Surprisingly high levels of biodiversity and endemism amongst Antarctic rotifers uncovered with mitochondrial DNA

<div><p>Antarctica is one of the harshest environments on the planet because of its extreme climatic conditions, with prolonged winters, freezing temperatures and lack of liquid water. While almost the entire continent (99.7%) is covered year round by snow and ice, some mountain peaks and coastal areas are ice-free and sustain life. Invertebrates dominate in this environment, but despite their obvious abundance, little is known of one major player, the rotifers. In this study, we examine the distribution and diversity of rotifers from across continental Antarctica using mitochondrial <i>c</i> oxidase subunit I DNA sequences, and compare to sequences extracted from specimens collected in limited locations in the Antarctic Peninsula (AP) and in Tierra del Fuego (TF) in South America. We identified rotifers of the Class Bdelloidea to be the most frequently sampled micro-organisms in soil and limno-terrestrial environments. From the Antarctic samples, 514 sequences were generated and 37 distinct lineages were identified (40 putative species based on the PTP model) within <i>Philodina</i>, <i>Adineta</i> and unidentified bdelloids (all currently considered endemic to Antarctica). Overall, we observed widespread ranges for some rotifers in continental Antarctica, many of them exceeding 2000 km. Only one bdelloid lineage (<i>Adineta</i> cf. <i>gracilis</i>) from continental Antarctica was also present in maritime Antarctica. No close similarities were found with worldwide locations, or amongst AP and TF. Our broad coverage across Antarctica shows unique lineages that may represent potential species surpassing what is presently known from morphology, even when conservative approaches are applied for species delimitation.</p></div>