If asked what animal is genetically closest to a hippo, you might point at any number of four legged, land-roving mammals with hooves, such as a pig or a very fat cow, because we have a natural tendency to think that animals that look similar will also be genetically related. In this case, however, the right answer is whales… obviously. An animal’s morphology can hide a great deal about its phylogenetic history but a recent concerted effort to map all of the earth’s living organisms on a single phylogenetic tree may help make such surprising relationships more obvious.
Evolutionary trees use genetic information to create visual representations of the evolutionary history of a group of species. Most trees are limited to a single group of organisms but the Open Tree Taxonomy (OTT) attempts to cover everything – vertebrates, invertebrates, plants, fungi, archaea and bacteria – and it’s built to keep growing. It highlights portions of the tree that require more support and, as a public database, OTT hopes that scientists will continue to upload and update it with new genetic sequences. We may not discover any new evolutionary relationships with the OTT, but it will make finding and comparing branches of the tree quicker and more efficient.
An evolutionary tree, however, is only as good as the data that supports it. Due to the massive size of the OTT and the existence of both conflicting and outdated trees available in the literature, it’s inevitable that some branches will be inaccurate. Such is the case for a family of neotropical songbirds, the Thraupidae. According to Harvard Ph.D. candidate Allison Schultz, the taxonomy tree on the OTT is not representative of the current knowledge for this group of birds despite a more correct tree – one that Schultz helped construct – being present in the OTT’s database. As such, while the OTT can be a very useful tool, it can also lead a researcher astray if they decide not to look for the evidence that backs up the OTT’s tree. So give the whale-hippo connection a quick Google search, before running around claiming that hippos and whales are basically cousins because “the Open Tree Taxonomy told me so”.
Special thanks to Aaron Lin, a Ph.D. student at Harvard’s Virology Program, and Allison Schultz, a Ph.D. student at Harvard’s Department of Organismic and Evolutionary Biology (OEB), for their time, expertise and commentary.
Synthesis of phylogeny and taxonomy into a comprehensive tree of life
Scientists have drafted a complete tree of life