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This Week in Science: May 23, 2014

In Science this week, a team of Australian and New Zealand researchers report data showing that the evolution of flightless birds was not as straightforward as previously thought. It has long been believed that large, flightless ratite birds evolved into various species after the supercontinent Godwana split — a theory that implies that the ostrich and the extinct elephant bird are the oldest ratite lineages. The scientists sequenced ancient mitochondrial DNA from two species of elephant bird and, surprisingly, found through phylogenetic analysis that its closest living relative is the kiwi and that ostriches are only distant relatives. As a result, ratite speciation appears to have been driven by the divergence of species from ancestors capable of flight that independently lost their ability to fly. The researchers say their data also indicate that the evolution of large flightless birds likely began after the extinction of dinosaurs.

Also in Science, a multi-institute team reports data showing that the canonical genetic code — three unique nucleotides that code for an amino acid or start/stop codon — can undergo recoding in nature, not just in the lab. By scanning 5.6 trillion base pairs of metagenomic data for stop codon reassignment events, the researchers detected recoding in a substantial fraction of the more than 1,700 environmental samples examined. They observed extensive stop codon reassignments in bacteriophages and bacteria, indicating that bacteriophages can infect hosts with a different genetic code and demonstrating phage-host antagonism based on code differences. The findings reveal the diversity of stop codon reassignments among taxa in the wild and suggests that this should be considered in the design of engineered organisms to prevent the exchange of genetic information between engineered and naturally occurring species.