De‐extinction and evolution

Abstract

Summary1. De-extinction, the process of resurrecting extinct species, is in an early stage of scientific implementation. However, its potential to contribute effectively to biodiversity conservation remains unexplored, especially from an evolutionary perspective. 2. We review and discuss the application of the existing evolutionary conservation framework to potential de-extinction projects. We aim to understand how evolutionary processes can influence the dynamics of resurrected populations and to place de-extinction within micro-and macro-evolutionary conservation perspectives. 3. In programmes aiming to revive long-extinct species, the most important constraints to the short-term viability of any resurrected population are (i) their intrinsically low evolutionary resilience and (ii) their poor eco-evolutionary experience, in relation to the absence of (co)adaption to biotic and abiotic changes in the recipient environment. 4. Assuming that some populations of resurrected species can persist locally, they have the potential to bring substantial benefits to biodiversity if the time since initial extinction is short relative to evolutionary dynamics. The restoration of lost genetic information could lead, along with the reinstatement of lost ecological functions, to the restoration of some evolutionary patrimony and processes, such as adaptation and diversification. 5. However, substantial evolutionary costs might occur, including unintended eco-evolutionary changes in the local system and unintended spread of the species. Further, evolutionary benefits are limited because (i) the use of resurrected populations as 'evolutionary proxies' of extinct species is meaningless; (ii) their phylogenetic originality is likely to be limited by the selection of inappropriate candidate species and the fact that the original species might be those for which de-extinction is the most difficult to achieve practically; (iii) the resurrection of a few extinct species does not have the potential to conserve as much evolutionary history as traditional conservation strategies, such as the reduction of ongoing species declines and extinction debts. 6. De-extinction is a stimulating idea, which is not intrinsically antagonistic to the conservation of evolutionary processes. However, poor choice of candidate species, and most importantly, too long time scales between a species' extinction and its resurrection are associated with low expected evolutionary benefits and likely unacceptable eco-evolutionary risks.

Maximising evolutionary potential in functional proxies for extinct species: a conservation genetic perspective on de‐extinction

“…Namely, conservation geneticists routinely partner with conservation practitioners to develop management strategies that seek to maintain the EVOLUTIONARY POTENTIAL (see Glossary of Terms; Box 2) of translocated populations by minimising INBREEDING to avoid INBREEDING DEPRESSION and minimising the loss of GENETIC DIVERSITY via GENETIC DRIFT (Weeks et al 2011(Weeks et al , 2015Groombridge et al 2012;Jamieson & Lacy 2012;Keller et al 2012). Given that any successfully translocated populations of functional proxies are likely to be categorised as threatened (critically endangered, endangered, vulnerable) due to small population size or restricted range (IUCN/ SSC 2016), or at least managed as such Iacona et al 2017), it is logical to apply conservation genetic principles to increase the probability of their longterm persistence in the wild (Robert et al 2017).…”

“…While valid arguments exist for the potential difficulties in establishing viable functional proxy populations of 'woolly mammoth-like' animals (McCauley et al 2017;Robert et al 2017;Wood, Perry & Wilmshurst 2017), recent research suggests that the presence of more mammalian herbivores in the Arctic tundra could help offset global impacts of climate change by reducing shrub abundance and subsequently increasing summer albedo (te Beest et al 2016). The total number of mammalian herbivores necessary to contribute towards a significant cooling effect on a global scale is not known, but large, genetically diverse 'woolly mammoth-like' populations could have a significant impact on shrub land densities and thereby could help mitigate future warming for the foreseeable future (see also Zimov, Zimov & Chapin 2012).…”

The ecology of de‐extinction

“…Alexandre Robert et al aim to understand how the evolutionary processes might influence the dynamics of populations of resurrected species, for the first time considering de-extinction from micro-and macro-evolutionary conservation perspectives (Robert et al 2017). Extinction marks a discontinuity of biological processes and essentially removes the extinct organism from exposure to the selection pressures of future environmental change.…”

“…This would place the emphasis on selecting de-extinction candidates from the recent extinctions, and these candidates would also be those species for which cloning, rather than genomic engineering, would be feasible. Robert points out a paradox arising from a focus on evolutionarily distinct species as the best candidates to restore lost ecosystem functions because they have no extant replacements; such species might prove to be the hardest to resurrect because of an absence of egg donors, host surrogates, or reference species for genome reconstruction (Robert et al 2017). The take-home message is that, whilst ecological roles might be restored through de-extinction, the evolutionary loss caused by extinction is irreversible.…”

“…Extinction marks an irreversible break in the eco-evolutionary trajectory of a species (Robert et al 2017); there is a need to preserve the evolutionary potential of resurrected species by overcoming genetic bottlenecks at every stage of a project (Steeves, Johnson & Hale 2017); there is some uncertainty around whether a resurrected species might ever be restored to functionally meaningful densities (McCauley et al 2017), and our knowledge of past ecosystems will be incomplete for all but recent extinctions, making it difficult to predict the implications and impacts of attempts to restore the ecological interactions that have been lost with extinction (Wood, Perry & Wilmshurst 2017). But let's assume that we have been able successfully to resurrect through interspecies cloning, sufficient numbers of sufficiently genetically diverse individuals of a reasonable proxy of a species that went extinct relatively recently, and that its reintroduction has the potential to restore, within a largely intact and well-understood ecosystem, some ecological function lost through extinction.…”