Specimens from old museums can illuminate wildlife history and contribute to biodiversity now
As the climate crisis threatens millions species in the world, biodiversity conservation is now an operation at all levels. Natural history collections play a vital role in this effort as repositories of historical changes in biodiversity, such as libraries made up of biological specimens.
In response to the extinction crisis, the the call went out browse Australian collections for data to fill knowledge gaps.
For many species, however, the recovery of historical genetic data has been severely hampered, not by the lack of specimens, but by the methods used to preserve them. This is where my new research comes in.
Our paper shows how natural history collections people around the world can extract every drop of historical genetic data from their specimens, from dried iridescent butterfly wings to platypus bills floating in alcohol.
Opening of safes
To have a chance to tackle biodiversity loss, we must use all resources to learn more about our unique corner of the world.
Long before the discovery of DNA, museums collected biological specimens to create a picture of where species live and their relationships. Today the Atlas of Living Australia, which serves as the national database for Australian museums, contains approximately 2 million records of vertebrate specimens.
Armed with modern techniques, we can now recover genetic data from specimens collected over the past 200 to 300 years. This data can then improve conservation outcomes for species struggling to cope with current environmental changes.
For example, I recently used museum specimens determine the historic range of the endangered North American antelope. This guided its reintroduction into the wild.
Time capsules on biodiversity
When you visit natural history museums, most of the specimens on display will have been dried to beautifully preserve their physical appearance. Specimens of plants and insects are dried and pressed or pinned, while birds and mammals are stuffed and dried.
Research-oriented collections do not prepare or pose specimens for public display. When drying does not sufficiently preserve physical characteristics, large collections of cloudy jars containing specimens are usually found behind the scenes.
This is called “liquid fixation”, where we use chemicals such as formaldehyde to preserve fish, amphibians and reptiles. It is also used for birds and mammals, when scientists want to preserve their internal organs.
Almost a third of the 2 million specimens in our national database are held in cash. Each of these specimens has a story to tell about how this species has coped (or not) with our changing environment.
Together, the dried and liquid-preserved specimens held in collections around the world represent an irreplaceable record of changes in biodiversity in this time of rapid environmental change.
The formaldehyde problem
Although the drying and liquid fixation methods (as with chemical formaldehyde) both help preserve biological tissue, no method has been developed with modern genomic sequencing in mind.
Yet drying slows down DNA degradation, and a treasure trove of historical genetic data has been recovered from specimens dried in recent decades.
Recent examples include the use of eggshell DNA to solve the mysteries surrounding extinct paradise parrots, and dried tissue DNA to examine the rapid extinction of native Australian rodents after European colonization.
On the other hand, formaldehyde preserves tissue by stopping decomposition in its tracks by cross-linking molecules in the tissue. Frustratingly, these cross-links turn DNA extraction into an exercise akin to chiseling strands of delicate thread out of a block of cement.
But in recent decades, museums have started taking fresh tissue samples from newly collected specimens and storing them specifically for DNA extraction.
This marks a pivot in conservation practices. Coupled with advances in DNA extraction from older dried tissues and those preserved in ethanol, it ushered in a whole new field of museum genetics.
Meanwhile, DNA extraction from specimens preserved with formaldehyde was largely left in the “too hard” bucket. This left a gaping hole in the availability of older historical DNA for most fish, amphibians, and reptiles.
Thanks to advances in research, scientists have managed to find a way to successfully sequence a handful of museum specimens fixed with formaldehyde – lizards, snakes, salamanders, and fish – which would otherwise have been lost to history.
But to collect on a larger scale, an important obstacle remains: the trust of the community.
Improve Conservative Confidence
Until now, obtaining usable genetic information from specimens preserved in formaldehyde has been largely haphazard, with the emphasis on failure. Despite the falling costs of DNA sequencing, many scientists are unwilling to spend their limited research budgets on the pursuit of specimens at risk.
DNA extraction requires the destruction of at least part of a sample, such as removing a small section of liver or muscle tissue. Thus, museum curators hesitate to grant precious fabrics for studies with low expected success rates.
In our recent to study, we looked for ways to minimize this risk. We have found that, in essence, a quick inspection of the preserved animal’s gut and measuring the formaldehyde in the jar can allow researchers and curators to identify valuable specimens worth damaging to recover. genomic data.
We also present a unique DNA extraction method that works surprisingly well on samples fixed in formaldehyde and those preserved in ethanol.
This is useful because the conservation history of a specimen, especially the oldest, is often unknown. Although all of our Australian National Wildlife Collection wet specimens are currently in ethanol, like most collections, our records generally do not indicate whether they have been in contact with formaldehyde.
By reducing the need for specimen-specific methods, we can collect high-quality historical data faster, even from long-ignored viscous specimen jars.