Nicolas Bech

Follow-up of the genetic diversity and snail infectivity of a Schistosoma mansoni strain from field to laboratory

Schistosoma mansoni is an endoparasite causing a serious human disease called schistosomiasis. The quantification of parasite genetic diversity is an essential component to understand schistosomiasis epidemiology and disease transmission patterns but some studies on parasite genetic diversity are performed using parasite laboratory strains. However, a potential discrepancy in level of genetic variation between field populations and laboratory strains may have various implications in our deductions. In this study, 246 adult worms were analysed on 15 microsatellite markers to investigate variation of genetic diversity between a founder field isolate and the nine successive laboratory generations during three years of laboratory maintenance. In parallel, we measured a parasite life trait (snail infectivity) at each generation in order to test a potential link between inbreeding and snail infectivity. Our genetic analyses demonstrate a significant genetic differentiation between all parasite generations and a significant isolation by time associated with a decrease in neutral genetic diversity that is likely to be the result of successive bottleneck events. However, while snail infectivity decreases sharply between field isolate and the first laboratory generation, this parasite life trait does not evolve between other laboratory generations and appeared disconnected from this continuous neutral genetic diversity loss. We hypothesize that a sufficient level of compatibility polymorphism at a genomic level is maintained independently of an increase of inbreeding, ensuring the stability in the parasite life trait.

Multi-Infections of Feminizing Wolbachia Strains in Natural Populations of the Terrestrial Isopod Armadillidium Vulgare

Maternally inherited Wolbachia (α-Proteobacteria) are widespread parasitic reproductive manipulators. A growing number of studies have described the presence of different Wolbachia strains within a same host. To date, no naturally occurring multiple infections have been recorded in terrestrial isopods. This is true for Armadillidium vulgare which is known to harbor non simultaneously three Wolbachia strains. Traditionally, such Wolbachia are detected by PCR amplification of the wsp gene and strains are characterized by sequencing. The presence of nucleotide deletions or insertions within the wsp gene, among these three different strains, provides the opportunity to test a novel genotyping method. Herein, we designed a new primer pair able to amplify products whose lengths are specific to each Wolbachia strain so as to detect the presence of multi-infections in A. vulgare. Experimental injections of Wolbachia strains in Wolbachia-free females were used to validate the methodology. We re-investigated, using this novel method, the infection status of 40 females sampled in 2003 and previously described as mono-infected based on the classical sequencing method. Among these females, 29 were identified as bi-infected. It is the first time that naturally occuring multiple infections of Wolbachia are detected within an individual A. vulgare host. Additionally, we resampled 6 of these populations in 2010 to check the infection status of females.

Isolation and characterization of microsatellite loci for the isopod crustacean Armadillidium vulgare and transferability in terrestrial isopods.

Armadillidium vulgare is a terrestrial isopod (Crustacea, Oniscidea) which harbors Wolbachia bacterial endosymbionts. A. vulgare is the major model for the study of Wolbachia-mediated feminization of genetic males in crustaceans. As a consequence of their impact on host sex determination mechanisms, Wolbachia endosymbionts are thought to significantly influence A. vulgare evolution on various grounds, including population genetic structure, diversity and reproduction strategies. To provide molecular tools for examining these questions, we isolated microsatellite loci through 454 pyrosequencing of a repeat-enriched A. vulgare genomic library. We selected 14 markers and developed three polymorphic microsatellite multiplex kits. We tested the kits on two A. vulgare natural populations and found high genetic variation, thereby making it possible to investigate the impact of Wolbachia endosymbionts on A. vulgare nuclear variation at unprecedented resolution. In addition, we tested the transferability of these kits by cross-species amplification in five other terrestrial isopod species harboring Wolbachia endosymbionts. The microsatellite loci showed good transferability in particular in Armadillidium nasatum and Chaetophiloscia elongata, for which these markers represent promising tools for future genetic studies.

Cross-species amplification tests and diversity analysis using 56 PCR markers in Dactylis glomerata and Lolium perenne.

