First extensive multilocus phylogeny of the genus Milnesium (Tardigrada) reveals no congruence between genetic markers and morphological traits.

The largest apochelan genus, Milnesium , is increasingly gaining attention. However, our knowledge on the phylogeny of Milnesiidae is strongly limited. In fact, so far, apochelan species usually served only as outgroups in phylogenetic analyses of other tardigrade groups. Thus, the goal of this study was to reconstruct the first multilocus molecular phylogeny of Milnesium and test several hypotheses on the evolution and dispersion of species in the genus by mapping taxonomically important morphological traits, reproductive mode and geographic distribution onto the phylogenetic tree. The phylogeny was inferred from four DNA markers (nuclear 18S rRNA, 28S rRNA, ITS2 and mitochondrial COI) and for 34 populations representing 25 species collected across the globe. Phylogenetic analysis revealed distinct molecular lineages within the genus, but rather than by morphological characters, species clustered by zoogeographic zones. In fact, no obvious patterns of phenotypic traits or reproductive mode were observed, which may indicate high levels of convergent evolution in morphology throughout the genus. The lack of congruence between morphology and phylogeny did not allow splitting this largest apochelan genus into separate taxonomic units such as genera or subgenera. On the other hand, the correlation between phylogeny and geography may suggest limited dispersal of at least some Milnesium species. [ABSTRACT FROM AUTHOR]