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Animal-bacterial symbioses are highly dynamic in terms of multipartite interactions, both between the host and its symbionts as well as between the different bacteria constituting the symbiotic community. These interactions will be reflected by the titres of the individual bacterial taxa, for example via host regulation of bacterial loads or competition for resources between symbionts. Moreover, different host tissues represent heterogeneous microhabitats for bacteria, meaning that host-associated bacteria might establish tissue-specific bacterial communities. Wolbachia are widespread endosymbiotic bacteria, infecting a large number of arthropods and filarial nematodes. However, relatively little is known regarding direct interactions between Wolbachia and other bacteria. This study represents the first quantitative investigation of tissue-specific Wolbachia-microbiota interactions in the terrestrial isopod Armadillidium vulgare. To this end, we obtained a more complete picture of the Wolbachia distribution patterns across all major host tissues, integrating all three feminizing Wolbachia strains (wVulM, wVulC, wVulP) identified to date in this host. Interestingly, the different Wolbachia strains exhibited strain-specific tissue distribution patterns, with wVulM reaching lower titres in most tissues. These patterns were consistent across different host genetic backgrounds and might reflect different co-evolutionary histories between the Wolbachia strains and A. vulgare. Moreover, Wolbachia-infected females carried higher total bacterial loads in several, but not all, tissues, irrespective of the Wolbachia strain. Taken together, this quantitative approach indicates that Wolbachia is part of a potentially more diverse bacterial community, as exemplified by the presence of highly abundant bacterial taxa in the midgut caeca of several A. vulgare populations.

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BackgroundEmerging methods of massive sequencing that allow for rapid re-sequencing of entire genomes at comparably low cost are changing the way biological questions are addressed in many domains. Here we propose a novel method to compare two genomes (genome-to-genome comparison). We used this method to identify sex-specific sequences of the human blood fluke Schistosoma mansoni.ResultsGenomic DNA was extracted from male and female (heterogametic) S. mansoni adults and sequenced with a Genome Analyzer (Illumina). Sequences are available at the NCBI sequence read archive http://www.ncbi.nlm.nih.gov/Traces/sra/ under study accession number SRA012151.6. Sequencing reads were aligned to the genome, and a pseudogenome composed of known repeats. Straightforward comparative bioinformatics analysis was performed to compare male and female schistosome genomes and identify female-specific sequences. We found that the S. mansoni female W chromosome contains only few specific unique sequences (950 Kb i.e. about 0.2% of the genome). The majority of W-specific sequences are repeats (10.5 Mb i.e. about 2.5% of the genome). Arbitrarily selected W-specific sequences were confirmed by PCR. Primers designed for unique and repetitive sequences allowed to reliably identify the sex of both larval and adult stages of the parasite.ConclusionOur genome-to-genome comparison method that we call "whole-genome in-silico subtractive hybridization" (WISH) allows for rapid identification of sequences that are specific for a certain genotype (e.g. the heterogametic sex). It can in principle be used for the detection of any sequence differences between isolates (e.g. strains, pathovars) or even closely related species.

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BackgroundCorrelational studies strongly suggest that both genetic similarity and heterozygosity can influence female mate choice. However, the influence of each variable has usually been tested independently, although similarity and heterozygosity might be correlated. We experimentally determined the relative influence of genetic similarity and heterozygosity in divorce and re-mating in the monogamous endoparasite Schistosoma mansoni.Methodology/Principal FindingsWe performed sequential infections of vertebrate hosts with controlled larval populations of parasites, where sex and individual genetic diversity and similarity were predetermined before infection. Divorce rate increased significantly when females were given the opportunity to increase genetic dissimilarity through re-mating with a new partner, independently of the intensity of male-male competition. We found however no evidence for females attempting to maximize the level of heterozygosity of their reproductive partner through divorce.Conclusions/SignificanceFemale preference for genetically dissimilar males should result in more heterozygous offspring. Because genetic heterozygosity might partly determine the ability of parasites to counter host resistance, adaptive divorce could be an important factor in the evolutionary arms race between schistosomes and their hosts.

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Host exploitation induces host defence responses and competition between parasites, resulting in individual parasites facing highly variable environments. Alternative life strategies may thus be expressed in context-dependent ways, depending on which host species is used and intra-host competition between parasites. Coitocaecum parvum (Trematode) can use facultative progenesis in amphipod intermediate hosts, Paracalliope fluviatilis, to abbreviate its life cycle in response to such environmental factors. Coitocaecum parvum also uses another amphipod host, Paracorophium excavatum, a species widely different in size and ecology from P. fluviatilis. In this study, parasite infection levels and strategies in the two amphipod species were compared to determine whether the adoption of progenesis by C. parvum varied between these two hosts. Potential differences in size and/or egg production between C. parvum individuals according to amphipod host species were also investigated. Results show that C. parvum life strategy was not influenced by host species. In contrast, host size significantly affected C. parvum strategy, size and egg production. Since intra-host interactions between co-infecting parasites also influenced C. parvum strategy, size and fecundity, it is highly likely that within-host resource limitations affect C. parvum life strategy and overall fitness regardless of host species.