We report results of cross‐species amplification in Dactylis glomerata and Lolium perenne of 12 simple sequence repeats (SSRs) isolated from Lolium multiflorum×Festuca glaucescens, 42 SSRs from Festuca arundinacea and two sequence tagged sites from Oryza sativa. We compared the transferability and diversity between D. glomerata and L. perenne, which are important forage crops. While Neis gene diversity values were equivalent in both species (from 0.14 to 0.92), the mean number of allele per locus was more important in D. glomerata than in L. perenne (5.45 vs. 4.50). These markers will be used for analysing population structure in grassland populations under agronomic practices.

Transferability of microsatellite markers among economically and ecologically important galliform birds

We used the partially sequenced genomes of the turkey and chicken to find a large number of microsatellite markers. We then characterized 10 polymorphic microsatellite markers developed by cross-species amplification from economically and ecologically important birds to various European sub-species of the grey partridge. Even though we used cross-species amplification, a high degree of polymorphism was conserved in all microsatellite markers. Cross-species amplification from birds of economic and ecological interest, such as chicken and turkey, could be an attractive approach to develop microsatellite markers and to use these to manage wild and captive populations of other galliforms, such as the grey partridge.

Pyrenean ptarmigans decline under climatic and human influences through the Holocene

In Europe, the Quaternary is characterized by climatic fluctuations known to have led to many cycles of contraction and expansion of species geographical ranges. In addition, during the Holocene, historical changes in human occupation such as colonization or abandonment of traditional land uses can also affect habitats. These climatically or anthropically induced geographic range changes are expected to produce considerable effective population size change, measurable in terms of genetic diversity and organization. The rock ptarmigan (Lagopus muta) is a small-bodied grouse occurring throughout Northern hemispheric arctic and alpine tundra. This species is not considered threatened at a continental scale, but the populations in the Pyrenees are of concern because of their small population size, geographical isolation and low genetic diversity. Here, we used 11 microsatellites to investigate genetic variations and differentiations and infer the overall demographic history of Pyrenean rock ptarmigan populations. The low genetic variability found in these populations has been previously thought to be the result of a bottleneck that occurred following the last glacial maximum (i.e., 10u2009000 years ago) or more recently (i.e., during the last 200 years). Our results clearly indicate a major bottleneck affecting the populations in the last tenth of the Holocene. We discuss how this decline can be explained by a combination of unfavorable and successive events that increased the degree of habitat fragmentation.

Multiple paternity in a wild population of Armadillidium vulgare : influence of infection with Wolbachia ?

Female multiple mating has been extensively studied to understand how nonobvious benefits, generally thought to be of genetic nature, could overcome heavy costs such as an increased risk of infection during mating. However, the impact of infection itself on multiple mating has rarely been addressed. The interaction between the bacterium Wolbachia and its terrestrial crustacean host, Armadillidium vulgare, is a relevant model to investigate this question. In this association, Wolbachia is able to turn genetic males into functional females (i.e. feminization), thereby distorting the sex ratio and decreasing the number of available males at the population scale. Moreover, in A. vulgare, females have been shown to mate multiply under laboratory conditions and males prefer uninfected females over infected ones. Additionally, different Wolbachia strains are known to infect A. vulgare and these strains differ in their transmission rate and virulence. All these elements suggest a potential impact of different Wolbachia strains on multiple mating. To investigate this assumption, we collected gravid females in a wild A. vulgare population harbouring both uninfected females and females infected with one of two different Wolbachia strains (wVulM and wVulC) and performed paternity analyses on the obtained broods using microsatellite markers. We demonstrate that (i) multiple paternity is common in this wild population of A. vulgare, with a mean number of fathers of 4.48 ± 1.24 per brood and (ii) females infected with wVulC produced broods with a lower multiple paternity level compared with females infected with wVulM and uninfected ones. This work improves our knowledge of the impact of infections on reproductive strategies.

