Worldwide host associations of the tick genus Ixodes suggest relationships based on environmental sharing rather than on co-phylogenetic events

ESTRADA-PEÑA, AGUSTÍN; GUGLIELMONE, ALBERTO A.; NAVA, SANTIAGO

PARASITES AND VECTORS

BIOMED CENTRAL LTD

Año: 2023 vol. 16

1756-3305

Background This study aims to capture how ticks of the genus Ixodes gained their hosts using network constructs.We propose two alternative hypotheses, namely, an ecological background (ticks and hosts sharing environmentallyavailable conditions) and a phylogenetic one, in which both partners co-evolved, adapting to existing environmentalconditions after the association took place.Methods We used network constructs linking all the known pairs of associations between each species and stage ofticks with families and orders of hosts. Faith’s phylogenetic diversity was used to evaluate the phylogenetic distance ofthe 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).Results We report highly clustered associations among Ixodes ticks and hosts, supporting the influence of theecological adaptation and coexistence, demonstrating a lack of strict tick-host coevolution in most cases, except fora few species. Keystone hosts do not exist in the relationships between Ixodes and vertebrates because of the highredundancy of the networks, further supporting an ecological relationship between both types of partners. Theontogenetic switch of hosts is high for species with enough data, which is another potential clue supporting the ecologicalhypothesis. Other results suggest that the networks displaying tick-host associations are different accordingto the biogeographical realms. Data for the Afrotropical region reveal a lack of extensive surveys, while results for theAustralasian region are suggestive of a mass extinction of vertebrates. The Palearctic network is well developed, withmany links demonstrating a highly modular set of relationships.Conclusions With the obvious exceptions of Ixodes species restricted to one or a few hosts, the results point to anecological adaptation. Even results on species linked to groups of ticks (such as Ixodes uriae and the pelagic birds orthe bat-tick species) are suggestive of a previous action of environmental forces.