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Diversity and geographic distribution of ciliates (Protista: Ciliophora)

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About 4,500 free-living ciliate morphospecies have been described, applying an average synonymy rate of 20%. We estimate that 83–89% of the ciliate diversity is still undescribed, using the following probabilities: detailed habitat studies suggest that the described number of morphospecies must be doubled: 4,500 → 9,000; this figure has to be increased by about 50% due to species with similar interphase morphology but different resting cysts: 9,000 → 13,500; the genetic and molecular data suggest that this value must be doubled or trebled: 13,500 → 27,000 to 40,000 free-living, biological ciliate species. The knowledge on geographic distribution of ciliates heavily depends on flagship species and statistical analyses because reliable faunistic studies are rare and molecular data are still in its infancy. We present a list of 52 ciliate flagship species as a testable hypothesis, i.e., the hypothesis of restricted distribution of certain ciliate species must be refused when a considerable number of them is found in all or most biogeographic regions. Flagship species and statistical analyses consistently show Gondwanan and Laurasian ciliate communities, suggesting that the split of Pangaea deeply influenced ciliate distribution and rare species play a key role in geographic differentiation. However, there is also substantial evidence for continental, regional, and local endemism of free-living ciliates. The molecular studies usually show a high level of genetic diversity underlying ciliate morphospecies, suggesting that morphologic and molecular evolution may be decoupled in many ciliate species. Molecular studies on ciliate biogeography are at variance, possibly because most are still focusing on single molecular markers. In sum, the data indicate that ciliate biogeography is similar to that of plants and animals, but with an increased proportion of cosmopolites, favouring the moderate endemicity model.

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Supported by the Austrian Science Foundation (FWF, projects P-15017 and P-19699-B17), the Taiwan National Science Council (projects NSC-94-2118-M006-001, 95-2118-M007-003), and the United States National Science Foundation (LAK DEB-0092908 and DEB-043115). The technical assistance of Mag. Birgit Peukert and Mag. Gudrun Fuss is gratefully acknowledged.

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Correspondence to Wilhelm Foissner.

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Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.

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Foissner, W., Chao, A. & Katz, L.A. Diversity and geographic distribution of ciliates (Protista: Ciliophora). Biodivers Conserv 17, 345–363 (2008). https://doi.org/10.1007/s10531-007-9254-7

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  • Actual and estimated diversity
  • Cyst species
  • Flagship species
  • Floodplains
  • Genetic and molecular diversity
  • Gondwana
  • Laurasia
  • Moderate endemicity model
  • Pangaea