Phylogenomic analysis of Wolbachia genomes from the Darwin Tree of Life biodiversity genomics project

Wolbachia: A bacterial weapon against dengue fever- a narrative review of risk factors for dengue fever outbreaks

Arboviruses constitute the largest known group of viruses and are responsible for various infections that impose significant socioeconomic burdens worldwide, particularly due to their link with insect-borne diseases. The increasing incidence of dengue fever in non-endemic regions underscores the urgent need for innovative strategies to combat this public health threat. Wolbachia, a bacterium, presents a promising biological control method against mosquito vectors, offering a novel approach to managing dengue fever. We systematically investigated biomedical databases (PubMed, Web of Science, Google Scholar, Science Direct, and Embase) using "AND" as a Boolean operator with keywords such as "dengue fever," "dengue virus," "risk factors," "Wolbachia," and "outbreak." We prioritized articles that offered significant insights into the risk factors contributing to the outbreak of dengue fever and provided an overview of Wolbachia's characteristics and functions in disease management, considering studies published until December 25, 2024. Field experiments have shown that introducing Wolbachia-infected mosquitoes can effectively reduce mosquito populations and lower dengue transmission rates, signifying its potential as a practical approach for controlling this disease.

Low Wolbachia incidence in Bactrocera and Zeugodacus species from Thailand and genome analysis of Wolbachia associated with Zeugodacus apicalis

Wolbachia are bacterial endosymbionts found widely in arthropods and filarial nematodes. Infecting about half of all arthropod species, Wolbachia manipulate their hosts in various ways, including cytoplasmic incompatibility. Here, we investigated Wolbachia diversity in Bactrocera and Zeugodacus, two prevalent tephritid fruit fly genera, using molecular methods. Wolbachia was only detected in Zeugodacus apicalis (de Meijere) (Diptera: Tephritidae) and not in the other 7 studied species. This newly discovered strain, named wZap, belongs to supergroup B with a 1.3 Mb genome containing 1,248 genes. Phylogenetic analysis of its cytoplasmic incompatibility factor genes cifA and cifB revealed their placement within the Type I clade. Given the presence of cif genes in the wZap genome, further research into their roles in fruit flies could be crucial for developing pest control strategies that exploit CI mechanisms.

Pervasive horizontal transmission of Wolbachia in natural populations of closely related and widespread tropical skipper butterflies

BACKGROUND

The endosymbiotic relationship between Wolbachia bacteria and insects has been of interest for many years due to their diverse types of host reproductive phenotypic manipulation and potential role in the host's evolutionary history and population dynamics. Even though infection rates are high in Lepidoptera and specifically in butterflies, and reproductive manipulation is present in these taxa, less attention has been given to understanding how Wolbachia is acquired and maintained in their natural populations, across and within species having continental geographical distributions.

RESULTS

We used whole genome sequencing data to investigate the phylogenetics, demographic history, and infection rate dynamics of Wolbachia in four species of the Spicauda genus of skipper butterflies (Lepidoptera: Hesperiidae), a taxon that presents sympatric and often syntopic distribution, with drastic variability in species abundance in the Neotropical region. We show that infection is maintained by high turnover rates driven mainly by pervasive horizontal transmissions, while also presenting novel cases of double infection by distantly related supergroups of Wolbachia in S. simplicius.

CONCLUSIONS

Our results suggest that Wolbachia population dynamics is host species-specific, with genetic cohesiveness across wide geographical distributions. We demonstrate that low coverage whole genome sequencing data can be used for an exhaustive assessment of Wolbachia infection in natural populations of butterflies, as well as its dynamics in closely related host species. This ultimately leads to a better understanding of the endosymbiotic population dynamics of Wolbachia and its effects on the host's biology and evolution.

Wolbachia in Antarctic terrestrial invertebrates: Absent or undiscovered?

