RESUMO
Ciliates within the order Mobilida comprise a group of ectosymbionts that form ecologically and economically important symbioses with aquatic organisms. However, despite their significance, the factors driving mobilid diversification are poorly understood. To address this, we sought to examine the genetic diversity of two mobilid families, the trichodinids and urceolariids, over geographical areas and from different hosts. To this end we collected and provide morphological and molecular characterizations of three species of Trichodina: Trichodina domerguei and Trichodina tenuidens from three-spined sticklebacks, and Trichodina unionis from snails. We also sequenced the small subunit rRNA gene from Urceolaria korschelti collected from its type host at the type locality of Helgoland, Germany. The Trichodina from sticklebacks show intra-specific genetic variation that is not related to geographic distribution. Furthermore, we find evidence of fish to mollusc host transitions within the Trichodinidae and suggest that the most recent common ancestor of the Trichodina was a symbiont of vertebrates. Lastly we confirm that U. korschelti constitutes a cryptic species complex, which in turn justifies the description of Urceolaria parakorschelti sp. nov. These data suggest that not only host transitions, but allopatric and or genetically-driven sympatric speciation play a role in facilitating the diversification of mobilid ciliates.
