The “time-dependency of molecular rates of evolution” revisited
Citation
The “time-dependency of molecular rates of evolution revisited”: how well-calibrated paleontological evidence can clear the mess in the Bayesian debate generated by poorly calibrated uninformative molecular data.
Régis Debruyne & Hendrik Poinar.
Journal of Vertebrate Paleontology 2009, 29(Supplement to 3):86A.
Published Abstract
One of the predictions of the neutral theory of molecular evolution is that the long-term rate of substitution between two lineages can only be inferior to their instantaneous rate of mutation, due to the fixation of transient polymorphisms through time. Accordingly, some recent work supports that a drastic acceleration in the molecular rates as divergence time approaches zero is a general and predictable feature. It has become since then a hotly debated topic in both systematics and evolutionary biology. Although, observations of such ‘accelerations’ in the molecular rates within recent evolutionary time have been documented, some recent models describe a phenomenon an order of magnitude beyond them. Indeed, it allows a variation within a wide range of rates (beyond 20 fold) during an extended period of time (up to two million years). Although intuitively appealing and explaining well the original data, this model supports a serious and prolonged impact of deleterious mutations and would thus require large adjustments in the current evolutionary paradigm of genomes.
Recently, both the model of the time-dependency and the significance of the rate acceleration phenomenon have been put in question. In this communication, our primary objective is to re-address the nature of the causal factor(s) of the rate acceleration described by previous models, as well as their biological meaning. Based on previously published material, we suggest that the emphasis placed upon the divergence time in the current explanation of this phenomenon has hidden other relevant factors such as the information content of the datasets. In order to compare the performance of the strict “time-dependency” model with a more inclusive “signal-dependency” hypothesis, we examine both the impact of sequence length and the relative advantages & disadvantages of alternative calibration methods over the estimates of the rates. We illustrate the theoretical benefits of well-documented paleontological evidence on the inference of the rates through a case-study of modern and extinct Elephantoids. We thus conclude that the hypothesis for a signal-dependent artifact appears to model the data more accurately and explains some inconsistencies between published reports on evolutionary rates and paleontological data.
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