Genetic and fitness consequences of interpopulation mating in Dianthus guliae Janka: conservation implications for severely depleted and isolated plant populations

Genetic constraints may increase the extinction risk in small and isolated plant populations. Introducing foreign genes may restore their genetic variability and fitness, but it could also be harmful, especially when recipient and donor populations have diverged. In such cases, data on genetic relationships and the possible consequences of different patterns of gene flow are essential for effective conservation. We examined five microsatellite loci to study the genetic relationships among three core populations and an isolated peripheral one of the threatened endemic Dianthus guliae Janka. This provided a base for further genetic analyses and experimental pollinations illustrating links between genetic richness and fitness, and the effects of inter-population mating in two contrasting populations (a large core vs. a small peripheral). Microsatellite loci did not show significant deviations from Hardy-Weinberg expectations. However, the peripheral population had lower heterozygosity, a higher inbreeding coefficient, and significant divergence from core units. Fitness and genetic data indicated an enhanced fitness, along with an improved capacity to rebound heterozygosity deficit after occasional selfing, in the core-population compared to the peripheral one. Crossing within-population did not enhance genetic diversity and fitness in the small peripheral unit, while between-population crossing improved its heterozygosity and fitness. Finally, in the study system, current genetic divergence did not preclude heterosis in the small and isolated population after mating with a larger donor unit.