Admixture on the northern front: population genomics of range expansion in the white-footed mouse (Peromyscus leucopus) and secondary contact with the deer mouse (Peromyscus maniculatus).

Range expansion has genetic consequences expected to result in differentiated wave-front populations with low genetic variation and potentially introgression from a local species. The northern expansion of Peromyscus leucopus in southern Quebec provides an opportunity to test these predictions using population genomic tools. Our results show evidence of recent and post-glacial expansion. Genome-wide variation in P. leucopus indicates two post-glacial lineages are separated by the St. Lawrence River, with a more recent divergence of populations isolated by the Richelieu River. In two of three transects we documented northern populations with low diversity in at least one genetic measure, although most relationships were not significant. Consistent with bottlenecks and allele surfing during northward expansion, we document a northern-most population with low nucleotide diversity, divergent allele frequencies and the most private alleles, and observed heterozygosity indicates outcrossing. Ancestry proportions revealed putative hybrids of P. leucopus and P. maniculatus. A formal test for gene flow confirmed secondary contact, showing that a reticulate population phylogeny between P. maniculatus and P. leucopus was a better fit to the data than a bifurcating model without gene flow. Thus, we provide the first genomic evidence of gene flow between this pair of species in natural populations. Understanding the evolutionary consequences of secondary contact is an important conservation concern as climate-induced range expansions are expected to result in new hybrid zones between closely related species.

Landscape resistance and habitat combine to provide an optimal model of genetic structure and connectivity at the range margin of a small mammal.

We evaluated the effect of habitat and landscape characteristics on the population genetic structure of the white-footed mouse. We develop a new approach that uses numerical optimization to define a model that combines site differences and landscape resistance to explain the genetic differentiation between mouse populations inhabiting forest patches in southern Québec. We used ecological distance computed from resistance surfaces with Circuitscape to infer the effect of the landscape matrix on gene flow. We calculated site differences using a site index of habitat characteristics. A model that combined site differences and resistance distances explained a high proportion of the variance in genetic differentiation and outperformed models that used geographical distance alone. Urban and agriculture-related land uses were, respectively, the most and the least resistant landscape features influencing gene flow. Our method detected the effect of rivers and highways as highly resistant linear barriers. The density of grass and shrubs on the ground best explained the variation in the site index of habitat characteristics. Our model indicates that movement of white-footed mouse in this region is constrained along routes of low resistance. Our approach can generate models that may improve predictions of future northward range expansion of this small mammal.

Investigation of the population structure of the tick vector of Lyme disease Ixodes scapularis (Acari: Ixodidae) in Canada using mitochondrial cytochrome C oxidase subunit I gene sequences.

Genotyping of Ixodes scapularis Say (Acari: Ixodidae) ticks could enhance understanding of the occurrence and genotypes of I. scapularis-borne pathogens. We investigated the utility of mitochondrial (mt) Cytochrome C Oxidase subunit I gene (cox1) sequences as a tool for understanding the population structure of I. scapularis collected in Canada, where we also investigated the geographic occurrence of different cox1 haplotypes. Sequences obtained from 414 ticks were one of 55 unique haplotypes, most of which grouped into one of six clades. Demographic analysis suggested that cox1 sequences have haplotype and nucleotide diversity comparable to other mt genes. All haplotypes were connected in a single minimum spanning network tree. Despite low fixation index values there were significant differences in the frequency of occurrence of haplotypes of different clades among four geographic regions: 1) Alberta to western Ontario, 2) eastern Ontario, 3) Quebec, and 4) Atlantic Provinces; suggesting that cox1 sequences could reveal population structure differences between I. scapularis in geographically separated populations of northeastern and midwestern North America. Spatial clusters of ticks of the same haplotype identified in regions of southern Quebec and southern Ontario where I. scapularis is invading were consistent with population bottlenecks associated with founder events. These findings suggest that cox1 sequences are useful for the study of I. scapularis population structure, are of sufficient diversity that spatial analyses of haplotypes can be used to identify where I. scapularis is emerging in southern Canada, and may be useful for exploring differences between northeastern and midwestern populations of I. scapularis.

It's about time: small mammal communities and Lyme disease emergence.

Theory predicts that biodiversity changes due to climate warming can mediate the rate of disease emergence. The mechanisms linking biodiversity-disease relationships have been described both theoretically and empirically but remain poorly understood. We investigated the relations between host diversity and abundance and Lyme disease risk in southern Quebec, a region where Lyme disease is rapidly emerging. We found that both the abundance of small mammal hosts and the relative abundance of the tick's natural host, the white-footed mouse (Peromyscus leucopus), influenced measures of disease risk in tick vectors (Borrelia burgdorferi infection abundance and prevalence in tick vectors). Our results suggest that the increase in Lyme disease risk is modulated by regional processes involving the abundance and composition of small mammal assemblages. However, the nature and strength of these relationships was dependent both on time and geographic area. The strong effect of P. leucopus abundance on disease risk we report here is of significant concern, as this competent host is predicted to increase in abundance and occurrence in the region, with the northern shift in the range of North American species under climate warming.

[Vasospastic angina: An under-diagnosed pathology]. / L'angor spastique : une pathologie sous-diagnostiquée.

The clinical and physiopathological clinical entity known as spastic angina or variant angina has been long documented. It remains, however, an under-estimated condition, which is insufficiently diagnosed and explored. This pathology is associated with severe complications such as heart rhythm disorders, which may potentially result in ventricular fibrillation and cause sudden death. In Japan, this condition occurs more frequently and is better documented. Stimulation tests are also carried out more often and have a higher positivity rate than in France where vasospastic angina is less frequently reported and where provocation tests are associated with negative results and are, consequently, performed less often. In order to improve the detection of this pathology, its potential presence should be explored in patients with rest angina who experience chest pain in the second half of the night and also in instances of acute coronary syndrome with sudden death and no angiographically visible coronary artery disease. The diagnosis should be confirmed by means of ergonovine provocation tests. In order to enhance the sensitivity of these tests without increasing the risk of complications, injection of ergonovine should be preferably carried out via the intracoronary route. By increasing the frequency and sensitivity of these tests, this pathology, which responds well to medical treatment in many cases, could be amenable to therapeutic management as any other form of coronary artery disease.

Liver microbiome of Peromyscus leucopus, a key reservoir host species for emerging infectious diseases in North America.

Microbiome studies generally focus on the gut microbiome, which is composed of a large proportion of commensal bacteria. Here we propose a first analysis of the liver microbiome using next generation sequencing as a tool to detect potentially pathogenic strains. We used Peromyscus leucopus, the main reservoir host species of Lyme disease in eastern North America, as a model and sequenced V5-V6 regions of the 16S gene from 18 populations in southern Quebec (Canada). The Lactobacillus genus was found to dominate the liver microbiome. We also detected a large proportion of individuals infected by Bartonella vinsonii arupensis, a human pathogenic bacteria responsible for endocarditis, as well as Borrelia burgdorferi, the pathogen responsible for Lyme disease in North America. We then compared the microbiomes among two P. leucopus genetic clusters occurring on either side of the St. Lawrence River, and did not detect any effect of the host genotype on their liver microbiome assemblage. Finally, we report, for the first time, the presence of B. burgdorferi in a small mammal host from the northern side of the St. Lawrence River, in support of models that have predicted the northern spread of Lyme disease in Canada.