Interactions between a host organism and its associated microbiota, including symbiotic bacteria, play a crucial role in host adaptation to changing environmental conditions. Antarctica provides a unique environment for the establishment and maintenance of symbiotic relationships. One of the most extensively studied symbiotic bacteria in invertebrates is Wolbachia pipientis, which is associated with a wide variety of invertebrates. Wolbachia is known for manipulating host reproduction and having obligate or facultative mutualistic relationships with various hosts. However, there is a lack of clear understanding of the prevalence of Wolbachia in terrestrial invertebrates in Antarctica. We present the outcomes of a literature search for information on the occurrence of Wolbachia in each of the major taxonomic groups of terrestrial invertebrates (Acari, Collembola, Diptera, Rotifera, Nematoda, Tardigrada). We also performed profiling of prokaryotes based on three marker genes and Kraken2 in available whole genome sequence data obtained from Antarctic invertebrate samples. We found no reports or molecular evidence of Wolbachia in these invertebrate groups in Antarctica. We discuss possible reasons underlying this apparent absence and suggest opportunities for more targeted future research to confirm bacteria's presence or absence.

Disentangling cobionts and contamination in long-read genomic data using sequence composition

The recent acceleration in genome sequencing targeting previously unexplored parts of the tree of life presents computational challenges. Samples collected from the wild often contain sequences from several organisms, including the target, its cobionts, and contaminants. Effective methods are therefore needed to separate sequences. Though advances in sequencing technology make this task easier, it remains difficult to taxonomically assign sequences from eukaryotic taxa that are not well represented in databases. Therefore, reference-based methods alone are insufficient. Here, I examine how we can take advantage of differences in sequence composition between organisms to identify symbionts, parasites, and contaminants in samples, with minimal reliance on reference data. To this end, I explore data from the Darwin Tree of Life project, including hundreds of high-quality HiFi read sets from insects. Visualizing two-dimensional representations of read tetranucleotide composition learned by a variational autoencoder can reveal distinct components of a sample. Annotating the embeddings with additional information, such as coding density, estimated coverage, or taxonomic labels allows rapid assessment of the contents of a dataset. The approach scales to millions of sequences, making it possible to explore unassembled read sets, even for large genomes. Combined with interactive visualization tools, it allows a large fraction of cobionts reported by reference-based screening to be identified. Crucially, it also facilitates retrieving genomes for which suitable reference data are absent.

Sequencing and Analysis of Wolbachia Strains from A and B Supergroups Detected in Sylvatic Mosquitoes from Brazil

Wolbachia are endosymbiotic bacteria that infect a wide range of arthropods and filarial nematodes, often manipulating host reproduction. The efficacy of Wolbachia-based interventions for dengue and chikungunya control has been validated through numerous field studies in recent years. This study aimed to investigate the diversity and prevalence of Wolbachia infections in sylvatic mosquitoes from two locations in Recife, Brazil. Multiple mosquito species were screened for Wolbachia using both target marker gene amplification coupled with Sanger sequencing and whole-genome sequencing (WGS) approaches. Phylogenetic analyses were conducted to classify Wolbachia strains into supergroups and assess their evolutionary relationships. Results revealed the presence of Wolbachia in eleven mosquito species examined, with different infection rates. Both supergroups A and B of Wolbachia strains were identified, with Aedes albopictus showing co-infection by both supergroups through the WGS approach. We also detected indirect evidence of Wolbachia horizontal transmission among mosquitoes and other distant host orders. This study provides valuable insights into the distribution and diversity of Wolbachia in sylvatic mosquitoes from Brazil and adds new important data about Wolbachia detection through target marker gene amplicon coupled with Sanger sequencing and WGS methods, highlighting its complementarity to ascertain the presence of Wolbachia in mosquito samples.

Genome evolution in intracellular parasites: Microsporidia and Apicomplexa

Microsporidia and Apicomplexa are eukaryotic, single-celled, intracellular parasites with huge public health and economic importance. Typically, these parasites are studied separately, emphasizing their uniqueness and diversity. In this review, we explore the huge amount of genomic data that has recently become available for the two groups. We compare and contrast their genome evolution and discuss how their transitions to intracellular life may have shaped it. In particular, we explore genome reduction and compaction, genome expansion and ploidy, gene shuffling and rearrangements, and the evolution of centromeres and telomeres.

