The Molecular Diversity and Biogeography of Tardigrades

Abstract: Tardigrades can handle extreme conditions such as heat, cold and drought, thanks to a process called cryptobiosis which can be found in a limited amount of taxa on Earth. More knowledge about such animals may help us to understand the potential and limitations of life both on Earth and possibly in space. Such knowledge may also help develop novel, useful applications for the society, such as better storage of sensitive medicine. However, our knowledge about tardigrades is limited. We know little about their distribution and diversity, especially in Sweden, and above all in northern Sweden. The aim of this study was threefold; i) to explore the biogeography of the tardigrades based on molecular data; ii) to screen for tardigrades in Umeå by examining moss samples from different locations; and iii) to explore some of the associates of tardigrades in moss (such as bacteria and micro- and meiofauna). The biogeography was explored by collecting all published ribosomal gene sequences (the small subunit 18S rRNA) from the Silva gene database. These sequences were used for plotting the locations from which these gene sequences had been retrieved on a world map and the correlation between gene sequence, country and biotope was examined. The tardigrade groups most sequenced are Macrobiotus, Ramazottius and Echiniscus, and the milieu most studied seems to be different types of soil. Other investigated isolation sources are drinking water, cryconite and church walls. However, much remains to be further explored. For example, the world map showed that the only molecular data on Swedish tardigrades have been retrieved from Öland. In the lab, tardigrades were found in some of the moss samples, together with other micro- and meiofauna. Three groups of bacteria (Betaproteobacteria, Gammaproteobacteria and Firmicutes) could be identified in one of the investigated mosses. These results suggest that tardigrades live in a diverse environment with different types of organisms both on the microbial as well as on the micro-meio-fauna level.