Séminaire CEFE : Evolutionary spikes: fast molecular divergence at speciation

Mardi 19 mars 2019 – 11h00

grande salle de réunion

Amaury Lambert

Sorbonne Université – Collège de France

 

In the standard view of macro-evolution, quantitative traits evolve as continuous diffusion processes with constant or time-varying parameters. This view conforms to the theory of phyletic gradualism, where traits evolve through small, gradual mutations arising throughout the lifetime of species. Recent models of trait evolution have embraced the alternative punctuated equilibrium view, by allowing the trait to jump at random times. In the standard view of molecular evolution, DNA sequences evolve through asynchronous substitutions like Poisson processes with constant rate (called molecular clock) or time-varying rate (relaxed clock). Models where sequences also undergo jumps in their evolution have so far never been proposed. Here, we argue that during the speciation process, as a consequence of divergent selection and outbreeding depression, DNA sequences can undergo episodes of fast divergence that appear in the macro-evolutioanry timescale as instantaneous jumps called evolutionary spikes, when several sites can mutate simultaneously. We propose a way to model both a smooth, basal molecular clock, together with spikes arising at speciation events. We develop a method taking as input a multiple sequence alignment and its time-calibrated species phylogeny, that is able to detect for which speciation events if any, including hidden ones, the sequence has undergone spikes and to estimate the probability and amplitude of these spikes on the phylogeny.

 

 

(Seminar in English or French, depending on the audience)


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