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‘Everything is not everywhere’: time-calibrated phylogeography of the genus Milnesium (Tardigrada)
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  • Witold Morek,
  • Bartłomiej Surmacz,
  • Alejandro López,
  • Lukasz Michalczyk
Witold Morek
Jagiellonian University in Krakow
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Bartłomiej Surmacz
Jagiellonian University in Krakow
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Alejandro López
Jagiellonian University in Krakow
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Lukasz Michalczyk
Jagiellonian University in Krakow
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Abstract

There is ample evidence that macroscopic animals form geographic clusters termed as zoogeographic realms (zones), whereas distributions of species of microscopic animals are still poorly understood. The common view has been that micrometazoans, thanks to their putatively excellent dispersal abilities, are subject to the ‘Everything is Everywhere but environment selects’ hypothesis (EiE). One of such groups, <1 mm in length, are limnoterrestrial water bears (Tardigrada), which can additionally enter cryptobiosis that should further enhance their potential for long distance dispersion (e.g. by wind). However, an increasing number of studies, including the most recent phylogeny of a eutardigrade genus Milnesium, seem to question the general applicability of the EiE hypothesis to tardigrade species. Nevertheless, all the Milnesium phylogenies published to date were based on a limited number of populations, which are likely to falsely suggest limited geographic ranges. Thus, in order to comprehensively test the EiE hypothesis, here, we considerably enlarged the Milnesium dataset both taxonomically and geographically, and we analysed it in tandem with climate type and reproductive mode. Additionally, we time-calibrated our phylogeny to align it with major geological events. Our results show that, although cases of long distance dispersal are present, they seem to be rare and mostly ancient. Overall, Milnesium species are restricted to single zoogeographic realms, which suggests that these tardigrades have limited dispersal abilities. Finally, our results also suggest that the breakdown of Gondwana may influenced the evolutionary history of Milnesium. In conclusion, phylogenetic relationships within the genus seem to be determined mainly by paleogeography.

Peer review status:ACCEPTED

30 Dec 2020Submitted to Molecular Ecology
31 Dec 2020Submission Checks Completed
31 Dec 2020Assigned to Editor
15 Jan 2021Reviewer(s) Assigned
20 Feb 2021Review(s) Completed, Editorial Evaluation Pending
23 Mar 2021Editorial Decision: Revise Minor
31 Mar 20211st Revision Received
31 Mar 2021Review(s) Completed, Editorial Evaluation Pending
29 Apr 2021Editorial Decision: Accept