It takes three to tango: tripartite interaction between cabbage root flies, their gut microbiome and host plant defense compounds

Plants are constantly attacked by herbivores. To defend themselves, they produce chemical compounds. The plant family Brassicaceae synthesizes glucosinolates (GSL) that are hydrolyzed to toxic isothiocyanates (ITCs) and other compounds during herbivory. Several insect herbivores adapted to their host plant defense system. Microbial communities can play a crucial role in allowing insects to thrive in recalcitrant habitats and feed on toxic food sources. However, adaptation mechanisms in belowground herbivores and the role of gut bacterial communities (GBCs) in this adaptation process remained uninvestigated so far. This thesis aims to understand the molecular mechanisms underpinning the adaptation of the cabbage root fly D. radicum and the turnip root fly D. floralis larvae to the GSL-ITC defense system in their host plants. Biochemical response of roots to D. radicum and D. floralis infestation indicated that the larvae of both Delia species are exposed to the GSL-ITC system while feeding. To elucidate molecular mechanisms that underlie the adaptation processes of Delia species to their host plant's defense system, the genome of D. radicum was assembled and annotated. A combination of metabolomic and transcriptomic analyses revealed that the larvae possess the enzymatic machinery to detoxify ITCs by activating the mercapturic acid conjugation pathway and a hydrolytic pathway. Both mechanisms are likely the results of co-evolutionary processes with their host plants. In addition, 16S amplicon sequencing revealed that the larval GBCs responded to ITCs and likely express their own detoxification mechanism (hydrolytic pathway). How essential the GBCs are for the larvae to detoxify ITCs remains an unanswered question. The results of this thesis provide a knowledge base for understanding mechanisms that underpin co-evolutionary processes between host plants and belowground herbivores

Wolbachia distribution in selected beetle taxa characterized by PCR screens and MLST data

Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia’s effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia–arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages

Infection patterns and fitness effects of Rickettsia and Sodalis symbionts in the green lacewing Chrysoperla carnea

Endosymbionts are widely distributed in insects and can strongly affect their host ecology. The common green lacewing (Chrysoperla carnea) is a neuropteran insect which is widely used in biological pest control. However, their endosymbionts and their interactions with their hosts have not been very well studied. Therefore, we screened for endosymbionts in natural and laboratory populations of Ch. carnea using diagnostic PCR amplicons. We found the endosymbiont Rickettsia to be very common in all screened natural and laboratory populations, while a hitherto uncharacterized Sodalis strain was found only in laboratory populations. By establishing lacewing lines with no, single or co-infections of Sodalis and Rickettsia, we found a high vertical transmission rate for both endosymbionts (>89%). However, we were only able to estimate these numbers for co-infected lacewings. Sodalis negatively affected the reproductive success in single and co-infected Ch. carnea, while Rickettsia showed no effect. We hypothesize that the fitness costs accrued by Sodalis infections might be more tolerable in the laboratory than in natural populations, as the latter are also prone to fluctuating environmental conditions and natural enemies. The economic and ecological importance of lacewings in biological pest control warrants a more profound understanding of its biology, which might be influenced by symbionts

A high‐quality functional genome assembly of delia radicum L. (diptera: anthomyiidae) annotated from egg to adult

