Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

Abstract

Biodiversity is defined as the presence of a variety of living organisms on the Earth that is essential for human survival. However, anthropogenic activities are causing the sixth mass extinction, threatening even our own species. For many animals, dwindling numbers are becoming fragmented populations with low genetic diversity, threatening long-term species viability. With extinction rates 1000-10,000 times greater than natural, ex situ and in situ conservation programmes need additional support to save species. The indefinite storage of cryopreserved (-196°C) viable cells and tissues (cryobanking), followed by assisted or advanced assisted reproductive technology (ART: utilisation of oocytes and spermatozoa to generate offspring; aART: utilisation of somatic cell genetic material to generate offspring), may be the only hope for species' long-term survival. As such, cryobanking should be considered a necessity for all future conservation strategies. Following cryopreservation, ART/aART can be used to reinstate lost genetics back into a population, resurrecting biodiversity. However, for this to be successful, species-specific protocol optimisation and increased knowledge of basic biology for many taxa are required. Current ART/aART is primarily focused on mammalian taxa; however, this needs to be extended to all, including to some of the most endangered species: amphibians. Gamete, reproductive tissue and somatic cell cryobanking can fill the gap between losing genetic diversity today and future technological developments. This review explores species prioritisation for cryobanking and the successes and challenges of cryopreservation and multiple ARTs/aARTs. We here discuss the value of cryobanking before more species are lost and the potential of advanced reproductive technologies not only to halt but also to reverse biodiversity loss.

Lay summary: The world is undergoing its sixth mass extinction; however, unlike previous events, the latest is caused by human activities and is resulting in the largest loss of biodiversity (all living things on Earth) for 65 million years. With an extinction rate 1000-10,000-fold greater than natural, this catastrophic decline in biodiversity is threatening our own survival. As the number of individuals within a species declines, genetic diversity reduces, threatening their long-term existence. In this review, the authors summarise approaches to indefinitely preserve living cells and tissues at low temperatures (cryobanking) and the technologies required to resurrect biodiversity. In the future when appropriate techniques become available, these living samples can be thawed and used to reinstate genetic diversity and produce live young ones of endangered species, enabling their long-term survival. The successes and challenges of genome resource cryopreservation are discussed to enable a move towards a future of stable biodiversity.

Keywords: assisted reproductive technology; biobanking; biodiversity; conservation; cryopreservation.

Figure 1

Critically endangered mountain chicken frog (Leptodactylus fallax), photo © Chester Zoo, 2022; photo shared with permission. Chytridiomycosis, volcanic eruptions and habitat loss have resulted in a catastrophic decline in mountain chicken frog numbers, with less than 150 mature individuals now surviving (IUCN SSC Amphibian Specialist Group 2017). Fortunately, somatic tissue samples have been cryopreserved in living biobanks, and with poor ex situ breeding success, aART may be an additional conservation tool to prevent this species from going extinct.

Figure 2

Outline of the interspecific somatic cell nuclear transfer (iSCNT) procedure. The nucleus from an endangered species’ somatic cell (species Y) is fused with the enucleated oocyte from a closely related, domestic species (species X). Following electrical or chemical activation, an early embryo of species Y developed in vitro. The early embryo is transferred into a surrogate mother of domestic species X, resulting in a clone containing the nuclear genome of endangered species Y.

Figure 3

Species preservation using induced pluripotent stem (iPS) cells, which can be differentiated into oocytes or spermatozoa using the rhinoceros as an example. After a biopsy of a recently deceased animal, cells can be cryopreserved until the moment they are needed to produce oocytes or spermatozoa. Those differentiated cells will first need to be reprogrammed to obtain pluripotency. Afterwards, growth factors can re-differentiate the cells into the desired cell population (oocytes or spermatozoa). In vitro fertilisation will result in an embryo, which can be transplanted into a surrogate mother leading to offspring.