Spatial patterns of neutral and functional genetic variations reveal patterns of local adaptation in raccoon (Procyon lotor) populations exp

Local adaptation is necessary for population survival and depends on the interplay between responses to selective forces and demographic processes that introduce or retain adaptive and maladaptive attributes. Host-parasite systems are dynamic, varying in space and time, where both host and parasites must adapt to their ever-changing environment in order to survive. We investigated patterns of local adaptation in raccoon populations with varying temporal exposure to the raccoon rabies virus (RRV). RRV infects approximately 85% of the population when epizootic and has been presumed to be completely lethal once contracted; however, disease challenge experiments and varying spatial patterns of RRV spread suggest some level of immunity may exist. We first assessed patterns of local adaptation in raccoon populations along the eastern seaboard of North America by contrasting spatial patterns of neutral (microsatellite loci) and functional, major histocompatibility complex (MHC) genetic diversity and structure. We explored variation of MHC allele frequencies in the light of temporal population exposure to RRV (0-60 years) and specific RRV strains in infected raccoons. Our results revealed high levels of MHC variation (66 DRB exon 2 alleles) and pronounced genetic structure relative to neutral microsatellite loci, indicative of local adaptation. We found a positive association linking MHC genetic diversity and temporal RRV exposure, but no association with susceptibility and resistance to RRV strains. These results have implications for landscape epidemiology studies seeking to predict the spread of RRV and present an example of how population demographics influence the degree to which populations adapt to local selective pressures

Co-administration of the Campylobacter jejuni N-glycan based vaccine with probiotics improves vaccine performance in broiler chickens.

Source attribution studies report that consumption of contaminated poultry is the primary source for acquiring human campylobacteriosis. Oral administration of an engineered Escherichia coli strain expressing the Campylobacter jejuni N-glycan reduces bacterial colonization in specific-pathogen-free leghorn chickens, but only a fraction of birds respond to vaccination. Optimizing the vaccine for commercial broiler chickens has great potential to prevent pathogen entry into the food chain. Here, we tested the same vaccination approach in broilers and observed similar efficacy in pathogen load reduction, stimulation of host IgY response, lack of C. jejuni resistance development, uniformity in microbial gut composition, and bimodal response to treatment. Gut microbiota analysis of leghorn and broiler vaccine responders identified one member of the Clostridiales XIVa cluster, Anaerosporobacter mobilis, significantly more abundant in responder birds. In broilers, co-administration of the live vaccine with A. mobilis or Lactobacillus reuteri, a commonly used probiotic, resulted in increased vaccine efficacy, antibody response, and weight gain. To investigate whether the responder/non-responder effect was due to selection of a C. jejuni 'super colonizer mutant' with altered phase-variable genes, we analysed all polyG-containing loci of the input strain compared to non-responder colony isolates and found no evidence of phase state selection. However, untargeted NMR-based metabolomics identified a potential biomarker negatively correlated with C. jejuni colonization levels possibly linked to the increased microbial diversity in this subgroup. The comprehensive methods used to examine the vaccine response bimodality provide several opportunities to improve the C. jejuni vaccine and the efficacy of any vaccination strategy.ImportanceCampylobacter jejuni is a common cause of human diarrheal disease worldwide and listed by the World Health Organization as a high priority pathogen. C. jejuni infection is typically through the ingestion of contaminated chicken meat, so many efforts are targeted to reduce C. jejuni levels at the source. We previously developed a vaccine that reduces C. jejuni levels in egg-laying chickens. In this study, we improved vaccine performance in meat birds by supplementing with probiotics. In addition, we demonstrated that C. jejuni colonization levels in chickens are negatively correlated with Clostridial abundance, another group of common gut microbes. We describe new methods for vaccine optimization that will assist in improving the C. jejuni vaccine and other vaccines under development

Selection, drift, and introgression shape MHC polymorphism in lizards

The major histocompatibility complex (MHC) has long served as a model for the evolution of adaptive genetic diversity in wild populations. Pathogen-mediated selection is thought to be a main driver of MHC diversity, but it remains elusive to what degree selection shapes MHC diversity in complex biogeographical scenarios where other evolutionary processes (e.g. genetic drift and introgression) may also be acting. Here we focus on two closely related green lizard species, Lacerta trilineata and L. viridis, to address the evolutionary forces acting on MHC diversity in populations with different biogeographic structure. We characterized MHC class I exon 2 and exon 3, and neutral diversity (microsatellites), to study the relative importance of selection, drift, and introgression in shaping MHC diversity. As expected, positive selection was a significant force shaping the high diversity of MHC genes in both species. Moreover, introgression significantly increased MHC diversity in mainland populations, with a primary direction of gene flow from L. viridis to L. trilineata. Finally, we found significantly fewer MHC alleles in island populations, but maintained MHC sequence and functional diversity, suggesting that positive selection counteracted the effect of drift. Overall, our data support that different evolutionary processes govern MHC diversity in different biogeographical scenarios: positive selection occurs broadly while introgression acts in sympatry and drift when the population sizes decrease