35th NPS abstract book

Microevolution in Populus trichocarpa driven by
introgression
S1.2
CARL J. DOUGLAS 1 , ADRIANA SUAREZ-GONZALES 1 , 10:15–10:45
CAMILLE CHRISTE 2 , ARMANDO GERALDES 1 , CHARLES
HEFER 1 , ATHENA D. MCKOWN 3 , SUBINOY BISWAS 4 ,
JUERGEN EHLTING 4 , ROBERT D. GUY 3 , SHAWN D.
MANSFIELD 5 , CHRISTIAN LEXER 2 and QUENTIN C.B.
CRONK 1
carl.douglas@ubc.ca
1 Department of Botany, University of British Columbia, Vancouver, BC,
Canada; 2 Unit of Ecology & Evolution, Department of Biology, University
of Fribourg, Fribourg, Switzerland; 3 Department of Forest and
Conservation Sciences, University of British Columbia, Vancouver, BC,
Canada 4 Department of Biology, University of Victoria, Victoria, BC
Canada; 5 Department of Wood Science, University of British Columbia,
Vancouver, BC, Canada
Introgression between closely related species can provide allelic variation underlying adaptation.
Populus trichocarpa and P. balsamifera are attractive sister species to study the effects of natural
hybridization on local adaptation in forest trees, since they diverged recently, are adapted to
contrasting environments in western and northern North America, and hybridize in contact zones.
Using genome-wide scans of population differentiation, based on extensive SNP genotype data from
collections of P. trichocarpa and P. balsamifera individuals, we showed that introgression from P.
balsamifera plays a role in shaping the landscape genomics of P. trichocarpa in northern and eastern
parts of its range and identified 396 candidate genes for local adaptation in P. trichocarpa. On
chromosomes 6 and 15, two genomic regions showed strong patterns of population structure and
association with latitude and a number of environmental variables. Several genes involved in light
signaling, secondary metabolism and transcriptional control (e.g., FAR1, FHY3, PRR5, COMT1, TTG1,
ANAC062) in these regions had SNPs associated with adaptive traits. In order to further address the
role of introgression from P. balsamifera in the microevolution of P. trichocarpa, we selected 25
pure P. trichocarpa, 25 pure P. balsamifera, and 68 admixed individuals, and used whole genome
resequencing data to carry out ancestry analysis. This revealed that the candidate region for local
adaptation on chromosome 15 introgressed from P. balsamifera into P. trichocarpa, and that these
balsamifera alleles are restricted to interior and northern populations of P. trichocarpa. We
implemented genomic and gene ontology enrichment tests to test for signals of selection and
overrepresented biological themes, respectively. To determine if introgressed alleles are functionally
different from P. trichocarpa alleles, we analyzed gene expression levels, and compared phenotypes
of admixed vs. pure P. trichocarpa individuals. Our results support the hypothesis that the
introgression of functionally distinct alleles from P. balsamifera contributes to local adaptation in P.
trichocarpa.
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