Project description:A number of genes associated with sexual traits and reproduction evolve at the sequence level faster than the majority of genes coding for non-sex-related traits. Whole genome analyses allow this observation to be extended beyond the limited set of genes that have been studied thus far. We use cDNA microarrays to demonstrate that this pattern holds in Drosophila for the phenotype of gene expression as well, but in one sex only. Genes that are male-biased in their expression show more variation in relative expression levels between conspecific populations and two closely related species than do female-biased genes or genes with sexually monomorphic expression patterns. Additionally, elevated ratios of interspecific expression divergence to intraspecific expression variation among male-biased genes suggest that differences in rates of evolution may be due in part to natural selection. This finding has implications for our understanding of the importance of sexual dimorphism for speciation and rates of phenotypic evolution. Keywords: other
Project description:Sexual selection on males is predicted to have widespread effects on genetic variation as a consequence of the pleiotropic allelic effects on sexual and non-sexual traits. We manipulated the opportunity for sexual selection on males during 27 generations of mutation accumulation in inbred lines of Drosophila serrata, and used a microarray platform to investigate the effect of sexual selection on the expression of 2689 genes. While gene expression signal was, on average, higher in the absence of sexual selection, this difference was small (0.1%). In contrast, sexual selection impacted substantially on the mutational variance in gene expression. Over all genes, mutational variance in gene expression was, on average, 42% higher when sexual selection operated than when it was absent. Our results indicate that sexual selection on males can generate widespread effects across the genome. An increase in mutational variance without a corresponding change in mean suggested that most expression traits were unlikely to be under direct sexual selection. Instead, the mutational variance in gene expression traits is consistent with divergence generated by widespread pleiotropic associations with traits affecting male mating success.
Project description:Transcript abundance was measured in whole-body virgin male Drosophila serrata from 41 inbred lines that had diverged through 27 generations of mutation accumulation that were sexually selected Sexual selection is predicted to have widespread effects on the genetic variation generated by new mutations as a consequence of the genic capture of condition by male sexual traits. We manipulated the opportunity for sexual selection on males during 27 generations of mutation accumulation in inbred lines of Drosophila serrata, and used a microarray platform to investigate the effect of sexual selection on the expression of 2685 genes, representing a broad coverage of biological function. Sexual selection had little effect on mean gene expression levels, with only 4 genes diverging significantly at a false discovery rate of 5% . In contrast, sexual selection impacted on both the magnitude and nature of mutational variance accumulating in these genes. The magnitude of mutational variance increased under sexual selection by an average of 29%. Mutational variance was less commonly generated by extreme phenotypes less commonly under sexual selection. Furthermore, analysis of random sets of five genes revealed that the mutational variance that accumulated under sexual selection was less pleiotropic in nature than that found in the absence of sexual selection. The generation of greater mutational variance without a general concomitant change in mean expression under sexual selection suggested that gene expression traits were be under apparent rather than direct sexual selection. We discuss two main explanations for the broad-based increase in mutational variance under sexual selection that both require extensive pleiotropy between traits affecting male mating success, standard metric traits represented here by gene expression traits, and general fitness. We measured gene expression of male Drosophila serrata from 41 mutation accumulation lines (whole-body) that were sexually selected. Data from two replicates for each line are presented.
Project description:Most B cell lymphomas arise in the germinal center (GC), where humoral immune responses evolve from potentially oncogenic cycles of mutation, proliferation, and clonal selection. Although lymphoma gene expression diverges significantly from GC-B cells, underlying mechanisms that alter the activities of corresponding regulatory elements (REs) remain elusive. Here we define the complete pathogenic circuitry of human follicular lymphoma (FL), which activates or decommissions transcriptional circuits from normal GC-B cells and commandeers enhancers from other lineages. Moreover, independent sets of transcription factors, whose expression is deregulated in FL, target commandeered versus decommissioned REs. Our approach reveals two distinct subtypes of low-grade FL, whose pathogenic circuitries resemble GC-B or activated B cells. Remarkably, FL-altered enhancers also are enriched for sequence variants, including somatic mutations, which disrupt transcription factor binding and expression of circuit-linked genes. Thus, the pathogenic regulatory circuitry of FL reveals distinct genetic and epigenetic etiologies for GC-B transformation. Molecular profiling of follicular lymphoma, resting peripheral blood and tonsillar B cells using Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) and chromatin immunoprecipitation (H3ac and H3K27ac).
