Niche modelling and molecular phylogenetics unravel the invasion biology and worldwide colonization of three species of the freshwater planarian genus Girardia (Platyhelminthes, Tricladida)

Abstract

Abstract Several species of the freshwater planarian genus Girardia have been introduced into freshwater ecosystems all over the world, but little is known about the actual number of species involved and about possible detrimental effects on autochthonous ecosystems. In the present study, we used molecular phylogenetics and niche modelling under present and future climatic scenarios to examine the human-induced dispersal and spread of alien species of Girardia from their original areas of distribution in the Americas to other parts of the globe. Our results corroborate that the Girardia populations spreading worldwide belong to three species of North American origin: G. dorotocephala, G. sinensis, and G. tigrina. Our study emphasizes that G. sinensis is native to North America, from where it colonised China, as well as Europe, Africa and Australia. It also shows that G. dorotocephala has a broader range of localities where it was introduced than previously known, including Europe and Brazil. Niche modelling revealed that the three colonising species have a broad range of potential distribution in extensive regions of the Northern Hemisphere; regardless of the climatic scenario, in the future, 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, explain their successful colonization. In the Iberian Peninsula, introduced G. tigrina and G. sinensis have extensive areas of high suitability, overlapping with the more limited suitable areas of autochthonous freshwater planarians, pointing to potential detrimental effects of Girardia invaders.