The Genetic Signature of Range Expansion in a Disease Vector-The Black-Legged Tick.

Monitoring and predicting the spread of emerging infectious diseases requires that we understand the mechanisms of range expansion by its vectors. Here, we examined spatial and temporal variation of genetic structure among 13 populations of the Lyme disease vector, the black-legged tick, in southern Quebec, where this tick species is currently expanding and Lyme disease is emerging. Our objective was to identify the primary mode of tick movement into Canada based on observed spatial and temporal genetic patterns. Upon genotyping 10 microsatellite loci from 613 tick specimens, we found multiple genetic signatures of frequent long-distance dispersal events, supporting the hypothesis that migratory birds are the primary carriers of black-legged ticks into southern Quebec. When we compared results from analyses of pairwise differences among ticks collected from 8 different sites at different years between 2011 and 2014, we found that genetic variation observed among tick individuals appeared to be better explained by collection year than sampling locality. This suggests that while cohorts of black-legged ticks can rapidly invade large areas across southern Quebec, they also appear to be undergoing frequent turnover. Finally, the amount of genetic variation in tick populations across our study area appeared to be related to their degree of establishment, with established populations displaying a lower amount of temporal genetic variation than adventitious ones. Given that Lyme disease infection risk in a region can be influenced by the relative presence of established and/or adventitious tick populations, our results are useful for understanding both the seasonality and spatial variation of Lyme disease.

Microsatellite markers reveal low frequency of natural hybridization between the white-footed mouse (Peromyscus leucopus) and deer mouse (Peromyscus maniculatus) in southern Quebec, Canada.

In some parts of southern Quebec, two closely related rodent species - the white-footed mouse (Peromyscus leucopus) and the deer mouse (Peromyscus maniculatus) - have recently come in contact because of climate-driven changes in the distribution of the former. Both species share similar morphology, ecology, and life history traits, which suggests that natural hybridization may be possible. Hybridization among these two species can have important implications on the ecological roles these rodents play in disease transmission, yet few researchers have attempted to examine this phenomenon and results from previous hybridization experiments have remained inconclusive and conflicting. In this study, we attempt to investigate the occurrence of hybridization among white-footed mice and deer mice in southern Quebec by genotyping wild caught specimens with selectively neutral, polymorphic microsatellite markers. Our analyses suggest that hybridization may be occurring at extremely low frequency between both species in our study area. The presence of such hybridization events, even at low frequencies, may have implications on disease transmission risk in the region and further detailed studies are necessary.

Multi-taxa integrated landscape genetics for zoonotic infectious diseases: deciphering variables influencing disease emergence.

Zoonotic disease transmission systems involve sets of species interacting with each other and their environment. This complexity impedes development of disease monitoring and control programs that require reliable identification of spatial and biotic variables and mechanisms facilitating disease emergence. To overcome this difficulty, we propose a framework that simultaneously examines all species involved in disease emergence by integrating concepts and methods from population genetics, landscape ecology, and spatial statistics. Multi-taxa integrated landscape genetics (MTILG) can reveal how interspecific interactions and landscape variables influence disease emergence patterns. We test the potential of our MTILG-based framework by modelling the emergence of a disease system across multiple species dispersal, interspecific interaction, and landscape scenarios. Our simulations showed that both interspecific-dependent dispersal patterns and landscape characteristics significantly influenced disease spread. Using our framework, we were able to detect statistically similar inter-population genetic differences and highly correlated spatial genetic patterns that imply species-dependent dispersal. Additionally, species that were assigned coupled-dispersal patterns were affected to the same degree by similar landscape variables. This study underlines the importance of an integrated approach to investigating emergence of disease systems. MTILG is a robust approach for such studies and can identify potential avenues for targeted disease management strategies.

Origin of Dermacentor albipictus (Acari: Ixodidae) on elk in the Yukon, Canada.

Winter ticks (Dermacentor albipictus) on elk (Cervus elaphus canadensis) have recently increased in numbers in the Yukon, Canada, potentially posing risks to other indigenous host species in the region. To evaluate the regional source of winter ticks in the Yukon, we sequenced one nuclear (ITS-2) and two mitochondrial (16SrRNA and COI) genes, and genotyped 14 microsatellite loci from 483 winter tick specimens collected across North America. We analyzed genetic variation across the geographic and host ranges of this tick species with the use of variance partitioning, Bayesian clustering, and standard population genetic analyses. Based on our results, winter ticks on elk in the Yukon could have originated either by translocation from central Alberta or by northward range expansion of more geographically proximate populations in northern Alberta and British Columbia. Although there was some genetic structuring of winter ticks on different hosts in the same region, we found little evidence of host specificity in winter ticks from five ungulate host species, suggesting that the winter ticks on elk in the Yukon could potentially become established on other locally available host species such as moose (Alces alces).

Deep mitochondrial DNA lineage divergences within Alberta populations of Dermacentor albipictus (Acari: Ixodidae) do not indicate distinct species.

The winter tick Dermacentor albipictus (Packard) has a single-host life cycle that allows it to reach severe infestation levels on ungulates, particularly moose. Genotypic variation within these and related ticks has been a source of taxonomic confusion, although the continuity in their morphology and life history has generally been interpreted as indicating the existence of a single species. To further investigate this variation, we sequenced regions of two mitochondrial DNA (mtDNA) genes (COI and 16S rDNA),two nuclear genes (lysozyme and ITS-2), and two bacterial markers from Francisella-like endosymbionts found in these ticks (eubacterial mtDNA 16S rRNA and a homolog of Francisella tularensis [Dorofe'ev] 17-kDa lipoprotein). We sampled 42 D. albipictus individuals from whitetail and mule deer culled from three populations in east-central Alberta, as well as four D. albipictus and two Dermacentor variabilis (Say) from other locations. We then compared DNA sequence variation between the genes and related this to variation in the morphology of spiracle plates. Both mtDNA regions indicated two deeply diverged lineages (mean difference of 7.1% for COI and 4.5% for 16S) that would normally be considered diagnostic of distinct species in DNA barcoding studies. However, very little divergence was revealed by nuclear gene sequences, bacterial endosymbionts, and morphometric analyses, and any variation that did occur in these markers was not congruent with mtDNA divergences. We conclude that the sampled populations in Alberta represent a single species, D. albipictus, and reiterate the importance of integrative approaches in species delimitation.