The evolution of animal body plans has traditionally been difficult to study because their origins lie in an ancient period for which fossils are extremely rare. Recent advances in developmental biology and genomics techniques now provide alternative methods to reconstruct the evolutionary steps that gave rise to animal body plans. Studies of water bear (Tardigrade) development may be especially informative for investigating two important themes of body plan evolution—segmentation and miniaturization. Segmentation is a common characteristic of animals. This project will investigate tardigrade development in order to reconstruct the evolutionary steps that underlie the origins of the segmentation mechanisms that are present in modern animals. Miniaturization has evolved independently in several animal lineages, including in the tardigrade lineage, but very little is known about the developmental underpinnings of miniaturization. This project aims to identify the developmental origins of the compact tardigrade body plan, and to determine the consequences of miniaturization on the developmental mechanisms that control development of the tardigrade gut. Results of this work may reveal general developmental principles that underlie miniaturization. This project will provide training to eleven undergraduate students. A key aim is to provide training to students from underrepresented groups in biology. Research on tardigrades also provides an excellent opportunity to foster public science outreach. This project uses research activities to enhance public science literacy in Jacksonville, FL.

A recent study of Hox genes revealed that the tardigrade body plan evolved by the loss of mid-trunk segments. This result raises several questions. (1) What is the developmental basis for the loss of mid-trunk segments? In many bilaterians, before growth of a mid-trunk region, antagonistic interactions between the canonical Wnt signaling pathway and inhibitors of this pathway specify anterior and posterior regions of the body axis. This work will test whether this mechanism specifies the entire body axis of a tardigrade, as predicted if tardigrades simply lost the ability to grow a mid-trunk region. (2) Do the remaining segments in tardigrades develop by the same segmentation mechanisms that have been identified in arthropods? To address this question, experiments will test whether the segment polarity gene network that specifies segment boundaries in arthropods also specifies segment boundaries in tardigrades. Results of this study will illuminate where in panarthropod phylogeny this network evolved a role in specifying segment boundaries. (3) What was the impact of the loss of mid-trunk segments on the gut, an unsegmented part of the body axis? To address this question, this work will determine the extent to which mechanisms that pattern the gut during development in other bilaterians have diverged in tardigrades. Experiments will utilize RNA interference to disrupt gene function and situ hybridization to characterize gene expression patterns during development of the tardigrade Hypsibius exemplaris. This research will provide insight into developmental underpinnings of the evolution of segmentation and secondary simplification.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Paulyn Cartwright
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University of North Florida
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