By Guest Work 09/05/2017

Could we really bring an extinct species back from the dead, and, if we did – what happens next? Sciblogs is running a series of posts on de-extinction to coincide with a special issue of the journal Functional Ecology focusing on the topic.

In this guest post, special issue author Dr Tammy Steeves from the University of Canterbury examines the genetic hurdles involved in de-extinction . 

Somebody has to say something

When I returned from my second stint of parental leave approximately 3 years ago, the first scientific paper I read was Phil Seddon and colleagues’ provocative paper entitled Reintroducing resurrected species: selecting DeExtinction candidates. To realise the ecological benefit of de-extinction (that is, to restore lost ecological function), they argued, resurrected animals must be released to the wild. Thus, de-extinction is a translocation issue. Yes, of course, I thought. Excellent point.

But then I thought, conservation genetics plays an important role in the management of the long-term genetic ‘health’ of translocated populations for threatened species around the globe (for example, 3 of the 14 chapters in the field’s go-to book are dedicated to genetics), so in addition to being a translocation issue, de-extinction is a conservation genetics issue.

Brimming with energy and enthusiasm, I had just (officially) returned to work after all, I emailed Phil and asked why he and his colleagues hadn’t considered the conservation genetic implications of de-extinction. The paper wasn’t about how to resurrect extinct species, but how to best address the challenges of creating and maintaining self-sustaining populations of resurrected species in the wild, he said. To which I said, understood. But surely to be self-sustaining, these populations also need be genetically viable. To which he said, yes, of course, excellent point – how about you give a talk about it at a de-extinction symposium that I’m organising? Yikes, I thought. I hadn’t anticipated that.

Upon reflection (read, discussion with my long-term research collaborator Marie Hale), I reasoned this: Well, somebody has to say something. And that somebody might as well be me and my colleagues. So, one research talk, two (or was it three?) failed submissions and numerous re-writes later, myself, Marie Hale and Jeff Johnson, published our paper with the not-so-jazzy title: Maximising evolutionary potential in functional proxies for extinct species: a conservation genetic perspective on de-extinction in the ‘Ecology of De-extinction’ Special Feature in Functional Ecology.

It’s a thing and it matters

Perhaps a jazzier title could have been Conservation genetics of de-extinction: it’s a thing and it matters. Before I describe what conservation genetics is and why it matters in a de-extinction context, first some disclaimers:

  1. The current pathways to de-extinction will not result in exact replicas of extinct species, so when I say de-extinction, I mean the resurrection of unique phenotypic traits once possessed by extinct species to create living ‘functional proxies’ for release to restore lost ecological function (for example, consider the restoration of ecosystem services like seed dispersal).
  2. I am not an advocate for or against de-extinction. Rather, I see my role as one of critic and conscience and my motivation is to show that the genetic challenges associated with the survival and recovery of living threatened species are also relevant to the potential use of functional proxies of extinct species as a conversation tool.

Conservation genetics is a subdiscipline of conservation biology which uses genetic data to inform the management of threatened species in collaboration with conservation practitioners. For conservation geneticists, the ultimate goal is to minimise the loss of genetic diversity in small isolated populations because, all else being equal, the more genetic diversity a threatened species has, the more likely it is that it will be able to adapt to a changing environment.

The reason why conservation geneticists worry about the loss of genetic diversity is because the fewer individuals a species has, the more likely it is that it will randomly lose genetic diversity over time. This is called genetic drift. And because it is a random process, it means that advantageous genetic diversity can be lost. On the flipside, disadvantageous genetic diversity can be retained, or even become predominant. Indeed, for living species, small isolated populations that lack genetic diversity are in danger of spiraling to the point of extinction. This is called the extinction vortex.

To visualise the perils of resurrecting functional proxies using only a few, genetically similar individuals, my colleagues and I describe the ‘re-extinction vortex’. Briefly, if the loss of genetic diversity is not adequately mitigated (for example, via periodic supplementation with genetically different individuals), functional proxies may face imminent re-extinction.

conservation genetics
Re-extinction vortex. Random sh*t happens, otherwise known as demographic (e.g., age-structure, sex-ratio, family size) and environmental (e.g., disease outbreaks, severe weather events) stochasticity. Modified from Steeves, Johnson & Hale (2017).

Having said this, we readily acknowledge that long-term persistence (of any species) should not be determined based on genetic data alone, and how to best determine whether populations are large enough and genetically diverse enough to be viable in the long-term is open for debate.

Let’s take it one bottleneck at a time

Philosophers at the University of Canterbury are eager to see huia resurrected. Source: Wikimedia.

