BackgroundOne of the most widespread prokaryotic symbionts of invertebrates is the intracellular bacteria of Wolbachia genus which can be found in about 50% of insect species. Wolbachia causes both parasitic and mutualistic effects on its host that include manipulating the host reproductive systems in order to increase their transmission through the female germline, and increasing the host fitness. One of the mechanisms, promoting adaptation in biological organisms, is a non-specific neuroendocrine stress reaction. In insects, this reaction includes catecholamines, dopamine, serotonin and octopamine, which act as neurotransmitters, neuromodulators and neurohormones. The level of dopamine metabolism correlates with heat stress resistance in Drosophila adults.ResultsTo examine Wolbachia effect on Drosophila survival under heat stress and dopamine metabolism we used five strains carrying the nuclear background of interbred Bi90 strain and cytoplasmic backgrounds with different genotype variants of Wolbachia (produced by 20 backcrosses of Bi90 males with appropriate source of Wolbachia). Non-infected Bi90 strain (treated with tetracycline for 3 generations) was used as a control group. We demonstrated that two of five investigated Wolbachia variants promote changes in Drosophila heat stress resistance and activity of enzymes that produce and degrade dopamine, alkaline phosphatase and dopamine-dependent arylalkylamine N-acetyltransferase. What is especially interesting, wMelCS genotype of Wolbachia increases stress resistance and the intensity of dopamine metabolism, whereas wMelPop strain decreases them. wMel, wMel2 and wMel4 genotypes of Wolbachia do not show any effect on the survival under heat stress or dopamine metabolism. L-DOPA treatment, known to increase the dopamine content in Drosophila, levels the difference in survival under heat stress between all studied groups.ConclusionsThe genotype of symbiont determines the effect that the symbiont has on the stress resistance of the host insect.

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Background Maternally inherited Wolbachia symbionts infect D. melanogaster populations worldwide. Infection rates vary greatly. Genetic diversity of Wolbachia in D. melanogaster can be subdivided into several closely related genotypes coinherited with certain mtDNA lineages. mtDNA haplotypes have the following global distribution pattern: mtDNA clade I is mostly found in North America, II and IV in Africa, III in Europe and Africa, V in Eurasia, VI is global but very rare, and VIII is found in Asia. The wMel Wolbachia genotype is predominant in D. melanogaster populations. However, according to the hypothesis of global Wolbachia replacement, the wMelCS genotype was predominant before the XX century when it was replaced by the wMel genotype. Here we analyse over 1500 fly isolates from the Palearctic region to evaluate the prevalence, genetic diversity and distribution pattrern of the Wolbachia symbiont, occurrence of mtDNA variants, and finally to discuss the Wolbachia genotype global replacement hypothesis. Results All studied Palearctic populations of D. melanogaster were infected with Wolbachia at a rate of 33–100%. We did not observe any significant correlation between infection rate and longitude or latitude. Five previously reported Wolbachia genotypes were found in Palearctic populations with a predominance of the wMel variant. The mtDNA haplotypes of the I_II_III clade and V clade were prevalent in Palearctic populations. To test the recent Wolbachia genotype replacement hypothesis, we examined three genomic regions of CS-like genotypes. Low genetic diversity was observed, only two haplotypes of the CS genotypes with a ‘CCG’ variant predominance were found. Conclusion The results of our survey of Wolbachia infection prevalence and genotype diversity in Palearctic D. melanogaster populations confirm previous studies. Wolbachia is ubiquitous in the Palearctic region. The wMel genotype is dominant with local occurrence of rare genotypes. Together with variants of the V mtDNA clade, the variants of the ‘III+’ clade are dominant in both infected and uninfected flies of Palearctic populations. Based on our data on Wolbachia and mtDNA in different years in some Palearctic localities, we can conclude that flies that survive the winter make the predominant symbiont contribution to the subsequent generation. A comprehensive overview of mtDNA and Wolbachia infection of D. melanogaster populations worldwide does not support the recent glob...

Maternally inherited intracellular bacteria Wolbachia cause both parasitic and mutualistic effects on their numerous insect hosts, including manipulating the host reproductive system in order to increase the bacteria spreading in a host population, and increasing the host fitness. Here, we demonstrate that the type of Wolbachia infection determines the effect on Drosophila melanogaster egg production as a proxy for fecundity, and metabolism of juvenile hormone (JH), which acts as gonadotropin in adult insects. For this study, we used six D. melanogaster lineages carrying the nuclear background of interbred Bi90 lineage and cytoplasmic backgrounds with or without Wolbachia of different genotype variants. The wMelCS genotype of Wolbachia decreases egg production in infected D. melanogaster females in the beginning of oviposition and increases it later (from the sixth day after eclosion), whereas the wMelPop Wolbachia strain causes the opposite effect, and the wMel, wMel2 and wMel4 genotypes of Wolbachia do not show any effect on these traits compared with uninfected Bi90 D. melanogaster females. The intensity of JH catabolism negatively correlates with the fecundity level in the flies carrying both wMelCS and wMelPop Wolbachia. The JH catabolism in females infected with genotypes of the wMel group does not differ from that in uninfected females. The effects of wMelCS and wMelPop infection on egg production can be levelled by the modulation of JH titre (via precocene/JH treatment of the flies). Thus, at least one of the mechanisms promoting the effect of Wolbachia on D. melanogaster female fecundity is mediated by JH.