Tardigrade module

In 1997, a new molecular phylogeny revealed that C. elegans and Drosophila were much more closely related to each other than had been thought previously. Before then, Drosophila was thought to be more closely related even to humans than to C. elegans. The 1997 work placed the nematodes (which include C. elegans) and arthropods (which include Drosophila) together in a clade now known to include six other animal phyla. These eight phyla together are named the Ecdysozoa, or molting animals. Ecdysozan phyla closely related to the nematodes and arthropods might serve as valuable models for evo-devo biology and for modern comparative biology more generally, assuming it would be possible to find a tractable lab model among these animals. Animals related to but not within the nematodes and arthropods might be used to take advantage of having two reference model systems — C. elegans and Drosophila. In the long term, the use of a relative of C. elegans and Drosophila might dramatically expand the set of genes and mechanisms that are of interest for comparative studies beyond the narrower set of genes and mechanisms that are known to have conserved functions only across a greater breadth of animal diversity. But little modern work had been done in any of the phyla closely related to nematodes and arthropods, suggesting that it might be necessary to develop a new model. One ecdysozoan phylum in particular, the tardigrades, has useful characteristics for lab study. 

Tardigrades, also known as water bears, are a phylum of microscopic, eight-legged animals estimated to include thousands of species, over a thousand of which have been described to date. One species, Hypsibius exemplaris, can be cultured in the lab, frozen as live stocks, and has a short, 12-day generation time. Embryos are laid by mothers just before molting, and the embryos are left behind in the clear cuticles, making it easy to film synchronous batches of embryos.

Tools for studying Hypsibius exemplaris have now been developed, and these animals can be used as an evo-devo model and as a model for understanding how living materials can survive extreme conditions. In this module, students will get their own culture of this species, and they’ll learn to fluorescently mark components of cells and film embryogenesis. Students will also have an opportunity to collect wild tardigrades along with the other kinds of microscopic animals that share an unusual superpower: they all survive desiccation. One of the joys of working with an emerging model system is that many of the things we decide to look at have never been seen before, so students will be able to try many new things.