In the meantime, what are three conservation geneticists to do? Well, we can use conservation genetic principles to describe impediments to the creation and maintenance of genetic diversity in functional proxies as a series of potentially unavoidable genetic bottlenecks: pre-extinction, resurrection, captive and translocation. In other words, to realise the ecological benefit of de-extinction, we argue that it will be necessary to minimise the loss of genetic diversity at (minimum) four stages of the project. In our paper, we use an extinct grouse, the heath hen, to demonstrate this.

Here, I (ever so) briefly consider these same challenges for huia, Aotearoa New Zealand’s largest, and arguably most iconic, wattlebird. In addition to having dramatically different bills in shape and size (in the associated image, the bird with the long, slender, strongly curved bill is a female and the bird with the short, stout, less curved bill is the male), this glossy black songbird had long white-tipped tail feathers that were prized by Māori as head adornments, and signified high status. Last sighted (officially) in 1907, the demise of this taonga (treasured) species is attributed to a combination of factors including overhunting for natural history collections and a fashion craze for its feathers.

Before I continue, first some (more) disclaimers:

  1. I am not an advocate for or against the resurrection of huia (or, more correctly, the resurrection of a ‘huia-like’ functional proxy). Please see disclaimer 2 above.
  2. Huia have been proposed as a candidate for resurrection by philosophers at the University of Canterbury but, to my knowledge, no current efforts are being made to resurrect the species.
  3. Before any extinct taonga species, including huia, is (ever) seriously considered for resurrection, there should be social license to do so from all relevant publics, Māori communities (iwi, hapū).
  4. I am not an expert on huia. However, as a conservation geneticist that routinely conducts research on threatened (living) taonga species, I am capable of considering the conservation genetic implications of resurrecting huia. And, please remember, I readily acknowledge that the long-term persistence (of any species, including huia), should not be determined based on genetic data alone.

So, with that out of the way:

Pre-extinction: How much genetic diversity was there before extinction? Available evidence suggests that there may be a reasonable amount of genetic diversity harboured in museum collections.

Resurrection: How much genetic diversity can be resurrected? It’s hard to say, but it’s unlikely to be all of it. DNA in museum specimens is hard to find, and when you find it, it tends to be highly damaged (for example, recently published huia mitogenome, is just that, a mitogenome).

Captive: How easily could genetic diversity be lost in a captivity? It appears (read, I haven’t conducted a comprehensive literature review), high-ranking Māori kept huia as pets, Buller had a pair, and many live birds were shipped to collectors overseas, but I’ve got no idea whether any of these birds were ever successfully bred in captivity. However, my understanding (read, I haven’t conducted a comprehensive literature review), captive breeding doesn’t appear to work all that well for other New Zealand wattlebirds (kōkako and tīeke). But, for arugment’s sake, if huia were able to be bred in captivity – beyond the risk of adaptation to captivity itself – due consideration would need to be given to constraints on the number of genetically different founding individuals could be maintained, as well as the challenges associated with equalising and monitoring founder representation. By the way, we’re not even sure which of these two species huia is most closely related to so it’s currently impossible to know whether it would be better to edit the genome of  kōkako or tīeke to resurrect huia in the first place. But I digress.

Translocation: How easily could genetic diversity be lost in the wild? Again, it’s not really possible to make any meaningful comparisons to species closely related to huia, but it’s worth noting that even when translocations “succeed” genetic diversity can be readily lost if there are low survival rates, differential reproductive rates, slow population rates or long generation times – and many, if not all, of these are likely to apply to huia.

The reverse may be true at the University of Canterbury. Source: Advocacy for Animals.

Spending the de-extinction dollar

I appreciate that I’ve spent this entire blog sitting on the fence, and it may seem like I’m about to jump off, but please stick with me. For argument’s sake, let’s say it’s actually feasible to create and maintain functional proxies, and we’ve got the social license to do so, should we?

If it was my money or at least money coming out of an existing conservation budget for threatened living species, I’d say no. Indeed, my colleagues and I recently published a paper that shows spending limited resources on de-extinction could lead to net biodiversity loss. But, thanks in part to robust and open discussions with members of the de-extinction community, I am willing to concede that de-extinction need not be a zero-sum game. For example, one could argue that genomic resources developed for huia could inform the conservation genetic management of kōkako and tīeke one day.

In the meantime, as conservation geneticists, my colleagues and I often have no choice but to work with small isolated populations, many of which would be extinct without intensive management. To give any successfully translocated populations of functional proxies the best chance to survive and thrive in the future, we urge the de-extinction community to embrace a holistic framework, that begins with the creation of populations that are sufficiently large and genetically diverse.

Dr Tammy Steeves is a Senior Lecturer in Conservation Genetics/Genomics at the University of Canterbury. You can read her article (co-authored with Marie Hale and Jeff Johnson) in Functional Ecology here.

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