Evolution of Xenacoelomorpha, the earliest extant bilaterian animals
Flagellophora apelti, a 1 mm long worm collected from the Gullmar fjord at 55 m. Photo: Ulf Jondelius
Summary
Molecular phylogenetics have resolved the relationships of many of the animal phyla, but deeper branches have been notoriously difficult. One of the most contentious issues was the initial split within Bilateria, animals with anterior - posterior differentiation and mesoderm. The origin of Bilateria was a milestone in animal evolution: more than 98% of animal species are bilaterians. Recently we showed in a phylogenomic study that Bilateria is split into two sister groups, Xenacoelomorpha and Nephrozoa. Nephrozoans comprise more than 1 million species, whereas Xenacoelomorpha are simple marine worms with less than 500 known species. My aim is to understand events and patterns in the evolution of Xenacoelomorpha and contrast them with their mega-diverse sister group. We are testing our hypothesis that extant Xenacolelomorpha represent the phylogenetic diversity of the whole group, i.e. they are not a surviving subset of closely related species. We are also working to estimate the time of divergence between Nephrozoa and Xenacoelomorpha using transcriptome data calibrated with fossils, and to reconstruct ancestral features of Xenacoelomorpha and Bilateria. Finally I am interested in testing the hypotheses that rates of molecular evolution differ in the two groups, and that rates of molecular and morphological evolution are correlated. Data for this come from from sequencing of xenacoelomorph transcriptomes.
Projekt Participants at NRM
Ulf Jondelius (principal investigator)
Carina Svensson (laboratory assistant)
External Projekt Participants
Johanna Cannon, UCSB (researcher)
Andreas Hejnol, Sars Centre UiB (researcher)
Olga I Raikova, RAS (researcher)
Selected Publications
Cannon, J. T., Vellutini, B. C., Smith, J., Ronquist, F., Jondelius, U., & Hejnol, A. (2016). Xenacoelomorpha is the sister group to Nephrozoa. Nature, 530(7588), 89–93. doi:10.1038/nature16520
Meyer-Wachsmuth, I., & Jondelius, U. (2016). Interrelationships of Nemertodermatida. Organisms Diversity & Evolution, 1–12. doi: 10.1007/s13127-015-0240-8
Raikova, O. I., Meyer-Wachsmuth, I., & Jondelius, U. (2016). The plastic nervous system of Nemertodermatida. Organisms Diversity & Evolution, 16(1), 85–104. doi:10.1007/s13127-015-0248-0
Meyer-Wachsmuth, I., Galletti, M. C., & Jondelius, U. (2014). Hyper-cryptic marine meiofauna: species complexes in Nemertodermatida. PLoS ONE, 9(9), e107688.