Mixing gene pools to prevent inbreeding issues in translocated populations of clonal species.

Assisted gene flow by plant translocations is increasingly implemented for restoring populations of critically endangered species. The success in restoring genetically healthy populations may depend on translocation design, in particular the choice of the source populations. Highly clonal populations may show low genetic diversity despite large census sizes, and disrupted and geitonogamous pollination may result in selfing and inbreeding issues in the offspring intended for translocation. We carried out a genetic monitoring of translocated populations of the clonal Dianthus deltoides using 14 microsatellite markers and quantified fitness traits over two generations (transplants, F1 seed progeny and newly established individuals). Inbreeding levels were higher in the offspring used as transplants than in the adult generation of the source populations, as a result of high clonality and pollination disruption leading to self-pollination. The F1 generation in translocated populations showed high genetic diversity maintained across generations, diminished inbreeding levels, low genetic differentiation, pollen flow and genetic mixing between the four sources. New individuals were established from seed germination. Fitness patterns were a combination of inbreeding depression in inbred transplants and F1 progeny, heterosis in admixed F1 progeny, source population adaptive capacities, phenotypic plasticity, maternal effects and site environmental specificities. The strategy in the translocation design to mix several local sources, combined with large founding population sizes and ecological management has proved success in initiating the processes leading to the establishment of genetically healthy populations, even when source populations are highly clonal with low genetic diversity leading to inbreeding issues in the transplants.