The molecular clock: a powerful tool to study the evolution of animals and their microbiota

The molecular clock is a powerful technique used in systematics and biogeography to estimate evolutionary timescales. Because the clock varies in different clades, it should be locally tuned using calibration points. In the case of animals characterised by a rich fossil records, the clock can be calibrated using paleontological data: this procedure was successful in the last two decades in estimating the timing of key macro-evolutionary events such as the origin of major Metazoa body plans or their colonisation of lands. For recent radiations, the clock can be calibrated using mutation rates and ancient DNA: this approach generally requires whole genome data and has the potential of revealing not only the timing of speciation, but also hybridisation and adaptive events as exemplified by various examples in Insecta and Mammalia. The clock can also be used to study the microbiota of animals: using complete genomes and ancient DNA it is now possible to reconstruct for example the origin of the Wolbachia infection in Ecdysozoa or the evolution of gut microbiota in primates. Overall, the molecular clock is a powerful and versatile technique for exploring the diversity of animals and tracing the timing of their evolution.