Poster Presentation Society for Molecular Biology and Evolution Conference 2016

A molecular palaeobiological approach of arthropod terrestrialisation (#418)

Jesus Lozano-Fernandez 1 , Robert Carton 2 , Alastair R Tanner 1 , Mark N Puttick 3 , Mark Blaxter 4 , Jakob Vinther 1 3 , Jørgen Olesen 5 , Gonzalo Giribet 6 , Gregory D Edgecombe 7 , Davide Pisani 1 3
  1. School of Biological Sciences, University of Bristol, Bristol, United Kingdom
  2. Department of Biology, The National University of Ireland, Maynooth, Ireland
  3. School of Earth Sciences, University of Bristol, Bristol, United Kingdom
  4. Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, United Kingdom
  5. Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
  6. Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States of America
  7. Department of Earth Sciences, The Natural History Museum, London, United Kingdom

Animals have marine origins, and only few animal phyla include lineages that can complete every phase of their life cycle outside the water. The process through which animals adapted to life on land is referred to as terrestrialisation and it is one of the most extreme cases of adaptation. Arthropoda (insects, spiders, centipedes and their allies) represent the largest majority of terrestrial biodiversity and have an extensive and rich fossil record that suggests they were the first fully terrestrial animals. Arthropods colonised the land multiple times independently, which allow rigorous comparison of the alternative solutions adopted by the different (but genomically and morphological comparable) groups to the same adaptive challenge.

In this study we implemented a molecular palaeobiological approach, merging molecular and fossil evidence, to elucidate the deepest history of the terrestrial arthropods. We focused on the three, independent, Palaeozoic arthropod terrestrialisation events (those of Myriapoda, Hexapoda and Arachnida) and showed that a marine route to the colonisation of land is the most likely scenario. Molecular clock analyses confirmed an origin for the three terrestrial lineages bracketed between the Cambrian and the Silurian. While molecular divergence times for Arachnida are consistent with the fossil record, Myriapoda and Hexapoda are inferred to have colonised land earlier. An estimated origin of myriapods by the early Cambrian substantially predates trace or body fossil evidence, precedes the appearance of embryophytes and raise the possibility of independent terrestrialisation events  in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems.