Niche modelling and molecular phylogenetics unravel the colonisation biology of three species of the freshwater planarian genus Girardia (Platyhelminthes Tricladida)

Abstract

Freshwater planarians of the genus Girardia have been introduced all over the world, but little is known about the species involved and their possible impact on autochthonous ecosystems. Using molecular phylogenetics and niche modelling under different climatic scenarios we examine the human-induced spread of alien Girardia species from their original areas of distribution in the Americas to other areas. Our results corroborate that Girardia populations spreading worldwide belong to three species: G. dorotocephala, G. sinensis, and G. tigrina. Our study emphasizes that G. sinensis is native to North America and shows that G. dorotocephala has a broader range of introduced localities than previously known. Niche modelling revealed that the three species have a broad range of potential distribution in extensive regions of the Northern Hemisphere. Regardless of the future climatic scenario, their distributional range will increase towards northern Europe, without diminishing the high suitability of regions in the south. Their environmental requirements, being generalists with high suitability for human-modified habitats, and fissiparous reproduction explain their successful colonization. In the Iberian Peninsula, G. tigrina and G. sinensis have extensive areas of high suitability, overlapping with the more limited suitable areas of autochthonous planarians, pointing to potential detrimental effects of Girardia invaders.