Road to extinction: Archival samples unveiled the process of inbreeding depression during artificial breeding in an almost extinct butterfly species

Abstract

During ex-situ conservation of endangered species, reproductive disruption risk due to inbreeding depression increases when genetic diversity is reduced due to founder effects or population declines. Elucidating the population genetic process of reproductive disruption will help understand the risks and mechanisms associated with inbreeding depression. A comprehensive understanding of these processes would require a comparison of reproductive traits and genetic diversity in the populations of endangered species that have experienced reproductive disruption. However, such previous studies, which focus on endangered species, are limited. Ex-situ conservation was initiated for the Ogasawara Holly Blue (Celastrina ogasawaraensis) (Lepidoptera, Lycaenidae), endemic to the Ogasawara Islands, Japan, in 2016 using two mated females as founders. The wild populations might have already been extinct since 2020. All the ex-situ conserved populations were also disrupted in their 20th generation in 2020. Archival samples have been preserved for genetic analysis for the last 20 years. Here, we examined the population genetic background behind reproductive disruption in this ex-situ conserved species for these samples. We used ISSR genotyping by sequencing (MIG-seq) to analyse the individuals from the wild and ex-situ conserved populations collected during 2001–2020. Genetic diversity, hatchability and the number of sperm decreased after the start of progressive breeding in ex-situ conservation. At least 26 individuals were required to retain the genetic diversity of the wild populations at the start of ex-situ conservation. This study highlights the significant risk of failure in ex-situ conservation efforts due to the small number of founders and breeding individuals.