An American termite in Paris: temporal colony dynamics

Termites of the genus Reticulitermes are widespread invaders, particularly in urban habitats. Their cryptic and subterranean lifestyle makes them difficult to detect, and we know little about their colony dynamics over time. In this study we examined the persistence of Reticulitermes flavipes (Kollar) colonies in the city of Paris over a period of 15xa0years. The aim was (1) to define the boundaries of colonies sampled within the same four areas over two sampling periods, (2) to determine whether the colonies identified during the first sampling period persisted to the second sampling period, and (3) to compare the results obtained when colonies were delineated using a standard population genetic approach versus a Bayesian clustering method that combined both spatial and genetic information. Herein, colony delineations were inferred from genetic differences at nine microsatellite loci and one mitochondrial locus. Four of the 18 identified colonies did not show significant differences in their genotype distributions between the two sampling periods. While allelic richness was low, making it hard to reliably distinguish colony family type, most colonies appeared to retain the same breeding structure over time. These large and expansive colonies showed an important ability to fuse (39% were mixed-family colonies), contained hundreds of reproductives and displayed evidence of isolation-by-distance, suggesting budding dispersal. These traits, which favor colony persistence over time, present a challenge for pest control efforts, which apply treatment locally. The other colonies showed significant differences, but we cannot exclude the possibility that their genotype distributions simply changed over time.

Development of a microsatellite primer set to investigate the genetic population structure of Armadillidium nasatum (Crustacea, Oniscidea).

An essential tool in molecular ecology studies, the microsatellite markers allow the investigation of the genetic structure of populations. Here, we developed a panel of 12 polymorphic microsatellite markers isolated from a combination of two approaches: 454 pyrosequencing of a repeat-enriched genomic library and cross-species amplification. These microsatellite markers were isolated from Armadillidium nasatum for which they represent a promising tool regarding genetic studies. Moreover, this study increases the available number of microsatellite markers for A. vulgare and A. depressum for which some of these markers have also been amplified. A. nasatum is a terrestrial isopod (Crustacea, Oniscidea) belonging to the family Armadillidiidae (Vandel 1962). Terrestrial isopods are sensitive to environmental disturbances (Paoletti and Cantarino 2002) and pollutions (Sastrodihardjo and Van Straalen 1993). Thus, they provide information on the environmental quality of agroecosystems and are indeed considered as bioindicators (Souty-Grosset et al. 2005a). For example, grassland habitats in western France are managed in relation to woodlouse biodiversity (Souty-Grosset et al. 2005b). Terrestrial isopods are members of the detritivore guild promoting decomposition processes and nutrient cycling (Paoletti and Hassall 1999), consequently playing a key role in ecosystem services (Berg et al. 2010; David and Handa 2010). They constitute an interesting model because they are indispensable for biochemical ecosystem balance (Paoletti and Hassall 1999) and because of their suitability for measuring the direct effects of human activities on their habitats. Human practices such as soil tillage, pesticide application, chemical pollution, along with soil acidification adversely affect the soil macrofauna abundance

Spatial and genetic distribution of a north American termite, Reticulitermes flavipes, across the landscape of Paris

Urbanization often negatively impacts biological diversity. Some organisms, however, have traits that are preadapted to urban environments and thus may thrive. Reticulitermes flavipes is one such organism. Indigenous to the Eastern US, it has been introduced into multiple countries. In France, R. flavipes causes major damage to buildings. Although Paris is one of the country’s most infested cities, the factors determining R. flavipes’ distribution and propagation are poorly understood. Using data on termite occurrence, termite genetics, and environmental variables, our study aims to identify factors that explain the distribution and spread of R. flavipes within Paris. First, we explored the association between several environmental variables and the termite’s distribution pattern in Paris; since 2000, a total of 2106 infestations have been recorded. Second, we inferred termite population and colony genetic structure at 66 sample locations using 9 microsatellite loci. Third, we used least-cost models and partial Mantel tests to study the effects of environmental variables on the termite’s population genetic structure. Our analyses revealed that building-related variables were significantly associated with termite infestations and could thus help explain the termite’s spatial distribution pattern. Furthermore, railway networks also explain termite propagation and genetic patterns. Additionally, we found that the termite’s spread is likely driven by budding dispersal, which may be constrained by buildings and roads. Even if budding dispersal could facilitate R. flavipes’ spread in urban areas, it cannot explain the termite’s distribution in Paris all on its own. Indeed, termite propagation seems to be significantly driven by anthropogenic activities.