Genetic, morphological, and ecological diversity of spatially separated clones of Meseres corlissi Petz & Foissner, 1992 (Ciliophora, Spirotrichea).

We investigated the intraspecific variation of the spirotrich freshwater ciliate Meseres corlissi at the level of genes (SSrDNA, ITS), morphology (14 characters), and ecophysiology (response to temperature and pH). Five of the eight clonal M. corlissi cultures isolated from five localities on four continents were studied at all levels. The null hypothesis was that geographic distance plays no role: M. corlissi lacks biogeography. The intraspecific variation was low at the genetic level (0%-4%), moderate at the morphological level (5%-15%), and high at the ecophysiological level (10%-100%). One clone, isolated from subtropical China, differed significantly at all levels from all other clones, suggesting limited dispersal and local adaptation among M. corlissi. However, other clones from distant areas, such as Australia and Austria, were genetically identical and differed only slightly in morphology and temperature response. We speculate that our findings may be typical for rare species; the chances may be equally high for both global dispersal of most and local adaptation of some populations in areas where dispersal has been permanently or temporarily reduced.