they receive in the laboratory. In species such as D. melanogaster and D. pseudoobscura, in which females receive thousands of sperm and remate infrequently compared with species such as D. hydei and D. nigrospiracula, where females receive only a few hundred sperm and remate many times in a day, wild caught females should produce far more progeny. We tested this prediction by collecting, directly from nature, females of six species whose remating rates and number of sperm received vary from high to low and assessing the proportion of females with sperm and the number of progeny females produce. Over 95% of D. pseudoobscura and D. melanogaster females were inseminated while far fewer of the other species contained any sperm. In addition, D, pseudoobscura females produced progeny for over two weeks, D. melanogaster for over a week, while D. hydei and D. nigrospiracula females ran out of sperm after 1-2 d. These observations suggest extreme sperm limitation in these latter species.     

Regulation of the segmentation gene fushi tarazu has been functionally conserved in Drosophila.

An evolutionary approach was applied to identify elements involved in the regulation of the segmentation gene fushi tarazu (ftz) by comparing the Drosophila melanogaster ftz gene with its Drosophila hydei homologue. The overall organization of the ftz gene is very similar in both species. Surprisingly, ftz proved to be inverted in the ANT-C of D. hydei with respect to D. melanogaster. Strong homologies extend over the entire 6 kb of the ftz upstream region with the best match in the 'upstream element'. We identified several highly conserved boxes embedded in unrelated sequences that correspond extremely well to two germ layer specific enhancers in the upstream element. Transformation experiments revealed that D. hydei ftz gene products can restore D. melanogaster ftz function and, furthermore, that trans-acting factors from D. melanogaster recognize and control D. hydei ftz regulatory elements. These findings indicate a conservation of the entire regulatory network among segmentation genes for several millions of years during the evolution of Drosophila.     

EXTINCTION DUE TO EVOLUTION OF A COMPETITOR

When Drosophila simulans and Drosophila funebris were cultured together in population cages over many generations, there was a prolonged period of apparently stable coexistence followed by a rapid exclusion of D. funebris. As both species maintained large population sizes in monocultures it follows that the extinctions of D. funebris in the mixed-species cultures must have been caused by D. simulans. The time to extinction of D. funebris ranged from 26 weeks in one cage, to between 40 and 48 weeks in the other five. To test the idea that an evolutionary increase in competitive ability of D. simulans had occurred during the course of its interaction with D. funebris, a single-generation experiment was set up. In this experiment the interspecific competitive ability of a population of D. simulans that had been in competition with D. funebris for 44 weeks was compared to that of a stock population that had had no previous contact with D. funebris. In this experiment both stock and precompeted populations of D. simulans increased the egg-to-adult development time of D. funebris. However, precompeted D. simulans caused a significantly greater increase in the development time of D. funebris than did stock D. simulans. Thus D. simulans had evolved an increase in competitive ability as a result of its interaction with D. funebris. Development time is important because in the population cages the resource bottles—in which the larvae reside—were replaced every three weeks. An increase in development time of D. funebris in the multigeneration experiment similar to that observed in the single-generation experiment would lead to a rapid decrease in adult population size, resulting in the extinction of this species, as was observed to happen.     

Intragenic recombination at the white locus of Drosophila hydei.

A fine-structure analysis of the white locus in Drosophila hydei was carried out by means of allele recombination. Four mutants, derived from wild type, mapped at three subloci. These are possibly homologous to the main subloci 2, 3, and 4 of D. melanogaster. Three secondary mutants, derived from the primary wiv allele, were located in the proximal part of the gene. One of them appeared as a homoallele of the original wiv, whereas the remaining two are better explained either as double mutants or as mutants which facilitate irregular exchange. Intragenic recombination at the white locus seems to be more frequent in D. hydei than in D. melanogaster. The comparatively high incidence is probably a general characteristic, common to intragenic and intergenic recombination in D. hydei.     

The Effect of Resource pH on Pupation Height in Drosophila (Diptera: Drosophilidae)

This paper describes the effects of the pH of the larval resource on the pupation height of two cosmopolitan species of Drosophila: D. melanogaster and D. hydei. The pH levels of artificial media were modified using solutions of acids (hydrochloric, acetic, and citric) and a positive relationship was found between pupation height and resource pH; i. e., the more acidic the resource, the closer the larvae pupated to the resource surface. The clearest trends were between pupation height and the final pH of the resource, the larvae apparently responding to the pH they encountered just before pupation commenced. When using natural resources a difference in pupation height was found between the types of fruits used but there was no obvious trend linking pupation height with pH. This suggests that some other environmental factor(s) was (were) overriding the effects of pH, and consequently resource pH may play only a minor role in determining pupation behavior in nature.     

