Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust, Schistocerca gregaria

Tychoparthenogenesis, a form of asexual reproduction in which a small proportion of unfertilized eggs can hatch spontaneously, could be an intermediate evolutionary link in the transition from sexual to parthenogenetic reproduction. The lower fitness of tychoparthenogenetic offspring could be due to either developmental constraints or to inbreeding depression in more homozygous individuals. We tested the hypothesis that in populations where inbreeding depression has been purged, tychoparthenogenesis may be less costly. To assess this hypothesis, we compared the impact of inbreeding and parthenogenetic treatments on eight life-history traits (five measuring inbreeding depression and three measuring inbreeding avoidance) in four laboratory populations of the desert locust, Schistocerca gregaria, with contrasted demographic histories. Overall, we found no clear relationship between the population history (illustrated by the levels of genetic diversity or inbreeding) and inbreeding depression, or between inbreeding depression and parthenogenetic capacity. First, there was a general lack of inbreeding depression in every population, except in two populations for two traits. This pattern could not be explained by the purging of inbreeding load in the studied populations. Second, we observed large differences between populations in their capacity to reproduce through tychoparthenogenesis. Only the oldest laboratory population successfully produced parthenogenetic offspring. However, the level of inbreeding depression did not explain the differences in parthenogenetic success between all studied populations. Differences in development constraints may arise driven by random and selective processes between populations. (Résumé d'auteur

Methodological optimization and standardization of the metabarcoding of insects gut microbiome

Metabarcoding analysis of microbiota could help understand how Orthopteran species cope with challenges associated with environmental changes. Since microbial symbionts have a mutually beneficial relationship with its host and play important roles in the immune and physiological systems, they likely impact its ecology and evolution (i.e. plant range, life history, behaviour). In addition, the analysis of the complex pathogenic communities associated with locusts could be useful to discover unexplored pathogens and develop future research on biological control innovation. Yet, current knowledge of Orthopteran-associated microbial communities is limited. This is partly because recognizing cryptic, diverse, and numerous microorganisms hosted by insects is a difficult task. Despite the design of standard genes for their identification and the latest advances in high throughput sequencing, difficulties persist when we look at the microbiota of insects, including Orthopterans. (1) DNA purification is an essential step in all cultivationindependent approaches to characterize microbial diversity. Indeed, the microbial composition is mainly biased by the efficiency of cell lysis. (2) Another critical step for unbiased representation analysis and high taxonomic resolution is the choice of amplicon and primers. In particular, we showed that Enterobacteriacea, common in insects, were poorly resolved with some of currently used amplicons. (3) Moreover, in the case of phytophagous insects, it is necessary to avoid the amplification of plant remains contained in the digestive tract. In this study, we use (1) three mock community standards that contained equal and logarithmic numbers of eight species (ZymoBIOMICS), and equal numbers of twenty other species (ATCC), and (2) six samplesrepresenting the six main orders of insects (Orthoptera, Diptera, Hemiptera, Coleoptera, Hymenoptera and Lepidoptera). On these dedicated samples, we first statistically evaluate the most commonly used DNA purification kit (Qiagen DNeasy Blood and Tissue), two microorganisms-specific DNA purification kits (ZymoBIOMICS-96 bashing beads and DNeasy UltraClean 96 Microbial Kit) and two homemade procedures (bashing beads and enzymatic cocktails added to Qiagen DNeasy Blood and Tissue). These methods are compared on the basis of DNA yield, DNA shearing, reproducibility, and most importantly representation of microbial diversityin 16S rRNA gene sequences. . Secondly, we are currently evaluating the taxonomic representativity and resolution of different 16S gene primers to avoid plant chloroplast genes amplifications. Second, we evaluate, using in silico analyses, (1) the PCR efficiency (representativity), (2) the taxonomic resolution and (3) the risk to amplify plant chloroplasts of already published primers on various variable regions of the 16S gene (V3, V4, V6, V9) and of the rpoB gene. We then test and validate in vitro the best primer candidates on the dedicated samples

Isolation and Characterization of Twelve Polymorphic Microsatellite Loci for the Cocoa Mirid Bug Sahlbergella Singularis

Mirids are the primary pests affecting cocoa production in Africa, but no genetic studies have been conducted on these insects. Here we report the isolation and characterization of 12 polymorphic microsatellite loci for Sahlbergella singularis. A microsatellite-enriched genomic DNA library was developed and screened to identify marker loci. Twelve polymorphic loci were identified by screening 28 individuals collected from one presumed population in cocoa plantations in Southern Cameroon. The number of alleles ranged from 5 to 25, whereas the observed and the expected heterozygosities ranged from 0.179 to 0.786 and from 0.671 to 0.946, respectively. Tests showed significant deviations from HW equilibrium for four loci, but no linkage disequilibrium was detected at any of the loci. No cross-species amplification was observed in two other mirid pests in Africa