Drosophila Subgenus Sophophora Research Articles

Expression of thermal tolerance genes in two Drosophila species with different acclimation capacities.

Heat tolerance increases at higher acclimation temperatures in D. melanogaster, but not in D. subobscura. The two species represent separate lineages of the subgenus Sophophora of Drosophila with contrasting tropical African and temperate Palearctic evolutionary histories. D. melanogaster has five copies of the inducible hsp70 gene distributed in two clusters, named A (with two copies) and B (three copies), while D. subobscura has only two copies arranged similarly to cluster A of D. melanogaster. The hsp70s of the two species also differ in their cis-regulatory regions, with D. melanogaster exhibiting features of a faster and more productive promoter. We predicted that the interspecific variation in acclimation capacity of heat tolerance is explained by evolved variation in expression of the major group of heat shock proteins. To test this prediction, we compared basal levels of gene expression at different developmental temperatures within each of the two species. Furthermore, we explored the heat hardening dynamics by measuring the induction of gene expression during a ramping assay. The prediction of a stronger heat shock protein response in D. melanogaster as compared to D. subobscura was confirmed for both long-term acclimation and short-term hardening. For D. melanogaster the upregulation with temperature ramping ranged from less than two fold (hsp26) to 2500 fold (hsp70A) increase. In all cases induction in D. melanogaster exceeded that of D. subobscura homologs. These differences correlate with structural differences in the regulatory regions of hsp70, and might explain differences in acclimation capacity among species. Finally, in D. melanogaster we found an indication of an inverse relationship between basal and induced levels of hsp70A and hsp83 expression, suggesting a divergent role for thermal adaptation of these genes at benign and stressful temperatures, respectively.

Phylogenetic position of the Drosophila fima and dentissima lineages, and the status of the D. melanogaster species group

The subgenus Sophophora of Drosophila, which includes D. melanogaster, is an important model for the study of molecular evolution, comparative genomics, and evolutionary developmental biology. Numerous phylogenetic studies have examined species relationships in the well-known melanogaster, obscura, willistoni, and saltans species groups, as well as the relationships among these clades. In contrast, other species groups of Sophophora have been relatively neglected and have not been subjected to molecular phylogenetic analysis. Here, we focus on the endemic African Drosophila fima and dentissima lineages. We find that both these clades fall within the broadly defined melanogaster species group, but are otherwise distantly related to each other. The new phylogeny supports pervasive divergent and convergent evolution of male-specific grasping structures (sex combs). We discuss the implications of these results for defining the boundaries of the melanogaster species group, and weigh the relative merits of “splitting” and “lumping” approaches to the taxonomy of this key model system.

Taxonomic review of the Australian Drosophila setifemur species group, a new name for the D. dispar species group (Diptera: Drosophilidae)

Examination of the holotype and a paratype of Drosophila setifemur Malloch, 1924 in the Australian Museum has resulted in the discovery that it is not a synonym of D. sulfurigaster as had previously been assumed. Instead, D. setifemur is a senior synonym of the widespread eastern Australian species D. dispar Mather, 1955. The so-called Drosophila dispar species group is renamed the Drosophila setifemur species group and Drosophila unguicula is removed from it. An illustrated key to Australian drosophilids with spinescent fore-femora is provided. Mcevey, Shane F., 2009. Taxonomic review of the Australian Drosophila setifemur species group, a new name for the D. dispar species group (Diptera: Drosophilidae). Records of the Australian Museum 61(1): 31–38. The genus Drosophila accommodates a great range of drosophilids, with numerous aggregations at various levels between genus and species (viz. subgenus, species group, subgroup, complex, etc.). A rapidly growing body of knowledge is allowing us to know with ever increasing certainty the true genetic relationship between species. But ultimately, even when the tree that relates every lab strain and every field-sampled specimen is known with a high level of confidence, there will remain the task of affixing the taxonomically valid names to each of those samples and to biological species. Drosophila currently has c. 1,600 described species; c. 350 are classified with D. melanogaster in the subgenus Sophophora, and another c. 730 species are treated as Drosophila s.str. Nearly all are attracted to fruit baits and can be established as cultures in the laboratory. The following synonymy involves Drosophila dispar Mather, 1955: 570 (a species in the dispar species group of the Drosophila subgenus Sophophora) and D. setifemur Malloch, 1924: 351 (a species incorrectly classified as synonymous with D. sulfurigaster (Duda, 1923: 48) in the nasuta subgroup, immigrans species group of Drosophila s.str.). Removing D. setifemur from synonymy with D. sulfuri­ gaster and placing it in synonymy with D. dispar leads to a need to rename the Drosophila dispar species group (established by Mather,1955).