寄生黑腹果蝇的日本开臂反颚茧蜂生物学特性及其寄生对寄主发育及免疫反应的影响

[目的]调查寄生黑腹果蝇Drosophila melanogaster的日本开臂反颚茧蜂Asobara japonica的生物学特性,明确其寄生对寄主生长发育及免疫反应的影响.[方法]运用解剖成像和实时荧光定量PCR技术调查分析了日本开臂反颚茧蜂的各发育阶段发育历期、形态特征,以及日本开臂反颚茧蜂寄生黑腹果蝇2龄幼虫后...     

Evolution of gypsy endogenous retrovirus in the Drosophila obscura species group

The Ty3/gypsy family of retroelements is closely related to retroviruses, and some of their members have an open reading frame resembling the retroviral gene env. Sequences homologous to the gypsy element from Drosophila melanogaster are widely distributed among Drosophila species. In this work, we report a phylogenetic study based mainly on the analysis of the 5' region of the env gene from several species of the obscura group, and also from sequences already reported of D. melanogaster, Drosophila virilis, and Drosophila hydei. Our results indicate that the gypsy elements from species of the obscura group constitute a monophyletic group which has strongly diverged from the prototypic D. melanogaster gypsy element. Phylogenetic relationships between gypsy sequences from the obscura group are consistent with those of their hosts, indicating vertical transmission. However, D. hydei and D. virilis gypsy sequences are closely related to those of the affinis subgroup, which could be indicative of horizontal transmission.     

Characterization of the long terminal repeats of micropia elements microdissected from the Y-chromosomal lampbrush loops "threads" of Drosophila hydei

Four micropia elements from Drosophila melanogaster and D. hydei have been analysed by sequencing. Two elements, from D. hydei, micropia-DhMiF8 and -DhMiF2, were recovered by cloning microdissected Y-chromosomal lampbrush loops "threads". This method allows isolation of repetitive sequences from defined chromosomal positions, but recovery of large and overlapping inserts is difficult. In case of the Y-chromosomal micropia elements it was not possible to define the endpoints of their long terminal repeat sequences precisely. Comparison of these locus-defined micropia elements to complete micropia elements isolated from D. melanogaster allowed identification of micropia-DhMiF8 and micropia-DhMiF2 long terminal repeats (LTRs). LTR sequences from the two Drosophila species are not conserved except for a few short sequences found at comparable positions that are believed to have functional significance. In contrast, the Leu-tRNA primer binding site and plus strand primer binding site are conserved between D. melanogaster and D. hydei.     

Structural analysis of glycerol-3-phosphate dehydrogenase from severalDrosophila species

This report describes preliminary protein structural studies of glycerol-3-phosphate dehydrogenase (alpha-GPDH) from Drosophila spp. and an important innovative feature of our enzyme purification protocol. The scheme involves the coupling of substrate (alpha-glycerophosphate) elution from CM-Sephadex and cofactor (NADH) elution from Affi-Gel blue resin. Using this method a 32.7% yield and a 111-fold purification were obtained from a D. melanogaster line carrying the alpha-GpdhS allele at the alpha-Gpdh locus. The product obtained from 0 to 3-day-old adult flies was electrophoretically homogeneous and consisted mainly of the adult alpha-GPDH-1 isozyme. The method was used to obtain alpha-GPDH protein from D. melanogaster (two lines), D. hydei, D. immigrans, and D. mercatorum. Peptide mapping revealed structural differences among the enzymes from the different species, and amino acid sequencing showed many similarities between D. melanogaster alpha-GPDH and the rabbit muscle enzyme.     

