Svitlana V. Serga

First record of the invasive pest Drosophila suzukii in Ukraine indicates multiple sources of invasion

Drosophila suzukii, commonly known as the spotted-wing Drosophila, is an invasive polyphagous fruit pest, which has emerged as a global threat to agriculture in the Americas and in Europe. Due to the rapid spread, great economic losses and its pest behavior, D. suzukii represents a powerful model for invasion biology and pest management studies. However, its current European distribution, invasion routes and levels of genetic diversity in populations of D. suzukii are poorly understood. We present the first report of D. suzukii from Ukraine, with the invasion likely occurring close to 2014. The pattern of genetic variation at cytochrome oxidase I among D. suzukii populations from Europe, USA and Asia reveals comparatively high genetic diversity in the Ukrainian population of this pest species, suggesting a complex invasion scenario from multiple sources. Further monitoring patterns of genetic variation across space and time, to better understand the invasion routes of this invasive insect pest, will be an essential part for developing successful pest management strategies.

Genomic analysis of European Drosophila melanogaster populations on a dense spatial scale reveals longitudinal population structure and continent-wide selection

Abstract Genetic variation is the fuel of evolution, with standing genetic variation especially important for short-term evolution and local adaptation. To date, studies of spatio-temporal patterns of genetic variation in natural populations have been challenging, as comprehensive sampling is logistically difficult, and sequencing of entire populations costly. Here, we address these issues using a collaborative approach, sequencing 48 pooled population samples from 32 locations, and perform the first continent-wide genomic analysis of genetic variation in European Drosophila melanogaster. Our analyses uncover longitudinal population structure, provide evidence for continent-wide selective sweeps, identify candidate genes for local climate adaptation, and document clines in chromosomal inversion and transposable element frequencies. We also characterise variation among populations in the composition of the fly microbiome, and identify five new DNA viruses in our samples.Genetic variation is the fuel of evolution. However, analyzing evolutionary dynamics in natural populations is challenging, sequencing of entire populations remains costly and comprehensive sampling logistically difficult. To tackle this issue and to define relevant spatial and temporal scales of variation, we have founded the European Drosophila Population Genomics Consortium (DrosEU). Here we present the first analysis of 48 D. melanogaster population samples collected across Europe in 2014. Our analysis uncovers novel patterns of variation at multiple levels: genome-wide neutral SNPs, mtDNA haplotypes, inversions, and TEs showing previously cryptic longitudinal population structure; signatures of selective sweeps shared among populations; presumably adaptive clines in inversions; and geographic variation in TEs. Additionally, we document highly variable microbiota and identify several new Drosophila viruses. Our study reveals novel aspects of the population biology of D. melanogaster and illustrates the power of extensive sampling and pooled sequencing of populations on a continent-wide scale.Genetic variation is the fuel of evolution. However, analyzing dynamics of evolutionary change in natural populations is challenging, genome sequencing of entire populations remains costly and comprehensive sample collection logistically challenging. To tackle this issue and to define relevant spatial and temporal scales of variation for a population genetic model system, the fruit fly Drosophila melanogaster, we have founded the European Drosophila Population Genomics Consortium (DrosEU). Our principal objective is to employ the strengths of this collaborative consortium to extensively sample and sequence natural populations on a continent-wide scale and across distinct timescales. Here we present the first analysis of the first DrosEU pool-sequencing dataset, consisting of 48 population samples collected across the European continent in 2014. The analysis of this comprehensive dataset uncovers novel patterns of variation at multiple levels: genome-wide neutral SNPs, mtDNA haplotypes, inversions and TEs that exhibit previously cryptic longitudinal population structure across the European continent; signatures of selective sweeps shared among the majority of European populations; presumably adaptive clines in inversions; and geographic variation in TEs. Additionally, we document highly variable microbiota among European fruit fly populations and identify several new Drosophila viruses. Our study reveals novel aspects of the population biology of D. melanogaster and illustrates the power of extensive sampling and pooled sequencing of natural populations on a continent-wide scale.

Longevity-modulating effects of symbiosis: insights from Drosophila–Wolbachia interaction

Microbial communities are known to significantly affect various fitness components and survival of their insect hosts, including Drosophila. The composition of symbiotic microbiota has been shown to change with the host’s aging. It is unclear whether these changes are caused by the aging process or, vice versa, they affect the host’s aging and longevity. Recent findings indicate that fitness and lifespan of Drosophila are affected by endosymbiotic bacteria Wolbachia. These effects, however, are inconsistent and have been reported both to extend and shorten longevity. The main molecular pathways underlying the lifespan-modulating effects of Wolbachia remain unclear, however insulin/insulin-like growth factor, immune deficiency, ecdysteroid synthesis and signaling and c-Jun N-terminal kinase pathways as well as heat shock protein synthesis and autophagy have been proposed to play a role. Here we revise the current evidence that elucidates the impact of Wolbachia endosymbionts on the aging processes in Drosophila.

