Effect of an altitudinal gradient on the morphology, molecular identification and distribution of Rhipicephalus linnaei in Veracruz, Mexico.

• The distribution and morphology of Rhipicephalus sanguineus sensu lato varies with altitude, this adaptability can encourage the expansion and survival of the species, and consequently, the risk of transmitting infectious agents. • Identifying the tick lineage helps to know the distribution area and supports the geographical limit that is known so far of both lineages. • The ecological niche in which the species lives helps us to know the factors and conditions that favor the presence of this tick and this can be key to better understanding how they are distributed and what environmental variables influence their presence. Studies of morphological and genetic variation in vector populations across environmental gradients can help researchers to estimate species' responses to climate change scenarios and the potential risk of disease-causing pathogen expansion, which impacts negatively on human health. In this study, we analysed the effect of altitudinal gradients on the phenotypic response of the hard tick of medical and veterinary importance, Rhipicephalus sanguineus sensu lato (s.l.). Specimens of R. sanguineus s.l. were collected from host animals in one of Mexico's regions with high climatic heterogeneity (Veracruz), and geometric morphometric theory was employed to assess the response of three morphological characters to the altitudinal gradient. Additionally, genetic similarity data were provided, and ecological niche models were used to project the climatic distribution in the region. Our results demonstrate that the shape and size of ticks respond to altitude. Molecular identification indicate that all analysed samples correspond to the tropical lineage recently named Rhipicephalus linnaei. According to ecological niche models, the mean annual temperature contributes significantly to the spatial distribution of this tick species, with areas of higher suitability in the mountainous region. These changes in morphological structure and the presence of ticks at higher altitudinal gradients suggest that R. linnaei has a high potential for adaptation. Due to the variability of ecosystems in the state of Veracruz, our results could be valuable in assessing the response of this tick in a changing environment, aiding in predicting future scenarios in the distribution and abundance of this species. [Display omitted] [ABSTRACT FROM AUTHOR]