The Adaptive Significance of Natural Genetic Variation in the DNA Damage Response of Drosophila melanogaster.

Despite decades of work, our understanding of the distribution of fitness effects of segregating genetic variants in natural populations remains largely incomplete. One form of selection that can maintain genetic variation is spatially varying selection, such as that leading to latitudinal clines. While the introduction of population genomic approaches to understanding spatially varying selection has generated much excitement, little successful effort has been devoted to moving beyond genome scans for selection to experimental analysis of the relevant biology and the development of experimentally motivated hypotheses regarding the agents of selection; it remains an interesting question as to whether the vast majority of population genomic work will lead to satisfying biological insights. Here, motivated by population genomic results, we investigate how spatially varying selection in the genetic model system, Drosophila melanogaster, has led to genetic differences between populations in several components of the DNA damage response. UVB incidence, which is negatively correlated with latitude, is an important agent of DNA damage. We show that sensitivity of early embryos to UVB exposure is strongly correlated with latitude such that low latitude populations show much lower sensitivity to UVB. We then show that lines with lower embryo UVB sensitivity also exhibit increased capacity for repair of damaged sperm DNA by the oocyte. A comparison of the early embryo transcriptome in high and low latitude embryos provides evidence that one mechanism of adaptive DNA repair differences between populations is the greater abundance of DNA repair transcripts in the eggs of low latitude females. Finally, we use population genomic comparisons of high and low latitude samples to reveal evidence that multiple components of the DNA damage response and both coding and non-coding variation likely contribute to adaptive differences in DNA repair between populations

Searching for genes involved in the adaptation of Drosophila melanogaster to the European climate

The aim of the present work was to identify the genes that played a role in ecological adaptation in D. melanogaster. This species, which originated in Africa, successfully adapted to a broad range of climates during the last 100.000 years. To find the genes involved, I used two different approaches: (1) a genomic region containing several ecologically relevant candidate genes and putatively carrying footprints of selection was investigated using selective sweep mapping, and (2) cold tolerance that might have been an important phenotype for the adaptation to the temperate climates was investigated using a QTL analysis. Using the technique of selective sweep mapping pioneered in the Stephan’s group, I detected evidence that recent strong positive selection has been acting on a small DNA region of 2.7 kb overlapping with the 3’ end of the HDAC6 gene in the ancestral African population. This gene codes for a newly characterized cell stress surveillance factor. HDAC6 is an unusual histone-deacetylase. It is localized in the cytoplasm and has a ubiquitin-binding and a tubulin-deacetylase activity. These properties make HDAC6 a key regulator of cytotoxic stress resistance. The phenotypic analyses show that the African and the European populations have very strong cold tolerance differences. By removing the effects of the autosomes, I showed that a significant amount of the phenotypic variance is due to genetic factors carried by the X chromosome. These factors were then more precisely mapped to two genomic regions of the X chromosome. By comparing the present results with other association studies and the Gene Ontology database, it was possible to determine a list of candidate genes influencing cold tolerance in D. melanogaster. As this list is limited to a very small number of genes, additional investigations for footprints of selection in these regions may be used to confirm their role in ecological adaptation

Evidence that natural selection maintains genetic variation for sleep in Drosophila melanogaster.

BackgroundDrosophila melanogaster often shows correlations between latitude and phenotypic or genetic variation on different continents, which suggests local adaptation with respect to a heterogeneous environment. Previous phenotypic analyses of latitudinal clines have investigated mainly physiological, morphological, or life-history traits. Here, we studied latitudinal variation in sleep in D. melanogaster populations from North and Central America. In parallel, we used RNA-seq to identify interpopulation gene expression differences.ResultsWe found that in D. melanogaster the average nighttime sleep bout duration exhibits a latitudinal cline such that sleep bouts of equatorial populations are roughly twice as long as those of temperate populations. Interestingly, this pattern of latitudinal variation is not observed for any daytime measure of activity or sleep. We also found evidence for geographic variation for sunrise anticipation. Our RNA-seq experiment carried out on heads from a low and high latitude population identified a large number of gene expression differences, most of which were time dependent. Differentially expressed genes were enriched in circadian regulated genes and enriched in genes potentially under spatially varying selection.ConclusionOur results are consistent with a mechanistic and selective decoupling of nighttime and daytime activity. Furthermore, the present study suggests that natural selection plays a major role in generating transcriptomic variation associated with circadian behaviors. Finally, we identified genomic variants plausibly causally associated with the observed behavioral and transcriptomic variation

