Paper: Parallel adaptations to high temperatures in the Archaean eon

Nature 456, 942-945 (18 December 2008) | doi:10.1038/nature 07393; Received
5 March 2008; Accepted 1 September 2008; Published online 26 November 2008

Parallel adaptations to high temperatures in the Archaean eon
Bastien Boussau 1,3, Samuel Blanquart 2,3, Anamaria Necsulea 1, Nicolas
Lartillot 2,4 & Manolo Gouy 1

1.. Laboratoire de Biométrie et Biologie Evolutive, CNRS, Université de
Lyon, Université Lyon I, 43 Boulevard du 11 Novembre, 69622 Villeurbanne,
France
2.. LIRMM, CNRS, 161 rue Ada, 34392 Montpellier, France
3.. These authors contributed equally to this work.
4.. Present address: Département de Biochimie, Université de Montréal,
C.P. 6128, succursale Centre-Ville, Montréal QC H3C3J7, Canada.
Correspondence to: Manolo Gouy1 Correspondence and requests for materials
should be addressed to M.G. (Email: mgouy@xxxxxxxxxxxxxxxxxxxxxx).


Abstract
Fossils of organisms dating from the origin and diversification of cellular
life are scant and difficult to interpret, for this reason alternative means
to investigate the ecology of the last universal common ancestor (LUCA) and
of the ancestors of the three domains of life are of great scientific value.
It was recently recognized that the effects of temperature on ancestral
organisms left 'genetic footprints' that could be uncovered in extant
genomes. Accordingly, analyses of resurrected proteins predicted that the
bacterial ancestor was thermophilic and that Bacteria subsequently adapted
to lower temperatures. As the archaeal ancestor is also thought to have been
thermophilic, the LUCA was parsimoniously inferred as thermophilic too.
However, an analysis of ribosomal RNAs supported the hypothesis of a
non-hyperthermophilic LUCA. Here we show that both rRNA and protein
sequences analysed with advanced, realistic models of molecular evolution
provide independent support for two environmental-temperature-related phases
during the evolutionary history of the tree of life. In the first period,
thermotolerance increased from a mesophilic LUCA to thermophilic ancestors
of Bacteria and of Archaea-Eukaryota; in the second period, it decreased.
Therefore, the two lineages descending from the LUCA and leading to the
ancestors of Bacteria and Archaea-Eukaryota convergently adapted to high
temperatures, possibly in response to a climate change of the early Earth,
and/or aided by the transition from an RNA genome in the LUCA to organisms
with more thermostable DNA genomes. This analysis unifies apparently
contradictory results into a coherent depiction of the evolution of an
ecological trait over the entire tree of life.

Source: Nature
http://www.nature.com/nature/journal/v456/n7224/full/nature07393.html

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