Impact of life stage-dependent dispersal on the colonization dynamics of host patches by ticks and tick-borne infectious agents

Sarah Kada,Thierry Boulinier,Karen D Mccoy

doi:10.1186/s13071-017-2261-y

Abstract

BackgroundWhen colonization and gene flow depend on host-mediated dispersal, a key factor affecting vector dispersal potential is the time spent on the host for the blood meal, a characteristic that can vary strongly among life history stages. Using a 2-patch vector-pathogen population model and seabird ticks as biological examples, we explore how vector colonization rates and the spread of infectious agents may be shaped by life stage-dependent dispersal. We contrast hard (Ixodidae) and soft (Argasidae) tick systems, which differ strongly in blood- feeding traits.ResultsWe find that vector life history characteristics (i.e. length of blood meal) and demographic constraints (Allee effects) condition the colonization potential of ticks; hard ticks, which take a single, long blood meal per life stage, should have much higher colonization rates than soft ticks, which take repeated short meals. Moreover, this dispersal potential has direct consequences for the spread of vector-borne infectious agents, in particular when transmission is transovarial.ConclusionsThese results have clear implications for predicting the dynamics of vector and disease spread in the context of large-scale environmental change. The findings highlight the need to include life-stage dispersal in models that aim to predict species and disease distributions, and provide testable predictions related to the population genetic structure of vectors and pathogens along expansion fronts.

Highlights

When colonization and gene flow depend on host-mediated dispersal, a key factor affecting vector dispersal potential is the time spent on the host for the blood meal, a characteristic that can vary strongly among life history stages
In order to explore the potential effect of life-stagedependent dispersal on vector colonization dynamics, we build a continuous-time model of vector population dynamics, structured in 3 life stages: larvae (L), nymphs (Np) and adults (A), on two patches (i and j). σL and σN are the maturation rates, i.e. the respective rates at which larvae moult to nymphs and nymphs to adults, provided they completed their blood meal. μL, μN and μA are the respective natural mortality rates of larvae, nymphs and adults
Population dynamics and Allee effects For a broad set of reasonable parameter values, soft tick population growth in the newly colonized patch is much slower compared to the invading population of hard ticks (Fig. 3a, b)

Summary

Introduction

When colonization and gene flow depend on host-mediated dispersal, a key factor affecting vector dispersal potential is the time spent on the host for the blood meal, a characteristic that can vary strongly among life history stages. Using a 2-patch vector-pathogen population model and seabird ticks as biological examples, we explore how vector colonization rates and the spread of infectious agents may be shaped by life stage-dependent dispersal. The dynamics of dispersal, its speed and frequency, are relevant for assessing vector expansion and the associated risk of spread of vector-borne infectious agents [12, 27, 29,30,31], but the key potential role of the dispersal stage is rarely considered in vector-borne disease models. Vector stage structure is thought to influence the speed and distance of vector colonization in ticks responsible for Lyme borreliosis [22, 35,36,37] Dispersal distance in these ectoparasites may vary because of stage-specific host feeding preferences (e.g. nymphs feeding on birds versus small mammals; Wilson et al [38]; Norte et al [39]). Some stages might be more successful than others at (i) establishing a local population; and (ii) contributing to

Methods

Results

Discussion

Conclusion