MICROORGANISMS ASSOCIATED WITH HARD TICKS (IXODIDAE):FROM SYMBIONTS TO TICK-BORNE PATHOGENS
Tesi di Dottorato
Data di Pubblicazione:
2012
Citazione:
MICROORGANISMS ASSOCIATED WITH HARD TICKS (IXODIDAE):FROM SYMBIONTS TO TICK-BORNE PATHOGENS / D. Pistone ; docente guida: C. Bandi ; supervisor esterno: M. Fabbi ; coordinatore del dottorato: G. Melone. Universita' degli Studi di Milano, 2012 Jan 18. 23. ciclo, Anno Accademico 2010. [10.13130/pistone-dario_phd2012-01-18].
Abstract:
The research activity I developed during my doctorate can be divided into three parts. First, I investigated the
genetic variability of Ixodes ricinus in Europe and North Africa also screening for the presence of bacteria
belonging to Borrelia burgdorferi sensu latu complex. A second part of the work focused on Midichloria
mitochondrii the principal endosymbiont of I. ricinus. This intramitochondrial bacterium is also present in
other tick species but information on the exact intracellular location are not available for the majority of them.
I decided to perform a molecular screening for detection of Midichloria-like organisms in vertebrates
comprehending humans. Finally, the last part of this work provide information on presence of Ixodes ricinus
and other tick species in areas (and from hosts) where record of the presence of these arthropods were
absent or fragmentary; the ticks collected were also screened for the presence of different tick-borne
pathogens.
The genetic analysis on both two mitochondrial loci (COI and COII) and two nuclear loci (Defensin and
TROSPA) of Ixodes ricinus confirmed the existence of two distinct groups of haplotypes showing a clear
geographic pattern. The first group comprises individuals collected in the European continent, while the
second group comprises individuals collected in Tunisia, North Africa. The existence of two groups of
populations genetically differentiated in the two continents is also supported by the spatial analysis of
molecular variance (SAMOVA), congruently for both mtDNA loci and the two nuclear loci. In previous studies
on European and Northern African populations the lacking of data from intermediate areas did not allow
determining the entity and the nature of the observed discontinuity. In our study, in addition to a considerable
number of individuals from Central and Northern Europe, Southern populations of Ixodes ricinus, sampled in
Italy (Sicily) were included. These individuals belong to European group, hence marking the existence of an
abrupt and strong genetic discontinuity. Several hypotheses had been proposed to explain this pattern. It
could be linked to geographic discontinuity due to the presence of the Mediterranean sea separating the two
continents. Anyway, the absence of discontinuity in the entire European continent and the possibility for I.
ricinus to cover large distance feeding on migratory birds, might make questionable this hypothesis. Besides,
there could be implicated ecological factors linked to I. ricinus biology and interactions with its hosts. Another
hypothesis, not necessary excluding the previous ones, considers the role of interaction between species.
Indeed, I. ricinus is a parasites and a vector of other parasites/pathogens, interacting both with its hosts and
with the transmitted pathogens, and this fact might be the cause of the genetic difference in the two
populations. All these selective pressures might have contributed to the insurgence of the observed
differences between European and Tunisian populations of I. ricinus. Nuclear and mitochondrial loci are
concordant in evidencing a genetic discontinuity between the two continents, but the two markers show
different patterns. For mitochondrial DNA, no Tunisian haplotypes were encountered in Europe and vice
versa. Nuclear loci show a degree of sharing of haplotypes of the two different haplogroups, probably due to
long-distance migration of avian hosts. Further interesting ecological and evolutionary scenarios, in a
speculative way, might be suggested to explain such differences. For example, genetic drift is able to drive
the loss of genetic variants in a totally random process. The flux of haplotypes might involve not only nuclear
genes, but also mitoch
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
D. Pistone
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