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In a victory for transparent research, a study is overturned and the tardigrade water bear is found to be a little less alien.

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Open research wins as tardigrades lose a lot of foreign DNA.

new study calls into question the finding that tardigrades contain the most foreign DNA of any species. Tardigrades, also known as water bears, are eight-legged microscopic animals that are members of the superphylum Ecdysozoa. 

These endearing animals are known for their ability to survive conditions normally incompatible with life, including temperatures ranging from −272 to 151°C, incubation in organic solvents, lack of water, intense radiation and pressure, and even the vacuum of space. 

In November 2015, tardigrades added another claim to fame to their list of superlatives when  a study was published in PNAS claiming that 17% of the tardigrade genome was made up of foreign DNA, acquired through horizontal gene transfer. Horizontal gene transfer occurs when genetic material is transferred between organisms without reproduction and is prominent among microscopic organisms. However, low levels of foreign DNA are common and comprise 0.5% of genes in primates. 

The surprising claim that was 17% of the tardigrade genome was acquired through horizontal gene transfer was more than double the amount or foreign DNA previously reported in bdelloid rotifers. This degree of functional horizontal gene transfer would call into question currently accepted theories that animal evolution is a tree-like process and notions that animal genomes are phylogenetically independent. 

A recent study from researchers at the University of Edinburgh put this bold claim to the test and found no evidence of extensive foreign DNA in tardigrades.The authors of the new study have concluded that horizontal gene transfer accounted for 1-2% of genes at most, a percentage much more in line with previous estimates.

The team compared an independently obtained tardigrade genome assembly to the genome assembly analyzed in the previously published study. The researchers found that the genome assembly containing 17% foreign DNA was heavily compromised by bacterial sequences and other contaminants. The authors explain that unfortunately, contamination from foreign sequences is “easy to generate and difficult to separate.”

Mark Blaxter, the lead investigator on the study commended the process. “What is evident is the amazing new ability of science to self correct rapidly,” he said. Another author on the study attributed the victory to open science and the willingness of the rival team to promptly release their data.

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