Genetic and morphological structure of a spruce hybrid (Picea sitchensis x P. glauca) zone along a climatic gradient.
OBJECTIVE
Historic colonization and contemporary evolutionary processes contribute to patterns of genetic variation and differentiation among populations. However, separating the respective influences of these processes remains a challenge, particularly for natural hybrid zones, where standing genetic variation may result from evolutionary processes both preceding and following contact, influencing the evolutionary trajectory of hybrid populations. Where adaptation to novel environments may be facilitated by interspecific hybridization, teasing apart these processes will have practical implications for forest management in changing environments.


METHODS
We evaluated the neutral genetic architecture of the Picea sitchensis (Sitka spruce) × P. glauca (white spruce) hybrid zone along the Nass and Skeena river valleys in northwestern British Columbia using chloroplast, mitochondrial, and nuclear microsatellite markers, in combination with cone morphological traits.


RESULTS
Sitka spruce mitotype "capture", evidenced by this species dominating the maternal lineage, is consistent with earlier colonization of the region by Sitka spruce. This "capture" differs from the spatial distribution of chloroplast haplotypes, indicating pollen dispersal and its contribution to geographic structure. Genetic ancestry, based on nuclear markers, was strongly influenced by climate and geography. Highly parallel results for replicate transects along environmental gradients provide support for the bounded hybrid superiority model of hybrid zone maintenance. •


CONCLUSIONS
This broad-scale analysis of neutral genetic structure indicates the importance of historic and contemporary gene flow, environmental selection, and their interaction in shaping neutral genetic variation within this hybrid zone, informative to seed transfer development and reforestation for future climates.
Centre for Forest Conservation Genetics and Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia. jillahamilton@gmail.com
Jill A
JA
Hamilton
Sally N
SN
Aitken
D000064:Acclimatization / Q000235:genetics*; D001955:British Columbia; D002467:Cell Nucleus / Q000235:genetics; D002736:Chloroplasts / Q000235:genetics; D002980:Climate; D018744:DNA, Plant / Q000235:genetics; D051456:Gene Flow; D040342:Genetic Structures; D014644:Genetic Variation; D005838:Genotype; D005843:Geography; D006239:Haplotypes; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats / Q000235:genetics; D008928:Mitochondria / Q000235:genetics; D010641:Phenotype; D028222:Picea / Q000235:genetics*; D018515:Plant Leaves / Q000235:genetics; D014197:Trees
D018744:DNA, Plant
Picea; Pinaceae; chloroplast; climate; hybrid zone; microsatellites; mitochondria; morphology; spruce