Although the Drosophila Y chromosome is degenerated, heterochromatic, and contains few genes, increasing evidence suggests that it plays an important role in regulating the expression of numerous autosomal and X-linked genes. Here we use 15 Y chromosomes originating from a single founder 550 generations ago to study the role of the Y chromosome in regulating rRNA gene transcription, position-effect variegation (PEV), and the link among rDNA copy number, global gene expression, and chromatin regulation. Based on patterns of rRNA gene transcription indicated by transcription of the retrotransposon R2 that specifically inserts into the 28S rRNA gene, we show that X-linked rDNA is silenced in males. The silencing of X-linked rDNA expression by the Y chromosome is consistent across populations and independent of genetic background. These Y chromosomes also vary more than threefold in rDNA locus size and cause dramatically different levels of PEV suppression. The degree of suppression is negatively associated with the number and fraction of rDNA units without transposon insertions, but not with total rDNA locus size. Gene expression profiling revealed hundreds of differentially expressed genes among these Y chromosome introgression lines, as well as a divergent global gene expression pattern between the low-PEV and high-PEV flies. Our findings suggest that the Y chromosome is involved in diverse phenomena related to transcriptional regulation including X-linked rDNA silencing and suppression of PEV phenotype. These results further expand our understanding of the role of the Y chromosome in modulating global gene expression, and suggest a link with modifications of the chromatin state.T he Y chromosome in Drosophila melanogaster is gene-poor, heterochromatic, and largely degenerate owing to the lack of recombination in males and the reduced effective population size of the Y (1-3). Beyond carrying a handful of factors essential for male fertility, the Y chromosome has been considered to have little function. Despite this relative lack of functional DNA, recent studies have shown that Y-linked genetic variation in Drosophila modulates the expression of hundreds of genes across the genome (4-6). Although it is presumed that this transacting transcriptional regulation is related to epigenetic modification of chromatin state by the Y chromosome, the functional basis for this effect has remained elusive (5).The D. melanogaster Y chromosome contains fewer than 20 single-copy coding genes (7-9), with the bulk of the chromosome composed of repetitive DNA. Among the best-studied Y-linked loci is the rDNA locus (designated bobbed), which physically accounts for ∼10% of the entire Y chromosome and is homologous to the X-linked rDNA locus. The rDNA locus in D. melanogaster is a tandemly repeated array consisting of hundreds of units, each of which encodes 18S, 5.8S, and 28S ribosomal RNA genes (Fig. 1A). In an rDNA cistron, many of the rDNA units cannot form functional ribosomes because of insertions of the site-specific retrotran...

The monogenean Gyrodactylus salaris Malmberg, 1957 is an economically important parasite on Atlantic salmon whereas the morphologically very similar G. thymalli Zitnan, 1960 on grayling is considered harmless. Even molecular markers cannot unambiguously discriminate both species. The nuclear internal transcribed spacer (ITS) sequences are identical in both species, and although mitochondrial cytochrome oxidase I (COI) sequences show substantial variation, no support for monophyly of either species is found. Analysis of nucleotide sequences of the intergenic spacer (IGS) have, however, been interpreted as support for 2 species. Here, IGS and COI sequences from 81 G. salaris and G. thymalli specimens of 39 populations across the species' distribution range were determined. Mitochondrial diversity was not reflected in the nuclear marker. Since various 23 bp IGS repeat types usually differ by just one nucleotide and sequences primarily differ in the number and order of repeat types, alignments may be biased and arbitrary, impeding meaningful phylogenetic analyses. The hypothesis that parasites on rainbow trout represent hybrids of both species is rejected. The presence or absence of particular repeat types is not considered informative. We interpret the IGS data as support for G. salaris and G. thymalli being a single species.

The pantropical subtribe Megacephalina represented by more than 100 species is the most diverse of the basal cicindelid groups. Today, most taxonomists recognize eight genera within the subtribe. This is in contrast to Horn who, back in 1910, conceded only two genus-level taxa: the monospecific Aniara and Megacephala sensu Horn (a genus which united the seven other taxa). In the present study we provide a molecular phylogeny of Megacephalina based on the nuclear 18S and the mitochondrial 16S and cytochrome oxidase III genes. The dataset includes 60 specimens of more than 40 mostly South American and Australian taxa. Three cicindelid species of derived lineages were used as outgroups. The resulting phylogenetic trees are basically in agreement with the current classification system. Megacephala and Grammognatha are placed basal in the dendrogram. Pseudotetracha and Australicapitona form a monophyletic Australian clade. Phaeoxantha, Tetracha and Aniara also form a monophyletic group. The position of Metriocheila remains uncertain. The most striking deviation from the traditional classification is the well-supported placement of Aniara within Tetracha, rendering the latter a paraphyletic taxon. Several monophyletic subgeneric species groups are observed in Pseudotetracha, Phaeoxantha and Tetracha/Aniara. Within the latter the monophyletic sobrina, carolina and brasiliensis clades together represent a monophyletic group. Additionally, habitat types were assigned to the taxa and mapped on the phylogenetic tree. The basal African species inhabit non-flooded uplands. The Australian species moved to inland and/or coastal salt plains. The American groups were most likely first confined to river margins and then colonized secondarily and independently non-flooded uplands and/or coastal habitats

BackgroundNon-coding satellite DNA (satDNA) usually has a high turn-over rate frequently leading to species specific patterns. However, some satDNA families evolve more slowly and can be found in several related species. Here, we analyzed the mode of evolution of the pDo500 satDNA family of Dolichopoda cave crickets. In addition, we discuss the potential of slowly evolving satDNAs as phylogenetic markers.ResultsWe sequenced 199 genomic or PCR amplified satDNA repeats of the pDo500 family from 12 Dolichopoda species. For the 38 populations under study, 39 pDo500 consensus sequences were deduced. Phylogenetic analyses using Bayesian, Maximum Parsimony, and Maximum Likelihood approaches yielded largely congruent tree topologies. The vast majority of pDo500 sequences grouped according to species designation. Scatter plots and statistical tests revealed a significant correlation between genetic distances for satDNA and mitochondrial DNA. Sliding window analyses showed species specific patterns of variable and conserved regions. The evolutionary rate of the pDo500 satDNA was estimated to be 1.63-1.78% per lineage per million years.ConclusionsThe pDo500 satDNA evolves gradually at a rate that is only slightly faster than previously published rates of insect mitochondrial COI sequences. The pDo500 phylogeny was basically congruent with the previously published mtDNA phylogenies. Accordingly, the slowly evolving pDo500 satDNA family is indeed informative as a phylogenetic marker.

After years of unprecedented growth in development assistance for health (DAH), the system is challenged on several fronts: by the economic downturn and stagnation of DAH, by the epidemiological transition and increase in non-communicable diseases, and by the economic transition and rise of the middle-income countries. This raises questions about which countries should receive DAH and how much, and, fundamentally, what criteria that promote fair and effective allocation. Yet, no broad comparative assessment exists of the criteria used today. We reviewed the allocation criteria stated by five multilateral and nine bilateral funders of DAH. We found that several funders had only limited information about concrete criteria publicly available. Moreover, many funders not devoted to health lacked specific criteria for DAH or criteria directly related to health, and no funder had criteria directly related to inequality. National income per capita was emphasised by many funders, but the associated eligibility thresholds varied considerably. These findings and the broad overview of criteria can assist funders in critically examining and revising the criteria they use, and inform the wider debate about what the optimal criteria are.