Dissecting spider embryos for light microscopy

INTRODUCTIONThe spider Cupiennius salei, commonly known as the American wandering spider, is a particularly useful laboratory model for embryological studies because of the availability of tools to study and manipulate its embryonic development. Cupiennius is used to study axis formation, segmentation, appendage development, neurogenesis, and silk production. These studies contribute to our understanding of the evolution of these processes, but they also help us to understand the origin and diversification of evolutionary novelties. Comparisons between spiders and insects can show the degree of conservation and divergence of developmental mechanisms during arthropod evolution. Any embryological feature conserved between spiders and insects is likely to represent an ancestral feature for arthropods. Comparative molecular embryological work in insects and spiders should eventually allow us to define a molecular archetype for the phylum Arthropoda. This in itself will be a necessary cornerstone for comparing the different metazoan phyla, including chordates. Spider embryos can be studied as whole mounts under the dissection microscope. Alternatively, the embryos can be dissected and observed under the compound microscope. Preparing and dissecting spider embryos for compound microscopy is difficult due to the high amount of yolk, which makes the embryos very fragile. The following protocol describes how to make the necessary tools, then use them to obtain good preparations. Not all embryonic stages can be dissected and prepared; very young stages can only be examined as whole mounts.