Dispersion and new shelters offered by ants: myrmecophoresy of tardigrades

The present study investigates the potential role of ants as dispersal hosts for tardigrades and for the first time provides evidence of ant-mediated tardigrade phoresy. Tardigrades are microscopic cosmopolitan animals which have limited autonomous dispersal abilities but can withstand extreme conditions in a desiccated state. Being dominant terrestrial organisms, ants interact with many components of ecosystems, yet their role in dispersing meiofaunal organisms is unknown. In a field survey, four arboreal ant species were first analyzed to test the presence of tardigrades in their nests (i.e. tree galls), and on their bodies. In another experiment, galls were maintained isolated, then exposed to ant colonization to evaluate any transport of tardigrades by ants. Finally, the behavior of the ant Colobopsis truncata was tested by crafting an experimental apparatus to verify the actual phoresy of tardigrades. The field survey and gall colonization experiments show an association of tardigrades, especially with C. truncata. Gall colonization and laboratory experiments reveal that the ants transport tardigrades and other meiofaunal organisms, such as nematodes and rotifers. This phoresy can be direct (transporting animals) or indirect (transporting substrates with animals), over significant distances, thereby suggesting an unknown ecological interaction. Thanks to the widespread presence and abundance of ant species, this myrmecophoretic dispersion could play a crucial role in the spreading of meiofaunal organisms in terrestrial environments. These findings may represent just the 'tip of the iceberg' of an unexplored passive dispersal modality for terrestrial meiofauna micrometazoans, expanding our knowledge of phoretic relationships.