This multi-disciplinary project aims to understand the evolutionary history of the modern brittle stars (Ophiuroidea), the most speciose class of echinoderms, which originated over 400 million years ago. After the evolutionary bottleneck of the Permian-Triassic mass extinction, 250 million years ago, the surviving lineages underwent fast radiation, filling many empty ecological niches, to form the modern-day crown group with about 2100 living species. The phylogenetic relationships within this group were long misunderstood due to difficulties with analyzing synapomorphies, and limitations in molecular methods that have now been overcome.
The main approach of this study is morphological to allow utilization of the rich fossil record, which consists of mainly dissociated skeletal elements. Also, a better understanding of the phenotype is needed to explore how genes create morphologies. We examine skeletal elements with scanning electron microscopy, and most recently, with x-ray micro-computed tomography. The project will build up a large dataset of high resolution images of micromorphological structures in 2D and 3D, in digital format. Our main target is the skeleton of the arms which has recently been discovered to be particularly rich in phylogenetically informative characters. We are also studying the effect of evolutionary mechanisms such as heterochrony, and trace the evolution of particular structures through time, compared to adaptation by selection acting on existing structures.
This research is a long-term effort with wide international collaboration.
Sabine Stöhr (Principal investigator)
Ben Thuy, Natural History Museum, Luxemburg City, Luxemburg
Elizabeth Clark, Yale Peabody Museum, New Haven, USA
Alexander Martynov, Zoological Museum, Moscow, Russia
Tim O’Hara, Museum Victoria, Melbourne, Australia
Anne Chenuil, University of Marseille, France
Alexandra Weber, University of Basel, Switzerland
Thuy, B. & Stöhr, S. (2016). A New Morphological Phylogeny of the Ophiuroidea (Echinodermata) Accords with Molecular Evidence and Renders Microfossils Accessible for Cladistics. PLoS ONE 11(5), e0156140. doi:10.1371/journal.pone.0156140
Stöhr, S. & Martynov, A. (2016). Paedomorphosis as an Evolutionary Driving Force: Insights from Deep-sea Brittle Stars. PLoS ONE.
O'Hara, T., Hugall, A. Thuy, B., Stöhr, S. & Martynov, S. (2017). Restructuring Higher Taxonomy using Broad-scale Phylogenomics: the Living Ophiuroidea. Molecular Phylogenetics and Evolution 107, 415-430. doi:10.1016/j.ympev.2016.12.006