AAA NEWSLETTER – summer 2013 Session Highlights — AAA ANNUAL MEETING/EB 2013 Boston, MA depositional environments that were completely unexplored Neil Shubin: Fossils, by vertebrate paleontologists. This area, known as the Fram formation, is where Shubin’s team set off to look for fossils Genes, and the Origin nearly 15 years ago. Shubin recounted the discovery of Tiktaalik, the of Organs intermediate fossil with a mosaic of features belonging to fish and limbed tetrapods. was a flat-headed fish by Mary Bates, PhD, Science Writer Tiktaalik with a neck and fins that probably lived in shallow water http://marybatessciencewriter.wordpress.com/ environments. Based on analysis of the bones in its limbs, eil Shubin, professor of organismal biology and along with evidence from preserved tracks of early walking anatomy at the University of Chicago, was the animals, the team concluded that the creature used its fins N first speaker on Sunday morning’s Evolutionary for support and propulsion. and Developmental Biology plenary session. He began his Shubin presented new data (which his team plans to talk by remarking on the impressively integrative nature publish in a few months) regarding the hind fin and pelvis of the field of anatomy, which draws from histology, of Tiktaalik. It had a very large pelvis, equivalent in size immunology, neurobiology, paleontology, and other to that of a tetrapod, and a mobile femur, suggesting an disciplines. This multidisciplinary integration is crucial emphasis on hind fin locomotion. Shubin thinks Tiktaalik may have moved around much like current-day lungfish, which use a form of bipedal locomotion of the hind fins when maneuvering in shallow environments. The discovery of creatures like Tiktaalik not only fills in gaps in the fossil record, it also allows scientists to see living animals in a new way and formulate new hypotheses about genetic development. Shubin discussed some of the ways his lab is trying to understand how gene expression and regulation have evolved during the origin of limbs. Much of this focus is on the homeobox (Hox) genes, which are known to be involved in limb development. Hox genes are expressed in two phases during development: an early phase associated with the specification of the proximal region of the limb, and a later phase during the specification of the hand or foot region. Shubin’s lab is interested in whether this late phase of expression is associated with the origin of Plenary Speaker Neil Shubin the tetrapod limb. To answer this, they are looking at the enhancer elements for understanding the great evolutionary transformations, near the Hox genes that drive these phases of expression Shubin argued, including the question that has driven and may have regulatory potential for making a hand or much of his research: the transition from lobe-finned fish to foot. Shubin’s group looked at sequence similarity of several limbed tetrapod. enhancer elements in diverse animals and found a nested There is a wide gulf in structure among the patterns of hierarchy, with some of the enhancer elements present in all fins and limbs belonging to existing animals. To bridge the creatures that have paired fins, other enhancer elements that gap, Shubin advocates targeting fossil expeditions to key are conserved among all tetrapods, and still other enhancer parts of the tree of life where this transition occurred. He elements that are only conserved among tetrapods and the and his colleagues have designed expeditions to rocks of the coelacanth. right age and type to look specifically for fossils of animals Shubin closed his remarks by again emphasizing the with intermediate structures between fins and legs. This integrative nature of his work. He and other paleontologists transition occurred during the middle to late Devonian look at antecedents in morphology in the fossil record, but era in deltaic environments where rivers and streams researchers can also look for antecedents in the genome drained into the sea. In North America, there are three itself using transgenic technology, molecular evolution, areas where deltaic sediments from the Devonian exist. and functional genomics. The reciprocal illumination that Two of them, in the eastern United States and Greenland, develops between these approaches allows scientists to see are well-explored. But extending 1500 km east to west the correlates between morphological and genetic evolution across the Canadian Arctic islands lies a setting of deltaic and how they assemble along the hierarchy of life.

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