Estimation of divergence times in the volvocine algae

Matthew D. Herron, Jeremiah D. Hackett, Frank Aylward, and Richard E. Michod

Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ

Based on comparisons of RNA and protein-coding sequences, the divergence between Chlamydomonas reinhardtii and Volvox carteri was proposed to have occurred between 50 and 75 MYA. Because C. reinhardtii has often been treated as the closest unicellular relative of the colonial volvocine algae, the radiation of the latter group into 50 or more extant species has often been inferred to have taken place in this interval. However, two factors have the potential to complicate this inference: first, C. reinhardtii is not the closest unicellular relative of the colonial volvocine algae, and second, substitution rates are known to vary among lineages. We have constructed a multigene dataset to estimate divergence times within the volvocine algae using multiple fossil calibrations with non-parametric rate smoothing and penalized likelihood methods.

e-mail address of presenting author: mherron@email.arizona.edu