Are large census‐sized populations always the best sources for plant translocations?

Abstract

Assisted gene flow by plant translocations is a solution for restoring populations when other measures were unsuccessful. An essential step for preparing the translocations is the selection of populations as seed sources, which should be large, genetically diverse, and produce good quality seeds. For asexually propagating species, census population size may largely exceed the number of genotypes, which means that genetic variation may be low, and inbreeding levels high. We developed 14 microsatellite markers to investigate the clonal extent and the genetic status of four large census‐sized populations used as seed sources for plant translocations and of two small populations of Dianthus deltoides in southern Belgium. Small and two large populations were highly clonal, with a low number of genotypes and low genetic variation. No inbreeding was detected among flowering plants, suggesting that these populations are relictual, consisting of old, asexually spreading individuals, with the risk of high inbreeding and so low plant fitness in the seed progeny. The high genetic differentiation between populations despite their close proximity suggests genetic drift effects and restricted gene flow. Mixing the four source populations may prevent inbreeding in the cross progeny, but also lead to outbreeding depression. Despite large census sizes, highly clonal populations may not be appropriate as seed sources for plant translocation. In case of (or suspicion of) clonal propagation ability, we recommend to use a genetic approach in translocation design. Also, seeds should be collected from more populations, and from individuals separated by larger distances.