Yew Only Live Twice

De-extinction is a popular topic among some scientists. People have talked about the possibility of bringing back the thylacine or dodo. In San Francisco, one billionaire is intent on building a thriving mastodon community. But plants have not been seriously considered – until now. In a paper in Nature Plants, Giulia Albani Rocchetti and many colleagues discuss what plants would have the best chance of returning from extinction.

What do we mean by extinction, and what do we mean by return?

Biologists have different types of extinct. Functionally extinct means that the species is still around but no longer has much effect in its ecosystem. The species may no longer have a viable population and cannot reproduce enough to replace dying members. A functionally extinct species is a problem, but it’s still possible to save with intervention. Another form of extinction could be locally extinct. This would be a species no longer found in part of its range but still viable elsewhere. Again, it’s a problem, but it is soluble with effort. What Albani Rocchetti and colleagues mean by extinct is extinct in the wild; you don’t have any wild populations to manipulate. That’s a more challenging problem.

They also have a difficult definition for return.

When (some) zoologists talk about reviving the mammoth, some problems get glossed over. To genuinely create mammoths, you need mammoths. So what is proposed is getting some DNA of the animal you want to revive and an egg donor from a similar species. In this case, an elephant is proposed to create a hybrid. Get enough of these hybrids and carefully manage their breeding programme, and you end up with a ‘mammoth’. It won’t be an actual mammoth, but it’ll be close enough for the people willing to spend millions of dollars cosplaying Jurassic Park.

This form of return, or back breeding and breeding down a new line to return to an imagined extinct species, isn’t good enough for Albani Rocchetti and colleagues. They’re talking about bringing the actual species back from the dead. To do that, they’ve gone to the dead to see what they can find.

Where do you find extinct species?

Botanical gardens collect plant species, but if their species are dead, something has gone wrong. Attached to many gardens are herbaria. A herbarium is a collection of preserved plant specimens. This collection would usually be dried plant material and can be just parts of a plant such as flowers, leaves, or roots. This can be interesting when the herbarium holds a plant’s fruit.

The preservation process is usually done to prevent decay. As well as preserving the fruit, the process could help protect the seeds within the fruit. Germinating these viable seeds in herbaria would allow botanists to bring back the plants and, with careful gardening, create a population to reintroduce to the wild.

Some plant families survive preservation better than others. If you could locate these better candidates, you would have a chance to discover the seeds before it’s too late for them. Unfortunately, finding these seeds is not easy.

Visiting all the herbaria in the world isn’t cheap, and that’s why records of what herbaria hold are essential. However, these records need to be up-to-date, and sometimes that isn’t the case.

What makes a plant a viable candidate for de-extinction?

First, it has to be extinct or thereabouts. Abeli and colleagues found that twelve species weren’t suitable for de-extinction as they were still alive either in botanic gardens or in the wild.

It’s also important to know if the species label matches the plant you’re looking at. Sometimes this isn’t easy, as Abeli and colleagues write:

Some inaccuracies are surprisingly difficult to be verified, like for instance, the case of Micrantheum micranthemoides, declared extinct but very common in the market of commercial plants. When verified, these specimens belonged to other species. However the name M. micranthemoides is so widespread in the market that a throughout verification of all specimens is impossible.

Abeli et al. 2022

When you find a seed of an otherwise extinct plant, you have a further problem. Is the seed alive or dead? If the seed is dead, then what you have in your hands is an irreplaceable asset. Attempt to germinate it, and what remains of the species could be lost forever. However, it could grow and produce further specimens if the seed is still viable. This confusion makes Albani Rocchetti and colleagues wary of the black-and-white categorisation of species as extinct.

In fact, the potentiality of a seed of an extinct species to germinate, in conjunction with the impossibility of knowing whether the seed is alive or if we can germinate it (with current technology), creates a condition of uncertainty such that we might consider our candidates as Schrödinger’s species. These species are both dead and alive, extinct and extant, and current technologies and knowledge do not allow this paradox to be solved. These Schrödinger’s species could therefore be considered possibly extinct (but differently from the IUCN’s ‘PE’ category conception), potentially extinct or in a state of ‘pre-extinction’ just one step away from real extinction. Consequently, by germinating these seeds we will not obtain a genuine resurrection but an ‘artificial awakening’ or the recovery of the life ‘stocked’ in the seed.

We therefore propose to use the term de-extinction sensu lato referring to the resurrection of EW species from seeds or tissues preserved in herbaria, although we acknowledge all the above-mentioned limitations in the use of this term.

Albani Rocchetti et al. 2022.

A herbarium isn’t a seed bank, so many of these seeds are no longer viable. However, Albani Rocchetti and colleagues point out there are over 400 million specimens in herbaria worldwide. Even a success rate of a fraction of a per cent could still revive many species.

Why de-extinct a species?

Trawling through so much material and then taking the time to wait to see if you were successful or not is a considerable effort. Why do it when there are already so many endangered species? Albani Rocchetti and colleagues provide a few reasons.

First, they hope that systematically attempting to revive seeds will allow scientists to learn a lot about the ageing and death mechanisms in seeds. This knowledge would have practical value for seed banks around the world.

Revived species would also improve the biodiversity of the world’s plants. These species may be able to help support ecosystems that they have departed.

Finally, Albani Rocchetti and colleagues say it would change how we think about extinction. “[T]he resurrection of an extinct species from seeds from herbaria would challenge the concept of extinction itself. Extinction in plants would not happen when the last living individual dies, but rather when the last seed does.”

READ THE ARTICLE

Albani Rocchetti, G., Carta, A., Mondoni, A., Godefroid, S., Davis, C.C., Caneva, G., Albrecht, M.A., Alvarado, K., Bijmoer, R., Borosova, R., Bräeuchler, C., Breman, E., Briggs, M., Buord, S., Cave, L.H., Da Silva, N.G., Davey, A.H., Davies, R.M., Dickie, J.B., Fabillo, M., Fleischmann, A., Franks, A., Hall, G., Kantvilas, G., Klak, C., Liu, U., Medina, L., Reinhammar, L.G., Sebola, R.J., Schönberger, I., Sweeney, P., Voglmayr, H., White, A., Wieringa, J.J., Zippel, E. and Abeli, T. (2022) “Selecting the best candidates for resurrecting extinct-in-the-wild plants from herbaria,” Nature Plants, 8(12), pp. 1385–1393. Available at: https://doi.org/10.1038/s41477-022-01296-7.
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