Tipping the Scales Using Cryopreservation: Modelling the Genetic Value and Management Potential of Integrated Cryopreservation for Threatened Ex‐Situ Pupfish Populations

Abstract

ABSTRACT Zoos and aquaria must retain genetic diversity for the species they house if the populations are to remain viable. The cryopreservation and storage of living animal cells is a potential strategy for minimising genetic diversity loss over time, when genetic diversity can be effectively reintroduced in the future as population genetic diversity decreases. Using population simulations, this study investigates the potential impact of using cryopreserved sperm on genetic diversity retention in 18 species of pupfish: a priority taxonomic group for ex‐situ conservation management for the European Association of Zoos and Aquaria (EAZA). First, genetic diversity simulations were conducted to determine the necessary population sizes required for each species to achieve a 90% genetic diversity target over a short (30‐year) or longer (100‐year) period without the integration of cryopreserved sperm into breeding management, with Ne/N simulated at either 0.05 (worst‐case scenario), 0.1 or 0.3 (best‐case scenario). Subsequently, these simulations were then compared against the required population sizes to achieve the same genetic diversity targets if cryopreserved sperm is used for 100%, 50%, 10% or 1% of breeding attempts. The simulations demonstrate that no species are currently being kept in sufficient numbers to achieve 90% genetic diversity. Specifically, the simulations projected that across the priority species ( n = 18) the average genetic diversity per species by 100 years would be 1.16% (±2.48% SD), 6.13% (±9.25% SD) and 23.57% (±25.28% SD) for Ne/N = 0.05, 0.1 and 0.3 respectively. To achieve the 90% target over 100 years, without the use of cryopreserved sperm (cryoARTs), the mean total number of fish required was 9498, 4747 and 1582 fish if Ne/N = 0.05, 0.1 or 0.3, respectively. Overall, the mean number of fish per species was 138.61 individuals (±128.61 SD) and to achieve the 90% genetic diversity target over 100 years, Ne/N = 0.3, all populations need to be increased by approximately 1400 individuals. Collectively, these scenarios demonstrate rapid loss of genetic diversity unless populations are substantially increased. Across the priority species ( n = 18), if cryoARTs is used at 10% of breeding attempts then the average total number of individual fish required to achieve the 90% genetic diversity target, for Ne/N = 0.05, 0.1 or 0.3, is 910, 455 and 152 fish respectively, over a 100‐year period. This study demonstrates that investment in greater pupfish population sizes in EAZA collections, alongside a strategy involving the integration of cryoARTs into species management, could aid in population viability by improving genetic diversity prospects.