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Diversité et adaptation des parasites : Formation de races d’hôtes chez la tique Ixodes uriae

 

Muriel DIETRICH

 

le Jeudi 13 Octobre 2011 à 9h30 dans l’amphithéâtre du bâtiment des plantes, au Centre IRD de Montpellier.

Le jury sera composé de :

- Sara Magalhães (Rapporteur)

- Philippe Christe (Rapporteur)

- Flavie Vanlerberghe (Examinateur)

- Denis Bourguet (Examinateur)

- Gwenaël Vourc’h (Examinateur)

- Karen McCoy (Directrice de thèse)

Abstract:

Host specialization and host-race formation may be key processes in maintaining and generating diversity within parasite populations. The objective of this thesis was to analyse these processes in the seabird tick Ixodes uriae, a common and  widely distributed ectoparasite that exploits a great diversity of seabird host species, to better understand the relative role of host-related constraints and geographic factors in the evolution and diversification of this tick species. I addressed this question using different approaches, including population genetic and phylogeographic analyses, morphometry and field experimentation. Results show that the spatial factor is a key component in shaping the diversity of I. uriae, as four geographical genetically isolated groups exist within the global distribution of I. uriae. The formation of host races is also a recurrent process in the evolution of I. uriae, but has evolved at different degrees in different geographical regions. Host preference in the tick, along with mechanical or physiological host-related constraints (e.g., beak morphology, blood digestion, immune response) are likely involved in the evolution of I. uriae host races. Overall, results fall in line with the geographic mosaic theory of evolution that predicts that the outcome of species interactions can vary across geographic landscapes, highlighting the role played by host ecological characteristics in the diversification of I. uriae. Given our results and those of colleagues, host specialization seems to be a common process within tick systems and thus may have strong epidemiological implications for the pathogens that they transmit.

 

Keywords: host-parasite interactions, adaptation, specialization, ticks, Ixodes uriae, population genetics, phylogeography, morphology.