Project description:By combining an experimental evolution approach with genomic techniques, we investigated the effects of seminal fluid on female gene expression. In our study, we experimentally manipulated the mating system in replicate populations of D. melanogaster, by removing post-copulatory sexual selection, with the aim of testing differences in short term post-mating reaction of females evolved under different mating strategies. We show that monogamous females suffer decreased fecundity, regardless of the type of male they were mated with, and that their post-mating gene expression profiles differ significantly from promiscuous females, involving 1141 transcripts (9% of the genes tested). These transcripts are active in several tissues, mainly ovaries, neural tissues, midgut and spermathecae, and are involved in metabolic processes, reproduction and signaling pathways. Our results provide a list of candidate genes responsible for the decrease in female fecundity in the absence of post-copulatory sexual selection, and demonstrate how the female post-mating response can evolve under different mating systems over relatively short time frames.
Project description:By combining an experimental evolution approach with genomic techniques, we investigated the effects of seminal fluid on female gene expression. In our study, we experimentally manipulated the mating system in replicate populations of D. melanogaster, by removing post-copulatory sexual selection, with the aim of testing differences in short term post-mating reaction of females evolved under different mating strategies. We show that monogamous females suffer decreased fecundity, regardless of the type of male they were mated with, and that their post-mating gene expression profiles differ significantly from promiscuous females, involving 1141 transcripts (9% of the genes tested). These transcripts are active in several tissues, mainly ovaries, neural tissues, midgut and spermathecae, and are involved in metabolic processes, reproduction and signaling pathways. Our results provide a list of candidate genes responsible for the decrease in female fecundity in the absence of post-copulatory sexual selection, and demonstrate how the female post-mating response can evolve under different mating systems over relatively short time frames.
Project description:The experimental approach seeks to test for sexual dimorphism in exuded non-volatile metabolites in C. purpureus. The proposed research is creative and original both in its inter-disciplinary approach and its use of a biochemically tractable phenotype to develop a much-needed link between natural selection for sexual dimorphism and the molecular targets of that selection pressure.
Project description:Due to its hemizygous mode of inheritance and role in sex determination, the X chromosome is expected to play an important role in the evolution of sexual dimorphism, and to be enriched for sexually antagonistic genetic variation. By forcing the X chromosome to only be expressed in males over many generations, we changed the selection pressures on the X to become similar to those experienced by the Y chromosome. This releases the X from any constraints arising from selection in females, and is predicted to lead to specialization for male fitness, including masculinization of phenotypes that normally experience sexually antagonistic selection. Indeed, we found evidence of this via upregulation of male-benefit sexually antagonistic genes, and downregulation of X-linked female benefit genes. Interestingly, we could detect evidence of microevolutionary changes consistent with previously documented patterns of macroevolutionary change, such as changes in expression consistent with previously established patterns of sexual dimorphism, an increase in the expression of metabolic genes related to mitonuclear conflict, and evidence that dosage compensation constitutes a constraint for male-benefit genes. These results confirm the importance of the X in the evolution of sexual dimorphism and as a source for sexually antagonistic genetic variation, and demonstrate that experimental evolution can be a fruitful method for testing theories of sex chromosome evolution. Microarray data was used to detect differences in gene expression as result of experimental evolution.
Project description:The experimental approach seeks to test for sexual dimorphism in exuded non-volatile metabolites in C. purpureus. The proposed research is creative and original both in its inter-disciplinary approach and its use of a biochemically tractable phenotype to develop a much-needed link between natural selection for sexual dimorphism and the molecular targets of that selection pressure.
Project description:Background: Eusociality is widely considered to evolve through kin selection, where the reproductive success of an individual’s close relative is favored at the expense of its own. High genetic relatedness is thus considered a prerequisite for eusociality. While ants are textbook examples of eusocial animals, not all ants form colonies of closely related individuals. One such example is the ectatommine ant Rhytidoponera metallica, which predominantly forms predominantly queen-less colonies that have such a low intra-colony relatedness that they have been proposed to represent a transient, unstable form of eusociality. However, R. metallica is among the most abundant and widespread ants on the Australian continent. This apparent contrast provides an example of how inclusive fitness may not by itself explain the maintenance of eusociality and raises the question of what other selective advantages maintain their eusocial lifestyle. Results: We provide a comprehensive portrait of the venom of R. metallica and show that the colony-wide venom consists of a, for an ant, exceptionally high diversity of functionally distinct toxins. These toxins have evolved under strong positive selection, which is normally expected to reduce genetic variance. Yet, R. metallica exhibits remarkable intra-colony variation, with workers sharing only a relatively small proportion of toxins in their venoms. We also find that this variation is not due to the presence of chemical castes, but that it has a genetic foundation that is at least in part explained by toxin allelic diversity. Conclusions: Taken together, our results suggest that the toxin diversity contained in R. metallica colonies may be maintained by a form of group selection, which selects for colonies that can exploit more resources and defend against a wider range of predators. We propose that increased intra-colony genetic variance resulting from low kinship may itself provide a selective advantage in the form of an expanded pharmacological venom repertoire. These findings provide an example of how group selection on adaptive phenotypes may contribute to maintaining eusociality where a prerequisite for kin selection is diminished.