Potential niche displacement in species of aquatic bdelloid rotifers between temperate and tropical areas

Bdelloids are commonly found in freshwaters or limno-terrestrial habitats. No formal attempt has yet been performed to define bdelloid niche and to identify whether species respond in a clear, consistent, and quantifiable fashion to environmental parameters. Therefore, we analysed the correlation between the occurrence of common Rotaria species in Thailand and environmental variables, including limnological, climatic, and biotic features. We followed two approaches to determine the niche of the investigated species: performing regression models for each species and reconstructing the niche spaces occupied by each species using n-dimensional hypervolumes. The effect of local-scale limnological and large-scale climatic variables was almost negligible at explaining the occurrence and distribution of Rotaria species. Surprisingly, primary productivity, known in temperate areas to be a major positive correlate of the occurrence of R. neptunia, appeared to have no effect on this species when measured as chlorophyll a, and a negative effect when measured as cyanobacterial productivity. Biotic variables revealed that different Rotaria species have a similar response to environmental variables. Two main messages are supported: (i) no clear environmental features unambiguously affected bdelloids species; (ii) features that are relevant for limnological processes at temperate latitudes may not be applicable for explaining processes in tropical latitudes.