Increased diversity of egg-associated bacteria on brown trout (Salmo trutta) at elevated temperatures.

The taxonomic composition of egg-associated microbial communities can play a crucial role in the development of fish embryos. In response, hosts increasingly influence the composition of their associated microbial communities during embryogenesis, as concluded from recent field studies and laboratory experiments. However, little is known about the taxonomic composition and the diversity of egg-associated microbial communities within ecosystems; e.g., river networks. We sampled late embryonic stages of naturally spawned brown trout at nine locations within two different river networks and applied 16S rRNA pyrosequencing to describe their bacterial communities. We found no evidence for a significant isolation-by-distance effect on the composition of bacterial communities, and no association between neutral genetic divergence of fish host (based on 11 microsatellites) and phylogenetic distances of the composition of their associated bacterial communities. We characterized core bacterial communities on brown trout eggs and compared them to corresponding water samples with regard to bacterial composition and its presumptive function. Bacterial diversity was positively correlated with water temperature at the spawning locations. We discuss this finding in the context of the increased water temperatures that have been recorded during the last 25 years in the study area

Declining diversity of egg-associated bacteria during development of naturally spawned whitefish embryos (Coregonus spp.)

Fish eggs are associated with microbes, whose roles range from mutualism to parasitism. Recent laboratory experiments have shown that the taxonomic composition of associated microbial communities on the egg influences embryonic development. Host genetics also plays an important role in determining the consequences for embryonic growth and survival in this interaction. Moreover, it has been found that the importance of host genetics increases during embryogenesis. These findings suggest that during embryogenesis, the host increasingly influences the composition of its associated microbial community. However, little is known about the composition of microbial communities associated with naturally spawned eggs in the wild. We sampled fertilized whitefish eggs (Coregonus spp.) of different developmental stages from six sub-Alpine lakes and used a universal primer pair and 454 pyrosequencing in order to describe the taxonomic composition of egg-associated bacterial communities. We found bacterial communities on early embryos to be very diverse and to resemble the bacterial composition of the surrounding water environment. The bacterial communities on late embryos were significantly less diverse than on early embryos and displayed a clear shift in taxonomic composition that corresponded poorly with the bacterial composition of the surrounding water environment. The main bacterial components on whitefish eggs in this study were Proteobacteria, Actinobacteria, and Firmicutes, while the five most common families were Leuconostocaceae, Streptococcaceae, Comamonadaceae, Oxalobacteraceae and Moraxellaceae. Their putative relationships with the host are discussed. We conclude that natural symbiotic bacterial communities become more specialized during embryogenesis because of specific interactions with their embryo host

Transmissible spongiforme Enzephalopathien beim Menschen

Transmissible spongiform encephalopathies (TSE) are dementing diseases and have been known to affect humans for over 90 years. The most common of these is the sporadic form of Creutzfeldt-Jakob disease (sCJD), followed by its familial (fCJD) and an iatrogenic (iCJD) form. 1996 a variant of CJD (vCJD) has been described in the UK, of which so far 131 cases have been observed worldwide. Specific biochemical and neuropathological signatures allow to distinguish between vCJD and sCJD and lead to the hypothesis that vCJD is due to transmission of BSE prions to humans. Although promising therapeutical approaches are being investigated, human TSE remain untreatable entities. Thus preventive measures are essential. In Switzerland the population has been exposed to BSE prions, too, but no case of vCJD as described in the UK has been observed until now. Since 2001, however, a so far unexplained increase of sCJD cases is being observed

Incidence of Creutzfeldt-Jakob disease in Switzerland.

The incidence of Creutzfeldt-Jakob disease (CJD) in Switzerland increased two-fold in 2001, and figures from the first quarter of 2002 indicate that it continues to rise. Neither age at onset nor duration of disease were different from previous years. Genetic analysis of the 27 reported cases revealed only one disease-associated mutation in the prion gene. None of the recognised risk factors for acquired CJD were reported on the official notification forms. Glycotype profiling, histopathology, and immunohistochemistry indicate that none of the cases fulfilled the definition of variant CJD, which is thought to be caused by bovine prions. Several scenarios could account for the increase in CJD, including improved reporting, iatrogenic transmission, and transmission of a prion zoonosis

Impact of polymorphic transposable elements on linkage disequilibrium along chromosomes

Abstract Recombination and selection drive the extent of linkage disequilibrium (LD) among loci and therefore affect the reshuffling of adaptive genetic variation. However, it is poorly known to what extent the enrichment of transposable elements (TEs) in recombinationally-inert regions reflects their inefficient removal by purifying selection and whether the presence of polymorphic TEs can modify the local recombination rate. In this study, we investigate how TEs and recombination interact at fine scale along chromosomes and possibly support linked selection in natural populations. Whole-genome sequencing data of 304 individuals from nearby alpine populations of Arabis alpina were used to show that the density of polymorphic TEs is specifically correlated with local LD along chromosomes. Consistent with TEs modifying recombination, the characterization of 28 such LD blocks of up to 5.5Mb in length revealed strong evidence of selective sweeps at a few loci through either site frequency spectrum or haplotype structure. A majority of these blocks were enriched in genes related to ecologically relevant functions such as responses to cold, salt stress or photoperiodism. In particular, the S-locus (i.e. supergene responsible for strict outcrossing) was identified in a LD block with high levels of polymorphic TEs and evidence of selection. Another such LD block was enriched in cold-responding genes and presented evidence of adaptive loci related to photoperiodism and flowering being increasingly linked by polymorphic TEs. These results are consistent with the hypothesis that TEs modify recombination landscapes and thus interact with selection in driving blocks of linked adaptive loci in natural populations. This article is protected by copyright. All rights reserved

Data from: Genome-wide variation in nucleotides and retrotransposons in alpine populations of Arabis alpina (Brassicaceae)

Advances in high-throughput sequencing have promoted the collection of reference genomes and genome-wide diversity. However, the assessment of genomic variation among populations has hitherto mainly been surveyed through single-nucleotide polymorphisms (SNPs) and largely ignored the often major fraction of genomes represented by transposable elements (TEs). Despite accumulating evidence supporting the evolutionary significance of TEs, comprehensive surveys remain scarce. Here, we sequenced the full genomes of 304 individuals of Arabis alpina sampled from four nearby natural populations to genotype SNPs as well as polymorphic long terminal repeat retrotransposons (polymorphic TEs; i.e. presence/absence of TE insertions at specific loci). We identified 291,396 SNPs and 20,548 polymorphic TEs, comparing their contributions to genomic diversity and divergence across populations. Few SNPs were shared among populations and overall showed high population-specific variation, whereas most polymorphic TEs segregated among populations. The genomic context of these two classes of variants further highlighted candidate adaptive loci having a putative impact on functional genes. In particular, 4.96% of the SNPs were identified as non-synonymous or affecting start/stop codons. In contrast, 43% of the polymorphic TEs were present next to Arabis genes enriched in functional categories related to the regulation of reproduction and responses to biotic as well as abiotic stresses. This unprecedented dataset, mapping variation gained from SNPs and complementary polymorphic TEs within and among populations, will serve as a rich resource for addressing microevolutionary processes shaping genome variation