Historical and contemporary factors driving the evolution of host specialisation in disease vectors

Informations

Funding country

France

Acronym

ESPEVEC

URL

http://www.agence-nationale-recherche.fr/projet-anr/?tx_lwmsuivibilan_pi2%5BCODE%5D=ANR-13-BSV7-0018

Start date

2/1/2014

End date

12/31/2018

Budget

260,000 EUR

Fundings

Organisations

Abstract

Vector-borne diseases are often maintained in complex transmission cycles that include several vectors and different reservoir host species. However, to date, we know little about how vectors adapt to different local host species and how this may in turn affect pathogen dynamics and disease risk. In the case of systems where numerous host species are available, it is therefore essential to establish whether vectors specialise to exploit different hosts and the role of these different local host-vector systems in pathogen transmission and evolution. It is also critical to identify the ecological factors and evolutionary mechanisms that lead to vector specialisation if we are to better predict pathogen transmission in a changing landscape. The ESPEVEC project aims to tackle these questions using three contrasting host-vector-pathogen systems involved in tick-borne disease and a highly qualified international research consortium consisting of 4 partner laboratories and several international collaborating institutes. The three tick systems to be studied are all of particular medical and economic interest, involving two hard tick vectors of Lyme borreliosis (Ixodes ricinus and Ixodes uriae) and one soft tick vector of human relapsing fever (Ornithodoros capensis complex). These systems vary in both their ecological characteristics and evolutionary histories enabling us to evaluate the relative contribution of different factors to overall patterns of host-associated vector divergence. Within the framework of the project, we will test the general hypothesis that the evolution of host-associated structure in ticks varies with the composition and history of the local host-vector community. The first two project tasks will evaluate within-community genetic structure of ticks across replicate sites in relation to host use, retrace these patterns using a phylogeographic framework and contrast results for different tick systems. We predict that host-associated structure should increase with the evolutionary age and stability of the local host community. Next, we will examine the mechanisms behind patterns of local divergence via genotypic and phenotypic patterns of variation. More specifically, morphometrical and chemical analyses will be performed to identify the potential selective forces responsible for host-associated divergences and will be completed by a genome-wide screening of divergence among host-associated groups. Finally, we will investigate the consequences of this structure for pathogen circulation and evolution at different spatial scales by typing selected bacterial pathogens within the sampled communities and comparing patterns of infection and population structure in the pathogen with that in the vector and hosts. This work will rely on a combination of field sampling, experimental quantifications, and modern approaches for quantifying phenotypic and genetic characteristics. Although applied to tick systems, we expect that the results of this project will alter the general view of vector-borne disease ecology. By combining results from the different project tasks, we will be able to 1) better understand vector-borne disease ecology and the origins of vector and pathogen diversity, 2) evaluate the relative role of different component species in disease risk and thus determine the importance of incorporating local divergence patterns into epidemiological models of disease risk, and 3) obtain essential information on how landscape modifications and species redistributions may alter pathogen emergence.