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

Abstract

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.

Mitochondrial phylogeography and population structure of the cattle tick Rhipicephalus appendiculatus in the African Great Lakes region

“…The most likely explanation for this is that the spatial pattern of R. appendiculatus lineages is not only driven by geographical separation as described in previous studies [ 52 ], but also related to their ecological preferences, as observed by the significant genetic differentiation among lowlands and highlands AEZs. On the other hand, adjacent AEZs shared more migrants, especially of lineage A, facilitated by short-distance seasonal movement of cattle [ 9 ], which may have reduced the geographical structuring of the tick [ 11 , 18 ]. Analysis of molecular variance (AMOVA) confirmed these findings showing that the variance explained by divergence between the six AEZs was lower (6%), while the largest fraction of genetic variation was observed among individuals within AEZs (94%).…”

“…Therefore, the spread and establishment of ticks from one geographical region to another might be setting up a complexity in the epidemiological status and control of the disease they transmit [ 15 – 17 ]. Thus, predicting vector-borne pathogen dynamics and emergence relies on better understanding of mechanisms underlying the genetic structure of their vectors [ 18 , 19 ].…”

“…Ecological establishment and population genetic structure of ticks can be affected by founder events and gene flow, largely due to their dispersal across geographical zones through host migration [ 18 , 20 ]. Arthropod vectors then respond differently to evolutionary forces such as migration, mutation, selection and genetic drift (promoted by bottlenecks) in their new environment [ 21 , 22 ].…”

The impact of strain-specific immunity on Lyme disease incidence is spatially heterogeneous

“…Lyme disease incidence continues to rise over time and expand geographically in the United States (e.g., Khatchikian et al 2015b, Leo et al 2017). The results of this study suggest that, without strain specific immunity, there would be as many as 2,516 additional human Lyme disease cases per year in the United States.…”

Learning from Chemical Coping Behaviors of Wildlife to Discover New Approaches for Pest Management

“…Beyond food security, changing climates are causing shifts in the ranges of arthropod vectors (Haines et al, 2006;Carvalho et al, 2017) and their pathogens (Rochlin et al, 2013;Samy et al, 2016;Wu et al, 2016;Armstrong et al, 2017;Sonenshine, 2018). For example, ticks are responsible for 95% of vector-borne disease in North America and some tick species are undergoing range expansion (Leo et al, 2017;Sonenshine, 2018). Human populations have experienced a spike in cases of tick-borne disease cases (Khatchikian et al, 2015;Kugeler et al, 2015;Oliver et al, 2017).…”