In order to better understand reptile and amphibian species, research institutions like the Chicago Academy of Sciences / Peggy Notebaert Nature Museum create and maintain extensive collections of specimens that are fundamental tools for studying our living environment.
Our institution houses a selection of 23,260 reptile and amphibian specimens in our fluid-preserved collection. Historically, “wet” collections were used to preserve whole specimens without compromising their physical integrity. Beginning in the 17th century, scientists used solutions of formaldehyde and ethanol to preserve specimens submerged in glass jars. The study of fluid-preserved collections is critical in many scientific studies. For instance, specimens have been used to research certain diseases, their effects, and way of spreading. Amazingly, scientists have been able to detect pathogens on the skin of frog specimens collected as early as 1888!
It is vital that scientists continue to collect and preserve animals in museums. For this reason, the Chicago Academy of Sciences / Peggy Notebaert Nature Museum and other scientific institutions work to undertake new techniques for more sustainable collection practices. In the United States, Federal and State laws govern how, when, and for what purpose scientists collect specimens. Often, modern collectors will choose to use non-lethal techniques to study species and rely on digital technologies, like shared databases and CT scanning, that bring new light to fluid-preserved collections and promote sustainability.
Historical context
Preservation in fermented liquids, particularly of food, has been used by people around the world for centuries. During the 17th century, scientists began seeking ways to preserve scientific specimens in fluid to prevent deterioration, inspired by pre-existing practices. Specimens were stored in a variety of fluids—vinegar, rum, cider, and brine (heavily salty water). In the 19th century, scientists began using formaldehyde to “fix”, or set, a specimen before storing it in ethanol in an effort to keep it from shriveling. It is now understood that the use of formaldehyde damages the specimen’s DNA, which presents challenges for some modern testing methods. The natural history collections community continues to build on best practices as new methods for using scientific specimens and preserving them are discovered.
Fluid preservation techniques
Bird and mammal specimens are commonly stuffed and dried, using a process known as taxidermy. With this preparation method, only the skin and skull, or maybe the entire skeleton, will be kept. Small tissue samples may be preserved, but not the whole animal. On the other hand, reptile and amphibian specimens are typically preserved in glass jars, immersed in a 70% to 95% ethanol solution. This technique enables the entire specimen to be preserved — the skin, skeleton, muscle tissue, organs, even stomach contents — and allows scientists to study them over many decades after their collection.
Many types of specimens may be preserved in an ethanol solution. Most of our herpetology collection (reptile and amphibian specimens) are preserved this way, as well as most of the arachnids (spiders), fish, some mollusks, and even some mammals. If there are such advantages to preserving a specimen in its entirety, why aren’t all specimens preserved this way? To preserve a specimen long term, it must first be injected with a fixative chemical, like formaldehyde. This sets the specimen to help prevent deterioration. However, that chemical has been found to disrupt accurate DNA analysis of those specimens. The natural history collections community is working to find ways to enable reliable DNA extraction and alternatives for preservation.
Proper labeling is also essential for tracing the specimen back to its very origin. Each specimen is labeled with an ethanol-resistant tag that contains its catalogue number, and when and where the specimen was collected. Sometimes, even the name of the scientist who collected the specimen is recorded here.
Collecting sustainably
Our living environment is a delicate system of interconnections. Human activity, including past collecting practices, can dangerously impact nature and its structure. In the past, early naturalists would collect indiscriminately and often destructively. While their work was foundational to the museum collections we use today, contemporary scientists support best practices for more sustainable collecting. In the United States, Federal and State laws strictly regulate the legal collection of specimens including reptiles and amphibians. Sustainable collecting practices rely on detailed knowledge of a species’ ecology and conservation status. This way, scientists try to minimize negative impacts to wildlife populations.
Innovations in the field of preservation
To extend the life of fluid-preserved collections and make their important data more accessible, scientific institutions are finding innovative ways of digitizing and sharing specimen data. Museums produce high resolution images of fluid-preserved specimens using squeeze boxes. These tools allow the specimen to remain submerged in ethanol when photographed to avoid physical damage. Scientists share specimen information through online databases, which may be used by researchers all around the world. Other innovative practices include using X-rays and CT scanning to create highly detailed 3D models of fluid-preserved specimens.
Other preservation methods
Reptiles and amphibians can be preserved in other ways. Preparing and preserving the specimen’s skeleton allows examination of the bones of the animal. A turtle’s shell is part of its skeleton — examining the inside of the shell shows how the vertebrae and ribs actually make up the framework of the animal’s shell.
To show what an animal looked like in life with a specimen, a mounted, life-like specimen must be created. Reptiles such as snakes, turtles, and alligators, can be taxidermied. To create a mounted specimen, the taxidermist needs to understand the skeletal and muscular system of the specific type of animal, be able to reconstruct the inner framework of the mount, and also be familiar with the behavior of the type of animal they are working with in order to create a life-like specimen. Taxidermists usually develop a specialty in one group of animals; the more they learn about mammal, bird, or reptile bodies and behaviors, the more effective they are at creating a mounted specimen of that group.
Freeze-drying is another process of preparation that is sometimes used. Freeze-drying removes water from the specimen in a low pressure environment, preventing tissue and skin from shrinking. This preparation method also allows for preservation of the entire animal, however it takes a long time and is most effective with a freeze-drying freezer.
