J. Limnol., 2013; 72(s1): 136-143 DOI: 10.4081/jlimnol.2013.s1.e17 INTRODUCTION Genetic variation in microscopic animals living in large water bodies has received some attention with a large amount of information available on various species, espe- cially of the rotifer genus Brachionus (Gómez et al., 2002; Suatoni et al., 2006; Gómez et al., 2007) and the crustacean genus Daphnia (Straughan and Lehman, 2000; De Gelas and De Meester, 2005; Ishida and Taylor, 2007). In contrast, the genetic structure of microscopic animals from mosses and lichens is almost unknown. A few studies have looked at geographic variation in tardigrades from mosses on a larger geographical scale (Jørgensen et al., 2007; Faurby et al., 2008), but so far, no study has looked into the intrapo- pulation or local clonal lineage variation. Tardigrades are microscopic metazoans inhabiting various terrestrial, limnic and marine substrates. The pres- ence of a film of free water is a prerequisite for active tardigrades. Many species of tardigrades, primarily those living in mosses and lichens, are famous for their ability to enter cryptobiosis, a form of latent life, during desic- cation (Wright et al., 1992; Møbjerg et al., 2011). Within echiniscoidean tardigrades, sequences from the mitochondrial gene cytochrome c oxidase subunit I (COI) have previously been used to investigate: i) the genetic di- versity in Echiniscus testudo (Doyère, 1840) over a large geographic area (Jørgensen et al., 2007); ii) the phylogeo- graphy of Echiniscoides (Faurby et al., 2011, 2012); iii) the taxonomic status, ecological patterns and phylogeography of various Echiniscus C:A.S. Schultze, 1840 species (Guil and Giribet, 2009); and iv) the phylogeny of Echiniscidae (Jørgensen et al., 2011). Our test species, E. testudo (Echiniscoidea: Echiniscidae), belongs to a large cosmo- politan genus of terrestrial tardigrades, comprising more than 150 species (Guidetti and Bertolani, 2005). It is a com- mon tardigrade in mosses in the temperate part of the Northern hemisphere, and it is highly tolerant of desiccation and freezing (R.M. Kristensen, personal observation). The genus was once thought to be entirely parthenogenetic (Kristensen, 1987), but later studies have found males to be common in some non-European species (Dastych and Kristensen, 1995; Miller et al., 1999). Mitchell and Ro- mano (2007) and Guil and Giribet (2009) reported the re- latively low occurrence of 7 and 2.6% males in Echiniscus mauccii Ramazzotti, 1956 (North America) and Echiniscus Genetic diversity in the parthenogenetic reproducing tardigrade Echiniscus testudo (Heterotardigrada: Echiniscoidea) Aslak JøRGENSEN, 1* Søren FAURBY, 2 Dennis KROG PERSSON, 1,3 Kenneth AGERLIN HALBERG, 3 Reinhardt MøBJERG KRISTENSEN, 1 Nadja MøBJERG 3 1 Laboratory of Molecular Systematics, The Natural History Museum of Denmark, University of Copenhagen, Sølvgade 83, DK-1807 Copenhagen; 2 Department of Bioscience, Aarhus University, Nordre Ringgade 1, 8000 Aarhus; 3 Department of Biology, August Krogh Centre, University of Copenhagen, Nørregade 10, DK-1017 Copenhagen, Denmark *Corresponding author: aslak@snm.ku.dk ABSTRACT Little is known about the genetic structure of microscopic animals from mosses and lichens. A few studies have investigated the ge- ographic variation in tardigrades from mosses, but so far no study has investigated the intra-population or local clonal lineage variation. Echiniscus testudo (Echiniscoidea: Echiniscidae) belongs to a large cosmopolitan genus of terrestrial tardigrades comprising more than 150 species. It is a common tardigrade in mosses in the temperate part of the Northern hemisphere, and is highly tolerant of de- siccation and freezing. In a previous study, we reported a maximum of 1.28% sequence variation (uncorrected p-distance) in cytochrome c oxidase subunit I (COI) haplotypes between clonal lineages covering a large geographical area. However, in this previous study we used pooled specimens to constitute a sample, and the genetic diversity from single specimens within a locality therefore remains un- known. Accordingly, the present study investigates the COI sequence variation and haplotype diversity between single specimens of E. testudo collected at three Danish localities, separated by 80 m and 186 km. A total of 10 COI haplotypes were found in the present study (Et2, Et3, Et9, Et12-Et18); only three of these were previously reported (Et2, Et3 and Et9). The uncorrected COI sequence diversity ranged between 0-2.07%, with haplotype Et18 having the highest genetic difference. The second most variable haplotypes (Et14, Et15, and Et17) all showed a maximum diversity of 1.19% compared to the other haplotypes. No general pattern of haplotype distribution was evident. Our data suggest that E. testudo has dispersed across the Baltic sea as haplotypes Et3, Et13 and Et14 are present at all three localities. The most likely dispersal mode is passive wind dispersal in the cryptobiotic tun stage. The current study emphasises that numerous sequences from single specimens are needed to describe the genetic diversity within single moss cushions. Key words: Tardigrada, Echiniscidae, sequence variation, COI, minimum spanning network. Non commercial use only