RESUMEN
Most tree species underwent cycles of contraction and expansion during the Quaternary. These cycles led to an ancient and complex genetic structure that has since been affected by extensive gene flow and by strong local adaptation. The extent to which hybridization played a role in this multi-layered genetic structure is important to be investigated. To study the effect of hybridization on the joint population genetic structure of two dominant species of the Eurasian boreal forest, Picea abies and P. obovata, we used targeted resequencing and obtained around 480 K nuclear SNPs and 87 chloroplast SNPs in 542 individuals sampled across most of their distribution ranges. Despite extensive gene flow and a clear pattern of Isolation-by-Distance, distinct genetic clusters emerged, indicating the presence of barriers and corridors to migration. Two cryptic refugia located in the large hybrid zone between the two species played a critical role in shaping their current distributions. The two species repeatedly hybridized during the Pleistocene and the direction of introgression depended on latitude. Our study suggests that hybridization helped both species to overcome main shifts in their distribution ranges during glacial cycles and highlights the importance of considering whole species complex instead of separate entities to retrieve complex demographic histories.
Asunto(s)
Flujo Génico , Genética de Población , Hibridación Genética , Picea , Polimorfismo de Nucleótido Simple , Picea/genética , Polimorfismo de Nucleótido Simple/genética , Noruega , ADN de Cloroplastos/genética , Evolución Biológica , Análisis de Secuencia de ADNRESUMEN
The impact of elevated ozone concentrations on early ontogenetic stages of pine (Pinus sylvestris) and spruce (Picea abies, Picea obovata, P. abies x P. obovata) seedlings originating from different provenances in Russia were studied in the open-field ozone fumigation system located in Kuopio, Finland, over a span of 2 y. The AOT40 value (accumulated ozone dose over the threshold 40 ppb during daylight hours) was 11 ppm hr per growing season, which was 1.4 times higher than the ambient air concentration. The plants were measured for germination rate; shoot increment; needle length; and dry mass of needles, shoots, and roots. Significant differences between pine and spruce provenance response to ozone were found in all parameters. Ozone stress immediately reduced the germination rate of Northern pine provenances, whereas biomass reductions became evident during the second year of the exposure in all pine provenances. Spruce species were more tolerant to elevated ozone concentrations. Our results indicate that seedling development is vulnerable to increasing ozone concentrations and that attention must be paid to the provenance selection.