Three feminizing Wolbachia strains in a single host species: comparative genomics paves the way for identifying sex reversal factors

Introduction

Endosymbiotic bacteria in the genus Wolbachia have evolved numerous strategies for manipulating host reproduction in order to promote their own transmission. This includes the feminization of males into functional females, a well-studied phenotype in the isopod Armadillidium vulgare. Despite an early description of this phenotype in isopods and the development of an evolutionary model of host sex determination in the presence of Wolbachia, the underlying genetic mechanisms remain elusive.

Methods

Here we present the first complete genomes of the three feminizing Wolbachia (wVulC, wVulP, and wVulM) known to date in A. vulgare. These genomes, belonging to Wolbachia B supergroup, contain a large number of mobile elements such as WO prophages with eukaryotic association modules. Taking advantage of these data and those of another Wolbachia-derived feminizing factor integrated into the host genome (f element), we used a comparative genomics approach to identify putative feminizing factors.

Results

This strategy has enabled us to identify three prophage-associated genes secreted by the Type IV Secretion System: one ankyrin repeat domain-containing protein, one helix-turn-helix transcriptional regulator and one hypothetical protein. In addition, a latrotoxin-related protein, associated with phage relic genes, was shared by all three genomes and the f element.

Conclusion

These putative feminization-inducing proteins shared canonical interaction features with eukaryotic proteins. These results pave the way for further research into the underlying functional interactions.

Franco D, Szklarzewicz T, Stroiński A, Łukasik P. Facultatively intrabacterial localization of a planthopper endosymbiont as an adaptation to its vertical transmission

Transovarial transmission is the most reliable way of passing on essential nutrient-providing endosymbionts from mothers to offspring. However, not all endosymbiotic microbes follow the complex path through the female host tissues to oocytes on their own. Here, we demonstrate an unusual transmission strategy adopted by one of the endosymbionts of the planthopper Trypetimorpha occidentalis (Hemiptera: Tropiduchidae) from Bulgaria. In this species, an Acetobacteraceae endosymbiont is transmitted transovarially within deep invaginations of cellular membranes of an ancient endosymbiont Sulcia-strikingly resembling recently described plant virus transmission. However, in males, Acetobacteraceae colonizes the same bacteriocytes as Sulcia but remains unenveloped. Then, the unusual endobacterial localization of Acetobacteraceae observed in females appears to be a unique adaptation to maternal transmission. Further, the symbiont's genomic features, including encoding essential amino acid biosynthetic pathways and its similarity to a recently described psyllid symbiont, suggest a unique combination of the ability to horizontally transmit among species and confer nutritional benefits. The close association with Acetobacteraceae symbiont correlates with the so-far-unreported level of genomic erosion of ancient nutritional symbionts of this planthopper. In Sulcia, this is reflected in substantial changes in genomic organization, reported for the first time in the symbiont renowned for its genomic stability. In Vidania, substantial gene loss resulted in one of the smallest genomes known, at 108.6 kb. Thus, the symbionts of T. occidentalis display a combination of unusual adaptations and genomic features that expand our understanding of how insect-microbe symbioses may transmit and evolve.IMPORTANCEReliable transmission across host generations is a major challenge for bacteria that associate with insects, and independently established symbionts have addressed this challenge in different ways. The facultatively endobacterial localization of Acetobacteraceae symbiont, enveloped by cells of ancient nutritional endosymbiont Sulcia in females but not males of the planthopper Trypetimorpha occidentalis, appears to be a unique adaptation to maternal transmission. Acetobacteraceae's genomic features indicate its unusual evolutionary history, and the genomic erosion experienced by ancient nutritional symbionts demonstrates the apparent consequences of such close association. Combined, this multi-partite symbiosis expands our understanding of the diversity of strategies that insect symbioses form and some of their evolutionary consequences.

