Evaluating conservation strategies for the endangered daisy Schoenia filifolia subsp. subulifolia (Asteraceae): fitness consequences of genetic rescue and hybridisation with a widespread subspecies.

Context: To establish translocated populations of threatened plants with the genetic resources to adapt to changing environmental conditions, the source of propagation material is an important consideration. Aim: We investigated the fitness consequences of genetic rescue and admixture for the threatened annual daisy Schoenia filifolia subsp. subulifolia, and the common S. filifolia subsp. filifolia, to inform seed-sourcing strategies for translocations of the threatened subspecies. Methods: We evaluated genetic diversity of two populations of S. filifolia subsp. subulifolia and four populations of S. filifolia subsp. filifolia by using microsatellite markers. We grew seedlings from each study population and cross-pollinated inflorescences within and among populations of the same subspecies, and between subspecies. We evaluated the fitness consequences of each cross by using seed set, seed weight and seed viability. Key results: There was a lower genetic diversity in the small (<50 plants, N[sub ar] = 3.28, H[sub e] = 0.42) compared to the large (>10 000 plants, N[sub ar] = 4.42, H[sub e] = 0.51) population of S. filifolia subsp. subulifolia, although none of the measures was significantly different, and seed fitness was slightly, although not significantly, reduced in interpopulation crosses compared with the small population. Genetic diversity was similar between the threatened and widespread subspecies; however, the subspecies were genetically divergent (F[sub st] = 0.242-0.294) and cross-pollination between subspecies produced negligible amounts of seeds (<3% seed set). Conclusions: Although genetic rescue or admixture of S. filifolia subsp. subulifolia would not necessarily result in greatly increased levels of genetic diversity or seed fitness, we still consider it a potential option. Negligible seed set in crosses between subspecies indicates that deliberate hybridisation is not a possibility. Implications: Studies of fitness consequences of admixture or genetic rescue are rare yet critical to assessing the benefits of different translocation strategies. Translocations, the augmentation or establishment of new populations, are a valuable management tool for plants at a risk of extinction. The source of propagation material is an important consideration to ensure that these populations persist. Using a mix of source populations didn't necessarily increase genetic diversity or improve seed fitness for the threatened daisy Schoenia filifolia subsp. filifolia. Whilst planting more seedlings from the same source population is a suitable management strategy, mixing source populations should also be considered. [ABSTRACT FROM AUTHOR]