Seasonal cues induce phenotypic plasticity of Drosophila suzukii to enhance winter survival

Additional file 7: Table S6. Table of differentially expressed genes in bodies of winter morphs of D. suzukii relative to those of summer morphs. Fold change represents the ratio of expression levels of winter to summer morphs

Seasonal cues induce phenotypic plasticity of Drosophila suzukii to enhance winter survival

Background: As global climate change and exponential human population growth intensifies pressure on agricultural systems, the need to effectively manage invasive insect pests is becoming increasingly important to global food security. Drosophila suzukii is an invasive pest that drastically expanded its global range in a very short time since 2008, spreading to most areas in North America and many countries in Europe and South America. Preliminary ecological modeling predicted a more restricted distribution and, for this reason, the invasion of D. suzukii to northern temperate regions is especially unexpected. Investigating D. suzukii phenology and seasonal adaptations can lead to a better understanding of the mechanisms through which insects express phenotypic plasticity, which likely enables invasive species to successfully colonize a wide range of environments. Results: We describe seasonal phenotypic plasticity in field populations of D. suzukii. Specifically, we observed a trend of higher proportions of flies with the winter morph phenotype, characterized by darker pigmentation and longer wing length, as summer progresses to winter. A laboratory-simulated winter photoperiod and temperature (12:12 L:D and 10°C) were sufficient to induce the winter morph phenotype in D. suzukii. This winter morph is associated with increased survival at 1°C when compared to the summer morph, thus explaining the ability of D. suzukii to survive cold winters. We then used RNA sequencing to identify gene expression differences underlying seasonal differences in D. suzukii physiology. Winter morph gene expression is consistent with known mechanisms of cold-hardening such as adjustments to ion transport and up-regulation of carbohydrate metabolism. In addition, transcripts involved in oogenesis and DNA replication were down-regulated in the winter morph, providing the first molecular evidence of a reproductive diapause in D. suzukii. Conclusions: To date, D. suzukii cold resistance studies suggest that this species cannot overwinter in northern locations, e.g. Canada, even though they are established pests in these regions. Combining physiological investigations with RNA sequencing, we present potential mechanisms by which D. suzukii can overwinter in these regions. This work may contribute to more accurate population models that incorporate seasonal variation in physiological parameters, leading to development of better management strategies.Availability of supporting data: The RNA sequencing data sets supporting the results of this article are available in the National Center for Biotechnology Information (NCBI) repository. [Bio- Project PRJNA294845   http://www.ncbi.nlm.nih.gov/bioproject/PRJNA294845/ , and Sequence Read Archives SRS1057327 (summer bodies)   http://www.ncbi.nlm.nih.gov/sra/?term=SRS1057327/;SRS1057275 (summer heads)   http://www.ncbi.nlm.nih.gov/sra/?term=SRS1057275/;SRS1057328 (winter bodies)   http://www.ncbi.nlm.nih.gov/sra/?term=SRS1057328/;SRS1057296 (winter heads)   http://www.ncbi.nlm.nih.gov/sra/?term=SRS1057296/ ]. NCBI accession for individual replicates are also provided in Additional file 2: Table S1.Keywords: Phenotypic plasticity, Transcriptome, High-throughput sequencing, Cold tolerance, Diapause, Drosophila suzuki

Social experience and pheromonal perception can change male-male interactions in Drosophila melanogaster

0022-0949 (Print) Comparative Study Journal Article Research Support, Non-U.S. Gov'tSocial interaction with conspecifics can influence the developing brain and behaviour of the exposed animal. This experience can involve the exchange and retention of visual, chemical, acoustic and tactile signals. When several Drosophila melanogaster male flies are associated with mated females in the presence of food, they show frequent aggressive interactions. To measure the role of social experience on male-male interaction, two tester males - naive or exposed to sibling(s) during a variable period of their adult development - were confronted in the absence of female and food. The two males displayed homosexual courtship and aggressive behaviours, the frequency, intensity and directionality of which varied according to their experience. The effect of social experience was greatly enhanced between transgenic males partially defective for pheromonal perception, indicating that male inhibitory pheromones are normally used to repress male-male interaction