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Genetic and Floral Trait Changes in Oenothera organensis (Onagraceae) during Long-Term Ex Situ Cultivation

Premise of research. This study examines the potential effects of long-term ex situ cultivation on genetic variation and floral traits using a rare endemic species, Oenothera organensis (Onagraceae), which has been cultivated ex situ since the 1930s. Ex situ conservation in botanic gardens is an important approach to safeguard endangered plant species, especially given current threats to global biodiversity from climate change and habitat destruction. The genetic consequences of ex situ living plant cultivation include reduction in genetic diversity and inbreeding depression owing to population bottlenecks. In addition, ex situ populations might experience trait changes because of shifted or relaxed selection pressure. These changes can cause fitness declines or failure when ex situ populations are reintroduced into the wild. This study examines potential drawbacks of ex situ cultivation by focusing on neutral genetic diversity and floral traits.

Methodology. To test the potential effects of ex situ cultivation on neutral genetic diversity, we used eight microsatellite markers to examine the genetic composition of multiple ex situ and wild populations of O. organensis. In addition, we applied a common-garden experiment to examine floral traits and phenology of ex situ and wild-derived populations to test whether ex situ cultivation can shift or increase the variance of floral traits.

Pivotal results. The ex situ populations of O. organensis generally had reduced neutral genetic diversity and failed to capture all of the alleles observed in the wild populations. High pairwise relatedness in the ex situ population also indicated potential inbreeding. Cultivated ex situ plants exhibited higher variability in floral traits and shifted phenotypic distribution compared with wild-derived plants, which may be due to relaxed or shifted selection pressure.

Conclusions. Without careful consideration and maintenance to preserve genetic variation and traits in plant populations, long-term ex situ cultivation can reduce neutral genetic diversity and change the phenotypes of conserved lineages. Most guidelines for ex situ conservation focus on increasing population sizes and pooling genetic diversity from multiple sources to maintain diversity. Our study demonstrates that relaxed or shifted selection in an ex situ setting may lead to shifted phenotypes, so management practices should also maintain ex situ plants under conditions that are as close as possible to the natural settings.