Abstract Belowground herbivores are overseen and underestimated, even though they can cause significant economic losses in agriculture. The cabbage root fly Delia radicum (Anthomyiidae) is a common pest in Brassica species, including agriculturally important crops, such as oilseed rape. The damage is caused by the larvae, which feed specifically on the taproots of Brassica plants until they pupate. The adults are aboveground‐living generalists feeding on pollen and nectar. Female flies are attracted by chemical cues in Brassica plants for oviposition. An assembled and annotated genome can elucidate which genetic mechanisms underlie the adaptation of D . radicum to its host plants and their specific chemical defences, in particular isothiocyanates. Therefore, we assembled, annotated and analysed the D . radicum genome using a combination of different next‐generation sequencing and bioinformatic approaches. We assembled a chromosome‐level D . radicum genome using PacBio and Hi‐C Illumina sequence data. Combining Canu and 3D‐DNA genome assembler, we constructed a 1.3 Gbp genome with an N50 of 242 Mbp and 6 pseudo‐chromosomes. To annotate the assembled D . radicum genome, we combined homology‐, transcriptome‐ and ab initio‐prediction approaches. In total, we annotated 13,618 genes that were predicted by at least two approaches. We analysed egg, larval, pupal and adult transcriptomes in relation to life‐stage specific molecular functions. This high‐quality annotated genome of D . radicum is a first step to understanding the genetic mechanisms underlying host plant adaptation. As such, it will be an important resource to find novel and sustainable approaches to reduce crop losses to these pests

Functional Variation in Dipteran Gut Bacterial Communities in Relation to Their Diet, Life Cycle Stage and Habitat

True flies and mosquitos (Diptera) live in habitats and consume diets that pose specific demands on their gut bacterial communities (GBCs). Due to diet specializations, dipterans may have highly diverse and species-specific GBCs. Dipterans are also confronted with changes in habitat and food sources over their lifetime, especially during life history processes (molting, metamorphosis). This may prevent the development of a constant species- or diet-specific GBC. Some dipterans are vectors of several human pathogens (e.g., malaria), which interact with GBCs. In this review, we explore the dynamics that shape GBC composition in some Diptera species on the basis of published datasets of GBCs. We thereby focus on the effects of diet, habitats, and life cycle stages as sources of variation in GBC composition. The GBCs reported were more stage-specific than species- or diet-specific. Even though the presence of GBCs has a large impact on the performance of their hosts, the exact functions of GBCs and their interactions with other organisms are still largely unknown, mainly due to the low number of studies to date. Increasing our knowledge on dipteran GBCs will help to design pest management strategies for the reduction of insecticide resistance, as well as for human pathogen control

Wolbachia distribution in selected beetle taxa characterized by PCR screens and MLST data

Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia’s effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia–arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages

Wolbachia distribution in selected beetle taxa characterized by PCR screens and MLST data

Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia’s effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia–arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages

Syllidae mitochondrial gene order is unusually variable for Annelida

Complete mitochondrial genomes of five syllids (Streptosyllis sp., Eusyllis blomstrandi, Myrianida brachycephala, Typosyllis antoni and Typosyllis sp.) have been obtained using Illumina sequencing. Together with two previous studied taxa (Ramisyllis multicaudata and Trypanobia cryptica), the analysed sequences represent most of the main lineages within the family Syllidae (Anoplosyllinae, Eusyllinae, Autolytinae and Syllinae). The genomic features, gene order and phylogenetic relationships are examined. Unusual for annelids, syllid mitochondrial genomes are highly variable in their gene order. Considering genomic features, such as length, skewness, gene content, and codon bias, most similar to the rest of annelids are the genomes of E. blomstrandi and M. brachycephala, while Streptosyllis sp. and the analysed sylline taxa (R. multicaudata, T. cryptica, T. antoni and Typosyllis sp.) are the most dissimilar. Two methionine tRNA's (trnM) have been found in T. antoni and Typosyllis sp. The mt genomes of these latter taxa are the longest with numerous non-coding regions. The 13 protein coding genes, as well as the rRNA's are used to perform phylogenetic analyses that recovered the relationships within the family explored before by previous authors. The gene order in Syllidae shows very different patterns. E. blomstrandi and M. prolifera show a similar pattern to the one found in Pleistoannelida; however this might have changed at least twice within Syllidae: in Streptosyllis sp. and within Syllinae. All analysed Syllinae show different gene orders, thereby illustrating more variability as all other pleistoannelids analysed so far. The information provided herein allows a more accurate reconstruction of the possible evolutionary scenarios in Syllidae.This study is a contribution of the project “Macroevolutionary transitions in Syllidae” CGL2015-63593-P MINECO/FEDER, UE. MTA was supported by the “José Castillejo” fellow by MINECO (Ministerio de Economía y Competitividad, Spanish Government), reference C2008-00006, for a research stay at the University of Leipzig (Germany). CB is supported by a “Ramón y Cajal” fellow by the MINECO, project no RYC-2014-15615. THS acknowledges support by the German Science Foundation (DFG STR-683/6-1, DFG STR-683/6-2 and DFG STR-683/8-1).Peer Reviewe

Syllidae mitochondrial gene order is unusually variable for Annelida.