With a little help from my friends: the roles of microbial symbionts in insect populations and communities

To understand insect abundance, distribution and dynamics, we need to understand the relevant drivers of their populations and communities. While microbial symbionts are known to strongly affect many aspects of insect biology, we lack data on their effects on populations or community processes, or on insects' evolutionary responses at different timescales. How these effects change as the anthropogenic effects on ecosystems intensify is an area of intense research. Recent developments in sequencing and bioinformatics permit cost-effective microbial diversity surveys, tracking symbiont transmission, and identification of functions across insect populations and multi-species communities. In this review, we explore how different functional categories of symbionts can influence insect life-history traits, how these effects could affect insect populations and their interactions with other species, and how they may affect processes and patterns at the level of entire communities. We argue that insect-associated microbes should be considered important drivers of insect response and adaptation to environmental challenges and opportunities. We also outline the emerging approaches for surveying and characterizing insect-associated microbiota at population and community scales. This article is part of the theme issue 'Towards a toolkit for global insect biodiversity monitoring'.

Comparative analysis of Wolbachia maternal transmission and localization in host ovaries

Many insects and other animals carry microbial endosymbionts that influence their reproduction and fitness. These relationships only persist if endosymbionts are reliably transmitted from one host generation to the next. Wolbachia are maternally transmitted endosymbionts found in most insect species, but transmission rates can vary across environments. Maternal transmission of wMel Wolbachia depends on temperature in natural Drosophila melanogaster hosts and in transinfected Aedes aegypti, where wMel is used to block pathogens that cause human disease. In D. melanogaster, wMel transmission declines in the cold as Wolbachia become less abundant in host ovaries and at the posterior pole plasm (the site of germline formation) in mature oocytes. Here, we assess how temperature affects maternal transmission and underlying patterns of Wolbachia localization across 10 Wolbachia strains diverged up to 50 million years-including strains closely related to wMel-and their natural Drosophila hosts. Many Wolbachia maintain high transmission rates across temperatures, despite highly variable (and sometimes low) levels of Wolbachia in the ovaries and at the developing germline in late-stage oocytes. Identifying strains like closely related wMel-like Wolbachia with stable transmission across variable environmental conditions may improve the efficacy of Wolbachia-based biocontrol efforts as they expand into globally diverse environments.

Comparative analysis of Wolbachia maternal transmission and localization in host ovaries

Many insects and other animals carry microbial endosymbionts that influence their reproduction and fitness. These relationships only persist if endosymbionts are reliably transmitted from one host generation to the next. Wolbachia are maternally transmitted endosymbionts found in most insect species, but transmission rates can vary across environments. Maternal transmission of wMel Wolbachia depends on temperature in natural Drosophila melanogaster hosts and in transinfected Aedes aegypti, where wMel is used to block pathogens that cause human disease. In D. melanogaster, wMel transmission declines in the cold as Wolbachia become less abundant in host ovaries and at the posterior pole plasm (the site of germline formation) in mature oocytes. Here, we assess how temperature affects maternal transmission and underlying patterns of Wolbachia localization across 10 Wolbachia strains diverged up to 50 million years-including strains closely related to wMel-and their natural Drosophila hosts. Many Wolbachia maintain high transmission rates across temperatures, despite highly variable (and sometimes low) levels of Wolbachia in the ovaries and at the developing germline in late-stage oocytes. Identifying strains like closely related wMel-like Wolbachia with stable transmission across variable environmental conditions may improve the efficacy of Wolbachia-based biocontrol efforts as they expand into globally diverse environments.

MarkerScan: Separation and assembly of cobionts sequenced alongside target species in biodiversity genomics projects

Contamination of public databases by mislabelled sequences has been highlighted for many years and the avalanche of novel sequencing data now being deposited has the potential to make databases difficult to use effectively. It is therefore crucial that sequencing projects and database curators perform pre-submission checks to remove obvious contamination and avoid propagating erroneous taxonomic relationships. However, it is important also to recognise that biological contamination of a target sample with unexpected species' DNA can also lead to the discovery of fascinating biological phenomena through the identification of environmental organisms or endosymbionts. Here, we present a novel, integrated method for detection and generation of high-quality genomes of all non-target genomes co-sequenced in eukaryotic genome sequencing projects. After performing taxonomic profiling of an assembly from the raw data, and leveraging the identity of small rRNA sequences discovered therein as markers, a targeted classification approach retrieves and assembles high-quality genomes. The genomes of these cobionts are then not only removed from the target species' genome but also available for further interrogation. Source code is available from https://github.com/CobiontID/MarkerScan. MarkerScan is written in Python and is deployed as a Docker container.

