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Recombinant hybrids retain heterozygosity at many loci: new insights into the genomics of reproductive isolation in P opulus
Author(s) -
Lindtke Dorothea,
Buerkle C. A.,
Barbará Thelma,
Heinze Berthold,
Castiglione Stefano,
Bartha Denes,
Lexer Christian
Publication year - 2012
Publication title -
molecular ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.619
H-Index - 225
eISSN - 1365-294X
pISSN - 0962-1083
DOI - 10.1111/j.1365-294x.2012.05744.x
Subject(s) - biology , reproductive isolation , hybrid , hybrid zone , genetics , genome , evolutionary biology , locus (genetics) , gene flow , epistasis , genetic variation , natural selection , selection (genetic algorithm) , gene , population , botany , demography , artificial intelligence , sociology , computer science
The maintenance of species barriers in the face of gene flow is often thought to result from strong selection against intermediate genotypes, thereby preserving genetic differentiation. Most speciation genomic studies thus aim to identify exceptionally divergent loci between populations, but divergence will be affected by many processes other than reproductive isolation ( RI ) and speciation. Through genomic studies of recombinant hybrids sampled in the wild, genetic variation associated with RI can be observed in situ , because selection against incompatible genotypes will leave detectable patterns of variation in the hybrid genomes. To better understand the mechanisms directly involved in RI , we investigated three natural ‘replicate’ hybrid zones between two divergent P opulus species via locus‐specific patterns of ancestry across recombinant hybrid genomes. As expected, genomic patterns in hybrids and their parental species were consistent with the presence of underdominant selection at several genomic regions. Surprisingly, many loci displayed greatly increased between‐species heterozygosity in recombinant hybrids despite striking genetic differentiation between the parental genomes, the opposite of what would be expected with selection against intermediate genotypes. Only a limited, reproducible set of genotypic combinations was present in hybrid genomes across localities. In the absence of clearly delimited ‘hybrid habitats’, our results suggest that complex epistatic interactions within genomes play an important role in advanced stages of RI between these ecologically divergent forest trees. This calls for more genomic studies that test for unusual patterns of genomic ancestry in hybridizing species.