Genetic and mating system assessment of translocation success of the long‐lived perennial shrub Lambertia orbifolia (Proteaceae)

Maternal effects and inbreeding depression in post-translocation progeny of Campanula glomerata

Evaluation of plant translocation success based on fitness-related quantitative traits combined with molecular markers may contribute to a finer assessment of inbreeding, selective and rescue processes, which might have long-term consequences for population dynamics and viability. We investigated fitness traits (seed germination, seedling viability, and juvenile growth and mortality) combined with 15 microsatellite loci of the first post-translocation seed progeny from two translocated populations of Campanula glomerata, an insect-pollinated, self-incompatible perennial herb. We examined whether inbreeding, heterosis through admixture, translocation site and maternal transplant seed source origin and lineage might affect seed quality and juvenile growth in controlled cultivation conditions. Flower production and seed germination of the transplants was higher in one of the two translocation sites, which might be related to differences in soil and vegetation composition and cover. Strong maternal effects related to seed source origin and lineage were found on progeny size, with the largest transplants producing the largest progeny. The differences in rosette diameter were maintained across the whole growth period measured. There was inbreeding depression (rather than heterosis) related to biparental inbreeding at the early progeny growth stage, also expressed through juvenile mortality. Our findings highlight that maternal transplant origin, especially when seed sources consisted of small, fragmented remnants, might have a selective value on fitness in the post-translocation generations. If maternal effects and inbreeding depression persist, they might affect global genetic diversity patterns in the long term. Further admixture in the next generations might buffer maternal and inbreeding effects or lead to outbreeding depression.

Genetic diversity assessment of Helichrysum arenarium (Asteraceae) for the genetic restoration of declining populations

Helichrysum arenarium (L.) Moench (Asteraceae) is a self-compatible, insect-pollinated herb occurring in sand grasslands, and is declining and endangered in many parts of its European distribution range. A recovery plan of H. arenarium has been conducted in southern Belgium, involving plant translocations. We developed multiplex genotyping protocol for nine microsatellite markers previously published for Helichrysum italicum and two newly developed microsatellite markers for H. arenarium. Eleven polymorphic loci were associated (pooled) in two multiplex panels, to assess the genetic status of the only small remaining population in Belgium and of three large German populations used as seed source for propagating transplants. The small Belgian population was characterized by high clonality, with only two, however heterozygous, genets detected. The three large German populations showed high genetic diversity (H e ranging from 0.635 to 0.670) and no significant inbreeding coefficient values, despite expectations of geitonogamous selfing. Management practices (grazing livestock) increasing seed dispersal distances, inbreeding depression at early stages of development, and mechanisms preventing or delaying selfing might be hypothesized to explain the observed patterns. The two Belgian genotypes remained within genetic variation range of German populations so that the high genetic differentiation between Belgian and German populations (F ST values ranging from 0.186 to 0.206) likely resulted from genetic drift effects and small sample size. Transplants obtained from seeds sampled from the three large source populations from Germany constitute a highly diverse, noninbred gene pool, and are thus of high genetic quality for plant translocations.

Assessing Population Genetic Status for Designing Plant Translocations

Assisted gene flow interventions such as plant translocations are valuable complementary techniques to habitat restoration. Bringing new genetic variants can contribute to increasing genetic diversity and evolutionary resilience, counteract inbreeding depression and improve plant fitness through heterosis. Large, highly genetically variable populations are usually recommended as sources for translocation. Unfortunately, many critically endangered species only occur as small populations, which are expected to show low genetic variation, high inbreeding level, paucity of compatible mates in self-incompatible species, and increased genetic divergence. Therefore, assessment of population genetic status is required for an appropriate choice of the source populations. In this paper, we exemplify the different analyses relevant for genetic evaluation of populations combining both molecular (plastid and nuclear) markers and fitness-related quantitative traits. We assessed the genetic status of the adult generation and their seed progeny (the potential translocation founders) of small populations of Campanula glomerata (Campanulaceae), a self-incompatible insect-pollinated herbaceous species critically endangered in Belgium. Only a few small populations remain, so that the species has been part of a restoration project of calcareous grasslands implementing plant translocations. In particular, we estimated genetic diversity, inbreeding levels, genetic structure in adults and their seed progeny, recent bottlenecks, clonal extent in adults, contemporary gene flow, effective population size (Ne), and parentage, sibship and seed progeny fitness variation. Small populations of C. glomerata presented high genetic diversity, and extensive contemporary pollen flow within populations, with multiple parentage among seed progenies, and so could be good seed source candidates for translocations. As populations are differentiated from each other, mixing the sources will not only optimize the number of variants and of compatible mates in translocated populations, but also representativeness of species regional genetic diversity. Genetic diversity is no immediate threat to population persistence, but small Ne, restricted among-population gene flow, and evidence of processes leading to genetic erosion, inbreeding and inbreeding depression in the seed progeny require management measures to counteract these trends and stochastic vulnerability. Habitat restoration facilitating recruitment, flowering and pollination, reconnecting populations by biological corridors or stepping stones, and creating new populations through translocations in protected areas are particularly recommended.