title: The influence of body size and net diversification rate on molecular evolution during the radiation of animal phyla.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Centre for the Study of Evolution, School of Life Sciences, University of Sussex, Falmer, Brighton, UK. eric.fontanillas@anu.edu.au
authors.forename: Eric
authors.initials: E
authors.lastname: Fontanillas
authors.forename: John J
authors.initials: JJ
authors.lastname: Welch
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Thomas
authors.forename: Lindell
authors.initials: L
authors.lastname: Bromham
mesh_terms: D000828:Animal Population Groups / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*; D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D004247:DNA / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D019143:Evolution, Molecular; D053476:Extinction, Biological; D050259:Genes, Mitochondrial / Q000235:genetics; D049810:Genetic Speciation; D008954:Models, Biological; D009154:Mutation; D010802:Phylogeny; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013997:Time Factors
chemical_list: D004272:DNA, Mitochondrial; D004247:DNA