Friday, 18 May 2018

Determining ages of different microbial groups


To learn about the past, paleontologists turn to the fossil record. The occurrence, abundance and diversity of fossils provides a window into the evolutionary history of animal and plant groups, anchoring them in absolute geological time.

But the fossil record is almost no good at all for microbial, single-celled life. Microbes rarely fossilise and, with a few notable exceptions, the available fossils are too indistinct to reveal which groups were already in existence at a particular time.

This is a major problem for students of evolutionary history, because almost all of life's genetic, biochemical and metabolic diversity is microbial -- both today and in the distant past.

While most microbes are invisible to the naked eye, their collective action in recycling nutrients, producing the oxygen we need to breathe, and maintaining the stability of global ecosystems is impossible to ignore.

Microbial dominance was, if anything, even higher in the past. The most familiar groups of large, multicellular life forms that exist today, animals, plants and fungi, are relative newcomers in evolutionary terms, evolving within the last half-billion years or so.

The researchers have developed a new method for working out the relative ages of microbial groups -- which lineages evolved first, and which came later?

Instead of using fossil dates, the method works by looking at events of horizontal gene transfer among ancient microbes, which can be detected by studying the genomes of their modern descendants.

Horizontal gene transfer is a process that many microbes use to obtain new genes from other cells living in the same habitat and it underlies the rapid spread of antibiotic resistance, but is also a more general way in which microbes can adapt to new ecological niches.

See:

Adrián A. Davín, Eric Tannier, Tom A. Williams, Bastien Boussau, Vincent Daubin, Gergely J. Szöllősi. Gene transfers can date the tree of life. Nature Ecology & Evolution, 2018; DOI: 10.1038/s41559-018-0525-3

Posted by Dr. Tim Sandle

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