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What's lurking in your freezer: a lasagna or deep-frozen pizza? Conservationists rely on freezers too—but they run much cooler than your model, with the thermostat set to a frosty -196°C, the temperature of liquid nitrogen. You won't find any burgers in there.

Conservationists use these freezers, known as "biobanks," to store animal cells including oocytes (egg cells), sperm and somatic cells (for example, skin cells). In the future, lost genetic diversity could be safeguarded in this way. This could be vital for the preservation of endangered species—and species that are not yet endangered, but soon could be.

Over the last 50 years, tissues of many animals have been frozen, including tigers, pandas and rhinos. But many other species have never been archived in this way, including some of the most threatened species on the planet, such as mountain gorillas. The consequences of not banking key species could well be their extinction.

A between researchers at Chester, Dublin and Toronto zoos and Nottingham Trent and York St Johns Universities has investigated the priorities for biobanking wildlife species. My supervisors and I worked with colleagues at these zoos to address the long-held assumption that wildlife organizations prioritize endangered species as the most important species for biobanking. The paper is published in Theriogenology Wild journal.

We found that several prioritization methods are used for selecting cell types and species. The local availability of cell samples was a key factor, as was the extent of reproductive science knowledge about a species.

In the 20th century, the most common prioritization method was to select endangered species. But conservationists would also prioritize the sampling of species that were local to them (for example, in a zoo), as well as sampling opportunistically—for instance, when an animal was undergoing veterinary care.

We tend to think of biobanking as a futuristic, science fiction concept, but these techniques have been developed over many decades. The earliest paper we found was from 1975 on wildlife cryopreservation.

In terms of species and material, cells from mammals were the most frequently biobanked throughout the study period, mirroring the pervasive taxonomic biases in conservation efforts globally.

It's also more straightforward to bank samples from, say, a gaur (a wild buffalo) because they are physiologically similar to domesticated cattle, which we know a lot about. A rare insect would be a different story.

Historically, biobanking efforts concentrated on saving sperm samples, which made sense as scientists could draw on generations of livestock husbandry methods to use the samples for artificial insemination. But that only captures part of the genetic picture, even for well-represented species.

Today, other cell types, such as somatic cells (body cells, such as skin cells or fibroblast cells that form connective tissue), are becoming increasingly valuable, as they capture a lot more genetic information.

From agoutis to acropora coral

There is a diverse array of species featuring in the biobanking literature. Previous studies cover species ranging from agoutis (a small rodent native to the rainforests of Central and South America) to acropora corals, harpy eagles to hellbender salamanders. For these species, tissue is therefore effectively saved for use in future conservation work.

The International Union for Conservation of Nature, an organization dedicated to assessing wildlife threat status, established its in 2022. This network aims to foster cooperation a broader approach to biobanking, which has until now been carried out on an individual, organizational basis.

Enabling scientists to coordinate their efforts internationally could help cryobanking organizations be more strategic about acquiring genetic material, avoiding duplicating samples and identifying species at risk of being left out.

Researchers also need to think about species that aren't critically endangered right now but might become so, such as (tropical tree snails native to Polynesia). By the time a species becomes endangered, the genetic diversity of the population has already significantly reduced.

Even if we do save their gametes and somatic cells, there will still be a genetic bottleneck among the remaining live animals. This can lead to reproductive and health issues in already small populations, further reducing the likelihood of the species' survival.

If we take samples from animals that are not yet critically endangered, those samples are likely to become valuable in the future. Ultimately, we need a unified plan so we don't let bias and a lack of strategy shape which species we see in the future—and which we lose.