Complete mitochondrial genomes of five syllids (Streptosyllis sp., Eusyllis blomstrandi, Myrianida brachycephala, Typosyllis antoni and Typosyllis sp.) have been obtained using Illumina sequencing. Together with two previous studied taxa (Ramisyllis multicaudata and Trypanobia cryptica), the analysed sequences represent most of the main lineages within the family Syllidae (Anoplosyllinae, Eusyllinae, Autolytinae and Syllinae). The genomic features, gene order and phylogenetic relationships are examined. Unusual for annelids, syllid mitochondrial genomes are highly variable in their gene order. Considering genomic features, such as length, skewness, gene content, and codon bias, most similar to the rest of annelids are the genomes of E. blomstrandi and M. brachycephala, while Streptosyllis sp. and the analysed sylline taxa (R. multicaudata, T. cryptica, T. antoni and Typosyllis sp.) are the most dissimilar. Two methionine tRNA's (trnM) have been found in T. antoni and Typosyllis sp. The mt genomes of these latter taxa are the longest with numerous non-coding regions. The 13 protein coding genes, as well as the rRNA's are used to perform phylogenetic analyses that recovered the relationships within the family explored before by previous authors. The gene order in Syllidae shows very different patterns. E. blomstrandi and M. prolifera show a similar pattern to the one found in Pleistoannelida; however this might have changed at least twice within Syllidae: in Streptosyllis sp. and within Syllinae. All analysed Syllinae show different gene orders, thereby illustrating more variability as all other pleistoannelids analysed so far. The information provided herein allows a more accurate reconstruction of the possible evolutionary scenarios in Syllidae

Green lacewings (Neuroptera: Chrysopidae) are commonly associated with a diversity of rickettsial endosymbionts

© The Author(s).[Background]: Bacterial symbionts transmitted from mothers to offspring are found in the majority of arthropods. Numerous studies have illustrated their wide impact on host biology, such as reproduction, behavior, andphysiology One of the most common inherited symbionts is Rickettsia spp. (Alphaproteobacteria, Rickettsiales),which are found in about one-quarter of terrestrial arthropods, as well as in other invertebrates. In insectpopulations, Rickettsia spp. have been reported to cause reproductive modifications and fecundity-enhancingeffects. Here, we investigated the incidence and genetic diversity of Rickettsia symbionts in green lacewings (Neuroptera, Chrysopidae), which are best known for their use as biological control agents against crop pests.[Results]: We screened 18 species of green lacewings and allies for Rickettsia and found the symbiont in 10 species, infecting 20–100% of sampled individuals. Strain characterization based on multiple bacterial loci revealed an unprecedented diversity of Rickettsia associated with lacewings, suggesting multiple independent acquisitions. Further, the detected Rickettsia lineages are restricted to a specific lineage (i.e., species or genus) of investigated lacewings, and these associations are stable across multiple sampled locations and points in time. .[Conclusions]: We conclude that Rickettsia-lacewing symbioses are common and evolutionarily stable. The role of these symbionts remains to be identified, but is potentially important to optimizing their use in biological pest controlMG is currently funded by the European Commission through a Marie Curie Fellowship (H2020-MSCA-IF-2015, 703,379). C.B. is a ‘Ramon y Cajal’ fellow supported by the Spanish Ministry of Science and Education (MEC) (RYC-2014-15,615). Additional funds for consumables were provided by the German Centre for Integrative Biodiversity Research (iDiv).Peer Reviewe