H. dujardini micrograph. The green in the middle is the remains of food algae; the animal is about 200 microns or 0.2 mm.AZIZ ABOOBAKER, EDINBURGHWhere tardigrades belong in the tree of life is a difficult question. Some previous work suggests that these tiny animals that can survive intense environmental challenges are most closely related to nematodes, while other studies and the animals’ morphology point to arthropods as water bears’ nearest relatives.
Now, an international team of scientists has compared detailed genome assemblies of two tardigrade species. While their analysis, published today (July 27) in PLOS Biology, sheds light on water bears’ ability to endure punishing circumstances, it does not resolve their evolutionary history.
“Even the full genomes of two tardigrades, which the authors report here, were not sufficient to decide whether tardigrades were closer to the arthropods or the nematodes,” Thorsten Burmester, a biologist at the University of Hamburg in Germany who did not participate in the study, writes in an email to The Scientist. “Genome sequences from related phyla, which are not yet available, may help in the future.”
Scientists have identified more than 1,200 species of tardigrades living on land, in freshwater, and in ...
