Taxonomic and ecological diversity of McMurdo Dry Valley tardigrades

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Tardigrades are found throughout many terrestrial habitats on the Antarctic mainland. These microscopic metazoans play an integral role in these ecosystems, grazing bacterial, algal, and moss populations. Characterizing tardigrade diversity in these environments is an important aspect in understanding the specific ecological roles each tardigrade species plays. For example, in other ecosystems Milnesium tardigradum is known to prey on micrometazoans, while Acutuncus antarcticus is likely a strict bacterial or algal grazer. As environmental pressure increases from impending climactic shifts, understanding the diversity and distribution of these tardigrade species coupled with further studies into their ecology will aid in our ability to predict, to some degree, the consequences of either their loss or their increase in abundance. Additionally, questions remain concerning the survival of Antarctic taxa during the last glacial maximum. Identifying biogeographic patterns of Antarctic taxa is one way to clarify whether the ice-free areas of post-glacial maxima Antarctica were recolonized via local refugia or dispersal from other southern continents. Here, we focus our study on augmenting our understanding of the biogeography of Antarctic tardigrades by adding molecular sequences from the McMurdo Dry Valleys in Antarctica (MDV). To our knowledge, little molecular data in regards to tardigrade diversity has originated from these valleys, although they are the largest ice-free areas on the continent. We therefore combine 18S ribosomal DNA sequences procured over the course of several field studies in the MDV with other datasets from other regions in Antarctica, primarily the Sor Rondane Mountains. Although to date there is a paucity of tardigrade sequences from around the continental mainland, our results still demonstrate that 1) Antarctic Milnesium tardigradum is much more diverse than previously thought, possibly comprising a complex of cryptic species, 2) Acutuncus antarcticus is widely distributed across the continent and appears to be a single species and 3) in contrast to Acutuncus, other tardigrade species are possibly regionally constrained. These results add evidence to the possible existence of an endemic, predatory Antarctic Milnesium species and supports arguments concerning the survival of Antarctic meiofauna during the most recent glacial maximum.