Measuring and managing genetic erosion in plant reintroductions

Background/Question/Methods

Plant reintroductions typically start from a limited genetic base. When that genetic base is known, an opportunity to quantify genetic erosion and test the genetic consequences of small founding population size through generations in a natural experiment is enabled. Long-term studies test ecological genetic theory, shed light on the long-term consequences of genetic erosion for reintroduction success, and suggest management actions to avoid genetic erosion. The Corrigin Grevillea, G. scapigera, has been the focus of a sustained recovery program for over 20 years. No plants remain in wild populations due to land clearing for agriculture in the Western Australian wheatbelt. The first successful translocation trials were established in 1996 with what were thought to be equal numbers of 10 genets, ramets of which were propagated by tissue culture, as germination from seed was at the time not possible. In this translocation site, subsequent plantings occurred in following years, largely from seed harvested at this site. Flowering and natural seed set has been very high in all years, and some natural recruitment occurred in most years from 2003. In 1998, we genotyped all founding plants and a sample of their seed to assess genetic fidelity and genetic erosion in the first generation. In 2012, we genotyped all surviving plants and a sample of their seed, to quantify genetic erosion over multiple generations. An assessment of inbreeding depression was also conducted by regressing F1 seedling mortality against genetic dissimilarity of their parents.

Results/Conclusions

Following establishment, we found that (i) eight genets, not ten, were present in the translocated population, and that 54% of all plants were a single genotype; (ii) the F1's were on average 22% more inbred and 20% less heterozygous than their parents, largely because (iii) paternity assignment revealed that 85% of all seeds were the product of only four clones.  Ultimately, effective population size of the founding population was approximately two. This initial dramatic erosion of genetic variability has strongly impacted the genetic variation present in their descendents 15 years later. Despite good flowering and seed set over most years, a positive association between survivorship and increasing genetic dissimilarity of parents of seedlings indicates inbreeding depression associated with genetic erosion. Our results highlight that rapid genetic erosion may be a feature of many small, translocated populations, which may ultimately threaten their long-term survival. Strategies to prevent genetic decline in rare species translocations are discussed.