SSRL Research Gets the Creepy Crawlies
Researchers at the Stanford Synchrotron Radiation Laboratory (SSRL) are looking at the things that creep and crawl and sting. Spiders, scorpions, crabs, worms and more are under examination on the nanoscale as part of a search for deposits of metal atoms in the creatures' claws, jaws and fangs. These metal deposits are an evolutionary feat of engineering—they make the structures significantly stronger and longer lasting. Researchers Robert M. S. Schofield of the University of Oregon, Michael H. Nesson of Oregon State University and Robert A. Scott of the University of Georgia are working at SSRL, on the microprobe at beam line 2-3. Together they are surveying a range of small invertebrates—mostly arthropods—shedding light on the development of these unique structures, and searching for common ancestors of these highly varied creatures.
Spiders don't have flashy metal fangs, but they do rely on metal deposits to make their fangs extra strong and fracture resistant. A shiny strip of tin foil is an example of an organized cluster of many metal atoms. In contrast, the metals in spider fangs and other critter appendages are single atoms held in place by non-metals. This is part of the reason that no one discovered these deposits until about 30 years ago: it is difficult to detect a single atom unless you are specifically looking for it. Moreover, the metals—mainly iron, copper, manganese and zinc—are present only in very small parts of the animal. This may include the very tips of scorpion or crab claws, the tiny fangs of spiders, or the jagged teeth on the mandibles of ants. The structures are small but undergo proportionally large stresses as they come into contact with the environment.
The metals accumulate after molting, as the animals grow into adulthood. Researchers monitored the percentage of metal deposits at different times during development and observed the channels through which the metals migrate into appendages. They found that different metals settle in different areas: zinc is found in the tips of spider fangs while manganese is found in the trunk. Often, metal atoms in the newly hardened structures are also paired with specific non-metals: zinc with chlorine, and manganese with calcium. In the image above, the upper right frame shows X-ray detection of zinc; the lower left shows X-ray detection of manganese. The lower right frame combines the images: zinc is green and manganese is red.
Now that researchers know to look for them, these deposits are surfacing in a wide variety of species. Including the current survey, metal atoms have been found in 136 species of insects, 30 species of arachnids, 12 species of polychaete worms and four species of centipedes. Even so, there are still thousands of species to examine. Ultimately, researchers hope that understanding this biological pattern found in so many current species will guide the search for a common ancestor. Schofield explains that the appearance of new biomaterials has played a central role in evolution, and these metal atom structures should be no different. Biomaterials can open the door for organisms to develop drastically new characteristics, and even lead to extinction or evolution of new species.
Calla Cofield, SLAC Today, July 14, 2008
Above image: The fangs of Araneus diadematus, the European garden spider. The frames (2x2 micrometers) show deposits of zinc (upper right), magnesium (lower left) or both (lower right). The metals strengthen the spider fangs.