Elevadas taxas de diversificação e presença de sinal filogenético reforçam a influência do habitat terrestre na dinâmica evolutiva do filo Ciliophora

Abstract

Ciliated protists are distributed worldwide, and can be found in different habitats, such as rivers, lakes and marine regions, but it is in the terrestrial environment, soils and those associated with mosses, with their specific and dynamic characteristics over time, where adaptations to terrestrial life are discovered. However, to date, evolutionary studies are scarce, especially those related to the evolution of ecological characteristics such as habitats, for the phylum Ciliophora. In the present study, we inferred a broad dated molecular phylogeny, based on the 18S-rDNA gene, for the entire phylum Ciliophora, which allowed us to map the life habit throughout the group's evolution and evaluate whether the different habitats in the ciliates are associated with variation in diversification rates and the mode of evolution in Ciliophora. Our results recovered that the last common ancestor of the phylum Ciliophora occupied an environment similar to the current marine/brackish habitats, and that terrestrial environments were occupied independently and numerous times during the group's evolution. For the first time using molecular and statistical data, we recorded two possible routes to reach the terrestrial environment: (i) through a marine ancestor, the most frequent route with three transition points, and (ii) from a freshwater ancestor, with just a transition record. Furthermore, we found a robust phylogenetic signal that reinforces the influence of habitats on the evolution of the group, and a significant increase in the diversification rates of terrestrial ciliates and symbionts, when compared to those that explore marine and freshwater habitats. We also noticed a strong influence of terrestrial ciliates on the evolutionary rates of their respective classes, mainly in the classes Colpodea, Litostomatea, Spirotrichea.