Evolution of stress resistance in Drosophila: interspecific variation in tolerance to desiccation and starvation

Summary 1. The extent to which variability in desiccation resistance among ecologically diverse Drosophila species is related to their ability to resist starvation is unknown. Resistance to desiccation and starvation was measured in females and males of ecologically and phylogenetically diverse Drosophila species. 2. We measured resistance to both stressors in ecologically and phylogenetically diverse species. In general females exhibited greater resistance to both stressors than males. Correcting for body size produces a highly significant correlation between resistances to both stressors in both sexes. 3. Phylogenetic relatedness, however, appears to have a large influence not only on resistance to both stressors, but also on the observed correlations between stressors. 4. Species of the Drosophila subgenus Sophophora examined in this study tend to be fruit breeders inhabiting more temperate and mesic habitats, whereas many of the species in the other major subgenus, Drosophila , tend to be cactophilic flies living in more xeric environments. 5. The difference between these two major subgenera, the Sophophora and the Drosophila , in the nature of the association we observed between desiccation and starvation resistance suggests that selection may have led to different mechanisms underlying resistance to these stressors in the two groups.

Molecular evolution of the Amy multigenes in the subgenus Sophophora of Drosophila.

Molecular evolution of the Amy multigenes in Drosophila was investigated using PCR amplification. Twenty-five partial Amy sequences from 13 species belonging mainly to the subgenus Sophophora were determine, and a molecular phylogeny of the Amy genes in Drosophila was constructed, together with published Amy sequences. Clustering of species are mostly consistent with the traditional classification and that inferred from other genes. From sequence divergence between PCR products, several species, including D. elegans and D. fuyamai, were suggested to have multiple copies of the Amy genes. The loss of an intron took place at least three times after the Sophophora radiation. In order to investigate the mechanism of sequence evolution, the numbers of amino acid replacement and synonymous substitutions in five lineages were estimated. The heterogeneity in the relative numbers of synonymous and replacement substitutions among the lineages was found. Possible roles of selection in the sequence evolution of the Amy gene are discussed.

Evolution of the transposable element mariner in the Drosophila melanogaster species group.

The population biology and molecular evolution of the transposable element mariner has been studied in the eight species of the melanogaster subgroup of the Drosophila subgenus Sophophora. The element occurs in D. simulans, D. mauritiana, D. sechellia, D. teissieri, and D. yakuba, but is not found in D. melanogaster, D. erecta, or D. orena. Sequence comparisons suggest that the mariner element was present in the ancestor of the species subgroup and was lost in some of the lineages. Most species contain both active and inactive mariner elements. A deletion of most of the 3' end characterizes many elements in D. teissieri, but in other species the inactive elements differ from active ones only by simple nucleotide substitutions or small additions/deletions. Active mariner elements from all species are quite similar in nucleotide sequence, although there are some species-specific differences. Many, but not all, of the inactive elements are also quite closely related. The genome of D. mauritiana contains 20-30 copies of mariner, that of D. simulans 0-10, and that of D. sechellia only two copies (at fixed positions in the genome). The mariner situation in D. sechellia may reflect a reduced effective population size owing to the restricted geographical range of this species and its ecological specialization to the fruit of Morinda citrifolia.

Molecular phylogeny of the subgenus Sophophora of Drosophila derived from large subunit of ribosomal RNA sequences

RNA sequencing has been used to assess the relationships among species of the subgenus Sophophora of the genus Drosophila. Two divergent domains, D1 and D2, of the large ribosomal RNA (28S), totalling 550 nucleotides have been sequenced using the rRNA direct sequencing method. A tree has been reconstructed from the neighbor-joining algorithm and the confidence intervals were evaluated by the bootstrap procedure. Results have shown that the branching of the willistoni and saltans groups of the subgenus Sophophora is very ancient and probably predates that of the subgenus Drosophila. The other groups and subgroups of Sophophora are clustered in three main lineages: 1) the melanogaster and oriental subgroups; 2) the montium subgroup; 3) the ananassae subgroup of the melanogaster group clustered with the fima and obscura groups. Thus, in comparison with our results, several taxa of various ranks appear paraphyletic (the genus Drosophila, the subgenus Sophophora and the melanogaster group). Our biochemical phylogeny is only in partial agreement with the pattern of Throckmorton's radiations as well as with classical taxonomy, both based on morphological data.