Investigating Genetic Spillage in a Mimulus cardinalis (Syn. Erythranthe cardinalis) Common Garden Experiment

Common gardens are critical to studying the trait variations in plant species and how environmental or genetic factors influence them. In common gardens, non-native species and non-local populations must be monitored closely to reduce their chances of escaping, as this can lead to genetic spillage, which is the introduction of foreign genetic material with potential unwanted phenotypes/genotypes into the native ecosystems. This could decrease the fitness of native populations and threaten natural habitats. This study investigated a possible spillage of genetic material from an existing common garden experiment of the Scarlet Monkeyflower (Erythranthe cardinalis). This garden consists of six populations that originated from three regions across its distribution (North, Central, and South) and were propagated at an Ecological Reserve in Southern California. A population of E. cardinalis was recently observed a kilometer away from the common garden, leading to the question of whether it is a wild population or an escapee. Leaf samples were collected from individuals of each provenance established at the common garden, and the "unknown" population. DNA was extracted from all samples and further processed for DArT sequencing to generate genome-wide SNPs. Genetic clustering analyses such as DAPC, PCoA, and ADMIXTURE were used to determine the genetic proximity of the unknown population to the six provenances from the common garden. Clustering analyses of all individuals revealed that the unknown population is genetically related to southern populations. A focused analysis of only the southern and unknown populations showed that the unknown individuals formed a distinct cluster, suggesting they are not escapees but represent a natural population in the Southern California region. Although a spillage was not detected, these findings serve as a reminder for researchers to monitor their garden experiments to control escapees and reduce the possibility of a spillage occurring.