Bacterial community and genome analysis of cytoplasmic incompatibility-inducing Wolbachia in American serpentine leafminer, Liriomyza trifolii

Liriomyza trifolii, an agricultural pest, is occasionally infected by Wolbachia. A Wolbachia strain present in Liriomyza trifolii is associated with cytoplasmic incompatibility (CI) effects, leading to the death of embryos resulting from incompatible crosses between antibiotic-treated or naturally Wolbachia-free strain females and Wolbachia-infected males. In this study, high-throughput sequencing of hypervariable rRNA genes was employed to characterize the bacterial community in Wolbachia-infected L. trifolii without antibiotic treatment. The analysis revealed that Wolbachia dominates the bacterial community in L. trifolii, with minor presence of Acinetobacter, Pseudomonas, and Limnobacter. To elucidate the genetic basis of the CI phenotype, metagenomic sequencing was also conducted to assemble the genome of the Wolbachia strain. The draft-genome of the Wolbachia strain wLtri was 1.35 Mbp with 34% GC content and contained 1,487 predicted genes. Notably, within the wLtri genome, there are three distinct types of cytoplasmic incompatibility factor (cif) genes: Type I, Type III, and Type V cifA;B. These genes are likely responsible for inducing the strong cytoplasmic incompatibility observed in L. trifolii.

Expression of the Wolbachia male-killing factor Oscar impairs dosage compensation in lepidopteran embryos

Wolbachia are intracellular bacteria in insects that can manipulate the sexual development and reproduction by male killing or other methods. We have recently identified a Wolbachia protein named Oscar that acts as a male-killing factor for lepidopteran insects. Oscar interacts with the Masculinizer (Masc) protein, which is required for both masculinization and dosage compensation (DC) in lepidopteran insects. Embryonic expression of Oscar inhibits masculinization and causes male killing in two lepidopteran species, Ostrinia furnacalis and Bombyx mori. However, it remains unknown whether Oscar-induced male killing is caused by a failure of DC. Here, we performed a transcriptome analysis of Oscar complementary RNA-injected O. furnacalis and B. mori embryos, and found that Oscar primarily targets the Masc protein, resulting in male killing by interfering with DC in lepidopteran insects.

Intracellular symbiont Symbiodolus is vertically transmitted and widespread across insect orders

Insects engage in manifold interactions with bacteria that can shift along the parasitism-mutualism continuum. However, only a small number of bacterial taxa managed to successfully colonize a wide diversity of insects, by evolving mechanisms for host-cell entry, immune evasion, germline tropism, reproductive manipulation, and/or by providing benefits to the host that stabilize the symbiotic association. Here, we report on the discovery of an Enterobacterales endosymbiont (Symbiodolus, type species Symbiodolus clandestinus) that is widespread across at least six insect orders and occurs at high prevalence within host populations. Fluorescence in situ hybridization in several Coleopteran and one Dipteran species revealed Symbiodolus' intracellular presence in all host life stages and across tissues, with a high abundance in female ovaries, indicating transovarial vertical transmission. Symbiont genome sequencing across 16 host taxa revealed a high degree of functional conservation in the eroding and transposon-rich genomes. All sequenced Symbiodolus genomes encode for multiple secretion systems, alongside effectors and toxin-antitoxin systems, which likely facilitate host-cell entry and interactions with the host. However, Symbiodolus-infected insects show no obvious signs of disease, and biosynthetic pathways for several amino acids and cofactors encoded by the bacterial genomes suggest that the symbionts may also be able to provide benefits to the hosts. A lack of host-symbiont cospeciation provides evidence for occasional horizontal transmission, so Symbiodolus' success is likely based on a mixed transmission mode. Our findings uncover a hitherto undescribed and widespread insect endosymbiont that may present valuable opportunities to unravel the molecular underpinnings of symbiosis establishment and maintenance.

