Effects of pollination distance on reproduction and offspring performance in Hypochoeris radicata: Experiments with plants from three European regions Original Research Article

Fragmentation of habitats has resulted in increased inbreeding for many plant species, while the introduction of foreign seed material for ecological restoration has resulted in crosses between plants from distant populations. Both processes may reduce plant fitness and increase the risk of extinction. Variation in the expression of inbreeding and outbreeding depression has been found among different genotypes and among populations, but little is known about large scale geographical patterns within species. We studied the effects of cross-proximity on seed production and offspring performance in the perennial meadow plant Hypochoeris radicata (Asteraceae) from five populations in each of three European regions (Bohemia in northwest Czechia, Northern Hesse in central Germany, and Salland in the central Netherlands). Five artificial cross types were conducted with varying proximity of mates: selfing (self), within family crosses (WF), within population crosses (WP), between population crosses (BP), and between region crosses (BR), and the offspring were grown in a common garden. Independent of the region of origin of the maternal plant, selfing, WF and BP crosses resulted in lower seed set and germination than WP crosses, indicating partial self-incompatibility, inbreeding depression and reduced performance in the F1 progeny resulting from outbreeding. However, crosses between regions resulted in similar seed set and germination as within population crosses. For late traits, the effects of inbreeding and interpopulation crosses differed among regions. WP crosses exhibited the highest survival, flowering and multiplicative fitness only in progeny from Czech maternal plants. Our results suggest that the sensitivity of populations to introgression may vary among regions and that outbreeding depression does not necessarily increase with interpopulation distance. However, the current study investigated only effects in the F1 in a common garden and outbreeding depression may be stronger in the F2 and in field populations.