Prevalence of a non-male-killing spiroplasma in natural populations of Drosophila hydei

Male-killing phenotypes are found in a variety of insects and are often associated with maternally inherited endosymbiotic bacteria. In several species of Drosophila, male-killing endosymbionts of the genus Spiroplasma have been found at low frequencies (0.1 to 3%). In this study, spiroplasma infection without causing male-killing was shown to be prevalent (23 to 66%) in Japanese populations of Drosophila hydei. Molecular phylogenetic analyses showed that D. hydei was infected with a single strain of spiroplasma, which was closely related to male-killing spiroplasmas from other Drosophila species. Artificial-transfer experiments suggested that the spiroplasma genotype rather than the host genotype was responsible for the absence of the male-killing phenotype. Infection densities of the spiroplasma in the natural host, D. hydei, and in the artificial host, Drosophila melanogaster, were significantly lower than those of the male-killing spiroplasma NSRO, which was in accordance with the hypothesis that a threshold infection density is needed for the spiroplasma-induced male-killing expression.     

Interspecific competition in Drosophila II. Competitive outcome in some 2–resource environments

Populations of Drosophila metanogaster and D. simulans were made to compete in a number of 2– resource environments. The resources used were all based on a standard Drosophila medium and differed from each other only in their concentrations of ethanol. Each experiment comprised three cages started at a species–frequency of 0.8 D. melanogaster and three at 0.2 D. melanogaster. This enabled screening for a wide range of equilibria.
Reversal of competitive superiority was achieved (unintentionally) by raising the alcohol level of one of the resources. Thus while D. simulans won in an environment with media containing 0 and 896 ethanol, D. melanogaster won if the ethanol concentrations were 0 and 10%, or 0 and 12%. This parallels the reversal of dominance reported earlier for single–resource systems. However, in none of the 2–resource systems studied was there a stable equilibrium in species–frequency–in fact there was no significant frequency–dependence at all.
An artificial selection experiment produced a stock of D. melanogaster ovipositing a higher proportion of eggs on the alcoholic resource. Thus, this stock was more divergent from D. simulans , in at least one aspect of resource use, than was the original stock of D. melanogaster. However, competition between stock D. simulans and selected D. melanogaster showed no frequency–dependence. Again, reversal of competitive dominance was unintentionally achieved.
The implications of these results are discussed, and the need for a comprehensive study of resource–utilization in a pair of competing species is stressed.     

The banding pattern of the salivary gland chromosomes of Drosophila hydei

The banding pattern of the salivary gland chromosomes of D. hydei was investigated in the electron microscope. We compared the banding pattern of squashed chromosomes with non-squashed preparations and observed that the fixation and squash procedure we used does not introduce artificial changes in the banding pattern of the chromosome. An electron microscopic map was made of the banding pattern of the distal half of the second salivary gland chromosome. On the basis of the number of bands in this part of the second chromosome we calculated a total of about 3700 bands for the whole set of polytene chromosomes of D. hydei. Our data indicate a similar number of bands in the salivary gland chromosomes of evolutionary remote Drosophila species like D. hydei and D. melanogaster.     

Adaptation to larval crowding in <Emphasis Type="Italic">Drosophila ananassae</Emphasis> and <Emphasis Type="Italic">Drosophila nasuta nasuta</Emphasis>: increased larval competitive ability without increased larval feeding rate

The standard view of adaptation to larval crowding in fruitflies, built on results from 25 years of multiple experimental evolution studies on Drosophila melanogaster, was that enhanced competitive ability evolves primarily through increased larval feeding and foraging rate, and increased larval tolerance to nitrogenous wastes, at the cost of efficiency of food conversion to biomass. These results were at odds from the predictions of classical K-selection theory, notably the expectation that selection at high density should result in the increase of efficiency of conversion of food to biomass, and were better interpreted through the lens of α-selection. We show here that populations of D. ananassae and D. n. nasuta subjected to extreme larval crowding evolve greater competitive ability and pre-adult survivorship at high density, primarily through a combination of reduced larval duration, faster attainment of minimum critical size for pupation, greater time efficiency of food conversion to biomass and increased pupation height, with a relatively small role of increased urea/ammonia tolerance, if at all. This is a very different suite of traits than that seen to evolve under similar selection in D. melanogaster, and seems to be closer to the expectations from the canonical theory of K-selection. We also discuss possible reasons for these differences in results across the three species. Overall, the results reinforce the view that our understanding of the evolution of competitive ability in fruitflies needs to be more nuanced than before, with an appreciation that there may be multiple evolutionary routes through which higher competitive ability can be attained.