2002 Annual Science Report

Marine Biological Laboratory Reporting  |  JUL 2001 – JUN 2002

Eukaryotic rRNA Evolution: Origins of "Crown Group Taxa".

Project Summary
4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

An important goal of Astrobiology is to identify major events in our evolutionary history and establish correlations with shifts in planetary processes. Analyses of rRNA genes, and more recently other protein families, demonstrate a massive radiation in the eukaryotic line of descent that gave rise to plants, animals, fungi, numerous other independent protist lineages and several complex protist assemblates, including Alveolates, (ciliates, dinoflagellates and sporozoans), Stramenopiles (diverse heterotrophic and phototrophic protists, e.g. diatoms, various chromophytes, slime nets, small flagellates etc.). This sudden radiation obscures the identification of protists that gave rise to animals and the potential common evolutionary history of chlorophytes and other photosynthetic groups such as red algae. We seek to understand relative branching orders for major groups that emerged from this massive radiation and to infer what kind of environmental changes on a planetary scale might have stimulated this massive diversification. To address this issue we have focused our attention on the analyses of both small and large rRNA genes from key taxa. We have shown than sponges are not monophyletic and that the bilateral animals are not more closely related to Ctenophora than to Cniadira. In a companion study we show that diverse Ctenophore lineages diverged relatively recently from a common ancestor. We also identified several protists that are likely candidates for the stem groups of animals. These include nuclerids and the protists Ancyromonas and Apusomonas. We have initiated a project to sequence the mitochondrial genomes Ancyromonas and Apusomonas, and these will be compared to mt sequences of other protists and diverse animals. For Apusomonas we have collected 669,533 nucleotides, resulting in 83contigs, most of which are within 5 supercontigs. The largest supercontig is 43,341 nucleotides; the smallest is 3,446 nucleotides. Approximately one-third of this sequencing effort is mitochondrial. For Ancyromonas we have sequenced 157,283 nucleotides, resulting in 13 contigs, of which one-third are mitochondrial. Our plan is to finish these mt genomes over the next year in an attempt to gain insights about the origins of the metazoa and other "crown group taxa". Finally, we have completed rRNA sequences for representatives of other crown group taxa, including gymnamoebae of the families Vexilliferidae, Paramoebidae and Vannellidae. Our analysis reconfirms the existence of the Leptomyxid/Hartmannellid (LH) clade and introduces the existence of the Paramoebid/Vexilliferid (PV) and Vannellid (V) clades.