ABSTRACT
A "metapopulation" is a group of populations of the same species separated by space but linked by dispersal and migration. Metapopulations of macroscopic organisms tend to have geographically-restricted distributions, but this does not seem to be the case in microbial eukaryotes due to their astronomical abundance. The term "metapopulation" was first applied to protists' biogeography in the article Finlay and Fenchel (2004), published in PROTIST, which contributed to the popularity of the paper. The article considered protist species as consisting of a single, cosmopolitan population. Here, we recall this paper, and assess developments during the last 15 years with respect to the question of protist species distribution on the surface of the earth.
Subject(s)
Eukaryota/physiology , PhylogeographyABSTRACT
Environmental sequences have become a major source of information. High-throughput sequencing (HTS) surveys have been used to infer biogeographic patterns and distribution of broad taxa of protists. This approach is, however, more questionable for addressing low-rank (less inclusive) taxa such as species and genera, because of the increased chance of errors in identification due to blurry taxonomic boundaries, low sequence divergence, or sequencing errors. The specious ciliate genus Euplotes partially escapes these limitations. It is a ubiquitous, monophyletic taxon, clearly differentiated from related genera, and with a relatively well-developed internal systematics. It has also been the focus of several ecological studies. We present an update on Euplotes biogeography, taking into consideration for the first time environmental sequences, both traditional (Sanger) and HTS. We inferred a comprehensive small subunit rRNA gene phylogeny of the genus including a newly described marine species, Euplotes enigma, characterized by a unique question mark-shaped macronucleus. We then added available environmental sequences to the tree, mapping associated metadata. The resulting scenario conflicts on many accounts with previously held views, suggesting, for example, that a large diversity of anaerobic Euplotes species exist, and that marine representatives of mainly freshwater lineages (and vice-versa) might be more common than previously thought.