Evolution

Lianas for Phylogenetic Trees

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Science  15 Jul 2005:
Vol. 309, Issue 5733, pp. 359
DOI: 10.1126/science.309.5733.359c

Patterns of evolutionary descent are traditionally depicted as phylogenetic trees. This concept has become too constraining for microbial taxonomists whose subjects appear to swap chunks of DNA promiscuously, gratuitously obscuring clean lines of descent.

Kunin et al. have developed a model, assuming that the main tracks of inheritance in microorganisms do follow vertical, treelike routes. Nevertheless, swapping events (lateral gene transfer, or LGT) between genomes can be traced and mapped as many, thin vines swinging through the branches of the tree of life to link phylogenetically distant organisms. The two types of inheritance mapping can be separated, allowing the consistency of the vine network to be tested. The vines tend to arise from definable nodes or network hubs, so LGT is not random or universal, although it is scale-free, and can occur at any time and very rapidly. One benefit of this approach is being able to locate sources of LGT. Whichever tree was used, some species, including Erwinia carotovora and Bradyrhizobium japonicum, were consistently revealed as hubs for LGT, and it appears that these species may act like bacterial gene banks for a particular environment. — CA

Genome Res. 15, 954 (2005).

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