The genome of Litomosoides sigmodontis illuminates the origins of Y chromosomes in filarial nematodes

Heteromorphic sex chromosomes are usually thought to have originated from a pair of autosomes that acquired a sex-determining locus and subsequently stopped recombining, leading to degeneration of the sex-limited chromosome. The majority of nematode species lack heteromorphic sex chromosomes and determine sex using an X-chromosome counting mechanism, with males being hemizygous for one or more X chromosomes (XX/X0). Some filarial nematode species, including important parasites of humans, have heteromorphic XX/XY karyotypes. It has been assumed that sex is determined by a Y-linked locus in these species. However, karyotypic analyses suggested that filarial Y chromosomes are derived from the unfused homologue of an autosome involved in an X-autosome fusion event. Here, we generated a chromosome-level reference genome for Litomosoides sigmodontis, a filarial nematode with the ancestral filarial karyotype and sex determination mechanism (XX/X0). By mapping the assembled chromosomes to the rhabditid nematode ancestral linkage (or Nigon) elements, we infer that the ancestral filarial X chromosome was the product of a fusion between NigonX (the ancestrally X-linked element) and NigonD (ancestrally autosomal). In the two filarial lineages with XY systems, there have been two independent X-autosome chromosome fusion events involving different autosomal Nigon elements. In both lineages, the region shared by the neo-X and neo-Y chromosomes is within the ancestrally autosomal portion of the X, confirming that the filarial Y chromosomes are derived from the unfused homologue of the autosome. Sex determination in XY filarial nematodes therefore likely continues to operate via the ancestral X-chromosome counting mechanism, rather than via a Y-linked sex-determining locus.

Detection and Analysis of Wolbachia in Plant-Parasitic Nematodes and Insights into Wolbachia Evolution

Since the discovery of Wolbachia in plant-parasitic nematodes (PPNs), there has been increased interest in this earliest branching clade that may hold important clues to early transitions in Wolbachia function in the Ecdysozoa. However, due to the specialized skills and equipment of nematology and the difficulty in culturing most PPNs, these PPN-type Wolbachia remain undersampled and poorly understood. To date, there are few established laboratory methods for working with PPN-type Wolbachia strains, and most research has relied on chance discovery and comparative genomics. Here, we address this challenge by providing detailed methods to assist researchers with more efficiently collecting PPNs and screen these communities, populations, or single nematodes with a newly developed PPN-type Wolbachia-specific PCR assay. We provide an overview of the typical yields and outcomes of these methods, to facilitate further targeted cultivation or experimental methods, and finally we provide a short introduction to some of the specific challenges and solutions in following through with comparative or population genomics on PPN-type Wolbachia strains.

The cellular lives of Wolbachia

Wolbachia are successful Gram-negative bacterial endosymbionts, globally infecting a large fraction of arthropod species and filarial nematodes. Efficient vertical transmission, the capacity for horizontal transmission, manipulation of host reproduction and enhancement of host fitness can promote the spread both within and between species. Wolbachia are abundant and can occupy extraordinary diverse and evolutionary distant host species, suggesting that they have evolved to engage and manipulate highly conserved core cellular processes. Here, we review recent studies identifying Wolbachia-host interactions at the molecular and cellular levels. We explore how Wolbachia interact with a wide array of host cytoplasmic and nuclear components in order to thrive in a diversity of cell types and cellular environments. This endosymbiont has also evolved the ability to precisely target and manipulate specific phases of the host cell cycle. The remarkable diversity of cellular interactions distinguishes Wolbachia from other endosymbionts and is largely responsible for facilitating its global propagation through host populations. Finally, we describe how insights into Wolbachia-host cellular interactions have led to promising applications in controlling insect-borne and filarial nematode-based diseases.

