Genetic assessment improves conservation efforts for the critically endangered oceanic island endemic Hibiscus liliiflorus.

Hibiscus liliiflorus, endemic to the Indian Ocean island of Rodrigues, is one of the rarest plant species in the world; only two wild individuals remain. Previously, when four wild individuals remained, the Mauritian Wildlife Foundation (MWF) in Rodrigues propagated cuttings of them in their nursery, then planted seedlings produced in the nursery into three outplanted populations on the island. Our goals were to: 1) assess whether all four original wild genotypes are represented in the MWF nursery; 2) determine whether ex situ living collections at international botanical gardens maintain unique genotypes of H. liliiflorus; 3) assess whether nursery individuals have crossed or self-fertilized to produce seed and quantify their relative contributions to outplanted populations; and 4) provide recommendations for future conservation actions. We used a 2b-RADseq approach to produce 2,711 genome-wide SNPs from 98 samples. Genotype identity analysis, principal component analysis and model-based clustering in STRUCTURE found four genotypes extant in Rodrigues but no unique genotypes in ex situ botanic garden collections. Only three genotypes are represented in the MWF nursery; the one remaining genotype is represented by an extant wild individual. Parentage analysis showed that seeds produced in the MWF nursery resulted from both self-fertilization and crossing between genotypes, a result supported by internal relatedness and hybrid index calculations. Each outplanted population is dominated by a subset of parental genotypes, and we propose actions to balance the parental contributions to outplanted populations. Our study highlights how genetic assessments of ex situ conservation projects help conserve critically endangered species.