Abstract
Ixodid ticks (Acari:Ixodidae) are essential vectors of tick-borne diseases in Japan. In this study, we characterized the population genetic structure and inferred genetic divergence in two widespread and abundant ixodid species, Ixodes ovatus and Haemaphysalis flava. Our hypothesis was that genetic divergence would be high in I. ovatus because of the low mobility of their small rodent hosts of immature I. ovatus would limit their gene flow compared to more mobile avian hosts of immature H. flava. We collected 320 adult I. ovatus from 29 locations and 223 adult H. flava from 17 locations across Niigata Prefecture, Japan, and investigated their genetic structure using DNA sequences from fragments of two mitochondrial gene regions, cox1 and the 16S rRNA gene. For I. ovatus, pairwise FST and analysis of molecular variance (AMOVA) analyses of cox1 and 16S sequences indicated significant genetic variation among populations, whereas both markers showed non-significant genetic variation among locations for H. flava. A cox1 gene tree and haplotype network revealed three genetic groups of I. ovatus. One of these groups consisted of haplotypes distributed at lower altitudes (251-471m.a.s.l.). The cox1 sequences of I. ovatus from Japan clustered separately from I. ovatus sequences reported from China, suggesting the potential for cryptic species in Japan. Our results support our hypothesis and suggest that the host preference of ticks at the immature stage may influence the genetic structure of the ticks. This information may be important for understanding the tick-host interactions in the field to better understand the tick-borne disease transmission and in designing an effective tick control program.
Highlights
Tick-borne diseases are a public health concern, and their control is often challenging because of the complex interactions between ticks and their vertebrate hosts in a changing environment (Dantas-Torres et al, 2012)
For the population genetic analysis, in which populations consisted of combined sites the number of individuals were as follows: cox1 I. ovatus (28 to 62), 16S I. ovatus (24 to 66), cox1 H. flava (8 to 81) and 16S H.flava (8 to 76) (Additional File 1 Table S1)
The greater genetic divergence among populations in I. ovatus might result from the restricted movement of its small mammalian hosts dur ing its development, while the homogenous structure in H. flava might be due to the more widespread movement of its avian and large mammalian hosts
Summary
Tick-borne diseases are a public health concern, and their control is often challenging because of the complex interactions between ticks and their vertebrate hosts in a changing environment (Dantas-Torres et al, 2012). Population genetic studies can shed light on the dispersal pat terns of ticks, including the direction, distance, and potential factors influencing movement, by estimating gene flow between tick pop ulations (McCoy, 2008; Araya-Anchetta et al, 2015). Studies of Ixodes scapularis (Qiu et al, 2002) and Ornithodoros coriaceus (Teglas et al, 2006) have reported low levels of gene flow despite the high mobility of their hosts. Other studies have reported low levels of gene flow in ticks with less mobile hosts (e.g., smaller mammals) and high levels of gene flow in ticks with highly mobile hosts (Araya-Anchetta et al, 2015). High levels of gene flow observed in Amblyomma americanum (Linnaeus, 1767) and A. triste (Koch, 1844) (Acari, Ixodidae) across spatial scales ranging from 137,000 km to 2.78 million km was attributed to their hosts' dispersal capabilities (large mammals and birds) (Mixson et al, 2006; Trout et al, 2010; Guglielmone et al, 2013). Lampo et al (2015) observed low levels of gene flow in A. dissimile (Koch, 1844) and concluded this was the result of its hosts' low mobility (small mammals, reptiles, and salamanders)
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