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.

Genetic monitoring of translocated plant populations in practice.

Plant translocations allow the restoration of genetic diversity in inbred and depauperate populations and help to prevent the extinction of critically endangered species. However, the successes of plant translocations in restoring genetically viable populations and the possible associated key factors are still insufficiently evaluated. To fill this gap, we carried out a thorough genetic monitoring of three populations of Arnica montana that were created or reinforced by the translocation of plants obtained from seeds of two large natural source populations from southern Belgium. We genotyped nine microsatellite markers and measured fitness quantitative traits over two generations (transplants, F1 seed progeny and newly established F1 juveniles). Two years after translocation, the genetic restoration had been effective, with high genetic diversity and low genetic differentiation across generations, extensive contemporary pollen flow, admixture between seed sources in the F1 generation and recruitment of new individuals from seeds. We detected site, seed source and maternal plant effects on plant fitness. The results also suggest that phenotypic plasticity may favour short-term individual survival and long-term adaptive capacity and enhance the evolutionary resilience of the populations to changing environmental conditions. We found no sign of heterosis or outbreeding depression at early life stages in the F1 generation. Our findings emphasize the importance of the translocation design (700 transplants of mixed sources, planted at high density) as well as the preparatory site management for the successful outcome of the translocations, which maximized flowering, random mating, and recruitment from seeds in the first years after translocation.