Inland Saline Lakes as Hotspots of Specialized, Nonmarine Protist Diversity: The Case of Arcellinida (Amoebozoa)

Inland saline lakes are dynamic environments with fluctuating salinity levels, sometimes reaching values higher than those of seawater. Their abiotic conditions are often extreme and more unpredictable than in marine systems, which could imply lower biotic pressures. This could have allowed nonmarine organisms to cross the salinity barrier and subsequently specialize and diversify there. Alternatively, inland saline lakes could host generalist species that are also found in other environments. In order to answer this question, we focused on a group of protists characterized by their narrow ecological tolerance, Arcellinida testate amoebae. We studied their diversity using a metabarcoding approach in different thalassic and athalassic saline systems from Spain and Chile. The majority of operational taxonomic units (OTUs) were exclusive to athalassohaline systems. Three clades included most diversity in athalassohaline systems, in addition to several specific colonization events. Inland saline systems have been colonized by freshwater species, which diversified there, turning these athalassohaline environments into hotspots of specialized Arcellinida biodiversity.