Old Museum Specimens Can Illuminate Wildlife History And Help Biodiversity Right Now

The climate crisis is threatening millions of species around the world, and biodiversity conservation has become a multi-faceted operation. As repositories of records about historical biodiversity shifts, natural history collections are crucial to this effort. They can be compared to libraries of biological specimens.
The extinction crisis has prompted a call for data-rich Australia to help fill the knowledge gap.

However, for many species, it has proved difficult to recover historical genetic data, not because there aren't enough specimens, but because of the preservation methods. My new research addresses this issue.

Our paper shows that natural history collections all over the globe can extract every bit of historical genetic data from their specimens. This includes platypus bills floating on alcohol and dried iridescent wings for butterflies.

Open the vaults

Australia has more than half a million species of native plants and is a major global leader in extinctions.

We must make every effort to understand our local area in order to combat biodiversity loss.

Museums collected biological specimens long before DNA was discovered to help create a picture about where and how species are related. The Atlas of Living Australia is a national database that houses approximately 2 million records of vertebrate specimens.

Modern techniques allow us to retrieve genetic data from specimens that were collected in the past 200-300 years. These data can be used to improve conservation outcomes for species that are struggling to adapt to current environmental changes.

To determine the historic native range of endangered Sonoran Pronghorn in North America, I used museum specimens. This helped to guide its reintroduction into the wild.

Biodiversity time capsules

Most specimens displayed in natural history museums have been dried to preserve their appearance. For plant and insect specimens, they are dried and pressed or pinched. Birds and mammals are dried and stuffed.

Researchers-focused collections do not prepare or pose specimens for public display. Large collections of specimens in murky jars can be found behind closed doors when drying fails to preserve their physical features.

This is known as "liquid fixation," where chemicals like formaldehyde are used to preserve reptiles, fish, and amphibians. This is also used by scientists to preserve the internal organs of birds and mammals.

Nearly one third of the 2,000,000 specimens in our national collection are kept in liquid. Each specimen has a story about how it has dealt (or failed) to adapt to our changing environment.

The irreplaceable record of biodiversity shifts during this time of rapid environmental change is made up of both liquid-preserved and dried specimens.

Problem with formaldehyde

While both liquid fixation and drying methods are useful in preserving biological tissues, modern genomic sequencing was not considered when developing either method.

However, drying can slow down DNA degradation. In recent decades, a treasure trove full of historical genetic data was recovered from dried specimens.

Recent examples include eggshell DNA being used to solve the mysteries surrounding extinct paradise pararots and dried tissue DNA being used to study the rapid extinctions of native Australian rodents after European colonization.

Formaldehyde, on the other hand, preserves tissues by stopping tissue decay by linking the molecules within the tissue. These cross-links make DNA extraction a tedious task. It is like chiseling delicate threads out of a block made of cement.

In recent years, however, museums began to collect fresh tissue from freshly collected specimens and store it for DNA extraction.

This is a significant breakthrough in preservation practices. This, along with the advancements in extracting DNA form older tissues and those preserved using ethanol, has opened up a whole new field in museum genetics.

While this has been happening, DNA extraction from formaldehyde-preserved specimens has been largely left in the "too difficult" bucket. This has created a huge gap in the availability and accessibility of historical DNA from most reptiles, amphibians, fish, and amphibians.

Scientists have been able to sequence a few formaldehyde-fixed museum specimens of lizards and snakes, salamanders and fish, thanks to advances in research.

However, to collect on a larger scale, there is one important obstacle: confidence in the community.

Enhancing curators' confidence

Formaldehyde specimens have been difficult to extract useful genetic information. Many scientists don't want to spend their limited research budgets on the search for risky specimens, despite declining DNA sequencing costs.

DNA extraction requires that at least a portion of the specimen be destroyed, such as small sections of liver or muscle tissue. Museum curators are reluctant to give precious tissue for research with low success rates.

We set out to reduce this risk in our recent study. Researchers and curators can identify valuable specimens that are worth damaging in order to recover genomic data by simply inspecting the preserved animal's stomach and measuring the formaldehyde present in the jar.

A single DNA extraction method is also presented that works well with both formaldehyde-fixed specimens as well as those kept in ethanol.

This is important because it is difficult to know the preservation history of older specimens. Although all our wet specimens are in ethanol at the Australian National Wildlife Collection, as with most collections, our records don't usually indicate if they have come into contact formaldehyde.

We can quickly collect high-quality historical data from disregarded specimens by reducing the need to use specimen-specific methods.

Erin Hahn, Postdoc, CSIRO.

This article was republished by The Conversation under Creative Commons. You can read the original article.