Broad geographic sampling reveals predictable and pervasive seasonal adaptation in Drosophila

Local adaptation in response to spatially varying selection pressures is widely recognized as a ubiquitous feature for many organisms. In contrast, our understanding of local adaptation to temporally varying selection pressures is limited. To advance our understanding of local adaptation to temporally varying selection pressures, we studied genomic signatures of seasonal adaptation in Drosophila melanogaster. We generated whole-genome estimates of allele frequencies from flies sampled during the spring and fall from 15 localities. We show that seasonal adaptation is a general feature fly populations and that the direction of seasonal adaptation can be predicted by weather conditions in the weeks prior to sampling. We find that seasonal changes in allele frequency are mirrored by spatial variation in allele frequency and that seasonal adaptation affects allele frequencies at ~1.0-2.5% of polymorphisms genome-wide. Our work demonstrates that seasonal adaptation is a major evolutionary force affecting D. melanogaster populations living in temperate environments.

Phenotypic and genomic analysis of P elements in natural populations of Drosophila melanogaster

The Drosophila melanogaster P transposable element provides one of the best cases of horizontal transfer of a mobile DNA sequence in eukaryotes. Invasion of natural populations by the P element has led to a syndrome of phenotypes known as “P-M hybrid dysgenesis” that emerges when strains differing in their P element composition mate and produce offspring. Despite extensive research on many aspects of P element biology, questions remain about the stability and genomic basis of variation in P-M dysgenesis phenotypes. Here we report the P-M status for a number of populations sampled recently from Ukraine that appear to be undergoing a shift in their P element composition. Gondal dysgenesis assays reveal that Ukrainian populations of D. melanogaster are currently dominated by the P’ cytotype, a cytotype that was previously thought to be rare in nature, suggesting that a new active form of the P element has recently spread in this region. We also compared gondal dysgenesis phenotypes and genomic P element predictions for isofemale strains obtained from three worldwide populations of D. melanogaster in order to guide further work on the molecular basis of differences in cytotype status across populations. We find that the number of euchromatic P elements per strain can vary significantly across populations but that total P element numbers are not strongly correlated with the degree of gondal dysgenesis. Our work shows that rapid changes in cytotype status can occur in natural populations of D. melanogaster, and informs future efforts to decode the genomic basis of geographic and temporal differences in P element induced phenotypes.

A HIGH FREQUENCY OF HERITABLE CHANGES IN NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER IN UKRAINE.

Spontaneous mutations are thought to have a stable rate for a given species. If non-adaptive, they appear at low frequencies and are governed by drift. However, environmental factors have been reported to cause spread of non-adaptive mutations in populations, governed by mechanisms, such as genetic assimilation. In the present study, we report a simultaneous appearance of a mutant and apparently non-adaptive C2 vein in Drosophila melanogaster at higher than expected frequencies in several distant populations, which excludes the role of drift or selection as the cause of the reported mutation frequencies. We discuss explanations of the phenomenon, including the role of external factors, such as temperature, in the possible genetic assimilation of the trait.

Effect of Wolbachia Infection on Aging and Longevity-Associated Genes in Drosophila

Microbiota is known to interact with metabolic and regulatory networks of the host affecting its fitness. The composition of microbiota was shown to change throughout the host aging. Such changes can be likely caused by aging process or, vice versa, changes in microbiota composition can impact the aging process. It is suggested that microbiota plays an important role in life span determination. Several species from the genus Drosophila, especially D. melanogaster, are powerful models to study many biological processes including microbiota functioning and its effects on the host aging. The host fitness can be substantially affected by endosymbiotic bacteria such as Wolbachia that infects up to two-thirds of insects taxa, including Drosophila. Wolbachia was shown to significantly affect Drosophila aging and life span. However, the molecular mechanisms underlying interactions between Wolbachia and Drosophila remain mostly unknown. In this chapter, we summarize data suggesting that Wolbachia-Drosophila molecular cross-talk associated with life span determination and aging can occur through the immune deficiency pathway, stress-induced JNK pathway, insulin/IGF signaling pathway, ecdysteroid biosynthesis and signaling pathway, as well as through the heat shock and autophagy-specific genes/proteins.