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Open Access Research article

The influence of body size and net diversification rate on molecular evolution during the radiation of animal phyla

Eric Fontanillas13*, John J Welch12, Jessica A Thomas13 and Lindell Bromham13

Author Affiliations

1 Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK

2 Institute of Evolutionary Biology; School of Biological Sciences; University of Edinburgh, West Mains Rd., Edinburgh, EH9 3JT, UK

3 Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra, A.C.T. 0200 Australia

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BMC Evolutionary Biology 2007, 7:95  doi:10.1186/1471-2148-7-95

Published: 26 June 2007

Abstract

Background

Molecular clock dates, which place the origin of animal phyla deep in the Precambrian, have been used to reject the hypothesis of a rapid evolutionary radiation of animal phyla supported by the fossil record. One possible explanation of the discrepancy is the potential for fast substitution rates early in the metazoan radiation. However, concerted rate variation, occurring simultaneously in multiple lineages, cannot be detected by "clock tests", and so another way to explore such variation is to look for correlated changes between rates and other biological factors. Here we investigate two possible causes of fast early rates: change in average body size or diversification rate of deep metazoan lineages.

Results

For nine genes for phylogenetically independent comparisons between 50 metazoan phyla, orders, and classes, we find a significant correlation between average body size and rate of molecular evolution of mitochondrial genes. The data also indicate that diversification rate may have a positive effect on rates of mitochondrial molecular evolution.

Conclusion

If average body sizes were significantly smaller in the early history of the Metazoa, and if rates of diversification were much higher, then it is possible that mitochondrial genes have undergone a slow-down in evolutionary rate, which could affect date estimates made from these genes.