Complete De Novo Assembly of Wolbachia Endosymbiont of Frankliniella intonsa

As an endosymbiont, Wolbachia exerts significant effects on the host, including on reproduction, immunity, and metabolism. However, the study of Wolbachia in Thysanopteran insects, such as flower thrips Frankliniella intonsa, remains limited. Here, we assembled a gap-free looped genome assembly of Wolbachia strain wFI in a length of 1,463,884 bp (GC content 33.80%), using Nanopore long reads and Illumina short reads. The annotation of wFI identified a total of 1838 protein-coding genes (including 85 pseudogenes), 3 ribosomal RNAs (rRNAs), 35 transfer RNAs (tRNAs), and 1 transfer-messenger RNA (tmRNA). Beyond this basic description, we identified mobile genetic elements, such as prophage and insertion sequences (ISs), which make up 17% of the entire wFI genome, as well as genes involved in riboflavin and biotin synthesis and metabolism. This research lays the foundation for understanding the nutritional mutualism between Wolbachia and flower thrips. It also serves as a valuable resource for future studies delving into the intricate interactions between Wolbachia and its host.

Morphological changes in female reproductive organs in the African monarch butterfly, host to a male-killing Spiroplasma

Background

Sexual selection and conflicts within and between sexes promote morphological diversity of reproductive traits within species. Variation in the morphology of diagnostic reproductive characters within species offer an excellent opportunity to study these evolutionary processes as drivers of species diversification. The African monarch, Danaus chrysippus (Linnaeus, 1758), is widespread across Africa. The species is polytypic, with the respective geographical ranges of the four colour morphs only overlapping in East Africa. Furthermore, some of the populations host an endosymbiotic bacterium, Spiroplasma, which induces son-killing and distorts the local host population sex-ratio, creating sexual conflicts between the females seeking to optimize their fecundity and the limited mating capacity of the rare males.

Methods

We dissected females from Kenya, Rwanda and South Africa, where Spiroplasma vary in presence and prevalence (high, variable and absent, respectively), and conducted microscopy imaging of their reproductive organs. We then characterized the effect of population, female body size, and female mating status, on the size and shape of different genitalia characters of the D. chrysippus female butterflies.

Results

We showed that although the general morphology of the organs is conserved in D. chrysippus, female genitalia vary in size and shape between and within populations. The virgin females have smaller organs, while the same organs were expanded in mated females. Females from highly female-biased populations, where the male-killing Spiroplasma is prevalent, also have a larger area of their corpus bursae covered with signa structures. However, this pattern occurs because a larger proportion of the females remains virgin in the female-biased populations rather than because of male depletion due to the symbiont, as males from sex-ratio distorted populations did not produce significantly smaller nutritious spermatophores.

Wolbachia springs eternal: symbiosis in Collembola is associated with host ecology

Wolbachia are endosymbiotic alpha-proteobacteria infecting a wide range of arthropods and nematode hosts with diverse interactions, from reproductive parasites to obligate mutualists. Their taxonomy is defined by lineages called supergroups (labelled by letters of the alphabet), while their evolutionary history is complex, with multiple horizontal transfers and secondary losses. One of the least recently derived, supergroup E, infects springtails (Collembola), widely distributed hexapods, with sexual and/or parthenogenetic populations depending on species. To better characterize the diversity of Wolbachia infecting springtails, the presence of Wolbachia was screened in 58 species. Eleven (20%) species were found to be positive, with three Wolbachia genotypes identified for the first time in supergroup A. The novel genotypes infect springtails ecologically and biologically different from those infected by supergroup E. To root the Wolbachia phylogeny, rather than distant other Rickettsiales, supergroup L infecting plant-parasitic nematodes was used here. We hypothesize that the ancestor of Wolbachia was consumed by soil-dwelling nematodes, and was transferred horizontally via plants into aphids, which then infected edaphic arthropods (e.g. springtails and oribatid mites) before expanding into most clades of terrestrial arthropods and filarial nematodes.

One strain may hide another: Cryptic male-killing Wolbachia

While heritable symbionts are common in insects, strains that act as male-killers are considered rare. A new study in PLOS Biology identifies a novel male-killer hidden by coinfection and host resistance, highlighting the complexity of host-microbial interactions in natural systems.