Abstract
BackgroundDuring the last decades a northward and upward range shift has been observed among many organisms across different taxa. In the northern hemisphere, ticks have been observed to have increased their latitudinal and altitudinal range limit. However, the elevational expansion at its northern distribution range remains largely unstudied. In this study we investigated the altitudinal distribution of the exophilic Ixodes ricinus and endophilic I. trianguliceps on two mountain slopes in Norway by assessing larval infestation rates on bank voles (Myodes glareolus).MethodsDuring 2017 and 2018, 1325 bank voles were captured during the spring, summer and autumn at ten trapping stations ranging from 100 m to 1000 m.a.s.l. in two study areas in southern Norway. We used generalized logistic regression models to estimate the prevalence of infestation of both tick species along gradients of altitude, considering study area, collection year and season, temperature, humidity and altitude interactions as extrinsic variables, and host body mass and sex as intrinsic predictor variables.ResultsWe found that both I. ricinus and I. trianguliceps infested bank voles at altitudes up to 1000 m.a.s.l., which is a substantial increase in altitude compared to previous findings for I. ricinus in this region. The infestation rates declined more rapidly with increasing altitude for I. ricinus compared to I. trianguliceps, indicating that the endophilic ecology of I. trianguliceps may provide shelter from limiting factors tied to altitude. Seasonal effects limited the occurrence of I. ricinus during autumn, but I. trianguliceps was found to infest rodents at all altitudes during all seasons of both years.ConclusionsThis study provides new insights into the altitudinal distribution of two tick species at their northern distribution range, one with the potential to transmit zoonotic pathogens to both humans and livestock. With warming temperatures predicted to increase, and especially so in the northern regions, the risk of tick-borne infections is likely to become a concern at increasingly higher altitudes in the future.Graphical
Highlights
During the last decades a northward and upward range shift has been observed among many organisms across different taxa
I. trianguliceps, has been recorded at altitudes as high as 2300 m.a.s.l. in Switzerland [30], but because it does not quest in open vegetation like I. ricinus, it is likely to be less exposed to limiting environmental conditions, especially temperature, and able to survive in more extreme environments [19]
5372 tick larvae were collected from the trapped voles at all altitudes of the gradient
Summary
During the last decades a northward and upward range shift has been observed among many organisms across different taxa. Ticks have been observed to have increased their distribution range northwards in the northern hemisphere [20,21,22], and several studies have demonstrated the occurrence of ticks at increasingly higher altitudes in central Europe [14, 23, 24]. According to Danielova et al [29], it may survive up to 1200 m.a.s.l. or higher if the habitat is favourable Another tick species, I. trianguliceps, has been recorded at altitudes as high as 2300 m.a.s.l. in Switzerland [30], but because it does not quest in open vegetation like I. ricinus, it is likely to be less exposed to limiting environmental conditions, especially temperature, and able to survive in more extreme environments [19]. With any upward shift in range limit, the risk of exposure to tick-borne infections is likely to increase for both humans and livestock [24, 28], and is predicted to further increase in the future [31,32,33]
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