Different meta-analyses clearly demonstrated that ecological specificity is more important than the association with a certain group of hosts. The compilation of available data from the literature produced positive correlations between the assigned host specificity and the sampling effort of a given species. However, this view linking the speciation of ticks as linked to the hosts has been criticized. These previous studies stated that almost 90% of the tick species described were “strict, or relatively strict” host specialists (as per categories in ). Pioneering views on the topic were supportive of a tick evolution linked to that of their hosts. Advances have been reached resulting from multidisciplinary approaches, combining the sequencing of large portions of genome, molecular clocks, phylogenetic trees, comparative analyses of the proteins secreted in salivary glands (including physiological functions) and morphological traits. The origin and evolution of ticks (Ixodoidea) is a topic that is still far from solved. Even results on species linked to groups of ticks (such as Ixodes uriae and the pelagic birds or the bat-tick species) are suggestive of a previous action of environmental forces. With the obvious exceptions of Ixodes species restricted to one or a few hosts, the results point to an ecological adaptation. The Palearctic network is well developed, with many links demonstrating a highly modular set of relationships. Data for the Afrotropical region reveal a lack of extensive surveys, while results for the Australasian region are suggestive of a mass extinction of vertebrates. Other results suggest that the networks displaying tick-host associations are different according to the biogeographical realms. The ontogenetic switch of hosts is high for species with enough data, which is another potential clue supporting the ecological hypothesis. Keystone hosts do not exist in the relationships between Ixodes and vertebrates because of the high redundancy of the networks, further supporting an ecological relationship between both types of partners. We report highly clustered associations among Ixodes ticks and hosts, supporting the influence of the ecological adaptation and coexistence, demonstrating a lack of strict tick-host coevolution in most cases, except for a few species. Faith’s phylogenetic diversity was used to evaluate the phylogenetic distance of the hosts of each species and changes occurring in the ontogenetic switch between consecutive stages of each species (or the extent of the changes in phylogenetic diversity of hosts for consecutive stages of the same species). We used network constructs linking all the known pairs of associations between each species and stage of ticks with families and orders of hosts. We propose two alternative hypotheses, namely, an ecological background (ticks and hosts sharing environmentally available conditions) and a phylogenetic one, in which both partners co-evolved, adapting to existing environmental conditions after the association took place. This study aims to capture how ticks of the genus Ixodes gained their hosts using network constructs.
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