Development and characterization of microsatellite markers for the tsetse species Glossina brevipalpis and preliminary population genetics analyses.

Tsetse flies, the vectors of African trypanosomes are of key medical and economic importance and one of the constraints for the development of Africa. Tsetse fly control is one of the most effective and sustainable strategies used for controlling the disease. Knowledge about population structure and level of gene flow between neighbouring populations of the target vector is of high importance to develop appropriate strategies for implementing effective management programmes. Microsatellites are commonly used to identify population structure and assess dispersal of the target populations and have been developed for several tsetse species but were lacking for Glossina brevipalpis. In this study, we screened the genome of G. brevipalpis to search for suitable microsatellite markers and nine were found to be efficient enough to distinguish between different tsetse populations. The availability of these novel microsatellite loci will help to better understand the population biology of G. brevipalpis and to assess the level of gene flow between different populations. Such information will help with the development of appropriate strategies to implement the sterile insect technique (SIT) in the framework of an area-wide integrated pest management (AW-IPM) approach to manage tsetse populations and ultimately address the trypanosomoses problem in these targeted areas.

Title: Développement et caractérisation de marqueurs microsatellites pour l'espèce de mouche tsé-tsé Glossina brevipalpis et analyses génétiques préliminaires des populations. Abstract: Les mouches tsé-tsé, vecteurs des trypanosomes africains, sont d'une importance médicale et économique majeure et l'une des contraintes pour le développement de l'Afrique. La lutte contre la mouche tsé-tsé est l'une des stratégies les plus efficaces et durables utilisées pour contrôler la maladie. La connaissance de la structure de la population et du niveau de flux de gènes entre les populations voisines du vecteur cible est d'une grande importance pour développer des stratégies appropriées pour la mise en œuvre de programmes de gestion efficaces. Les microsatellites sont couramment utilisés pour identifier la structure de la population et évaluer la dispersion des populations cibles et ont été développés pour plusieurs espèces de glossines mais manquaient pour Glossina brevipalpis. Dans cette étude, nous avons criblé le génome de G. brevipalpis pour rechercher des marqueurs microsatellites appropriés et neuf ont été trouvés suffisamment efficaces pour faire la distinction entre différentes populations de glossines. La disponibilité de ces nouveaux locus microsatellites aidera à mieux comprendre la biologie des populations de G. brevipalpis et à évaluer le niveau de flux de gènes entre différentes populations. Ces informations aideront à l'élaboration de stratégies appropriées pour mettre en œuvre la technique de l'insecte stérile dans le cadre d'une approche de lutte antiparasitaire intégrée à l'échelle de la zone pour gérer les populations de glossines et, en fin de compte, résoudre le problème des trypanosomoses dans les zones concernées.

Prevalence of Trypanosoma and Sodalis in wild populations of tsetse flies and their impact on sterile insect technique programmes for tsetse eradication.

The sterile insect technique (SIT) is an environment friendly and sustainable method to manage insect pests of economic importance through successive releases of sterile irradiated males of the targeted species to a defined area. A mating of a sterile male with a virgin wild female will result in no offspring, and ultimately lead to the suppression or eradication of the targeted population. Tsetse flies, vectors of African Trypanosoma, have a highly regulated and defined microbial fauna composed of three bacterial symbionts that may have a role to play in the establishment of Trypanosoma infections in the flies and hence, may influence the vectorial competence of the released sterile males. Sodalis bacteria seem to interact with Trypanosoma infection in tsetse flies. Field-caught tsetse flies of ten different taxa and from 15 countries were screened using PCR to detect the presence of Sodalis and Trypanosoma species and analyse their interaction. The results indicate that the prevalence of Sodalis and Trypanosoma varied with country and tsetse species. Trypanosome prevalence was higher in east, central and southern African countries than in west African countries. Tsetse fly infection rates with Trypanosoma vivax and T. brucei sspp were higher in west African countries, whereas tsetse infection with T. congolense and T. simiae, T. simiae (tsavo) and T. godfreyi were higher in east, central and south African countries. Sodalis prevalence was high in Glossina morsitans morsitans and G. pallidipes but absent in G. tachinoides. Double and triple infections with Trypanosoma taxa and coinfection of Sodalis and Trypanosoma were rarely observed but it occurs in some taxa and locations. A significant Chi square value (< 0.05) seems to suggest that Sodalis and Trypanosoma infection correlate in G. palpalis gambiensis, G. pallidipes and G. medicorum. Trypanosoma infection seemed significantly associated with an increased density of Sodalis in wild G. m. morsitans and G. pallidipes flies, however, there was no significant impact of Sodalis infection on trypanosome density.

Infection with endosymbiotic Spiroplasma disrupts tsetse (Glossina fuscipes fuscipes) metabolic and reproductive homeostasis.

Tsetse flies (Glossina spp.) house a population-dependent assortment of microorganisms that can include pathogenic African trypanosomes and maternally transmitted endosymbiotic bacteria, the latter of which mediate numerous aspects of their host's metabolic, reproductive, and immune physiologies. One of these endosymbionts, Spiroplasma, was recently discovered to reside within multiple tissues of field captured and laboratory colonized tsetse flies grouped in the Palpalis subgenera. In various arthropods, Spiroplasma induces reproductive abnormalities and pathogen protective phenotypes. In tsetse, Spiroplasma infections also induce a protective phenotype by enhancing the fly's resistance to infection with trypanosomes. However, the potential impact of Spiroplasma on tsetse's viviparous reproductive physiology remains unknown. Herein we employed high-throughput RNA sequencing and laboratory-based functional assays to better characterize the association between Spiroplasma and the metabolic and reproductive physiologies of G. fuscipes fuscipes (Gff), a prominent vector of human disease. Using field-captured Gff, we discovered that Spiroplasma infection induces changes of sex-biased gene expression in reproductive tissues that may be critical for tsetse's reproductive fitness. Using a Gff lab line composed of individuals heterogeneously infected with Spiroplasma, we observed that the bacterium and tsetse host compete for finite nutrients, which negatively impact female fecundity by increasing the length of intrauterine larval development. Additionally, we found that when males are infected with Spiroplasma, the motility of their sperm is compromised following transfer to the female spermatheca. As such, Spiroplasma infections appear to adversely impact male reproductive fitness by decreasing the competitiveness of their sperm. Finally, we determined that the bacterium is maternally transmitted to intrauterine larva at a high frequency, while paternal transmission was also noted in a small number of matings. Taken together, our findings indicate that Spiroplasma exerts a negative impact on tsetse fecundity, an outcome that could be exploited for reducing tsetse population size and thus disease transmission.

Evidence for multiple introductions of an invasive wild bee species currently under rapid range expansion in Europe.

BACKGROUND: Invasive species are increasingly driving biodiversity decline, and knowledge of colonization dynamics, including both drivers and dispersal modes, are important to prevent future invasions. The bee species Megachile sculpturalis (Hymenoptera: Megachilidae), native to East-Asia, was first recognized in Southeast-France in 2008, and has since spread throughout much of Europe. The spread is very fast, and colonization may result from multiple fronts. RESULT: To track the history of this invasion, codominant markers were genotyped using Illumina sequencing and the invasion history and degree of connectivity between populations across the European invasion axis were investigated. Distinctive genetic clusters were detected with east-west differentiations in Middle-Europe. CONCLUSION: We hypothesize that the observed cluster formation resulted from multiple, independent introductions of the species to the European continent. This study draws a first picture of an early invasion stage of this wild bee and forms a foundation for further investigations, including studies of the species in their native Asian range and in the invaded range in North America.